The potential role of biotic mechanisms in baculovirus dispersal
The role of biotic mechanisms in baculovirus (BV) dispersal was investigated using three Lepidopteran pests; Plodia interpunctella (Hubner), Ephestia cautella Walker and Mamestra brassicae L. and their respective BVs. The first two, pyralid moths, are pests of stored products, and the third is a pest of brassicas. Detailed host biology and virus mortality studies were undertaken to provide background information for the main investigation of virus dispersal using P.interpunctella. BV infectionincreased larval activity and thus BV dispersal in all three species until the disease at an advanced stage caused sluggish behaviour and mortality. However, larva to larva virus transmission was limited, especially as the integuments of diseased pylarids did not rupture and cannibalism was rare when a suitable food supply was available. P.interpunctella adults which received a sub-lethal BV dose in the larval stages appeared normal but the proportion of eggs oviposited, the viability of the eggs and the survival of the progeny were reduced. However, no BV was detected in the adult stage. Transovum transmission occurred if the adults were externally contaminated with BV. Scavangers, predators and adult parasitoids which fed on diseased prey voided viable BV in their faeces. This contaminated the larval medium and resulted in larval infection. The predators tested readily fed on diseased prey but the parasitoids were less able to compete with BV for hosts, Bracon hebetor Say preferentially avoided diseased hosts. There was little evidence to indicate that BV can be mechanically vectored between host larvae on the ovipositor of a parasitoid or the mouthparts of a predator. The relative potential of the host and other biotic mechanisms to cause BV dispersal is discussed.