The behaviour of Oecophylla longinoda. How to manipulate or use Oecophylla ants 

in cocoa agro­ecosystems in order to suppress cocoa pests such as capsids?

Research subject of Machiel van Wijngaarden and Monique van Kessel in the framework of their MSc study at theLaboratory of Entomology, Wageningen University

Research proposalKeywords: Oecophylla longinoda, cocoa, pest management…

Students: Monique van Kessel*, Pieter Machiel van Wijngaarden*Supervisors: Godwin Ayenor^, dr. A van Huis*

*Laboratory of Entomology, Wageningen University, PO Box 8031, 6700 EH Wageningen, TheNetherlands^University of GhanaIndexPreface -Introduction -Research area -Material and Methods -References -

‘’In 1476, the farmers of Berne in Switzerland decided, according to this story, there was only one wayto rid their fields of the cutworms attacking their crops. They took the pests to court. The worms weretried, found guilty and excommunicated by the archbishop.’’ (Reference)

PREFACEAnts as a biological agent for controlling pests is already known and practiced for a long time

(Van Mele, 2000). The earliest report of Oecophylla ants at work among the orange trees is describedin a book on tropical and subtropical botany written by Hsi Han in AD 304. "The people of Chiao-Chihsell in their markets ants in bags of rush matting. The nests are like silk. The bags are all attached totwigs and leaves which, with the ants inside the nests, are for sale. The ants are reddish-yellow incolour, bigger than ordinary ants. In the south if the kan trees do not have this kind of ant, the fruitswill all be damaged by many harmful insects, and not a single fruit will be perfect." (REFERENCE)Around the 12th century the Chinese farmers already connected their fruit trees with bamboo sticks toprovide the ants a passage to move from one tree to another (Friederichs, 1920). This measureresulted in a spread of ants through whole of their orchards. Nowadays there are several places where ants do a very useful job as a biological pest agent.Vietnam, Cote d'Ivoire, and countries in the North of Australia are some of the places where thebenefits of this little creature have already been recognized and used. Ghana, as one of the majorcocoa-producing countries, could also use the advantages of ants in their struggle against pestswhich threaten the yield of the cocoa plantations. The research questions and methods which will be described in this proposal just represent a global idea of theresearch on O. longinoda, and the use of Oecophylla ants in the biological control of cocoa capsids, which stillcan be done. Mainly due to the limited time available for our research (approximately five and a half months),we will not be able to carry out all the described experiments in real terms. Another important reason for the

somewhat  global  way   in   which   we   describe   methods   in   this   proposal,   is   a   lack   of   practical   knowledgeconcerning cocoa and pest management. We hope we will be able to get to a more specific research plan inmeeting with Godwin Ayenor, a phd student participating in the ‘Convergence of Science’ project, who willsupervise us during our stay in Ghana. 

INTRODUCTIONCOCOA PLANTATIONS AND ITS PROBLEMS

Major problemsPests and diseases in cocoa plantations are a large threat for cocoa trees. Around the year

1999, 29.4% of the crop was lost due to capsid insects, cocoa swollen shoot virus and fungal diseasepod root (Gray, 2000). The same values were predicted for the following years. These numbersindicate how serious pests and diseases threaten the income of the farmers. Each year almost a thirdof potential income is lost. There are several major problems cocoa crops have to deal with. Fungi are a problem all over theworld and for Ghana this is no exception. An example of a deadly fungus attack is shown in figure 1.Fungi are difficult to control, because the ground acts as a natural barrier by which they are protectedand they are often widespread through the infected area. For example the fungi Phytophthoramegakarya occurs in Ghana, which destroys part of the crops (Opoku et al., 2002). Another major problem is the cocoa swollen root virus. This virus is transmitted by the mealybug.Mealybugs belong to the Homopteras, family Pseudococcidae. An infection leads to interveinalchlorosis, leaf mosaic, stem and root swellings, and pod distortion (Ollennu, 2004). This disease canbe easily governed, because the vectors of this disease can not travel over great distances. So, forexample a 10 meter long corridor would already prevent the disease from spreading. The onlyproblem is to make this a common policy and bring the knowledge to the people (Ollennu et al.,1989).However, our research will mainly focus on insect pests and particularly capsids. These insects areanother cause of great yield loss in the cocoa plantations (REFERENCE).

Introduction: insectsTwo capsid species are the mean cause of damage done to cocoa plantations by insects,

namely Distantiella theobroma (Dist.) and Sahlbergella singularis Hagl (Pictures) (REFERENCE). When capsids have injected their histolytic saliva, they leave a lesion behind. The shape of thelesions often appears to be somewhat characteristic for each capsid species. For example, lesionsresulting from the feeding of Distantiella and Sahlbergella tend to be elliptical with the long axisparallel with that of the stem, while for some other species the lesions are more or less round. The lesion which is left behind is very frequently infected by pathogenic fungi. Calonecrtia rigidiusculais the most common one (REFERENCE). This is the reason why many trees can die from just arelatively low number of capsids being present. Therefore these pest insects have to be controlledefficiently in order to prevent much damage as a result of fungi.From August till December the capsid population is at its highest level of impact (REFERENCE),attacking young branches and jorquettes (young sprouted branches) which they prefer. By attackingplanted seedlings the capsids can delay the plantation to bear fruit several years (REFERENCE).A more complete list of insects which threaten the cocoa in Ghana is given on website 3. For thepaper version of this article, the part about which species threaten cocoa, is pasted below:“In addition to capsids, termites have in recent times been of economic importance in some parts ofGhana (Ackonor, 1994). Sporadic attacks by other insect pests of minor importance also occur,causing varying degrees of damage. These insects include the pod feeders Bathycoelia thalassina(H.-S.) (Heteroptera: Pentatomidae) and Pseudotheraptus devastans (Dist.) (Heteroptera: Coreidae)(Owusu-Manu, 1971; Padi, et al., in press), the stem borer Eulophonotus mermeleon Fldr.

(Lepidoptera: Cossidae) (Anon, 1995) and the pod borer Characoma stictograpta Hmps. (Lepidoptera:Noctuidae) (Akotoye, 1975). Anon (1995) observed that damage caused by termites and stem borersis becoming increasingly important in the whole country and recommended that CRIG must intensifyresearch for a quick solution to these problems. Other insect pests which are particularly important onyoung cocoa include the Lepidopteran foliage pests Earias biplaga Wlk., Anomis leona Schaus.,Orgyia basalis Wlk. and Prodenia litura F., the psyllid Tyora tessmanni (Aulm.), the aphid Toxopteraaurantii (Fonsc.), the thrip Selenothrips rubrocinctus (Giard.) the stem tip feeder Tragocephala spp.(Coleoptera: Cerambycidae) and Empoasca devastans Dist. (Homoptera: Fulgoroidae) which causesthe tip burn disease (Collingwood & Marchart, 1971; Entwistle, 1972)”.

CONTROLLING METHODS

Control by insecticidesControl of pests through insecticides is an option, but there are many disadvantages. First of

all, natural populations which are neutral or even beneficial are also being destroyed or distorted.Besides that, important natural enemies of the pests are wiped out or suppressed by the insecticideas well. Second, the effectiveness of the insecticide reduces as the pest insects become more and moreresistant to the chemicals. In the long term the insecticide will not be of any use anymore and mighteven have a negative effect on the environment. Third, the use of insecticides can suppress a primary pest, but meanwhile promote a secondary pest.This is demonstrated in the study by Dunn (1963). The common insecticide in these days, lindane,suppressed the pest S. singularis, which was sensitive to that insecticide. Yet, by destroying thisspecies, D. theobroma flourished and replaced S. singularis. The outbreak of this secondary pest waspossible because D. theobroma was much more resistant to lindane.The fourth disadvantage is the effect on health of producer and consumer. The effect on health of thepeople who eat the products is not too dangerous -otherwise they would have been forbidden- butthey are not healthy either. However, this is not the major problem. The farmers, who have to applythe insecticide, are in contact with a much higher dosage when spraying the insecticide on their crops.Therefore the insecticide must be harmless for mammals –which automatically mean the insecticidewill be harmless for humans too- (REFERENCE). The last disadvantage is the insecticide affecting the taste of the cocoa. By applying insecticide thequality of the cocoa is being reduced (Leiter & Harding, 2004).

