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Heliothis Nuclear Polyhedrosis Virus for Bollworm Control
Introduction
R.E. Teakie, EnlomoJogy Rranch,
Department of Primat'y Intiuslries, J nctooroopj .lly, Queensland 4068.
H~jjoth)s armjgcra anti Heliothis punc:Ugera are Lhe key insect pests on cotton in Australia and measures to control them are vita.I.IV .important: .in cotton management. Th~ computcr-t>ased management program t'or cotton, SrnATAC (Heac·n et '!.!.·, 1981) makes recommendations on the bas.is of:' reguhtr and systematic moniloring of both pest aml bene1'iciaJ specjcs on l.he <:roi> and recommendations are designed to conserve the ofLen considerable level of natural cont.ro.I pres en l, Wh<ire tlOSS l bJ E!. Jn a precursor program named FLY, a commercial formulation ot' a v.irus imporl.ed tl'om the IJniled
S\ates, IUcarTM, (Sldeh, J978) was used i:lS Ute nrst optlon for controlling Ile.Li.othis species on i;otlou. fn the first two season's t.r.ia.ls, y.ie.i<ts were ma.inl.ainc<t wjth fcw<~r pesUcj<te api•Jications than 1n t:he convenllonally ma.na~e<l cot.Lon (Room, 1979). However, .I u t.cr resu.l t.s were not encour<lf!j ng, hut t tie reasons for the
incons.i.stenl performance ol' the v.irus insecl:i.eide wec·e not
est.abJished. PossJo.ly, unfavourable compar·hwn w.ilh t.he new synthetic pyt'ethroids al Lile Li.me was involved. E Lca.t' was provJsiona1Jy rcmovcct as a pcsticJoc optJon from lhe SJHATAC
in·ogram in 1980 81, and production was recently di.scontinued owing t.o insnl'f.ic.ient. neman<I jn the Unit.eel Stal.E:s. E:xpf:H·ience Lhere had
142
iudicatod Lhal t L was mos I. effect i. ve against low or modet·ate infestations (Yearian et ~..:!.·, 1980).
An AuslraJJan firm, HiocontroJ Ltd, based at Warwick, Queensland, is now preparing to produce an lmproved formulation of the virus for use on cotton, sorghum and grajn legumes. Resistance to the syn ttrntic py1·ethl'oids and enctosu l hm has been l'ecot'ded in Heliothis armigera (GunnJng et al . , 1984), and no cJear
alternatives to these are in sight. In view of the threat posed by resJstancc anrt the proposed release of the new formuJatJon, i t is
timely to reconsider the possible role
or
the vtrus in Hellothis contro.l on cotton. SJRATAC r.td has now accumulated datarepresenting a considerable body of experience, and quantitative re.iaUonships bctwccm the virus and the Australian Heliothis hosts are now better undel'stood {Teakle, 1986).
Characteristics of the Virus
Hc.l.lothis NPV is infcct..ive onJy for larvae ot' Heliothis species.
Natural epizootics at·e observed in Austr·al ia on sorghum, 111r.erne ano peanuts, where Hellothis control .is not as rigorous as on cotton, and can also occur 011 unspcayed, experimental cotton
(Wilsm1 and Greenup, 1977). The Jnfectcd larvae tend Lo move to the top of plants to die, after which Lhey darken and l'latten onto the rl.iant substrate or he:rng vertlcal.ly by abdominal Jcgs. The new.ly dead larvae are typica Uy sot'L and "squashy" and fragile.
The skjn ruptures readJ.ly reJea:·dng vir·us-laden body contents. The
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disease sµrca<1s to other He.l ioth is I a1·vae wit ich consume contamjnated pJant material or cann.ibaJjsc ttrn cadavers.
The virus was the first to gain registration as an
jnsecticicte and is notable for jts virulence, safety and
specificity, and relative ease of production and storage. It is
produ<:ed commerciaJJy jn infected, laboratory· reared HeJiothjs Larvae (lgnorro, 1973).
