|The Assoc. Of Va, Gypsy Moth M|
Submitted to: Journal of Entomological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2002
Publication Date: 4/3/2003
Citation: Webb, R.E., White, G.B., Thorpe, K.W., The Assoc. Of Va, G.A. 2003. Low incidence of viral and fungal entomopathogens in gypsy moth (lepidoptera; lymantriidae) populations in northern virginia.. Journal of Entomological Sciences. Interpretive Summary: The gypsy moth is a serious defoliator of forest and shade trees. Northern Virginia experienced its first cycle of defoliation from the gypsy moth in 1986 (11,000 ha.), peaking in 1995 (340,000 ha). The gypsy moth population collapsed throughout the state of Virginia in 1996, and remained at low levels through 1999. The current paper reports monitoring of natural enemy populations in a number of additional northern and northwestern Virginia locations in 1997, 1998, and 1999. Results from the present study suggest that both LdNPV and E. maimaiga remain at undetectable levels in the very low gypsy moth populations characteristic of the latency phase in the generally infested areas and in the newly-infested sites of the transition zone in Slow-the Spread areas. Thus, while E. maimaiga remained active at reduced levels throughout the northern Virginia area during the period of intergradation of 1997 to 1999, LdNPV fell to levels below detection except tfor a few remnant populations such as Orange-1 and Fairfax-1. These observations led us to consider the possibility that the reintroduction of LdNPV into building populations of gypsy moth after release from intergradation might be facilitated by egg mass treatments, and we have undertaken such research. Results should be of interest to local, state, and federal workers charged with managing the gypsy moth.
Technical Abstract: The gypsy moth population collasped in northern Virginia in 1996, primarily due to the fungus Entomophaga maimaiga, but with help from the gypsy moth nuclear polyhedrosis virus (LdNPV). We measured levels of E. maimaiga and LdNPV in the remnant, low-density populations of gypsy moths in the northern Virginia region for the years 1997-1999. Mortality of gypsy moth larvae from E. maimaiga tended to be present at low levels when gypsy moth populations were at low densities, but such mortality was generally detectable when gypsy populations began to rise. Correlative analysis revealed that E. maimaiga was significantly and positively correlated with gypsy moth population level in Lexington in 1996, and in northern Virginia in 1998. However, E. maimaiga impact was not significantly correlated with gypsy moth population level in the Lexington plots in 1995. We postulate E. maimaiga is usually positively population dependent, but that a large region-wide cloud of late-season E. maimaiga conidia overwhelmed in-plot disease dynamics the 1995 plots. LdNPV persisted in a few gypsy moth populations, but LdNPV-induced mortality was below detectable levels in most of the low-density populations studied in the region. Thus, while E. maimaiga-induced mortality was manifested quickly as gypsy moth population increased, LdNPV lagged behind the rebounding gypsy moth population.