Biological controlThe reduction of pests without, or at least with less pesticide, can be done in many different

ways. Research has been done on the use of parasites and pheromones to control pests in cocoa(Beevor et al., 1993; REFERENCE). Fungi can be used for example to promote the plants’ defencesystem. Other crops can be sown which have a negative effect on the pest. Another possibility is the promotion of natural enemies (natural enemy enhancement/ conservationbiological control). Conditions are favoured for the natural enemy of the pest, for example by addingadditional food sources or growing host plants at the border of the field. More individuals of the naturalenemies are able to survive and attack the pest, resulting in a reduction of the pest population size. Ants are often not specialists, and therefore not specific enemies of one species of insects. Theirgeneralistic predation and aggressiveness makes them very effective for biological control, so theycan be used for introduction in areas where pest insects are too numerous.

Aim of the researchAt this moment there is an inefficient controlling of pest insects by insecticide, which is shown

by the amount of crops lost due to pest insects. The purpose of this research is to give an alternativeto this chemical control, by investigating the possibility of the application of Oecophylla longinoda as abiological agent for controlling the major pests in cocoa plantations in Ghana.During the study of literature the question about which species to introduce can be answered quite

easily. The Oecophylla ants are quite common in Ghana (REFERENCE) and considered to be a goodagent for biological control (Way & Khoo, 1992). Since native species are most easily to introduce andless dangerous on a long-term (because it is their own environment) this research will focus on O.longinoda. Although many articles are found on the use of Dolichoderus thoracicus as a biologicalcontrol agent, this ant species occurs to be absent in Ghana. Therefore this species, although wellcompetent for biological control, will not be discussed in this paper as a possible biological controlagent (Way and Khoo, 1991).

The following question will guide our research:• How can we introduce and maintain Oecophylla longinoda colonies in order to suppress

capsid pests in cocoa plantations in Ghana and why is O. longinoda not being effectivelyused already?

This question can be divided into many subjects. All these subjects have to be investigated to carryout a proper research in the field. The basic information is required for a good outline of the fieldresearch which will be preformed in Ghana from June till November. Godwin Ayenor, a phd studentparticipation in the project ‘Convergence of Science’, will supervise us during the research.

OECOPHYLLA LONGINODA

IntroductionAs mentioned before, weaver ants (Hymenoptera, Formicidae, Formicinae, Oecophylla) belong to the

group of insects which can be used in biological control of capsid pests in cocoa plantations. For these arborealOecophylla ants two species have so far been described (website 1). The genus Oecophylla occurs in tropical Asia, Australasia and Africa and the most well known and widely usedant for biological control within this group is  Oecophylla smaragdina  (Way, 1954 and Way & Khoo, 1992).Van Mele & Cuc (2003) mention all countries in which weaver ants have been reported (table 2). The Africanrepresentative  of   the   genus   is  Oecophylla   longinoda  and   has,   among   others,  been   described   by   Latreille(Vanderplank, 1960).  Oecophylla longinoda  has five varieties (as reviewed in Way, 1954), but Vanderplank(1960) questions whether or not there are sufficient grounds to consider these five varieties of O. longinoda andO. smaragdina as separate species. Also Way & Khoo (1992), mention that the biology of both O. longinodaand O. smaragdina can be treated as one, though their geographical distribution is very distinct.About  O. longinoda  relatively little literature has been found, and if so, it  was often quite ‘old’. About  O.smaragdina a bit more has been written and since we assume that both species show significant similarities inecology, in some cases we use information on O. smaragdina for both Oecophylla species.  

Castes and nest buildingOecophylla colonies may cover up to 1600 m², comprising approximately a million workers and brood

and the life of a colony might exceed five years if not being destroyed by other ants (Vanderplank, 1960 andWay & Khoo, 1992). Five different castes of O. longinoda can be distinguished; small and large workers, andthe reproducing males, virgin females and queens, according to Way (1954) and Vanderplank (1960). However,virgin females are not being mentioned in other studies, so in this research only four castes will be considered.The (female) workers are thus dimorphic with major (large) workers outnumbering the minors (small workers),which is a common feature among ants (Greenslade, 1972). Small workers can often be found inside the nest where they attend the developing brood and the sexual forms,and sometimes  also  honey­dew­producing Homoptera within   the  nest.  The  functions  of   large  workers  aredefending the colony, foraging, nest­construction and attending Homoptera outside the nest (Way, 1954 andVan Mele & Cuc, 2003). Queens are the largest of the colony with a big abdomen for egg production. Queensstart life winged, but lose their wings soon after the mating flight. Males are much smaller than the queen,winged, and their only task is mating with the queen which results in a longevity of only a few days (Van Mele

& Cuc, 2003). It has been shown by studies of, among others, Way (1954) and Vanderplank (1960) that within acolony  there   is  always only  one  queen present.  The queen moves between  the  nests   (escorted  by severalhundreds of large workers). This would then result in many nests within a colony without a queen. However,Van Mele & Cuc (2003) speak of one or several queens within a colony, in one (dry season) or in more (wetseason) nests. They also mention that more queens are being produced during the wet season than during thedry season (Van Mele & Cuc, 2003). Peng  et  al.   (1998), which developed a  method to  determine which nests within an  O. smaragdina  colonycontains a queen, also often found more than 1 queen (up to 6) per colony always occurring in just 1 nest.Within queen­nests there always were large numbers of large workers, eggs, small larvae and just a few smallworkers were found. However no pupae or medium­ or large larvae were present. According to Peng  et al.(1998) it seems that the queens stay in one nest to lay eggs, and that larvae later on are carried to other nests.This   is   contrary  with   findings of  Vanderplank   (1960).  The  study  by Way  (1954)  showed  that  queen­lesscolonies eventually die out, unless brood is being added from time to time (also reviewed in Van Mele & Cuc,2000). Nests   are   always being built   in   tree/shrub  crowns.  The nest­building process   involves  a  highly organisedprocess. First, the ants seem to determine whether or not there are leaves enough to form a nest. Secondly, thelarge workers start drawing leaves together, sometimes forming chains up to twelve workers to bridge the gap(Vanderplank, 1960). When the leaves are in the right position they are held together by workers, whereasothers start carrying medium­sized larvae in their mandibles. The larvae then are continuously stimulated tosecrete silk from one leave to the other which will hold the leaves together (Way, 1954 and Van Mele & Cuc,2003). Small shelters of only a few leaves are sometimes being build in the same way over clusters of Homopterawhich are being attended (Way, 1954 and Van Mele & Cuc, 2003). Way (1954) also observes that the part ofthe tree selected for nest­building varies according to the season, and seems to depend on both sunlight andwind direction. 

DistributionAs O. smaragdina mainly occurs in the tropical parts of Asia and Australia, O. longinoda can thus be

found   in   West­   and  east   Africa   (as   reviewed   in   Löhr,   1992).   In   the   article   by   (Way,   1954)   the   generalenvironmental conditions determining the ants’ abundance are briefly being described.  O. longinoda  ants areespecially abundant in areas with relatively high rainfall and temperature, suitable soils, and evergreen tree andbush  vegetation   (Way,   1954).   The   article   by   Van   Mele   &   Cuc   (2003)   describes  O.   smaragdina  preferstemperatures between 26 and 34 ºC and relative humidities between 62 and 92 %. For O. longinoda we assumepreferences will be quite similar. Since  Oecophylla  ants do build nests of living leaves, vegetation should not be deciduousness, leaves mustexceed a certain size and leaves must be strong but flexible, though often Oecophylla can adapt the foliage ofmost trees for nest­building (Greenslade, 1972 and Van Mele & Cuc, 2003). Sometimes  Oecophylla ants arealso satisfied with trees for nest­ building having smaller leaves, but then leaves should be abundant (Van Mele& Cuc, 2003). Beside this, choice of host plants for nest building might also depend on the ability of the plant tosupport suitable Homoptera clusters. O. longinoda is less present or totally absent in areas with higher altitudes(Way, 1954).In Zanzibar O. longinoda ants has been found colonising some 89 species of trees and shrubs belonging to 35families in Zanzibar (Way, 1954), but other numbers and species may hold for other areas. 

