32 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 21, 1974

INSECTS DAMAGING BEECH (NOTHOFAGUS) FORESTS

R.H. MILLIGAN

Production Forestry Division, Forest ResearchInstitute, Rangiora

INTRODUCTION

The distribution ofliving and fossil Nothofagusin the southern hemisphere (Skottsberg 1949)

suggests the possibility that it once played a partin colonising primitive and unstable soils

comparable with that played by Pinus in thenorthern hemisphere. Each genus includesspecies which colonise rocky soils of mountainranges and glacial, alluvial and volcanic deposits;each genus is, or has been, represented fromcircumpolar regions to the highlands of thetropics. Those species best adapted as pioneersare most tolerant of variations in soil moisture,nutrients and temperature, but either requireinsolation of the soil for germination or areintolerant of shade as seedlings so that HItleregeneration survives under closed canopy.Since adjacent trees are commonlyinterconnected through root grafts, deaths ofindividual stems do not normally provide rootspace for the development of seedlings. Larger

gaps in the canopy resulting from storm damageor other natura] causes of group mortality tendto be rapidly filled with dense regeneration. Forthese reasons, forests of pioneer species are

typically even-aged except near advancingmargins or where group mortality has occurred(Wardle 1970, Wardle 1974, p. 23 for Nothofagussolandri). Mortality as a result of competition ineven-aged stands ensures a continuing supply ofhost material in addition to that providedintermittently by climatic damage andsenescence for those organisms which thrive onweakened or moribund tissues. Such a couplingof extensive geographic distribution andmortality resulting from intraspecificcompetition has probably providedenvironments conducive to the evolution ofaggressive insects and pathogens of forest trees.To the extent that this is so, comparison of theinsect complexes of Pinus and Nothofagus may bemeaningful although the genera belong in

different subdivisions of the Spermatophyta.

A further reason for attempting such a

comparison arises because Pinus has beenextensively managed in conjunction with itsendemic complex of insects and diseases, whilestem rots and insect damage in untended standsof New Zealand Nothofagus have seriouslyrestricted utilisation Oohnston 1972). There islittle doubt that the New Zealand beeches -especially silver beech (N. menziesii) - couldbecome a much more valuable hardwoodresource if insect and rot defects could beobviated. With this purpose in mind, it is relevantto enquire whether the insect problem is any less

capable of solution in Nothofagus than it is inPinus.

THE INSECTS INFESTING PINUS ANDNOTHOFAGUS

It seems characteristic of forest trees belongingto pioneer genera that they support a numerousand diverse fauna of insects, a few of which

precipitate the local losses of canopy trees whichthese tree genera are so well adapted towithstand. Most of the insects which utilise livingtree tissues are present in numbers which arecontrolled by the physiologicalstate of the host aswell as by parasites and predators. Water stress inthe host has the effecI of reducing thetranslocation of photosynthesate; increasedphotosynthesate levels in foliage accelerate thedevelopment of defoliators and sapsuckers.Water stress in the stem has the effect ofreducing the rate of flow of gums and resinswhich are produced in response to wounding, sothat insects and attendant fungi can enter andestablish themselves more readily. Nitrogenlevels in soils affect the water uptake of roots(Goyer & Benjamin 1972) and thus affect thesusceptibility of trees to insect damage. Pioneertrees persist on infertile and shallow soils fromwhich highly soluble nitrogenous compoundstend to be leached. In brief, it appears that the

INSECTS DAMAGING BEECH FORESTS33

susceptibility of pioneer species to insects isdirectly related to moisture stress - in partinduced by overstocking and hence intraspecific

competition, in part by seasonal variations in soilmoisture, and in part because of impaired root

uptake of moisture associated with the lownitrogen levels of the soils where they persist.Whether onc considers Pinus or Nothofaf:Us, few

of the insects arc restricted to one host species,

though the relative abundance may vary bothbetween hosts and between sites.

I. Sap-suckers

Eriophyid gall mites are associated with allNew Zealand species of Nothofagus. Pouch gallscertainly occur on leaves of N. fusca and N.solandri and probably on the other two species.Flower buds ofN.fusea are galled, and other budgalls occur in all the species. Most conspicuously,terminal buds of N. menziesii form "witches'brooms" when they are invaded by eriophyids.

Eriophyidae seem to be mOfC common on

angiosperms than gymnosperms.

