Biological control of the South American Tomato Pinworm, Tuta

absoluta (Lep.: Gelechiidae), with releases of Trichogramma

achaeae (Hym.: Trichogrammatidae) on tomato greenhouse of

Spain

T. Cabello1, J.R. Gallego

1, E. Vila

2, A. Soler

2, M. del Pino

3, A. Carnero

3, E.

Hernández-Suárez3, A. Polaszek

4

1Dpto. Biologia Aplicada, Universidad de Almeria. Ctra. Sacramento s/n, 04120-

Almeria, Spain.E-mail: tcabello@ual.es; 2Agrobío, Ctra Nacional 340, Km. 419,

04745-La Mojonera, Almería, Spain; 3Instituto Canario de Investigaciones Agrarias

ICIA, Valle de Guerra, P.O. 60, 38200-La Laguna, Tenerife, Spain; 4Department of

Entomology, Natural History Museum, Cromwell Road, London SW7 5BD, U.K.

Abstract: The egg parasitoid Trichogramma achaeae has been identified as a candidate for

biological control of the South American Tomato Pinworm, Tuta absoluta. On laboratory

conditions a marginal attack rate of 100 % was found and 83.3 % of the parasitized eggs

developed until the blackhead stage (apparent parasitism). On greenhouse conditions a high

efficacy (91.74 % of damage reduction) was obtained when releasing 30 adults/ plant (= 75

adults/ m2) every 3-4 days on August and September of 2008. This shows that this parasitoid

can be a good weapon to control T. absoluta on greenhouses of the southeast of Spain.

Key words: greenhouse, tomato, exotic pest species, oophagous parasitoid, biological

control, Tuta absoluta, Trichogramma achaeae.

Introduction

The South American Tomato Pinworm, Tuta absoluta (Meyrick), has spread from

Central America to most of South America, and it is considered one of the major pests

on tomato and other solanaceous crops (EPPO, 2005). Its chemical control is difficult,

firstly due to its biology, because of the mine-feeding behaviour of larvae (Branco. &

Franca, 1993; Urbaneja et al., 2007), which has originated an intensive use of chemical

treatments. Secondly, it has developed insecticide resistance to the active ingredients

used until now (Siqueira et al., 2000; EPPO, 2005; Lietti et al., 2005). Consequently,

biological control has been developed and it is being applied on several South American

countries, especially using the oophagous parasitoids Trichogramma pretiosum (Riley)

and T. nerudai Pintureau and Gerding (Riquelme & Botto, 2003; Parra & Zucchim,

2004; Bueno, 2005; Faria et al., 2008).

T. absoluta was accidentally introduced in Castellón, Spain, in 2006; it has spread

from Comunidad Valenciana to Murcia and Ibiza (Urbaneja et al., 2007; EPPO, 2008)

and first infestations were detected in the greenhouses of Almeria in 2008. This

quarantine pest has caused severity damage on tomato crops in Murcia area (Lucas et

al., 2009), although impact is still fairly low in Andalucía (Gonzalez-Garcia, 2009).

Several species of autochthonous predators have been evaluated as biological control

agents in Spain with promising results, mainly the mirid bugs Nesidiocoris tenuis

(Reuter) and Macrolophus pygmaeus (Rambur) (Urbaneja et al., 2008) and the damsel

bug Nabis pseudoferus Remane (Cabello, 2009). However, the establishment of these

predators into the crops is often too slow to avoid damage of the pest, and consequently

chemical treatments are needed, which disturbs biological control. Then, several works

are being conducted to evaluate autochthonous parasitoids, using them alone or

combined with predators, on tomato greenhouse crops from the southeast of Spain.

Preliminary results with the specie Trichogramma achaeae Nagaraja & Nagarkatti are

presented on this work.

T. achaeae has a world wide distribution; it has been mentioned in Asia (China,

India and Russia), Europe (France, Russia), Africa (Cabo Verde) and the New World

(Argentina, Barbados, Chile, Trinidad & Tobago, U.S.A.). Recently, it has been

reported in Spain (unpublished data). It is an egg parasitoid of 26 Lepidoptera species

belonging to 10 families: Gelechiidae, Geometridae, Noctuidae, Notodontidae,

Oecophoridae, Pieridae, Pyralidae, Sphingidae, Tortricidae and Yponomeutidae

(Polaszek, not publ.). T. achaeae has been evaluated as a biological control agent of

different lepidopteran pests (Jalali et al., 2001; Jalali & Singh, 2002; Jalali et al., 2002;

Chandrashekhar et al., 2003; Yadav & Anand, 2003) and is commercially available in

India (Nagaraja et al., 2002).

Material and methods

Insects rearing The individuals of T. absoluta used in the trials were obtained from a laboratory rearing

on tomato leaves. The rearing of T. achaea, also in the laboratory, was conducted using

eggs of Ephestia kuehniella Zeller as alternative host, according to the methodology

described by Cabello (1985).

Laboratory bioassay

A preliminary test under laboratory conditions (25±1º C, 60-80 % RH and 16:8 hours

L:D) was carried out to evaluate acceptance and parasitation of T. absoluta eggs by

females of the parasitoid. Methodology was adapted from Brotodjojo & Walter (2006),

with the exception that 10 eggs of T. absoluta (less than 24 hours aged) were offered to

each female. 10 repetitions were conducted. All the parasitized eggs were developed

until adult emergence.