Feeding habits & foraging activityO. longinoda  is intermediate in its feeding habits, being both an active predator but also feeding on

honeydew produced by several Homoptera species. According to Vanderplank (1960) both food sources evenappear   to   be   essential   for   the   survival   and   reproduction   of   a   colony.   Because   ants   benefit   from   severalHomoptera species they often take care of them in several ways. First by protecting them from various enemies(though often accidentally), secondly by removing honeydew and fungi contaminations, and third by offering

shelter (Way, 1954a).  The ants thus live in a close mutualism with certain Homoptera species (Greenslade,1972). However,  Oecophylla  does keep Homoptera populations at levels at which they provide the requiredamount of food for the ants,  and thus sometimes attacks and kills  part of  the Homoptera  populations. TheHomoptera species Stictococcus sjostedti Cockerell and Planococcoides njalensis (Laing) are the most commonin   cocoa   and   important   in   honeydew  production   for   ants.   Also  Parastictococcus   multispinosus  has   beenobserved being attended by O. longinoda (Bigger, 1981).O. longinoda is a generalist and therefore predates on a great variety of insects, among which are many pests(Vanderplank, 1960). Oecophylla ants are being observed foraging on both the ground and over trees and shrubsattacking most insects with which they come into contact (Way, 1954). Way (1954) briefly lists the insectswhich were observed being killed by O. longinoda  in a study in Zanzibar. Among these insects were severalHemiptera Heteroptera (e.g. Coreid species),  Hymenoptera species (e.g.  honey bees,  wasps and some otherants),   Coleoptera   species   (e.g.   Carabidae,   Curculionidae,   and   Cetoniidae),   but   also   limbs   and   wings   ofgrasshoppers, cockroaches and other Arthropod species were being found in their nests. A study by Wojtusiaket al.  (1995) reported cases of capture of very large prey by workers of  O. longinoda,  and even remains ofvertebrate prey were being found in their nests. They compare the hunting behaviour of O. longinoda with thatof army ants (Wotjusiak et al., 1995). In  many  studies   it  has   been  observed   that  Oecophylla  worker  colour   depends partly  on  diet.   If   coloniesexclusively  feed on sugar sources  (or  some specific   insect  species),  only  small,  yellow workers  are  beingproduced which show decreased aggression. In case of feeding on insect prey only, the newly produced workersare relatively larger, deep red coloured and are much more aggressive (Greenslade, 1972 and Vanderplank,1960). It can therefore be suggested that feeding Oecophylla ants exclusively with insects would result in highlyaggressive  ants,  which could be advantageous  in biological  control.  Besides  that,   they  would  require   lessHomoptera   to   anticipate   their   needs.   However,   according   to   Way   (1954a),   ant   populations   which  solelydependent   on   insect   prey   can   only   maintain   at   relatively   low   populations   levels.   Besides   that,   a   higheraggressiveness could also lead to a greater loss of beneficial insects. If additional prey would be added higherpopulation numbers might be achieved, but this should be thoroughly investigated. Probably there will be anequilibrium state which gives the optimum predation with negative effects of aggressiveness as low as possible.According to Greenslade (1972) O. smaragdina ants are diurnal and are thus mainly active during the period ofdaylight. Dejean (1990) looked specifically at  the circadian rhythms of activity of  O. longinoda  in a studyconducted   in  Zaire.   In  his   introduction  he describes   several  contradicting  conclusions   from studies  whichinvestigated the activity pattern of Oecophylla species. Dejeans’ (1990) study clearly shows that O. longinodaants are diurnal in foraging behaviour, but that there is also a low nocturnal level which is associated withguarding of workers in the ‘central’ territories (located within the immediate areas around the nest, often in thetree canopy). Foraging occurs mainly in the ‘ground’ territories (located in areas where the number of potentialprey is  consistent  and high,  often on ground  levels)  (Dejean, 1990). There seems to be a  clear  distinctionbetween prey captured in ‘central’ territories (winged insects) and those captured in the secondary territory(‘crawling’  insects).  Dejean (1990) suggests this  might be the result of either  ‘worker specificity’,  relativeabundance of flying versus walking prey in each territory, or both. It appears that light is the main factor indetermining foraging activity (Dejean, 1990).

Territoriality & orientation In several studies by among others Dejean and Hölldobler & Wilson, aspects of territoriality and trail

pheromones have been looked at. Since this does not seem to be an important aspect of our study we will not gointo too much detail about this subject, but few notes will be given below. Weaver ants are strongly territorial at both inter­ and intraspecific level. Therefore  O. longinoda  secretes acolony­specific territorial pheromone produced in the rectal sac. If deposits of another colony of ants are beingdetected   by   workers,   these   will   respond   with   an   increased   amount   of   aversive   and   aggressive   behaviour(Hölldobler   &   Wilson,   1977).   According   to   Dejean   (1991)   this   anal   drop   deposition   has   two   importantfunctions, namely territorial and orientational marking. Beugnon & Dejean (1992) show that trail pheromonescan even be used for orientation after a period of 11 months! The chemical trail also appears to be resistance to

water, which Beugnon & Dejean (1992) consider as an adaptation to the high amount of rainfall in the WestAfrican rain forest. Orientation by weaver ants is achieved by the use of several methods. Jander & Jander (1998) show that  O.smaragdina ants use a directional light compass. Like has been shown for other ant genera, they also concludethat compass orientation based on the polarised light of blue sky strongly outweighed compass orientation onlight coming directly from the sun. In times of absence of sufficient 'light', O. smaragdina ants use a landmarkcompass, and they even seem to respond to changes in the earth's magnetic field and thus also possibly use amagnetic compass (Jander & Jander, 1998).

Natural enemiesAccording   to   Greenslade   (1972)   it   has   been   recorded   that   vertebrates   (such   as   birds   and   frogs)

occasionally predate on Oecophylla. Also the pseudoscorpion Paratemnus salomonis sometimes feeds on them.Except   for   these   predators   it   are   especially   several   other   dominant   ant   species   which   possibly   threatenOecophylla ants (as reviewed in Greenslade, 1972). Several   ant   species   which   are   dominant   over  Oecophylla  are   mentioned   in   the   literature.   These   includeAnoplepis longipes, Anoplepis custodiens, Pheidole punctulata (Way, 1953, Vanderplank, 1960), Iridomyrmexmyrmecodiae,  Pheidole megacephala  (as  reviewed in  Way, 1953 and as  reviewed  in Way & Khoo, 1992,Vanderplank, 1960), Pheidole devastans  (as reviewed in Way & Khoo, 1992),  Dolichoderus thoracicus  (VanMele & Cuc, 2003),  Crematogaster castanea, Crematogaster rectinota  (Vanderplank, 1960), Crematogasterclariventris (Bigger, 1981) and Vanderplank (1960) mentions several ant species which do not destroy wholecolonies but kill solitary queens which are attempting to establish a new colony. Although these ant species allmight outcompete or kill Oecophylla ants, some are also potential biological control agents for several pests inmany different plantations and areas (Way, 1953, Way & Khoo, 1992).  Vanderplank (1960) describes  thatPheidole species often outcompete Oecophylla ants during the dry seasons when conditions are more favourableto them, whereas during the wet season Oecophylla wins territory from Pheidole ants. According to website 1,several Crematogaster species and Pheidole megacephala are quite common in cocoa plantations in Ghana. Adult workers of individual Oecophylla colonies are mutually antagonistic (as reviewed in Way & Khoo, 1992),but striking is the absence of antagonism towards immature forms of other colonies (Way, 1954). 

OECOPHYLLA IN PEST MANAGEMENT

ExamplesIn the introduction several examples are given of ants which are being used as a biological

control agent. The example of citrus farmers in Mekong Delta, Vietnam, which have a long tradition ofmanaging the weaver ant O. smaragdina is one of them (Van Mele & Cuc, 2000).However in the last century, since the introduction of insecticides, most of the original and historical(which were often biological) ways of reducing pests, have become replaced by ‘chemicalmanagement’ (Way & Khoo, 1992). The insecticide was considered as the new way of dealing withpests. Now the old knowledge has to be revalidated and presented to the farmers as the bestalternative. Yet biological control in Northern Australia is carried out with O. smaragdina in commercial cashewplantations. This was based on the old age knowledge and extensive scientific research (Peng et al.,1995, 1997, 1998). Another example of experiments in which pest insects were controlled by O.smaragdina and D. thoracicus is given by Van Mele et al. (2002). It is reported that O. longinoda caneffectively control several pests on coconuts including the devastating coreid P. wayi Brown oncoconuts in East Africa and P. devastans in Cote d'Ivoire. Also the mirid D. theobroma on cocoa inWest Africa and other examples of among other O. smaragdina as a control agent are beingdescribed (all referred to in the article by Way & Khoo, 1991).The examples above show that the use of ants in pest management is very common, and especiallybeing practised in Asia. They prove that ants, and particularly O. Longinoda, could be used as a

biological control agents.

Ant husbandryIn many of the examples it was necessary the ants were looked after. This is called ant

husbandry and involves several ways of for example field manipulations (Van Mele & Cuc, 2000).Aspects are listed below.

