title: Transmission of a Gammabaculovirus within Cohorts of Balsam Fir Sawfly (Neodiprion abietis) Larvae.
abstract: Nucleopolyhedroviruses (NPV: Gammabaculovirus: Baculoviridae) of diprionid sawflies (Diprionidae: Hymenoptera) are highly host specific and only infect the midgut epithelium. While still alive, infected sawfly larvae excrete NPV-laden diarrhea that contaminates food sources. The diarrhea can then be consumed by conspecific larvae, resulting in rapid horizontal transmission of the virus. To better understand the efficacy of Gammabaculovirus-based biological control products, the horizontal spread of such a virus (NeabNPV) within cohorts of balsam fir sawfly (Neodiprion abietis) larvae was studied by introducing NeabNPV-treated larvae into single-cohort groups at densities similar to those observed during the increasing (field study) and peak (laboratory study) phases of an outbreak. In field studies (~200 N. abietis larvae/m² of balsam fir (Abies balsamea) foliage), NeabNPV-induced mortality increased positively in a density-dependent manner, from 23% (in control groups) to 51% with the addition of one first-instar NeabNPV-treated larva, to 84% with 10 first-instar-treated larvae. Mortality was 60% and 63% when one or 10 NeabNPV-treated third-instar larva(e), respectively, were introduced into groups. Slightly higher levels of NeabNPV-induced mortality occurring when NeabNPV-treated larvae were introduced into first- rather than third-instar cohorts suggests that early instars are more susceptible to the virus. In the laboratory (~1330 N. abietis larvae/ m² of foliage), NeabNPV-caused mortality increased from 20% in control groups to over 80% with the introduction of one, five or 10 NeabNPV-treated larvae into treatment groups of first-instar larvae.
authors.affiliation: Faculty of Forestry and Environmental Management, P.O. Box 4400, The University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada. rogergraves19@gmail.com.
authors.forename: Roger
authors.initials: R
authors.lastname: Graves
authors.affiliation: Faculty of Forestry and Environmental Management, P.O. Box 4400, The University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada. quiring@unb.ca.
authors.forename: Dan T
authors.initials: DT
authors.lastname: Quiring
authors.affiliation: Faculty of Forestry and Environmental Management, P.O. Box 4400, The University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada. clucarot@nrcan.gc.ca.|Natural Resources Canada, Canadian Forest Service - Atlantic Forestry Centre, 1350 Regent Street, Fredericton, New Brunswick, E3C 2G6, Canada. clucarot@nrcan.gc.ca.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lucarotti
keywords: Abies balsamea; Gammabaculovirus; Neodiprion abietis; balsam fir sawfly; disease transmission; nucleopolyhedrovirus; pest management