Greenhouse bioassay To evaluate the efficacy of T. achaea a test was conducted in a commercial greenhouse

of Almeria (Spain), between August the 27th and September the 22

th of 2008. Eight

cages (8 m2) were placed into the greenhouse with 20 tomato plants (Cherry variety) per

cage arranged on pots. Plants were infested with T. absoluta (4 adults/ plant) when

reaching one meter height.

A total of seven releases of T. achaeae (30 adults/ plant) were conducted every

three or four days on four cages. The other four cages were leaved as a control. The

number of larves of T. absoluta, leaf mines and damaged fruits were counted alter 27

days. Data was analyzed using one-way ANOVA and means were compared with LSD,

SPSS software v. 15 (SPSS, 2006).

Results and discussion

Laboratory bioassay The eggs of T. absoluta were well accepted as hosts by T. achaea (100 % of the eggs

received a laying of the parasitoid). However, only 83.3 % of the eggs developed to the

blackhead stage (prepupa of the parasitoid) (apparent parasitism), while the rest did not

and finally collapsed. The eggs of T. absoluta are smaller than the eggs of the rearing

host, E. kuehniella. Adult females of T. achaeae, both reared on Chrysodeixis chalcites

(Esper) or E. kuehniella, are larger than the eggs of Tuta absoluta but shorter than the

eggs of E. kuehniella (fig.1). It has been described that the size of the rearing host does

affect the parasitism rate of natural hosts (Brotodjojo & Walter, 2006); female

parasitoids in these cases accept host eggs with about the same size as their natal host or

larger ones (Salt, 1940; Nurindah et al., 1999). In the present work T. achaeae accepted

all the offered eggs of T. absoluta, although the small size of the host may have affected

the development of the parasitoid, which could explain why a percentage of the eggs

collapsed.

Adults of Trichogramma also kill host eggs by feeding on them; the host egg is

stung and the female feeds on the drop of liquid appearing at the site of the sting. The

host egg dies, leaving no evidence of parasitism (Knutson, 1998). In some species of

Trichogramma, host feeding contributes significantly to pest control (Vasquez et al.,

1997). In the present work host feeding by female parasitoids was not observed.

However, all the individuals had a supplier of food, a drop of honey:water (1:1), during

the bioassay, and host feeding could happen under field conditions.

T. absoluta egg E. kuehhniella

egg

T. achaeae (from Ch. chalcites egg) T. achaeae (from E.

kuehniella egg)

Population

0

200

400

600

Ave

rag

e (µµ µµ

m)

Length

W idth

Figure 1. Comparative size of E. kuehniella eggs, T. absoluta eggs and adult females of

the parasitoid (T. achaeae) when reared on eggs of Chryxodeixis chalcites or Ephestia

kuehniella (C.L. at P=0.05).

This means that checking the colour as a way to evaluate the ratio of parasitism,

both on field or laboratory conditions, can underestimate the real impact. For this

reason, egg hatch should be recorded in addition to egg parasitism (Knutson, 1998).

It could also explain why data about the rate of parasitism, in this case of T.

pretiosum, shows low values, among 1.5 % (Faria et al., 2008), 22.7-24.4 % (Villas-

Boas & Franca, 1996) and 49.0 % as the maximum (Haji et al., 1995), although it is a

real effective field method to control the pest on several countries of South American.

Then, it is a subject to be considered when establishing the methodology to estimate the

efficacy of Trichogramma to control this pest on field conditions.

Greenhouse bioassay On figure 2 the number of larvae, leaf mines and damaged fruits on tomato plants after

27 days from the beginning of the trial are showed. Number of larvae and damaged

leaves are significantly lower where parasitoids had been released (P < 0.01) and the

numbers of damaged fruits is also lower (P < 0.05) on this treatment. The number of

larves of T. absoluta was 12 times lower on plots where T. achaeae was released

compared with the control. This means a 91.74 % of efficacy.

On one hand, the doses of releases used in this bioassay are similar to that used

commercially in Brasil with T. pretiosum (Freitas et al., 1994: Parra & Zucchim, 2004).

Likewise, the levels of damaged fruits are similar to that described when using T.

pretiosum, with cited values from 2.0 % (Villas-Boas & Franca, 1996) to 13.0 %

(Domingues et al., 2003). On the other hand, the determined efficacy (91.7 %) is lightly

higher than the cited when using T. pretiosum (87.7 %) on said country (Parra &

Zucchim, 2004).

4.95a

0.42b

23.5a

5.86b

0.85a 0.18b

Control T. achaeae releases

Treatment

0

5

10

15

20

25

Nu

mb

er p

er p

lan

t

Larvae

Leaf miners

Damaged fruits

Figure 2. Number of Tuta absoluta larvae and damage on tomato plants counted in a

greenhouse according to the treatment (with or without releases of T. achaeae).

Showed data are promising, but must be completed with other studies (now in

course), mainly to establish the needed releases on greenhouses according to the density

of the pest and the growth stage of the crop, in the protected crops of the southeast of

Spain. A good possibility may be to combine releases of T. achaeae with the mirid

predator N. tenuis. One of the major problems of using N. tenuis in Almeria is his

slowly establishment, needing at least around 4 weeks. Tomato crop is mainly planted at

the end of the summer, so releases are made in autumn, when temperature is dropping.

During this period Tuta absoluta can cause heavy damage, and weekly releases of the

parasitoid could help to guaranty an effective control of the pest.

Acknowledgements

This publication has been realized with the support of the Ministry of Sciences and

Innovation (of Spain): CDTI Programme, CENIT-MEDIODIA Project.

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