Factors which influence the efficacy of an NPV application
These inc.lndc: (i) the initial actjvity ut· the virus preparu t i on,
(.i.i) lts rate
or
applicat.lon arid clislr.ibut.ion on the crop,(Jji) Jts persJstence on the crop,
and liv) the susceptibility
or
the target Larvae.Initial activity
The actjvjty of the vJrus proparilLJon ls standardized by
Uw manut'aG tm·er by bioassay using lal.Jot·at or y ·reared He l iothis larvae. l ts aclivj ty aft.er ~lorage depern..i~ on lite storage
temperature. Ir the ma.Leri.al is stored under refrigerati.on (70C)
i 1. shou.Ld remain stab le for a L least two years. Il degrades s Low! y at normal envjronment.aJ temperatures ;md v.irmi stored for Jong
per i.ods under these cond .i lions should be t•ettssuyed r or potency.
144
The v.i:rus would be quilc thermostable durjng sJ:rnrL-·tcrm storage on the farm and handling and uppl i.cation in the field {Teakle, 1986).
Rate of application
Calibration to determine ctose-mortaJity responses on the crop is required in order to avoid waste through the use of unnecessar.i.Jy hJgh rates and the us~? of ru'Les wt1ich are ina<tt~quate
to uchieve effective control.
The dccisjon on ttie .Level of kLlJ desired w.i.lJ ctcpenct on the farmer's objective:
eJther (a) to protect the flr~t crop of bo!Js and thereby reduce lho overall growing perloct and associated risks due to
pes Ls or wea Uier,
or (b) to accept the Loss to insect damage of a proportion of
ho JJ s wh .i ch would be shed anyway, amt to budget r or
compensa tiou l>Y lhe plant.
Distribution of the virus
The requirement J'or .ingesUon of t.he vi rus by larvae means that H must be uniformly 1iisLt'ibuted on lhe crop. Fe:t ilure could
b<~ Uie reslll t. of ttiJs not being acrl.i<~ved, and also .inappropriate timing (see later).
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Persistence on the crop
The main cause or Joss of act..ivity of the v1rus is exposure to sunlight. The half -Life in exposed locations is
norma.i Jy about 1 to 2 <tays, but this stiould be extended for the new
Biocontrol Ltd formulation, which includes a sunscreen.
AppJication ln the late afternoon or evening js considered desirable. Treatment of shaded parts of the plants will also extend the "life'' of ttie vjrus, and this may be achit~ved
eleetrostatical ly hy equipment such as Ute E1eclrodyne.
susceptibility of target larvae
Thjs depends on the inherenl susceptlbJJlty and rate of virus acquisition or the larvae. lnhcrent susceptibility is influenced by the aee 01'. the iarvae, an<i decreases about l50·-foJtt during the first week of larval life (Teak!e et al .• 1985, 1986).
However, th.is can be largely countcractect by the increase jn reeding rate as the larvae i11erease in size. Large larvae are, however, virtua1Jy immune to lhc virus.
Larval feeding- b<:!haviou.t' is also critical on cotton.
Newly-hatched larvae tend to feed on the surface of the pJant, whereas larger larvae tend Li> burrow in anrt reed In structures such
ai:: tcrm.inals, squares or boJJs. rn th.is f~vent .. LtJe .larva<~ ac<tuire virus only durtnR entry and exit. Bttits included with Lhe virus can increase rnortaJJLy by encouragJng lhe Jarvae to i·eed on exposed surfaces such as on foliage.
146
Secondary spread
One advantage of' the virus disease is its capacity to spread to noninfected larvae. 'l'he amount of virus produced in a newJy·-hatched Jarva at. death i~ equivalent to 4 miJlion doses and
this increases to 400 million doses in larger larvae. The
biologjcaJ potentlaJ of tbjs amount ot' virus is consequently very large and increases with the proximity and density of the larvae at r:isl<. The period to death is norma.IJy 4 to 7 days, and this wou.ld govern the rate of release of the v.irus. I t should also be
mentjoned that infected larvae continue to feed at a reduced rate.