RequirementsTo introduce ants in cocoa farms, nests have to be moved into the plantations. This change of

habitat will not be a big problem if the plantations meet with the requirements of ants needed forsurvival. There is not much known about adaptations to habitat change. So we do not know how antsreact on transferring their nests to other habitats. However, an indication of the sources which have tobe included in the environment is available from many studies. These will briefly be discussed below. First the abundance of Homoptera, which provide an essential food source by production ofhoneydew, should meet the ants’ requirements (Way, 1954). Of an predatory species Formica rufa,which also has been considered as a biological control agent (Way & Khoo, 1992), a diet consist of62% honeydew, 5% resin, fungi, carrion and seeds and 33% insect prey. This indicates thatHomoptera are the greatest source of food. Observations of transport of Homoptera by O. longinodato new nesting sites confirm this statement. Ants give some protection against enemies ofHomoptera, but to what extend is not yet clear and often exaggerated (Nixon, 1951). O. longinoda isattending Homoptera species according to many studies (Way, 1954a, Vanderplank, 1960).Homoptera are controlled in both number and position (Way 1954a). If there are more individuals thanneeded to provide the ant colony with sufficient honeydew, the Homoptera are predated upon. Second, weaver ants need trees with big leaves to construct their nest. The abundance of the rightleaves is a prior to introduce ants. Even when whole nests are introduced, there should be still somevegetation suitable for the ants to build their nest in case they move to other nesting sites. After anaverage of 85 days they tend to move to another site to build a new nest, this because the leavesinside the old nest are rotten or climatic circumstances are not optimal anymore (Way, 1954).Although ants have often been observed in coconut palms, the ants do have preference for other treespecies for nest-building -for example clove trees- and rather not for coconut or cocoa (Way & Khoo,1991). Leaves should be big enough to fold but not too tough, so not too much effort has to be put inthe folding. However, while ants are so often observed in coconut palms, we doubt whether or notcoconut leaves meet preferred leave characteristics for O. longinoda ants. Climatic circumstances affect the ants in their way of living and wind is one of the factors ants doreact on (Way, 1954). Yet farmers do not have to participate in these processes, because the ants willmove themselves if they have to and farmers can not influence climatic changes. Only the fact thatants move when wind changes, should be known, so a farmer would not be disturbed by observationsof moving ants. Besides that, seasonal dispersion of nests and Homoptera clusters should be familiarto farmers (Way, 1954a). One of the factors which could actively be influenced and might have some advantages, is thecreation of shadow. Room (1971) states that shadow favours O. longinoda in comparison tocompeting species. Bigger (1981) gives another reason why creating shadow is not a waste of time; itprevents much damage by mirids, thribs and leaf eating caterpillars.Cocoa trees form tight and dense vegetation between overhead canopy and ground vegetation,hereby creating a close resemblance to natural situations. Also insect fauna composition oftenbecomes very ‘natural’ (Bigger, 1981). However, growing other trees than Theobroma cocoa L. wouldeven better resemble the natural situation and thus support natural balance. Little is known about the effects different composition of the underground can have. It is known thatO. longinoda forages on the ground and never in the soil itself, so a more open underground willprobably be favoured (Bigger, 1981).

DisadvantagesThe use of Oecophylla in biological control is not without any disadvantages. And even after

Oecophylla ants were considered to be a potential biological agent, different perspectives of authorsdid not give much intelligibility about the relation between the disadvantages and the advantages and

how they were correlated (Way, 1954, Way & Khoo, 1992). However, the latter study does notemphasize the disadvantages as much as the first one. The different opinions about thedisadvantages result in different suggestions about the way ants should be treated. One of the disadvantages is the aggressiveness of the ants. When harvesting the beans or coconutsthe ants will attack. This interference is not beneficial to the image of ants, especially to the localfarmers which have to stand not only one, but many bites during the harvest. The effect of a bite willbe different for each person, but it is generally experienced as painful, though pain will not last forlong. A description of a bite is found in the article by Vanderplank (1960). “Way (1954a) gives hisobservations on the predation by Oecophylla in Zanzibar. My observations do not differ in any wayexcept he mentions that ‘the “poison” does not seem to increase pain caused by the bite, nor doesthe pain persist after the removal of the ant.’ I cannot agree with this statement. I have allowed soldierants to bite the back of my hand, and before they are able to squirt any fluid over the site of the bite,cut their abdomens off with a sharp pair of scissors. The bite of the ant without any fluid is not painful,but the fluid makes the bite quite painful and in my case I find the pain persists for 10-15 min after theants have been removed. The local people also find the bite painful; hence Oecophylla’s Kiswahiliname maji ya moto or ‘hot water ant’A solution to this problem is given, but it is not sure whether this is applicable or not. Following anoften suggested strategy, the ants should be kept out of the harvest area by applying insecticidesduring the period of harvesting. As far as we know, this strategy has not yet been applied in the field,only suggested. However, we certainly doubt whether this strategy would work, for which we thinkthere are many reasons. First, the ants are reduced in number and driven out of the area they normally forage in (cocoa fields).Because this management has never been carried out, the adaptation of ants to this kind of control isuncertain. The ants might not survive or will abandon the nests to find a more undisturbed place, andtherefore possibly totally disappear from the plantations. Second, the amount of ants is thus being reduced, -especially that of large and small workers- andthe colony might easily being overrun by competing ants. Both problems occur after the harvest, but control of pests with chemicals is absent for a at least acertain period. The farmer could introduce the ants again next growing season, like the Chinesealready did in AD 304. For a broad application of O. longinoda there has to be a large stock of nestswhich can be introduced in the cocoa plantations. This is only possible with sufficient amount of nests.Because of the reduction of natural habitats of the ants, these might not be available (REFERENCE).Therefore a breeding programme would be necessary to obtain the required ants. As far as we knowthere is no experience or research done on breeding ants and in particular that of Oecophylla. An alternative which does not require a huge amount of nests is the transfer of nests to outside theplantation (REFERENCE). This must be done just before harvesting; otherwise the pest could stilldestroy a lot of yield. The nests must be transferred to a place where the ants are able to survive untilthe next growing season, so the requirements described above must be met in the area the ants arekept. Also the level of disturbance must be reduced as much as possible or otherwise the ants couldbe chased away. It has not yet been tested how disturbance affects the presence of ants, as far as weknow. Also, transfer of nests is still somewhat a problem.Another disadvantage is the requirement of Homoptera which the ants need for their honeydew. Antshave a certain preference for species of Homoptera they attend. O. longinoda is reported to attendStictococcids and S. zanzibarensis, which are both considered as quite harmless, when occurring insmall numbers (Vanderplank, 1960). Oecophylla largely depend on these insects for survival (Way,1954). These Homoptera are attended by the ants in exchange for their honeydew, howeverHomoptera might become a serious threat to the cocoa. If they become too numerous, they affect theyield negatively by causing severe mechanical damage or by being vectors of plant virus diseases (asreviewed in Way, 1954a). Hence the essential presence of Homoptera to provide the ants animportant food source is considered to be a negative aspect of the natural pest control by O.longinoda. However Way states in his article (1954a): ”To summarize: O. longinoda workers transportthe Saissetia zanzibarensis (a Homoptera species), establish them at suitable feeding sites, andmaintain the number of individuals in a cluster at a level which does not cause obvious injury to thetwigs of the host plant.” “Under experimental conditions the young twigs of clove trees were damagedby S. zanzibarensis, but this was not observed in the field”. This is contrary to what Way announces in

another article (1954). In this article the size of the population is determined for the damaging theHomoptera causes. This is not considered in the article of Way. It is not clear whether it depends onwhich tree the O. longinoda and especially the Homoptera live on, the species which is attended byO. longinoda, the type of area or the setup of the experiment. Our opinion is that the size of thepopulation and observations in the field should be taken into account; where upon a good overviewcan be given of the balance between the protection of Homoptera given by O. longinoda and thedamage caused by these aphids.

O. longinoda ants are quite a large Formicidea species. This enables them to attack large insects andeven small vertebrates (Wojtusiak et al., 1995). This aggressiveness against a large variety of insectsmakes it more likely that this species might not only attack pests , but also beneficial insectssimultaneously. Another problem is the neglection of small species, which also can develop intopests. Insects of 1 mm or less in length are not noticed or left alone (Way, 1954). And among theselittle fellows, there are some which are quite hazardous to the cocoa trees. So an important potentialsource of infections and carriers of diseases are overlooked.