Heavy attacks by spittle bugs belonging to thegenera TiloPhora and APhroPhora (Cercopidae)

may kill tops, branches and sometimes youngtrees of Pinus. t'me aphids (Eulachnus and Cinara)and Pinus spp, (Adelgidae) are common,

especially when pines are subject to drought. Thescale insects of Pinus include species of

Matsucoccus and Drosicha (Margarodidae),

Toumeyella (Coccidae) and the armoured scales

LePidosaPhes and Phenacaspis (Diaspidae),Nothofagus is not affected by spittle bugs oraphids. Nothofagus solandri growing in dryregions supports large numbers ofUltracoelostoma assimile (Margarodidae) on thickbarked parts of the stem, Honey dew is produced

by scale insects in such quantities on the stems ofN. solandri that it is utilised by commercialapiarists. On N othofagus the Eriococcidae arerepresented by 22 species, of which only one hasother hosts. An armoured scale, Inglisia sp.,

occasionally reaches outbreak levels on N. fuscaduring seasonal droughts. During droughts theupper crowns can become completely defoliatedand the lower foliage and that of the understoreyis smothered with sooty moulds. It appears thatpopulations of this scale insect are normally

controlled by parasitic fungi. When moistconditions are restored, the fungi rapidly regain

control and crowns appear to recover

completely.

Whereas Nothofagus recovers well after

outbreaks of sap-sucking insects, resin reactionsto stylet punctures in Pinus tend to restrictconduction and this may result in the death ofsmaller stems.

2. Defoliators and Foliage Miners

Amongst other defoliators and foliage minersfeeding on Nothofagus are three species ofProteodes (Oecophoridae). p, earnifex occurs on allthe species, normally in low numbers. Outbreaksof P. carnifex, which may persist and spread forseveral seasons, are known oniy or~N. solandri.

During outbreaks, ti'ees may be severelydefoliated during the summer but usuallyproduce some new foliage before the winter.Occasionally no new foliage appears until thefollowing spring. Even with two successiveseasons of severe defoliation there is noindication that trees are either killed or soweakened that they succumb to other insects orpathogens, Other tineoid defoliators of

Nothofagus are sometimes common on the foliageof larger trees though the irDury they cause

appears to be well tolerated.

Tortricoid defoliators of Pinus include thepine budworms (Choristoneura spp.) which preferto feed on the bases of the most recently

produced needles. Defoliation for severalsuccessive years greatly reduces wood growthand may so weaken the trees that they becomesusceptible to bark beetle attack. Nothofagussupports a number of Tortricidae at least threeof which also occur on other hosts. Epu:horista

emPhanes, which feeds exclusively on Nothofagusspp., is the only one of these which occurs inoutbreak numbers. Outbreaks have beenlocalised, do not appear to last for more than oneseason and are not known to cause any long term

injury to the trees, A related family affectingPinus, the Olethreutidae, includes the pine tip

moths (Rhyacionia spp.), the shoot moths(Eucosma spp.), and the pitch nodule moths(petro va spp.), While lacking olethreutids, allspecies of Nothofagus are affected by Carposina

34 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL 21, 1974

eriPhylla (Carposinidae) the larva of which teedson inner bark and callus at the margins of

wounds. Its chief importance seems to be that it

enlarges wounds made by other insects and

delays healing,

Caterpillars and pyraloid moths which affect

Pinus include the webworm TetraloPha robustella

(Pyralidae) in the eastern U.S,A., the inner barkborers, or pitch moths, of the genus Dioryctria.

Dioryctria spp. cause the formation of resin

pockets which become included in the wood. No

Pyralidae damage Nothofagus.

Bombycoidea arc represented on Pinus by

Dendrolimus spectabilis (Lasiocampidae) andColoradia spp, (Saturniidae). Most damaginglasiocampids (e,g. Malacosoma spp.) andsaturniids are associated with hardwood hosts,but the former do not occur in New Zealand andthe latter are represented only by the introduced

eucalypt silk mOIh Antheraea ew:alypti.

Butteryfly larvae which feed on Pinus foliageinclude those of SPindasis takanonis (Lycaenidae)

in Korea and Japan and the ponderosa pine

butterfly NeoPhasia menaPia (Pieridae) of westernNorth America which may kill its preferred host

during outbreaks. Nothofagus species do not

support butterfly larvae.

