Biological Control 33 (2005) 65–73 www.elsevier.com/locate/ybcon 1049-9644/$ - see front matter. Crown copyright  2005 Published by Elsevier Inc. All rights reserved. doi:10.1016/j.biocontrol.2005.01.008 Aerial application of nucleopolyhedrovirus induces decline in increasing and peaking populations of Neodiprion abietis G. Moreau a , C.J. Lucarotti a,¤ , E.G. Kettela a , G.S. Thurston a , S. Holmes a , C. Weaver a , D.B. Levin b , B. Morin a a Natural Resources Canada, Canadian Forest Service-Atlantic Forestry Centre, P.O. Box 4000, Fredericton, NB, Canada E3B 5P7 b Department of Biology, University of Victoria, P.O. Box 3020, Victoria, BC, Canada V8W 3N5 Received 4 October 2004; accepted 13 January 2005 Abstract The potential role of diseases in generating population cycles has often been advocated but has received little experimental sup- port from the Weld. We introduced a nucleopolyhedrovirus (NeabNPV) into Weld populations of Neodiprion abietis (Harris), the bal- sam Wr sawXy, to determine its role in the collapse of outbreaks and examine its potential for biological control. This was accomplished through the use of aerial applications of NeabNPV on increasing, peaking, and declining populations of its host. Results indicate that N. abietis densities were distinctly lower in the generation following an aerial application of NeabNPV, but only when treatments were directed against increasing or peaking populations. When directed against declining populations, NeabNPV applications apparently did not inXuence the natural collapse of outbreaks. Although the artiWcial introduction of NeabNPV did not consistently aVect densities of the treated generation, it had an eVect on host biology in the weeks following the treatment as the inci- dence of NeabNPV infection increased and frass production (concomitant with larval feeding) decreased in treated areas. This study supports the hypothesis that NeabNPV epizootics initiate the decline of N. abietis populations. Our results also indicate that NeabNPV may provide an eVective tactic to suppress increasing or peaking population outbreaks of N. abietis through the use of aerial applications of NeabNPV at rates as low as 1 £ 10 9 polyhedral occlusion bodies per hectare. Crown copyright  2005 Published by Elsevier Inc. All rights reserved. Keywords: Aerial application; Baculovirus; Balsam Wr sawXy; NeabNPV; Neodiprion abietis; Nucleopolyhedrovirus; Outbreak; Population Xuctuation 1. Introduction Baculoviruses are double-stranded DNA viruses with circular genomes (Mayo and Pringle, 1998) ranging in size from just under 82 to 180 kb (Herniou et al., 2003; Lauzon et al., 2004). Baculoviruses have been reported exclusively from arthropods and have been successfully recovered and genome sequenced only from Diptera, Hymenoptera, and Lepidoptera (Herniou et al., 2004). Currently, the family Baculoviridae is divided into two diverse genera, Granulovirus (GV) and Nucleopolyhedro- virus (NPV). NPVs can be transmitted horizontally through ingestion of virions, occluded in proteinaceous occlusion bodies (OBs), by a suitable host. SawXy NPVs are only known to infect the midgut epithelium so that, following viral replication, infected midgut cells contain- ing OBs are sloughed oV into the frass and out of the body where they can infect other host insects (Federici, 1997). Death normally occurs within one week (Federici, 1997) and, during that time, the hosts produce infective units of the disease. This combined with the gregarious nature of many sawXy species can lead to rapid horizon- tal transmission of the disease within populations. ¤ Corresponding author. Fax: +1 506 452 3525. E-mail address: clucarot@nrcan.gc.ca (C.J. Lucarotti).