Prevalence of viral diseases of the fruittree leafroller, Archips argyrospila (Walker) (Lepidoptera : Tortricidae), in Louisiana

A nucleopolyhedrovirus (NPV) and a granulovirus (GV) were found infecting f ield populations of fruittree leafroller, Archips argyrospila (Walker), lar vae in Louisiana. Both viruses were recovered from infected larvae at 7 of 8 widely separated sampling sites. Additionally, a small proportion (<5%) o f the larvae (maximum 10.2%) had double infections. Overall, infection rate s ranged from 0 to 24.4 percent and were statistically correlated with defo liation and host population levels in a positive, density-dependent manner. It appears that though high populations and warm temperatures favor develo pment of a widespread epizootic, the leaf rolls (shelters) protect larvae f rom contamination at low to moderate population levels. At outbreak larval densities. the rates of viral prevalence approached 25 percent, and the vir uses, coupled with other natural control factors may, in time, become effec tive in population control.