The Geometridae which feed on Nothofagus'

include the general feeders Selidosema suavis and

Declana floccosa. S. productata is common on beechbut also occurs on other hosts. D. feredayi and

Tatasoma fasciata appear to occur exclusively on

Nothofagus. Outbreaks of these geometrids onNuthofagus are unknown, although localoutbreaks of S. suavis have occurred on Pinus

radiata in Canterbury. Geometridae are usuallyof minor significance on endemic Pinus though anumber of species belonging to Semiothisa,

Ectropis, Zethenia, Nepytia, Lambdina, Eufidonia,etc., are known to feed on pine needles.

The larva of the black hawk moth, Hyloicus

caligineus (Sphingidae) occurs on pine foliage inChina, Japan and Korea, but again there is no

counterpart affecting the New Zealand beeches.

Sawflies belonging to the genera NeodiPrion,

NesodiPrion and Diprion (Diprionidae) andAcantholyda and Cephalcia (Pamphiliidae)defoliate Pinus. Some of these are serious forest

pests which have no counterpart on NothoJagus.

Some adult buprestid beetles, e,g. Buprestis

apricans, teed on pme needles for several weeks

before mating and ovipositing. Each adult

Nascioides en)'si has been found to consume ten

leaves of N. menziesii per day (Morgan, 1866). In

each case adulI buprestids are plainly a part of

the defoliating complex of insects, but in neither

case has their relative importance beenestablished, Adult chafer beetles (Scarabaeidae)feed on foliage of both Pinus and Nothofag"U.s

while their larvae feed on roots. Several speciesof Odontria are numerous in monotypic N.

solandri forest but as yet their significance is

unknown.

In general, in their countries of origin, Pinus

species are periodically subjected to severedefoHation by a great variety of caterpillars and

sawfly larvae. During outbreaks severedefoliation may check wood growth, \,,'eakentrees so that they become susceptible to bark

beetle attack and even kill them. On the other

hand outbreaks of an oecophorid moth whichlast for more than one season and extend over

considerable areas affect only one of the

indigenous Nothofagus species (N. solandri); evenin this case the trees rapidly regain full foliageand no long term injuries stem from defoliation.

3. Inner Bark Feeders

The bark feeding habits of caterpillars of

Carposina eriPhylla in Nothofagus and Di(1)'ctria

spp. in Pinus have been briefiy mentioned aboveand many of the sap-sucking insects are

essentially dependent on these tissues. Inaddition, the larvae, the adults (or both) ofbeetles belonging to the Buprestidae,

Cerambycidae, Scolytidae and CurcuHonidae

feed on inner bark.

Buprestids belonging to the genera

Melanophila and Chrysobothris are especially

associated with suppressed, dying or freshlyfelled Pinus, Eggs may be laid on living trees

which are growing very slmvly, but development

of the larvae is retarded until radial growth

ceases (Anderson 1960). Two buprestids,

Neocuris eremita and Nascioides enysi, are found in

Nothofagu5 forests. Larvae of the former occur insmall diameter dead branches of Nothofagus but

INSECTS DAMAGING BEECH FORESTS

are not restricted to beech. Nascioides enysi haslong been regarded as an important cause ofbeech mortality ( Cockayne 1926, Morgan 1966)and is restricted to the beech species. The writerhas recently suggested (Milligan 1972) that N.

enysi larvae do not develop beyond the first instarunless they reach the inner phloem, and areprevented from doing so by host gum reactionsas long as the tissues remain alive. Still morerecently, it has been observed a.A. Wardle pers,comm.) that early larval mines of the buprestid inpole sized N. solandri occur exclusively in thosestems in which growth is suppressed. It followsfrom this observation that ovipositing N. enysimust select specific physiological conditions inthe host. Similar conditions must prevail, at leasttemporarily, in branches of healthy trees sincelarvae also occur there. Since N. enysi do notoviposit when the temperautre is below 22'C, andhigher temperatures are required in the absenceof direct sunlight (Morgan 1966), it seems likelythat stem moisture stress is associated with

attractiveness to ovipositing females. If the stressis of a temporary nature the larvae fail todevelop; if it is indicative of a moribundcondition they are able to reach the cambial zoneand to complete their development. Nothofagusmortality previously attributed to N. enysi is nowmore convincingly interpreted as a consequenceof Platypus attack (see below): the part played byN. enysi appears to be closely comparable withthat played by MelanoPhila gentilis and M.drummondi in the death of pines.

The larvae of many longhorn beetles(Cerambycidae) feed in the inner bark of foresttrees. As a rule, the trees are dead when they areselected as host material. The sawyer beetles,Monochamus spp., lay their eggs on dying andfreshly felled Pinus. Later, larval mines enter thewood causing appreciable losses of otherwisesalvagable standing timber and of stockpiledpulpwood. In parts of Japan adults of a species ofMonochamus have the habit of biting holes in thethin bark of the upper stem of pines, and indoing so infect the wounds with a nematodewhich invades the wood and rapidly kills thetrees. Longhorn beetles which damage

Nothofagus are essentially wood feeders, and willbe considered below.