AdvantagesHowever, all the authors cited above do see Oecophylla as a potential biological agent. The

advantages outweigh the disadvantages according to the results of researches which have been donein the past. Therefore the effectiveness of ants against pests must be high. References for thisstatement can be found in Way & Khoo (1992), Van Mele & Cuc (2003) and Way (1954). So if O.longinoda is considered to be a beneficial biological agent, what are the advantages?As described before, O. longinoda is a very aggressive species. Besides the disadvantages for theharvesters, this is one of the major advantages the ant introduces in the battle against pests. If anypotential food source comes across the path of O. longinoda workers, it will be attacked and, ifpossible killed. So the numerous pests, which will be encountered many times, will be reduced innumber. Also, a possible secondary pest outbreak is less likely, because these will be attacked by theants as well. This is one of the advantages for a generalist as O. longinoda. O. longinoda is not likelyto become a pest itself, because the food sources will not be sufficient to provide for too largecolonies, although it is not excluded.While “small-size” species are actually neglected, the presence of O. longinoda is not without anyaffect on the populations of these little insects. Way (1954) concludes that the abundance of O.longinoda causes the population sizes of “mini-insects” to decrease. So this suppression, not bypredation but by ‘presence’, could be added to the beneficial aspects of O. longinoda. Yet to whatextend and how effective this control by ‘presence’ reaches, is not known. Therefore it is not sure if itis effective enough to use O. longinoda as a biological agent for these species. Neverthelessobserved trees, occupied by O. longinoda, did not accommodate any red spider, which cause seriousdamage in other cocoa trees. Since the abundance of O. longinoda is linked to the abundance of other species, it also influencesthe populations of the Homoptera attended by the other species. This is important for certain speciesof Homoptera which are considered to be a threat for the cocoa yield. Some Pheidole species tend and benefit species of Pseudococcidae. Some of these Pseudococcidaecause severe damage to plants or transmit virus diseases (as reviewed in Way, 1953). So, if O.longinoda is favoured by human interference, at the expense of Pheidole species, it is also beneficialin destroying these non beneficial Pseudococcidae because their attenders are gone. This could beanother reason why interference in favour of O. longinoda could be beneficial in fighting diseases orpests. Human interference might be needed before O. longinoda can be effective as a biological agent.What we will try to achieve is to develop an easy and labour-extensive way of introducing andmaintaining O. longinoda populations in cocoa plantations. We will also try to give advice on how theants can be taken care of in such a way they can carry out their function as good as possible. So oneof the aspects which have to be considered next to the ecological aspects is the amount of labour ourmethod will acquire. It has to be applicable to serve the farmers and let them adopt the results of ourfieldwork. And when the application of control by the use of ants is too labour-intensive or too difficult,it is likely the farmers will not adopt it. The costs for this application should also stay below the costs

spend for ‘general’ pest management. But before the fieldwork can begin, several other factors haveto be considered.

Cultural aspectsWhile the production was very high back in the seventies, the yield decreased in the nineties

till it was only a third of the yield of that in 1965. Several reasons are the cause of this reduction inyield. Government interference, social structures and declined forest rent prevented great yields asgained in the other parts of the world (Brazil and Malaise). Ghana -and most of West Africa's cocoaproducing countries- had only small stock farmers, which were not able to buy enough insecticides.This prevented the cocoa from damage by use of chemicals as was the case in other cocoaproducing countries. While these countries produced more in quantity, they lost in quality. Thisfavoured the Ghanese cocoa which gave Ghanese farmers the chance to get a higher price for thecocoa they produced, encouraging the production of cocoa in such a manner Ghana is now thesecond producer of cocoa in the world (Leiter & Harding, 2004).Cocoa is considered to be a crop with the potential to bring wealth to the Ghanese people. Andbesides gold, it is the most important export product, making Ghana a relatively prosperous land. The farmers in Ghana have to acknowledge the importance of IPM. We do not know how IPM andclassical methods of controlling pests are percepted. The project “Convergence of Science” is dealingwith this issue. Our supervisor, Godwin Ayenor, is closely related to these activities so we might directpart of our fieldwork in this direction.This leads us to the following question: Will we be able to introduce the ant successfully as abiological agent and will this be adopted by farmers. To answer this question part of our research willbe focussed on the perception of ants, and especially O. longinoda, by farmers. Also they possibly willbe questioned about their experience with these insects. If necessary and practical a protocol is triedto be established about how to familiarize farmers with these biological agents. What should be keptin mind is the applicability of the ants as a biological agent. When the application is as simple aspossible, the farmers will adopt it faster. The amount of work has to be considered -the farmers cannot be busy whole day long with ant husbandry-. Although not necessary a higher yield means more income -one of the objects which is tried to beachieved- the introduction of ants will be, with present knowledge only have a positive effect on theproduction of cocoa. Less insecticides, higher quality of cocoa and higher yield will be the expectedresults of our field study. Results which make it worth the effort!

RESEARCH AREA

The work will be carried out in a research field at the Cocoa Research Institute of Ghana (CRIG) inTafo, Ghana. Describe conditions of research fields. Ghana knows a tropical climate with temperatures ranging from 21 to 32 ºC. In the South, were Tafo is located,there are two rainy seasons, one from March to July and the other from September to October. In August thereoccurs a short dry season, and there is a relatively long one from mid­October to March. The South of Ghana isvery humid with an annual rainfall averaging 2,030 mm, while the North is relatively dry (website 2). ­Vegetation? (http://www.africanconservation.com/ghanaprofile.html)Both  crematogaster clariventris  and  O. longinoda  appear to be the most numerous species of ants in cocoafields in Tafo, which consist of Amelonado cocoa trees (Bigger, 1981). Bigger (1981) also describes whichother ants species are most abundant in cocoa fields and refers to different studies which estimate ant speciesoccurence. 

MATERIALS AND METHODS

­FUNDAMENTAL ASPECTS­

Structure and composition of the nestEstimates of population size and distribution of  O. longinoda and Oecophylla ants have already been

given  by  Way  (1954)   and  Vanderplank   (1960).  Both   studies  only  give   colony  size   estimates  of   coloniesoccurring in coconut and glove trees.   Way (1954) states there is a difference in nest composition betweendifferent tree species. However he mentions that outcomes of his study should be treated with reserve, sincethey are based on relatively few quantitative data. For colonies in cocoa trees we have not found any estimatesyet, and therefore we will look at this in our study. 

• What is the distribution and composition of the O. longinoda population within and outside thenest, of nests in cocoa plantations?

• What is the ratio of different castes of ants (small workers, large workers, males, queens, pupae andlarvae) within and outside the nest?

­Method; nest compositionTo find out how the ant’s population within the nest looks like we will study ant nests in the laboratory. Nests ofdifferent colonies of ants will be abscised from their trees, packed in plastic bags for transport and after that (assoon as possible) be frozen at ­20 ºC for x hour. We will open the nests after defrosting and all individual antswill be separated from the nest debris and grouped into castes  (small workers, large workers, males, queens,pupae and larvae).  This will be done with  x  different nests from  x  different colonies,  in x different periods(Way, 1954, Lommen et al., 2004). Alternatively, in absence of freezing possibilities we can knockdown theants with an effective insecticide (Haines & Haines, 1978, Vanderplank, 1960). To describe nest compositionwe will count the number of individuals per caste per nest population, determine weight of each stage, andcalculate percentages of stages (Haines & Haines, 1978, Lommen et al., 2004). Besides that,  we will collect  all  other  insects being present  in  the nests  in order  to detect possible naturalenemies of O. longinoda (see paragraph on ‘natural enemies’).Nests will be collected in the field, where O. longinoda occurs naturally and is relative abundant.­Measuring average body length, maximum head width, head length and wing length (etc.). ­How much time will it cost per nest? How many nests should we count?­We can look at number of leaves of nests. Is there a correlation between population size per nest, and numberof leaves used per nest?

­Method; ant distribution outside the nestTo determine the distribution of ants outside the nest we have to observe how many and what kind of ants(large/small workers, and perhaps males and queens) go in and out the nest. We can combine this with ourexperiment in which we would like to determine (foraging) activity of the ants. 

Natural enemiesNatural enemies of Oecophylla ants are mainly comprised by other ant species. The main Oecophylla

predators and competitors have already been discussed in the paragraph on O. longinoda (introduction). In this study we would like to investigate which ant species specifically predate and parasitize on/ or competewith O. longinoda in cocoa plantations in Ghana. Besides that we would like to find out whether or not there areany other natural enemies of O. longinoda which might be possible since numerous small hymenopterans anddipterans have been found  in  Oecophylla  nests, and some of  these have been suspected to be parasitic onOecophylla larvae (Vanderplank, 1960). 

• Which natural enemies of O. longinoda occur in cocoa plantations? • Which predatory ant species should definitely not be present in the cocoa plantation in order to

prevent competition with O. longinoda? And thus which plants related with these ‘enemies’ shouldbe avoided?

