THE EFFECTS OF A SUBLETHAL BACULOVIRUS INFECTION IN THE INDIAN MEAL MOTH, PLODIA-INTERPUNCTELLA

1. Baculoviruses are often highly pathogenic to their insect hosts, bu t theoretical studies have shown that sublethal infections may also pl ay an important role in host population dynamics. Previous experiments have suggested that deleterious effects are caused by sublethal infec tions in a number of host-pathogen interactions, but these studies hav e been criticized on the basis of the methodology used. 2. Using an im proved bioassay technique, the dose- and age-dependent response of the Indian meal moth, Plodia interpunctella, to sublethal levels of its g ranulosis virus was investigated. For the first time, significant subl ethal effects have been unequivocally demonstrated in the development rate and reproductive capacity of the host. 3. Sublethal effects on th e development rate of male and female virus-treated hosts were exhibit ed in a number of cases, and these strongly suggested stage-dependence . The most striking effects were found in males and females dosed as 4 th and 5th instars. 4. The most dramatic effect on the host was a high ly significantly reduced reproductive capacity in terms of egg product ion and egg viability. These effects were not stage-dependent, but wit h the exception of first instars, within a given stage, were consisten tly dose-dependent. 5. The mechanism underlying these sublethal effect s is equivocal, but the weight of evidence suggests that virus may be carried throughout development in a presymptomatic form. 6. The conseq uences for the population dynamics of this insect-virus interaction ar e discussed.