35

Some species of bark beetles belonging 10 the

genera Dendroctonus, Ips, Blastophagus

(Myelophi!us) and Cryphalus (Scolytidae) are thecause of most insect damage in the areas wherePinus is endemic. Outbreaks are commonlyinitiated by wind throw or droughts. Blastophagus

PiniPerda and B. minor occur throughouI thePalaearctic region but are absent from NorthAmerica. Broods are reared in the inner bark of

recently killed trees and the beetles feed in theleading shoots of young Pinus before theyestablish brood galleries, Damage to apical shootsduring maturation feeding leads to theformation of bushy trees which are of little usefor timber production. Aggressive species ofDendroctonus, Ips and Cryphalus bore into and feedon the inner bark of living Pinus. WhileDendroctonus attacks tend to occur mostly in thelower parts of the trunk, those of Ips areconcentrated in thinner barked regions and

CryPhalus attack branches and tops, Sapstainfungi carried either in specialised organs orexternally on the body surface(Francke-Grosmann 1963) invade sapwoodadjacent to the tunnels and playa part ininterrupting conduction so that the crown wiltsand the tree dies when a sufficient number ofattacks are concentrated on it. Brood galleries

may extend from the initial feeding tunnel ormay be made in other parts of the killed tree.Although weakened trees are preferentiallyattacked, adjacent healthy trees are killed whenbroods emerge some 4-5 weeks later. This leadsto group mortality, which occasionally extendsover large areas. Up to five broods are producedover the warmer months, so outbreaks developrapidly, Losses (of the order of I billion board

ft/year) caused by D. brevicomis attack onponderosa pine in the Pacific Cost States ofU.S.A. over a 25 year period were almost I y,times the increment, and more than 10 timesgreater than losses by fire (Anderson 1960).Bark below the green crown may be completelystripped by feeding adults of Ips grandicollis,which later make brood galleries in the lower

parIs of the killed tree, Outbreaks of Ips avuLsus

during droughts in Texas, U.S.A., have

necessitated extensive sanitation salvage

operations. The role of Cryphalus species in tree

36 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL 21, 1974

mortality is less well documented, but some aresaid to predispose trees to attack by other barkbeetles. The Scolytidae of indigenous Nothofagusare represented by one (or perhaps two) speciesof Hypocryphalus. These are commonly found insmall branches of felled trees and seem to berestricted to dead or moribund tissues.

4 . Wood-borers

Pinus is little affected by wood-boringcaterpillars, though minor damage is caused inNorth America by larvae of the clear-wing mothParhaTmonia Pini (Aegeridae). All species of

Nothofagus are susceptible to damage by thelarvae of the ghost moth, Aenetus virescens(Hepialidae), bUIA, viTescens fortunately is absentfrom the South Island, Early ins tars of A , virescens

feed under a silken tent, often at twig bases, onthe bark of seedlings. As they grow the larvaemigrate to larger and woodier stems in whichthey bore "7"-shaped refuges, the long armparallel with the stem axis and the shorter oneextending to the surface. From this shelter, andconcealed from the outside by a silk tent, thelarva feeds on inner bark and callus induced atthe margins of the wound. The bark is ofteneaten away for more than half the circumferenceof small stems and branches, and the wounds area common cause of breakage during gales orsnowfalls. When the bark of poles becomes toodifficult for the larvae to penetrate they tend tomove further up the stems; old damage thenbecomes overgrown by new wood. Cores ofdamaged wood tend to be of greater diameter inN. menzwsii than inN.Jusea or N. truncata, and thisappears to reflect the earlier development ofresistant bark in the latter two species. 'Vetas(Hemideina spp. : Tettigoniidae) take over thecaterpillar refuges, enlarge them and keep theentrances open for many years. When the wetas

emerge to forage after dark they serve as vectorsof sapstain and rot fungi. As long as the tUnnelsare kept open, aerobic conditions favour the

spread of rots, Core rots associated with old ghostmoth damage are usually most extensive in N.menzwsii. Current ghost moth damage may befound in the branches of mature trees of all the

Nothofagus species as well as in hosts belonging toother families.