Consequently it is highly c.1es.it'able that the vir·us be applied to cojncide with the presence of ncwJy· hatched Jarvae, antjcipated by
monitori11g. The relatively long incubation perlod would adversely inf.luence accept.ancc or the virus by ~rowers who mjght. expect as early a response as with chemical insecticides. It ls most important. that the grow<.!r j s weJ J jnformea mi the way the virus works and its limitations.
The virus can be used in conjunclion with lbe ovicide chlordimerorm and control can be superlor to thut uchieved w.ith the
"Dipel "-chJorclimcform mjxt.ure, cur·rentJy recommended by SIRATAt:
(Yearian el al., 1980). Additionally, unlike the bacterium in
"Hi peJ", ttw v.i ru~ has U1e capac:i ty to accumuJ ate in the top surface layer of the soil and lo be available to infect Heliothis on subsequmrl. crops, parU cu.I ar J y those in wM ch epi zoo-U cs are
liable Lo occur.
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The use of I.he virus would allow ex.ist.ing natural control to be exploited. Its use would decrease selection for resistance and consequent! y proJ ong the useful U fe ot· couventi on al
insecticides. The solving of the conceptual and technical pt'oblems associated wjth the use of the virus should therefore be a priority for researchet's in cotton protection.
148
References
GUNNING, R. V. , EASTON, C. S. , GREENUP, L. R. and EDGE, v. E. ( J 984) . Pyreth.roid resistance in Heliotllis arm.ig_r::.£ (Hubner)
tLepidoptera: Noctuidae) in AustrHlia. ~- ~£.2!!.· ~nt. 77:
1283-1287.
HEARN, A.R., IVES, P.M., THOMSON, N.J. and WILSON, l...T. (1981).
Computer ··based cotton pest management in Austral iu. Field Crops Res.
1.:
321--332 .IGNOFFO, C.M. (1973). Development of a vJraJ insecticide: concept to commercialization. Exf2.!.. Para~!!· 33: 380-·406.
ROOM, P.M. (1979). A prototype 'on--line• system for management of cotlon pests in lhe Namoi Valley, New South Wales.
~rolect ion Ji~~ .!_: 245-264.
SlHEH, T.R. (1978). Characteristics of a viral pesticide ElcarR, In ProceecUngs of the Second International Colloquium on Invertebrate Pathology and XIth Annual Meeting of the Society for Invertebrate Pa·thoJogy, Pra1~ue, September Jl·-
17. 1978. pp. 191 -193.
Tl·:AKl.E, R.E. (1986). Studies on i:1 nuclear polyheclrosjs vjrus in 1·e1ation to the contt·ol of He! iothls ~rm!_g_~ and !!eliotills
tlliOC ligera Wallengren. Pit. D. th es is. Uni versl ty of Queensland. 271 pp.
TEAKLM, R.E., JENSEN, J.M. and GILES, J.E. (1985). Susceptibility or J:!.~..-!_i o t.hJ s armiger Lo a commercj al nuc !ear polyhedrosi s virus.
f.
Invertebr. ~~ttlC21. 46: 166-173.TEAKI.E, R. E. , .JENSEN, J.M. and GJJ.ES, J.E. (.1986) . Age· J'tdatecl susceptil>i lily or !!.~Uothis punct!.g_~ to a commercia.l rormuli:l.tion or nuclear polyhedrosis virus. J. Tnvertebr.
Pathol. 47: 82-92.
WILSON, A.G. I,. and GHHENllP, L. H. (1977) . The re J a U ve injuriousness of insect pests of cotton tn the Namoi VaJ J ey. New South WaJ es. Aust..
J... l.iC.:.tl·
~: 319--328.YEAR IAN, W. C. , LUTTl{b:LL, ILG. , STACEY. A. L. and YOUNG, S. Y. ( 1980).
lifflcacy
or
Ba(~)J1~ thuringjensis and BacuJovirusheliothis · chlot·dimeform sp1·ay m ixtui·es ttgttinst !!_eliothis spp. on cotton . .j_. Geo!:.!{.ia ~Q_tomol. ~oc. 15: 260-271.
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