Microbial Viral Insecticides

Abstract

Microbial viral insecticides are pathogens that attack insects and other arthropods. Baculoviruses (BV) are parasitically replicating microscopic elements. Baculoviruses are extremely small and are composed primarily of double-stranded DNA required for the virus to establish itself and reproduce. The genus Baculoviruses contains three subgroups of viral types: nuclear polyhedrosis viruses (NPVs), granulosis viruses (GVs) and nonoccluded viruses. NPVs and GVs differ in the number and structure of the protective protein coat and are both relatively large and complex in structure in comparison to many other types of viruses. While little information is available for viruses from the third subgroup, several aspects of the infectivity and mode of action of NPVs and GVs have been studied. The most common route of entry into an insect is by ingestion. The primary site of infection is the midgut cells by membrane function. However, two distinct mechanisms of virus uncoating occur among the baculovirus, that is, NPVs uncoat within the nucleus, whereas GVs uncoat within the nuclear pore complex. NPVs may pass through the intestinal epithelium immediately after ingestion, thereby establishing a systematic infection of the haemocoel prior to virus replication in the midgut cells. The GVs do not appear to pass through midgut cells as rapidly as NPVs, and the developmental cycle of GVs is longer than that of NPVs.