Pinus is affected by Hymenopterouswood-borers belonging to the family Siricidae,

As a rule these are of minor importance in

endemic pine forests, butSirex noctilio, which hasbeen accidentally introduced into New Zealandand Tasmania, has occasionally caused extensive

damage in plantations of Pinus radiata.Outbreaks have been associated with sustaineddroughts and overstocked stands. SiTex noctiliolays its eggs in the wood of living trees, often ingreatest numbers just below the green crown. Afungal symbiont introduced with the eggs causeswilling of the crown and death of the tree. Only ifthe wood dies do the larvae develop. Brood is alsoreared in logging wastes, windthrown trees andthose snapped off in gales or snowfalls, Thenearest relative of the siricids in Nothofagus is

Xiphidryia dunniana (Xiphidryidae), Ihe larva ofwhich develops in dead twigs and small branches.There is no evidence that X. dunniana kills thetwigs which it utiJises.Buprestid and cerambycid wood-borers

associated with Pinus seem able to gain entry tothe wood only through wounds which areincompletely covered with resin and aretherefore unimportant except in forest produceand as agents which break down the stumps andother forest wastes. Upper parts of Nothofagusregeneration are girdled and killed by larvae ofthe longhorn beetle Navomorpha lineata, whichlater hollow out the lower living stem. Eggs of N.lineata are frequently laid at wounds such as thosemade by ovipositing cicadas. Similar damageoccurs in small branches of Nothofagus trees andoccurs in many other hosts. Where poles or lar-

g-er trees of N. solandri (and occasionally N. fusca)closely associated with Leptospermum they may bedamaged by larvae of the longhorn beetleOchTocydus huttoni, for which Lepwspermum is theusual host. Larval tunnels in the sapwood arelarge, predominantly vertical, and free of frass.The frass is ejected through small openingswhich are cut from the larval galleries to theexterior. Wetas utilise the flight holes, pupalchambers and larval galleries of O. huttoni just asthey use ghost moth refuges, Damage is unusual,except inN. solandri (which is little sought after asa timber producing species) and even in this host,diminishes in frequency with distance from scrub

.

margms.

INSECTS DAMAGING BEECH FORESTS

Species of Platypus (Platypodidae) are amongstthe first invaders of Pinus killed by bark beetlesbut do not invade the living stems. Coster (1969)found that P. flavicornis bored into Pinus treesfour to six days after they were infested by Den-droctonusfrontalis. Damage was restricted to thelower few feet of wilting stems where wood mois-ture content would remain highest. In New Zea-land Nothofagus forests there are three species of

Platypus - P. apicalis White, P. gracilis Broun andP. caviceps Broun - which readily breed infreshly fallen trees, logs and stumps. Platypuscaviceps is not known to br'eed in any other hostsbut the other two may breed in' a variety ofhardwoods and softwoods. All three species willattack living and apparently healthy Nothofagustrees. Rarely, stems only six centimetres indiameter are attacked, but abortive attack is notuncommon iri those 15 em or more in diameter.Brood of P. apicalis and P. gracilis are known toemerge from nests in large diameter trees whichare still alive, but attempted nests of P. ciwiceps'fail unless the tree dies. Attacks of P.apicalis andP. gracilis are concentrated on the lower' sixmetres of the living tree; those of P."caviceps alsooccur in this region but extend up to a height of21 m. This distribution of attack by the Platypusspecies on living'trees is perhaps. comparablewith that of Dendroctonus, 'Ips andCryPhaluson

living Pinus." .. .,., .

WhenNothofagus trees of sufficient diameter tocontain heartwood are attacked, the initially.radial Platypus tunnel curves through a rightangle as. the transition zone is approached andthen continues tangentially close to this zone. Itseems that this change of direction is linked withprogressive reduction ~f moisture content of the.sapwood. In stems with no heartwood the tunnelcontinues towards, and sometimes through. theorganic centre. If small stems have been attackedin a previous season. resulting in a core of deadand discoloured wood, the tunnels deviate as theouter margins of the dead core are approached.Fungal hyphae, tyloses in the .vessels and darkcontents in the ray cells and vertical parenchymaare found in such dead cores. In contrast withheartwood" these cores are readily invaded. bysapstain and rot fungi (Milligan 1972).