• Which ant species should be reduced or be controlled in order to promote O. longinoda abundance?

­Method: Parasites/predators?When investigating nest composition (see paragraph ‘Structure and composition of the nest’), we will not justlook at the ant population present, but also collect possible other insect species. After collecting these species,we will try to identify them and search in the literature whether or not these insects have the potential to beparasitic  or  predatory  on  O.  longinoda.  Whenever  we  find   these   insects  not   to  be  part  of   the  diet   of  O.longinoda  (see paragraph ‘food consumption’) a possible conclusion  is  that  either  these  insects are naturalenemies of O. longinoda or they live in, for example, a mutualism with the ants. If we suspect certain insects toparasitise on the ants we can also, instead of kill the population of ants within the nest, try to anaesthetise them,and select individuals (e.g. a certain number of workers and larvae) which we will observe in quarantine for theperiod they live. We then might observe certain parasites eventually hatching out of the workers/larvae. 

­Method: Ant enemies?We should first determine which ant species occur naturally in the region and cocoa plantations specifically,and which of these are known to be dominant species (literature and observations). We can also collect all antspecies occurring in the plantations and try to identify them. An ant collecting method has been described byBigger (1981). Secondly we will try to observe possible fights between O. longinoda and different ant species.We might already be able to conclude out of these observations which ant species are dominating O. longinoda. Alternatively, we can put two nests with equal ant populations (estimation) of two different species (of whichone is O. longinoda) close together (lab?). They probably start to fight with each other and maybe we can thensay something about dominance of one of the species over the other. Another possibility could hold observingwhich ant species occur in the same trees or else live closely together with O. longinoda, and which certainly donot. The first ones will possibly tolerate O. longinoda, or the other way around. The ant species which do notlive closely together, while physically possible, could be either dominant or inferior to O. longinoda.

Ecosystem distribution In the study by Way (1954) 5 up to 151 nests per colony of O. longinoda have been found, Peng et al.

(1998) found 25 up to 153 nests per colony of O. smaragdina and Vanderplank (1960) even found Oecophyllacolonies  with a  number of  nests  reaching up  to  192. Distribution  within systems often shows a clear   'antmosaic',   in which several distinct  ant  territories can be found mainly based on levels of  dominance of  thespecies (Bigger, 1981). For this study we would like to know how many nests per colony of O. longinoda occur on average in cocoaplantations. We would like to look at possible factors determining distribution of colonies through the cocoaplantations. For example, does O. longinoda significantly occurs in higher numbers on specific vegetation closeor within the cocoa plantations? Which kind of ‘disturbance’ (e.g. human activities close to the plantations)result in lower abundances? Etc. 

• How many nests per colony?• Distribution of ants within the ecosystem? • How far do O. longinoda ants they spread outside the nest to forage?

Method: number of nests per colonyTo determine how many nests can be found within each colony, we will transfer an x number of ants per nest toother nests. We will observe the ants after transfer for approximately 10 minutes and if they will start to fightwith ants in the other nests we can conclude the nests do not belong to the same colony. When ants appear notto fight, reciprocal transplants will be carried out to ensure that nests do belong to the same colony. If there aremany nests within one (cocoa) tree we can also assume the nests in this tree belong to the same colony, countthe number of nests within one tree, and only transfer ants between different trees to find out the actual number

of nests per colony. Colonies should be selected randomly, maybe in different plantations (Palmer, 2004). If weknow which nests belong to  the same colonies we can try  to map the colonies and might be able to drawconclusions on for example distribution, overlap of colonies, etc. and try to relate this with other aspects such asuse of chemicals etc. (Way & Khoo, 1991). Another method for determining colony size has been described byPeng et al. (1998). They determined the boundary of each ant colony by following the ant trail till were it ends,and then count the nests within these boundaries (Peng et al., 1998). 

­Method: distribution of ants within the ecosystemTo estimate the 'ant mosaic' pattern (Bigger, 1981) within the cocoa fields we should map the distribution ofants. We might be able to achieve this by observing ant species occurrence through the field. We will randomlychoose trees on which we will observe which ant species occur and map this. Due to differences in levels ofdominance we will be able to see which ant distribution patterns occur (Bigger, 1981). 

­Method: spreading of antsWe can possibly tag ants of a specific nest by for example the use of radioactive compounds (Vanderplank,1960).  After   a   time  period   of  x  days  (the   ants  have   been  offered   the  opportunity   to   spread   through   theenvironment) we can collect samples at different distances from the nest (e.g. put ant traps or collect deathants), and therefore observe how far ants spread outside the nest (possible?).

Food consumptionWay (1954) described, among others, that O. longinoda ants feed on a wide diversity of insect species,

representing many orders of insects. Since we are interested in whether or not  O. longinoda  does influenceimportant cocoa pests, it is important to know on which insects they exactly prey  on. In case  O. longinodamainly feeds on insects which just represent minor or no pests, it might come true these ants would not be sucha good candidate for use of biological control of cocoa pests. However, this is very unlikely, regarded theresults of other studies. Dejean (1990) presented clear differences between prey species being captured in the central territory and theones captured in the ground territory. On the tree, prey comprised mainly winged insects, whereas workersforaging on the ground caught insects running around or which were hiding under the leaf litter (Dejean, 1990).Regarding these results, there might be a difference in prey capture by ants living in nests which can only bereached by the stem of the tree in contrast to ants living in nests which can be reached both by the stem of thetree as well as tree branches from other trees.Probably the latter ant populations’ diet will represent a higher percentage of winged insects. 

• Which prey (especially cocoa pests) are consumed by O. longinoda ants, and are there any otherfood sources of importance?

• Do the ants prefer to feed on capsids (the major cocoa pests) above other insects?• Is there a difference in prey­diet between ants living in nests which can only be reached by the stem

of the tree, and ants living in nests which can be reached both by the stem of the tree and connectingbranches of surrounding vegetation? (Is there a wider diet range if ants can also disperse betweentree crowns?)

­Method; food consumptionWe will collect all prey which are being transported into the nest during  x  hours of several  (x number)  O.longinoda populations which can only be reached through the stem of the tree in which the nest in located. Theprey insects can be grouped into pests and non­pests, and the  total numbers of  insects  per species will  becounted. This collecting will also be done for ant populations which live in nests which can also be reachedthrough the tree canopy. Therefore prey will be collected, which are being transferred into the nest by trailsconnecting different trees.Out of these numbers the division of insect species will be calculated, as well as the proportion of pest insects inthe diet of ants. These results are correlated with the relative abundances of the prey species and conclusions

can be drawn concerning  food preferences.  Other   feeding  behaviours  will  be  observed,  such as  attendingHomoptera species for their honeydew. Outcomes will be taken into account in the experiments described in'Introduction of nests/ Transfer of nests/ Maintenance of nests'. 

­Method; prey preferenceWhen known what kind of  prey  O.  longinoda  feeds on, preference tests  can be carried out with  the  mostimportant prey insects (e.g. most important pest/capsid species). 

Orientation and communication of the ants• Do they use chemical cues (communication) or for example sunlight as well?­­> Has already been described by several studies, for O. smaragdina. 

­APPLIED ASPECTS­

Activity of the antsDejean (1990) showed that O. longinoda ants are the most active during the period of daylight, and thus

activity seems to be coupled with light presence/intensity. As mentioned in the introduction, the highest activityoccurs between 6.00 am and 6.00 pm. However, this are data about nests located in citrus trees in Zaire, andsince we would like to know whether or not there is a difference, activity will be measured again, but now fornests located in cocoa trees in Ghana. 

• At what time of the day the ants are the least active? 

­Method; foraging activityWe will count how many ants (and of which castes) go in and out the nest (which can only be reached by thestem of the tree in which the nest is located), to determine overall activity. However, high activity or numerousant trails  might make carrying out  the method described above quite difficult.  If  this  method will not givequalifying results or observations are thus hard to make, the method described by Greenslade (1972) can beused. This involves drawing a line close to the nest (e.g. on a foraging trail) and counting the number of antscrossing this line. Countings will be made every 20 minutes for x minutes, during 24 hours, for 2 days. Foragingactivity and caste ratio will be calculated. ­Foraging activity is correlated with caste ratio, different colonies, daytime, and way of disturbance (naturallyor experimentally)?

