Comparative Activity of the Codling Moth Granulovirus Against Grapholita molesta and Cydia pomonella (Lepidoptera: Tortricidae)

2005·1.3 MB·English

by  Lawrence A Lacey

J. Entomol. Soc.Brit. Columbia 102,December2005 79
SCIENTIFIC NOTE
Comparative Activity of the Codling Moth Granulovirus
Against Grapholita molesta and Cydiapomonella
(Lepidoptera: Tortricidae)
LAWRENCE A. LACEY^ ^ STEVEN P. ARTHURS^
and HEATHER HEADRICK^
—
ABSTRACT The granulovirus ofcodling moth, Cydiapomonella L., CpGV, is nowcom-
merciahzed for codling moth control in pome fruit in the USA and Canada. It is highly spe-
cific for codling moth and related species. Comparative assays of CpGV against neonate
larvae ofanotherintroduced tortricidpest, the oriental fruit moth, Grapholita molesta Busck,
revealed a 557 and 589 fold lower susceptibility ofneonate larvae compared with the LC50
andLC95 valuesderivedforC.pomonella.
Since its introduction into North America, (1969) (BioServ, Frenchtown, NJ, USA) was
the oriental fruit moth, Grapholita molesta used forboth species.
Busck, has become a widely establishedpest of Following initial bioassays to determine
peach,nectarine, apricot, and apple (Rothschild mortality ranges, five concentrations ofCyd-X
and Vickers 1991). There is little information that produced mortality in neonate larvae rang-
regarding naturally occurring disease of the ing from 10 to 96.7% in oriental fruitmoth and
oriental fruit moth, with the exception of mi- 36.7 to 96.7% in codling moth were bioassayed
crosporidia in adults (Simchuk and Komarova against 30 neonates per concentration. Bioas-
1983) and Bacillus thuringiensis in larvae says were conducted on artificial diet in 2-ml
(Grassi and Deseo 1984). Although field trials plastic conical autosampler vials (Daigger,
with various formulations of B. thuringiensis Lincolnshire, IL, USA). A 2-mm diameterhole
have been reported for oriental fruit moth, re- in the cap of each vial covered with stainless
sults indicate that it is relatively ineffective steel screen (0.16 mm mesh size) eliminated
(RothschildandVickers 1991). condensation. Ten \x\ ofaqueous virus suspen-
Following its initial discovery in infected sions or 10 1^1 ofwaterforcontrols was applied
codling moth Cydia pomonella L. larvae in to the surface of 1 ml of artificial medium
Mexico in 1964, numerous laboratory and field (approximately 100 mm^) in the autosampler
studies have confirmed the virulence of the vials. The label specified virus concentration of
codling moth granulovirus (CpGV), against its Cyd-X is 3 X 10^^ granules per liter. After the
homologous host (Falcon et al. 1968, Laing surface of the medium had dried, one neonate
and Jaques 1980, Arthurs and Lacey 2004, larva was added to each vial. The vials were
Cossentine and Jensen 2004). In early host incubated for 7 d at 25 ± 1.7 °C and then as-
specificity studies, CpGV was also noted to sessed for larval mortality. The study was re-
have larvicidal activity against the pea moth, peated for each species on four separate dates.
Cydia nigricana (Fabricius) (Payne, 1981) and Each date was treated as an individual replicate
oriental fruit moth (Falcon et al. 1968), but ofeach concentration (i.e. datawerenotpooled
quantitative assays ofthe virus have not been beforeprobitanalysis).
reported for the latter species. We conducted The results of the assays clearly indicated
bioassays ofthe Cyd-X formulation of CpGV that oriental fruit mothneonates are susceptible
(Certis USA, Columbia, MD) against oriental to CpGV, butat a significantly lowerlevel than
fruit moth and codling moth neonates from that observed in codling moth neonates (Table
coloniesmaintained atthe YakimaAgricultural 1). The oriental fruit moth were 557 and 589
Research Laboratory using the materials and times less susceptible to CpGV compared with
methods described by Lacey et al. (2002). The codling moth, based on probit (normal sig-
codling moth diet described by Brinton et al. moid) analysis of the LC50 and LC95, respec-
'YakimaAgricultural ResearchLaboratory,USDA-ARS, 5230KonnowacPassRd., Wapato, WA98908
^Authortowhomcorrespondenceshouldbeaddressed
80 J.Entomol. Soc.Brit.Columbia 102,December2005
tively (StatsDirect Ltd, v. 2.4). Based on our estimated that the LD50 for neonate larvae
methods, the calculated LC50 and LC95 of couldbe as lowas 1.2 granulesperlarva.
CpGV for oriental fruit moth are 35 and 540 First generation oriental fruit moth often
granules per mm", respectively, but only 0.06 feed on shoots andyoung foliage. Althoughnot
and 0.9 granules per mm"for codling moth. as active against oriental fruit moth as against
Although CpGV must be ingested in order to codling moth in laboratory bioassays, field
infect a larva, Ballard et al. (2000) demon- activity of Cyd-X against oriental fruit moth
strated that the point ofentry ofcodling moth neonates at label rates used for codling moth
larvae into fruit may not necessarily be where control (0.07-0.44 L/ha) could potentially re-
virus is acquired; larvae could become infected duce oriental fruit moth populations if signifi-
by walking orbrowsing on CpGV-sprayed leaf cant feeding ofearly instars ofthe first genera-
surfaces in as little as 3.5 min. Ostensibly virus tion occurred on treated foliage. Because natu-
pickedup on legs ormouthparts in the absence ral feeding behavior will influence their sus-
of browsing leaf surfaces could contaminate ceptibility to CpGV, further field studies are
the initial point ofentry. In ourbioassays, neo- warranted.
nates of both species may wander over the We are grateful to Rob Fritts Jr. (Certis) for
surface ofthe medium before boring into it. In Cyd-X samples and the Washington Tree Fruit
the case of codling moth larvae this would Research Commission for financial support.
provide ample opportunity to acquire virus We thank Don Hostetter and Joel Siegel for
even at the lower concentrations. Huber (1986) helpful reviewsofthemanuscript.
Table L
LC50 and LC95 values for CpGV bioassayed against Grapholita molesta and Cydiapomonella neo-
nates. The number ofgranules per 10 |il is based on dilutions ofCyd-Xwith a label specified virus
concentration of3 x 10^^ granules/L. All probit comparisons were significantly different, P< 0.001
basedondosagelog(io+i) andadjusted forcontrol mortality (< 7.1%).
Species n LC50 ( 95% CI) LC95(95% CI) Slope
C.pomonella 714 6.30 (4.74-7.91) 91.62 (63.00- 155.68) 1.41
G. molesta 708 3.51 x 10^(2.72-4.42 x 10^) 5.40x10^(3.66-9.04 x 10^) 1.39
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