Evidently a pathogenic sapstain fungus is

37

transmitted by the beetles and becomesestablished initially in the innermost sapwoodwhere wood moisture content is least. Butcher(1968) found that Ceratocystis piceae was the maincause of staining in untreated sapwood of N.fusca, and noted that the same fungus occurs inN. menziesii. Staining caused byC.pu:eae wasassociated with discolouration of ray cell contentsrather than with pigmented fungal hyphae.When Platypus .invades living trees, or whenscrapings from- nests are introduced into holesdrilled in living trees, a sapstain fungus whichdoes have pigmented hyphae and which causesextensive reactions in living wood cells, advancesfurther than other fungi from the wound (Faulds1973). This'fungus, designated "Fungus A" byFaulds, is associated with progressive death ofinner regions of the sapwood, It is readilycultured, and the pathogenicity of cultures isbeing examined; but, so' far, it has not beenidentified. On the other. hand, . a species ofCeratocystis is the dominant component of theflora..of older parts of Platypus tunnels. Thegenus Ceratocystis (Ceratostomella) includes anumber of sapstain fungi which are transmittedby the bark beetles which damage pines.

Whereas the bark beetles. feed on the innerbark, through. which. they tunnel,' Platypus andother ambrosia beetles do not feed on wood.Freshly bored' tunnels of the New. Zealandspecies soon acquire a lining of yeasts which arethe primary food of both adults and larvae.Yeasts are also transmitted by bark beetles, occurin all the feeding stages and are digested, buttheir. precise role in the nutrition of bark beetleshas not been determined (Callaham & Shifrine1960). .

.

Aggregation of attack on particular trees ischaracteristic of, and essential to, aggressive b~rkbeetles. Unless a sufficient number of woundsare made, and a sufficient pa'rt of the sapwoodexposed to the sapstain fungi which interrupt itsconducting function; the tree will not die and sowill not become a suitable medium for therearing of brood. Aggregating mechanisms havebeen demonstrated in a number of cases. Thosebeetles which initiate the galleries producevolatile chemicals in the hind gut which, incombination with volatiles emanating from the

38 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 21, 1974

wounded host, serve as powerful attractants toothers of both sexes. The insect-producedvolatiles (pheromones)becomeadsorbedon faecalmaterial which is discharged an hour or two afterfeeding begins. Madrid, Vite & Renwick (1972)have recently shown that. aggregatingpheromones are also produced in the hind gut ofmale P. flavicornis. Observations on thebehaviour of New Zealand Platypus have forsome time indicated the existence of such

aggregating pheromones. During the 1972-73flight season it was found that freshly emergedmales of P. apicalis emit an odour which is sodistinctive that the sexes can readily be separatedon this basis alone. So far it has not been shownthat the odour is attractive to others of the speciesunder laboratory conditions. In earlier fieldexperiments it was found that trees near cagescontaining emerging beetles became heavilyattacked by wild populations. Since the cagedbeetles could not reach these trees it appearedthat additional odours from the wounded hostwere not initially essential for attraction ofothers. On these grounds the existence of anattractant originating from the beetles wasdeduced.

Attempts to test the attractiveness of chemicalsto P. aPicalis in the laboratory have beenconfronted with the difficulty that freshlyemerged adults are initially attracted to light, andthis attraction over-rides those of a chemicalnature. Immediately before boring into the woodin the case of the male, or before a female joins amale in a tunnel, the attraction to light must bereversed. Such a phototropic reversal probablyoccurs as a result of flight (Graham 1961). The"male odour" of P. apicalis is emitted soon after

beetles emerge, so if the odour detected indicatesthe emission of an aggregating pheromone some

aggregation should occur in flight as well as at thesurface of host material.

Droughts have long been recognised as acommon cause of bark beetle outbreaks inconiferous forests. That flooding may alsorender trees susceptible to bark beetle attack(Anderson 1960) is comprehensible if it results inpartial death of the root systems, so that theuptake of water by Ihe roots becomes less thantranspiration losses during warmer weather. In

