Outbreak and declining populations of spruce budworm (Choristoneura fumiferana (Clem.)) were sampled extensively at three locations in New Brunswick, Canada, between 1982 and 1992 and were examined for the prevalence of granulosis and nuclear polyhedrosis viruses (Baculoviridae). Larvae, pupae, and adults were collected using a variety of methods. Spruce budworm nuclear polyhedrosis virus (CfMNPV) genomic DNA probes and wet-mount light microscopy were used to determine CfMNPV prevalence in 50 274 juvenile spruce budworms. Spruce budworm granulosis virus (ChfuGV) genomic DNA probes were used to determine the prevalence of ChfuGV in 25 703 of these same samples. The prevalence of both viruses was low, with ChfuGV and CfMNPV not found in more than 15% and 2%, respectively, of samples in any collection in a given year. Prevalence of ChfuGV was greatest in mid-to late June in sixth-instar larvae. Each virus was detected in only two of 2177 female moths and in none of the 420 male moths examined. In the entire collection, cytoplasmic polyhedrosis virus (Reoviridae) was detected in only two budworm larvae and entomopoxvirus (Poxviridae) was not detected in any. Lucarotti CJ, Eveleigh ES, Royama T, Morin B, McCarthy P, Ebling PM, Kaupp WJ, Guertin C, Arella M. 2004. Prévalence des baculovirus dans des populations de tordeuse des bourgeons de l'épinette (Lepidoptera : Tortricidae) au Nouveau-Brunswick. The Canadian Entomologist 136 : 255-264. 255 1 Corresponding author (e-mail: clucarot@nrcan.gc.ca). mêmes échantillons. La prévalence des deux virus était faible, ne dépassant pas 15% pour ChfuGV et pas plus de 2% pour le CfMNPV, pour chaque méthode d'échantillonage, pour chaque année d'étude. La prévalence du ChfuGV atteint son maximum entre le milieu et la fin de juin, au sixième stade de développement larvaire. Chaque virus n'a été détecté que chez deux des 2177 adultes femelles et chez aucun des 420 adultes mâles examinés. Parmis tous les specimens recueillis, le virus de la polyhèdrose cytoplasmique (Reoviridae) n'a été détecté que dans deux larves de la TBE alors que l'entomopoxvirus (Poxviridae) ne l'a été dans aucun.
Two newly identified geographic isolates of a nucleopolyhedrovirus (LdMNPV-H and LdMNPV-J) were evaluated against Disparvirus (LdMNPV-D), a baculovirus insecticide registered in Canada for the control of gypsy moth (Lymantria dispar (L.) (Lepidoptera: Lymantriidae)). Profiles of HindIII and EcoRI restriction enzyme digests of viral DNA from the three viral isolates are presented. Viral isolates were bioassayed using an inoculated diet plug method to determine the dose- and time-responses of second-instar larvae of both the European and Asian strains of gypsy moth. LdMNPV-D was found to be the most virulent isolate when tested against the European strain of gypsy moth, yielding an LD50 and an LD95 (estimates of the doses required to kill 50% and 95% of the test larvae, respectively) of 95 and 774 occlusion bodies (OBs), respectively. LdMNPV-H was the most virulent isolate when tested against the Asian strain, yielding an LD50 and an LD95 of 648 and 8540 OBs, respectively. Time-response data indicate that the three isolates differ little with respect to their speed of kill (ST50; estimate of the length of time required to kill 50% of the test insects) of either larval strain. These results indicate that both new isolates (LdMNPV-H and LdMNPV-J) should be investigated further for control of the Asian strain of the gypsy moth but not pursued for control of the European strain.
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