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

1. Baculoviruses are often highly pathogenic to their insect hosts, but theoretical studies have shown that sublethal infections may also play an important role in host population dynamics. Previous experiments have suggested that deleterious effects are caused by sublethal infections in a number of host-pathogen interactions, but these studies have been criticized on the basis of the methodology used. 2. Using an improved bioassay technique, the dose- and age-dependent response of the Indian meal moth, Plodia interpunctella, to sublethal levels of its granulosis virus was investigated. For the first time, significant sublethal effects have been unequivocally demonstrated in the development rate and reproductive capacity of the host. 3. Sublethal effects on the development rate of male and female virus-treated hosts were exhibited in a number of cases, and these strongly suggested stage-dependence. The most striking effects were found in males and females dosed as 4th and 5th instars. 4. The most dramatic effect on the host was a highly significantly reduced reproductive capacity in terms of egg production and egg viability. These effects were not stage-dependent, but with the exception of first instars, within a given stage, were consistently dose-dependent. 5. The mechanism underlying these sublethal effects is equivocal, but the weight of evidence suggests that virus may be carried throughout development in a presymptomatic form. 6. The consequences for the population dynamics of this insect-virus interaction are discussed.