either case reduced wood moisture is favourablefor the spread of sapstainfungi introduced bythe bark beetles. As a practical expedient, logsare stored in ponds or under water sprays so as tolimit. the spread of sapstain. Although the fungiassociated with pine bark beetles have not beenfound to be particularly virulent pathogens, theirassociation would appear to be an essential onefor the success of both organisms. When smalldiameter Nothofagus trees are attacked byPlatypus the associated pathogen first establishesitself in the drier, innermost sapwood and thenspreads oUtwards until it reaches limits imposedby wood moisture and defensive reactions of theouter sapwood. Duriug seasonal droughts, andespecially on severely drained sites, centrifugaladvance of the fungus may be accelerated. Radialprolongations of killed sapwood occur at thetunnels and where spearheads of the advancingfungus break through gum barriers. As a rulethese small trees do not die, even though they areseverely attacked. On the other hand trees whichwere only lightly and abortively attacked havesuccumbed to the pathogen when a droughtoccurred in the following summer. even withouta second attack in the drought year. Thisiridicates that the pathogen can survive for atleast a year in trees which were only abortivelyattacked by Platypus. Surviving trees are left witha core of pathological wood which is often stellatein section, or, if not stellate, then with theboundaries only rarely coincident with thegrowth rings. Rot fungi may erode these cores,especially where aerobic conditions prevail closeto the Platypus tunnels. In field experiments, allN. fusca over 35 em in diameter which wereseverely attacked died within two to four years.One tree, attacked over the summer of 1965-66suddenly died in the following October, that is inless than a year. Though susceptibility to this sortof mortality is not necessarily equal in the variousspecies of Nothofagus, none is immune. Platypusand the associated pathogen have been found tobe involved in most instances of deaths of matureNothofagus examined since 1965. An importantexception is the recent deaths of N. truncata eightto ninety centimetres in diameter in the RaiValley-Whangamoa area, where dieback anddeaths were associated with a stem canker notcaused by fungi and not linked with insect attack.

INSECTS DAMAGING BEECH. FORESTS 39

Nowhere else in the world have species ofPlatypodidae been implicated as vectors oftree-killing pathogens, so their role in forests hasnot been 'related to that of aggressive Scolytidae.Nevertheless a number of similarities appear.One that is perhaps crucial is that dfought, andhence wood moisture of the stem,'immediately

affects the spread of fungi which are introduced

by both groups of insects. Only if the fungispread rapidly is the tree killed. In the case of abark beetle which completes its life cycle in abouttwo months, eggs are laid about a week after theattack starts, hatch a week after laying and larvaeare fully grown after feeding for three weeks(Anderson 1960). Newly hatched larvaeprobably have least capacity to 'overcome hostresin reactions to wounding, so tissues near the

egg gallery must be effectively dead two weeksafter attack starts if the larvae are to survive.Anderson remarks that, once large bark. beetlepopulations are developed. even the mostvigorous trees are attacked and' killed, but thenumber of offspiing produced in such initiallyvigorous trees"is )ow. Death of vigorous' trees,whether of Pinus or Nothofagus, depends on therebeing large numbers of inoculated wounds at anyone level between roots and crown - or upOnconcentratioy ofi~se~t 'attack. TO. ensure highdensity attack; aggregating mechanisms arenecessary, so it is hardly, surprising that initialevidence of aggregating behaviour has beenfound in New Zealand Platypus. Platypus lifeqicles are completed in approximately two years,and small grou ps of eggs are laid over aconsiderable period, so it is less dependent onrapid tree death than are the bark beetles.Furthermore, when it attacks living trees inwhich heartwood is developed, wood with areduced moisture content for the initialestablishment of Ihe pathogen is always availableat the transition zone. In fact rapid drying of thestem above a block in conducting tissue may beinimical to the development of brood whichdepend on yeasts rather than on sapstain fungi.

PLATYPUS AND BEECH MANAGEMENT

Johnston (1972), referring to West Coast

Nothofagus and beech-podocarp forests, reportsthat the beech component has been little utilisedbecause of extensive hidden decay and

difficulties in sawing, seasoning and treating.There are, especially in western Southland,extensive areas of N. menzwsii which'is sawn,seasoned and treated without undue difficulty.

Furthermore,' in mixed N.fusca and N. menziesiiforests elsewhere, the proportion of the lattercould readily be increased by selective thinningof the regeneration. Natural Nothofagus forestsall suffer from the prevalence of insect and rotdefecIs so Ihat little interest has been aroused for

their"managemell;t on ,a commerCial s(:ale.

It seems that much of the stem, defect arisesdirectly from sublethal Platypus attack ongrowing trees, but rots of the upper stem arecommonly associated with dead branches, Ifpathological wood has been formed below thecrown, rots entering through dead snags, maymore readily s'pread downwards. D.A. Franklin(pers. comm.) has shown that rot fungi are absentfrom branch tra<;es p!,~ned fjve years previously,so there seems;' a real' prospect 'of minimisingdefects if trees are pruned to the height requiredfor a merchantable log, espeCially if pathologicalwood caused by Platypus attack can be minimisedat the same time (see also Frankliii 1974, p.19).

i'," ", '-\,' .., .," :.-;..'-': "