Introduction of nests/ Transfer of nests/ Maintenance of nests In   order   to   introduce  Oecophylla  nests   in   cocoa   plantations   many   aspects   should   be   taken   into

consideration  before   actually   being   practiced.   Two  main   topics   must   be  considered:   ant   competition  andenvironmental   conditions   (which   might   become   favourable   through   manipulations).   This   has   been   moreextensively described in the introduction, but a short summary is given below. As mentioned before, other ant species are often the main natural enemies of  Oecophylla. Therefore it is ofgreat   importance  to  reduce ant  competition as  much as possible,  since  otherwise  introduced  O.  longinodapopulations might possibly totally disappear from a system (Way & Khoo, 1992 and Van Mele & Cuc, 2003).This aspect will be looked at in the paragraph ‘interaction with environment’. If we know which ant speciesmight harm  O. longinoda  populations, we can for example remove nesting sites of these ants. Competitionbetween different colonies of  O. longinoda  should be minimised as well, for example by removing possibleconnections between trees which have been colonised by different colonies (Van Mele & Cuc, 2003). The second aspect  to consider  is  providing  the most  favourable conditions  for  Oecophylla  populations forestablishment and maintenance, which can be obtained by several different manipulations (Way & Khoo, 1992).Quality  and quantity  of   food sources,  possibilities   to  spread   through a plantation,  reduction of   the  use ofchemicals, habitat quality, number of good nesting sites and so on (Way & Khoo, 1992, Way & Khoo, 1991,

Van Mele & Cuc, 2000) are factors which should be looked at. Often  additional   food  sources  have  been  offered   to  Oecophylla  populations   in  order   to   increase   survival,reproduction and longevity. In some plantations  Oecophylla  populations are being encouraged by supplyingthem with honey or sugar (Vanderplank, 1960), others are being supplied with food such as fish or chickenintestines, as done in citrus orchards in the Mekong Delta (Van Mele & Cuc, 2000). Supplied honey or sugardoes not only directly encourage ants, but also indirectly by attracting insects, such as bees and wasps, whichcan serve  as  prey  (Vanderplank, 1960).  According  to  Van Mele  & Cuc (2003)  only  2   to  3   times  a  yearadditional food should be provided to prevent ants living from your food sources only. Place the food sources atdifferent parts of the plantations to keep the populations more evenly distributed. Tree connections can be madeby placing bamboo sticks or nylon ropes between different trees. Of course the reduction of human disturbance is very important in maintaining stable O. longinoda populations.The reduction of use of chemicals, such as insecticides and pesticides, is very important, since these do not onlynegatively influence the target organisms, but also O. longinoda ants and other beneficial organisms (Van Mele& Cuc, 2003). At least one of the nests within the colony being transferred should contain a queen in order to be able tosuccessfully transfer ant colonies. As discussed before, colonies often contain only one, or just a few queens,and transplanted queen­less populations are much less stable than those which do have a queen. Those without aqueen even often eventually die out (Vanderplank, 1960 and Peng  et al.,  1998). Besides  that, according toVanderplank (1960), it is impossible to introduce a ‘queen’ Oecophylla to a ‘queen­less’ colony, since all hisdifferent  methods of  trying to failed. The article  by Peng  et al. (1998) describes a method for locating  O.smaragdina queens without destructive sampling. They found that within a colony the tree with the queen nesthad most ant trails connecting to other trees in the colony and that trees with queen ant nests also had more antnests than the others. Trees with queen ant nests can not be characterised on tree size, species and positionwithin the colony (Peng et al., 1998). The most suitable moment for transfer is when O. longinoda shows the least activity, since then most ants willbe within  their  nests.  Dejean (1990) showed a clear  diurnal  pattern  in activity  of  O. longinoda  ants,  withforaging activity being highest in between approximately 6.00 am and 6.00 pm. We therefore assume that thebest moment for transfer of ant nests is between 6.00 pm and 6.00 am. However, these moments have beenestimated for Zaire, and depend on light intensity (Dejean, 1990). We thus think the best moment for transfer ofnests is in the period of darkness, for then the ants are considered to be the least active. At last, vegetational conditions should be matching the optimal criteria; deciduousness, relatively large leaves,and high leave quality are best for nest building of  Oecophylla  ants (Greenslade, 1972). Also environmentalconditions   should   be   considered   which   is   most   optimally   a   tropical   climate   (relatively   high   rainfall,temperature,   and   diurnal   and   seasonal   variation   less   pronounced)   (Way,   1954).   And   of   course   certainHomoptera species should be present for providing honeydew (Bigger, 1981). 

• Can the nests be transferred from one farm to another, or one plantation to another, and how?• Which Homoptera species should definitely be present?• Should additional food sources be supplied (does this significantly lead to stronger/larger colonies)?• At which location should the nest be placed? (Do we for example need a ‘fake’ nest structure?)

­Method: Homoptera presence?Compare colony survival, growth and longevity of ant populations which attend different Homoptera species.Observe which associations between ants and Homopteras can be seen, and score which are most abundant. Wecan use the scoring system used by Löhr (1992); for ants from 0­4 (0: no ants, 1: ≥1≤20 ants, 2:>20≤100 ants,3:>100≤250 ants, 4: ≥250 ants seen foraging on the for example the tree stem) and for aphids 0­5 (0: no aphids,1:single aphids on lower leaves only, 2: small groups of aphids on lower leaves only, 3: sizable colonies ofaphids on lower leaves and few aphids on youngest open spadices, 4: high numbers of aphids on older andyoung spadices, someone unopened spadices and spear leaf, 5: high aphid numbers all over the upper part of thecrown and all leaves and fruits). ­­> for coconut palms 

­Method: effects of different factors?An experiment to compare colony survival, growth and longevity of different O. longinoda populations underdifferent conditions has to be designed. For example the effect of offering additional food sources, effect ofconstructing tree connections, optimal time of transfer of nests, effect of occurrence of different environmentalconditions and many more could be considered. If we, for example, want to know whether or not there is a significant positive effect on ant populations whenproviding additional food sources, comparing yield of cocoa fields having ‘natural’  O. longinoda populationswith each other could give some clues. We have to make sure these cocoa fields comprise approximately thesame size of  O. longinoda  populations (e.g. approximately same number of nests),   that  other ‘disturbance’factors are kept at equal levels and that multiple replicas are being compared. These experiments should bestarted at the beginning of our research period, since we have to look at long­term effects. We will offer half ofthe number of fields additional food sources (distributed at several different places in the field) about x timesduring the period of x months. Cocoa yield (see the paragraph on 'number of ants required for capsid control')and population sizes (e.g. number of nests) will be estimated at the end of the research period, and comparedwith each other. When offering additional food sources does positively influence ant populations, and thereforepossibly cocoa yield, a significant difference between both tests is to be expected (control fields versus fields inwhich food sources have been offered). Similar experiments can be conducted for different factors.

Number of ants required for capsid controlIt has often been described that in order to develop sustainable biological control measures, one of the

most important things to achieve is an equal or even higher cocoa yield as achieved with 'general' management.Therefore a certain level of pest suppression, which should be at least equal to the suppression occurring inabsence of biological control, should be achieved. In order to find out which population level of  Oecophyllaants should be maintained, we first have to know whether damage by capsids can be reduced by ants at an equal(or  even higher)  level  compared to the reduction as a result of chemical use. Therefore, we would like  toestimate the mean population (/nest/colony) size needed for sufficient capsid suppression. We will conduct twostudies. First we will compare average cocoa yield of two plantations; one with Oecophylla ants (in densitiesoccurring under ‘natural’ conditions) and one without Oecophylla ants but managed through the ‘general’ use ofinsecticides. The other study will involve the comparison of cocoa yield in fields with different  Oecophylladensities  (ranging from level 0, natural conditions,  up to x,  introducing ants or adding several encouragingmanipulations). Among others Vanderplank (1960), has already shown that in coconut palm plantations therewas indeed a correlation between yield increase and increase in percentage of Oecophylla present. We have  to   take   into  account   that   there  might  be  severe  Homoptera damage  in  case  of  high  Oecophylladensities. However, this does not per se have to happen since there probably is a maximum density determinedby one of the following factors; available food sources, inter­ and intraspecific competition, available nestingsites etcetera. The ant density at which Homoptera damage will be a problem might thus never be reached. Thisconfirms several studies (e.g. as reviewed in Van Mele & Cuc, 2003) which say that Homoptera outbreaks havenever been associated with Oecophylla populations. 

• How many nests of ants are adequate on a certain number of cocoa trees/certain surface of cocoaplantations to keep capsids at more tolerable levels?

• What is the minimal ant density needed to keep this level? • Is the protection against pests by Oecophylla as sufficient as it is by the use of chemicals?

