Pathology of aGammabaculovirusin Its Natural Balsam Fir Sawfly (Neodiprion abietis) Host

Abstract

The Neodiprion abietis Gammabaculovirus (Baculoviridae: NeabNPV) is virulent, highly contagious, and infects only midgut epithelial cells of balsam fir sawfly larvae, but infections can carry through to adult sawflies in the midgut. Larval infections are characterized by hypertrophy of midgut epithelial cell nuclei, where virogenic stromata develop to produce nucleocapsids that are singly enveloped before occlusion into occlusion bodies. Infected, occlusion body-laden cells slough from the midgut epithelium as a result of a dissolution of the basal lamina. Infected cells undergo lysis, and viral occlusion bodies exit affected larvae in a watery diarrhea to infect other balsam fir sawfly larvae. A budded virus stage was not observed, but nucleocapsid and occlusion body formation resembled the development of occlusion-derived virions and occlusion bodies in lepidopteran alphabaculoviruses.

Spread of a Gammabaculovirus within Larval Populations of Its Natural Balsam Fir Sawfly (Neodiprion abietis) Host Following Its Aerial Application

“…In the present study and previously [ 17 ], it has been demonstrated that aerial application rates as low as 1 × 10 9 NeabNPV OBs/ha can be sufficient to prematurely collapse increasing and peaking populations of balsam fir sawflies. Efficacious applications of NeabNPV OBs at these low rates depend on sufficient balsam fir sawfly larval population densities where a few individuals can be infected and then efficiently transmit NeabNPV horizontally to other cohort members [ 30 , 47 , 48 ]. Additionally here, we have demonstrated how aerial application strategies, such as the one we used at Old Man’s Pond employing aerosol drift and horizontal transmission of NeabNPV, can be used effectively for gammabaculovirus-based biological control products like Abietiv™ that may be expensive and/or in limited supply.…”

Canadian contributions to forest insect pathology and to the use of pathogens in forest pest management

“…A sustained outbreak of this pest in Newfoundland during the 1990s precipitated a multi-year partnership between governments, private industry, and academia to investigate the pest's ecology and impact and to explore options for biological control (Lucarotti et al 2007a(Lucarotti et al , 2007b. A nucleopolyhedrovirus was isolated from a local population and massproduced in the field for further characterisation (Duffy et al 2006(Duffy et al , 2007Graves et al 2012b;Lucarotti et al 2012), field evaluation on~22 000 ha between 2001 and 2005 (Moreau et al 2005;Moreau and Lucarotti 2007) and environmental safety testing. The Canadian Forest Service obtained conditional registration in 2006 and full registration in 2009 of Abietiv TM for control of balsam fir sawfly.…”

Transmission of a Gammabaculovirus within Cohorts of Balsam Fir Sawfly (Neodiprion abietis) Larvae

“…The proteinaceous OBs dissolve in the larval midgut, releasing the virions that attach to and enter midgut epithelial cells. In sawflies, NPV infections are limited to the midgut [ 14 , 15 ]. Horizontal transmission (between individuals of the same generation) of sawfly NPVs occurs through the continuous release of OBs from infected epithelial cells, which slough off the midgut and pass directly into the larval frass and, subsequently, contaminate the foliage where other conspecific larvae can consume them [ 15 , 16 ].…”