A silvicultural regime which would producebeech logs wiIh least defect in the shortest time isplainly'needed. Widely spaced saplings of N.me'nzwsii;' arising" in a 'low' nUrSe crop such asFUchsin or Lepwsj"mnum will break crowns fromheights of about six metres and such trees, withlarge' crowns 'and correspondingly large rootcircles, are' known to increase in 'diameter at rates

:. ':', .:..'-~"

of up to 16 mm a year. Short, large diametertreeswhich were resistant to windthrow could also beproduced by thinning the thicket stage of denseregeneration to final crop spacing as soon as theminimum of height growth was obtained.Pruning to an appropriate height would berequired. The thinning operation would createminimal Platypus hazard because the wasteswould be too small to support broods, and the

crop stems would be below the diametersusceptible to attack. Windthrow, which favourslocal outbreaks of Platypus in untended stands,would be least likely in a stand of short trees withlarge root circles. Large crowns would promotemost rapid attainment of merchantablediameters, reducin!( the period of growth during

40 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 21, 1974

which the crop was susceptible to Platypus

damage. The only stage when the crop treeswould be prone to damage would be whenharvesting commenced, when Platypus from thesurroundings would be attracted by stumps and

logging wastes. However, logging of such a highquality tended stand is at least 50 years away, sothere is ample time to perfect methods ofcontrolling Platypus populations.

None of the other insects associated with

Nothofagus seem likely to create serious problemsin the management of N. menziesii. '

REFERENCESANDERSON,R.F. 1960. Forest and Shade Tree Entomology. John

Wiley & Sons, Inc., New York. 428 pp. '

BUTCHER,] .A. 1968. The causes of sapstain in red beech. NewZealand Journal of Botany 6: 376-85.

CALLAHAM, R.Z.; SHIFRINE,M. 1960. The yeasts associatedwith bark lJe-etles. Forest SciRnce 6: 146~54. '

COCKAYNE,L. 1926. MonograPh on the New Zealand Beech'Forests, Part 1. "New Zealand State Forest Service

Bulletin NO.'4,Government Printer, Wellington,,

COSTER, J.E. 1969. Observations on Platypus fiavicornis(Coleoptera: Platypodidae) in southern pine beetleinfestations. Annals of the Eniomologic'al Society of AmeriCa62: 1008.t 1.

. .

FAULDS, W. 1973. Discolouration, associated witli Platypuswounds in living Nothofagusfusca. New Zealandjournal of

Forestry Science 3: 331~41.,"

FRANCKE-GROSMANN,H. 1963. Die Ubertragung der Pi!lOora

bei dem Borkenkiifer Ips acuminatus Gyll. Zeitschriftfilr

Angewandte Entomologie 52: 355-61.

FRANKLIN,D.A. 1974. Beech silviculture in the South Island.

Proceedings of the New Zealand Ecowgi¤al Society: 21.

GOYER,R.A.; BENJAMIN,D.M. 1972, Influence of soil fertility

on infestation of jack pine plantations by the pine rootweevil. Forest Scieru;e 18: 139.47,

GRAHAM.K. 1961. Air-swallowing: a mechanism in photicreversal of the beetle Trypodendron. Nature 191: 519.20.

JOHNSTON, A.D. 1972. Management of West Coast beechforests. New Zealand journal of Forestry 17: 180-8.

MADRID.F.; VrTF.,J.P.; RENWICK,j.A.A. 1972. Evidence of

aggregation pheromones in the ambrosia beetle Platypusflavicornis (F.). Zeitschrift filr Angewandie Entomowgie 72:73-9,

.

Mr'LLIGAN,R.H.' '1972. A review of beech forest pathology.~,

New Zealand journal of Forestry 17: 201~11.

MORGAN.F.D. 1966. The biology and behaviour of the beech

buprestid Nascioides enyci (Sharp) (Coleoptera:Buprestidae) with notes on its eco}ogy and possibilitiesfor its contro!.' Transactions of the Royal Society of NewZealand 7; 159.70. '

SKOTTSBERG,C. 1949. Influence of the Antarctic Continent

on the vegetation of southern lands. Proceedings of the 7th

Pacific Scie1u:e Congress (New Zealand) 5: 92.9..

WARDLE, J .A. 1970, Ecology of Nothofagus solandri. NewZealand journal of Botany 8: 494~646.

WARDLE,j.A. 1974. The life history of mountain beech,

(Nothofagus solandri var Cliffortwides). Proceedings of theNew Zealand Ecologi¤al Society 21: 21-6