­Method; effect of ant predation on crop yieldThe performance of  the  cocoa trees,  with and without  O. longinoda  populations,  will  be compared by  thenumber of cocoa beans and the damage score (0; no damage, 1; slight damage but no reduction in bean size, 2;damage and slight reduction of bean size, 3; damage and much reduction in bean size.  (Proper definitions ofdamage and size reduction, and other possible effects can only be given after observations in the field)­Is this sufficient to eventually describe loss in yield?­Can other measuring methods be used? (e.g. such as damage to foliage expressed by loss in number of leaves

or surface damage?) (Löhr, 1992)

Interactions between different colonies It is known that  Oecophylla ants do show intraspecific competition. Ants of different colonies do not

accept each other in their territories, and when colonies are forced to mix, it results in one colony killing theother   (Vanderplank,   1960).  Vanderplank   (1960)   has   tried   several   methods,   which  often   are   successful   inhoneybee populations, for mixing different ant colonies, but all failed. We therefore suggest to keep contactbetween different Oecophylla colonies as low as possible. Different ant colony territories should definitely notshow overlap, and it even might be better to minimise the number of colonies used in one plantation. However,there might be a danger to be dependent on just one or a few colonies. 

• How can we avoid inter­boundary fight amongst nests that tend to reduce their numbers? In otherwords, how can we increase their numbers without upsetting the ecosystem? 

­Method; reduction interaction between different coloniesBesides minimising contact between different O. longinoda colonies, it might be possible to reduceaggressiveness in other ways. When forced to introduce more than one colony, physical barriers could becreated to prevent contact between species. Maybe we can do something with pheromones of different ant colonies?à Or leave this part out; we do not have a very specific idea on how to solve this problem.

Use of chemicals (Insecticides/pesticides/fungicides)Chemicals do not  often  only  influence pest   insects  but  also the  beneficial  organisms and humans.

Several studies have already shown the harmful effects of chemicals on Oecophylla ants. Vanderplank (1960)for example shows considerable increased movement of  Oecophylla  colonies or even total disappearance ofcolonies living in fields which were threatened severely with chemicals. In the course of biological control itmight be very good to show that chemicals do have a very negative effect on  O. longinoda  ants, and a niceoutcome would be as well if biodegradable or bio­insecticides appear to have less negative influence on  O.longinoda ants. 

• Are they susceptible in the presence of other cocoa insecticides­ both synthetic and biodegradableor bio­insecticides such as Aqueous Neem Seed Extracts? 

• How long does it take for an ant population to fully recover after spraying events?             Method: Effect of the use of chemicalsFirst we will select chemicals which are widely being used in cocoa plantations and try to estimate the generaldoses in which they are being applied. Like Vanderplank (1960) did, we will define an x number of plots ontowhich we will apply several different chemicals in different doses. We try to start with approximately equalnumber   of   nests   (/colonies)   of  O.   longinoda  in   each   plot,   and   apply   chemicals   at   certain   time   intervals(depending on  general   application   recommendations).  Re­counting   the  number of  nests   (/colonies)   after   aperiod of x months will tell us what kind of influence the chemicals have and which of those are the worst formaintenance of O. longinoda colonies is. After calculating the population increase/decrease we could also seehow long it would take for a population to recover till ‘normal’ size, if spraying has stopped. 

Cultural aspectsAs described in the introduction there are also few very important cultural aspects which should be

involved in the research, especially when it comes to true application of our (and other) findings concerning theuse of  Oecophylla  ants   in  the control  of  cocoa capsids.  First  of  all   farmers  should be made aware of   thealternative possibility of farming, that is in a biological way. They should know not all insects are pests, andmany even may contribute to a higher yield and a better natural environment. The IPM program of course is avery good way of participial learning in which knowledge concerning biological control measures can reach

farmers  effectively.  Farmers should be made familiar with  the advantages of  the use of  Oecophylla  like ahealthier environment, the saving of money and a possible higher yield. Therefore we would like to spend the very last part of our thesis on transforming our scientific findings into alanguage understandable for farmers. The possible findings which could be of interest for biological control ofcapsids in cocoa plantations should thus eventually become part of the  'Convergence of Science project'  inwhich the farmers actively contribute to a better knowledge on biological control.  

­Method; cultural aspects We will not thoroughly investigate the cultural aspects involved in the possible use of O. longinoda in controlof cocoa capsids, but we will report the things we will intercept concerning this subject as much as possible andtry to give some possible research implications on this. If time lets us to, we might even carry out a smallinterview research in which we will ask questions about experiences with ants, perception of the ants, abouthow much labour and costs farmers are willing to invest in promoting O. longinoda ants in their plantations andmany more. 

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smaragdina en herbivore insecten, docteraalverslag, Vakgroep Vegetatiekunde, Plantenecologie en Onkruidkunde, Landbouwhogeschool Wageningen

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relationship to the coconut bug Pseudotheraptus wayi Brown (Coreidae), Journal of animalecology, Vol. 29, pp. 15­33

*Van Mele, P., Cuc, N.T.T. and Van Huis, A. (2002) Direct and indirect influences of the weaver ant Oecophylla smaragdina on citrus farmers’ pest perceptions and

  management practices in Mekong Delta, Vietnam, International journal of pestmanagement, Vol. 48., pp. 225­232

*Van Mele, P. & Cuc, N.T.T. (2000) Evolution and status of Oecophylla smaragdina (Fabricius) as a pest control agent in citrus in the Mekong Delta, Vietnam, International journal of pest management, Vol. 46, pp. 295­301

*Van Mele, P. & Cuc, N.T.T. (2003) Ants as friends: Improving your tree crops with weaver ants, CABI Bioscience, pp. 67

*Way, M.J. (1954) Studies of the life history and ecology of the ant Oecophylla longinoda Latreille, Bulletin of entomological research, Vol. 45, pp. 93­112

*Way, M.J. (1954a) Studies on the association of the ant Oecophylla longinoda (Latr.) (Formicidae)with the scale insect Saissetia zanzibarensis Williams (Coccidae), Bulletin of entomologicalresearch, Vol. 45, pp. 113­134

*Way, W.J. & Khoo, K.C. (1991) Colony dispersion and nesting habits of the ants, Dolichoderus thoracicusand Oecophylla smaragdina (Hymenoptera: Formicidae), inrelation to their success as biological control agents on cocoa, Bulletin of entomological research, Vol. 81, pp. 341­35

*Way, W.J. & Khoo, K.C. (1992) Role of ants in pest management, annual review of entomology,Vol. 37, pp. 479­503

*Website 1; http://antbase.org/ants/africa (20 April)*Website 2; http://www.Ghana.com (20 April) *Website 3: http://nationalzoo.si.edu/ConservationsAndScience/MigratoryBirds/Research/Cacao

/padi.cfm (20 April)*Wojtusiak, J, Godzinska, E.J. & Dejean A. (1995) Capture and retrieval of very large prey by workers

of the African weaver ant, Oecophylla longinoda (Latreille 1802), Tropical zoology, Vol. 8, pp.

309­318

LITERATURE WHICH HAS NOT BEEN FOUND, OR WHICH HAS NOT BEEN USED YET

*Dejean, A. (1991) Adaptations of O. longinoda to spatiotemporal variations in prey density, Entomophaga, Vol. 36, pp. 29­54

*Dejean, A. & Beugnon, G. (1991) Persistent intercolonial trunkroute­marking in the African weaverant Oecophylla longinoda Latreille (Hymenoptera, Formicidae): Tom Thumb’s versusAriadne’s orienting strategies, Ethology, Vol. 88, pp. 89­98

*Dejean, A., Lenoir, A. & Godzinska, E.J. (1994) The hunting behaviour of polyrhachis­laboriosa, a non­dominant arboreal ant of the african equatorial forest (Hymenoptera, Formicidae, formicinae), Sociobiology, Vol. 23, pp. 293­313 (not in library)

*Dejean, A. (1996) Trail sharing in African arboreal ants (Hymenoptera: Formicidae), Sociobology, Vol. 27, pp. 1­10 (not in library)

*Dejean, A., Djiéto­Lordon, C. & Durand, J.L. (1997) Ant mosaic in oil palm plantations of thesouthwest province of Cameroon: Impact on leaf miner beetle (Coleoptera: Chrysomelidae), Journal of economic entomology, Vol. 90, pp. 1092­1096

*Mercier, J.L., Lenoir, A. & Dejean, A. (1997) Ritualised versus aggressive behaviours displayed byPolyrhachis laboriosa (F.Smith) during intraspecific competition, behavioural processes, Vol.41, pp. 39­50