Sublethal effects of iridovirus disease in a mosquito

Recognition of the importance of debilitating effects of insect virus disea ses is currently growing. Commonly observed effects of sublethal infection at the individual level include extended development times, reduced pupal a nd adult weights, and lowered fecundity. However, for the most part, sublet hal infections are assumed to be present in survivors of an inoculum challe nge, rather than demonstrated to be present by microscopy or molecular tech niques. Invertebrate iridescent viruses are dsDNA viruses capable of causin g disease with symptoms obvious to the naked rye, a "patent" infection. tha t is lethal. Furthermore, inapparent ''covert" infections may occur that ar e non-lethal and which can only be detected using bioassay or molecular tec hniques. In this study replication of Invertebrate ir iridescent virus 6 in Ae;ies aegypti larvae was demonstrated in the absence of patent disease. A sensitive insect bioassay (using Galleria mellonella) allowed the detectio n of covert infections, which were more common than patent infections. A co ncentration-response relationship was detected for the incidence of patent infections. Covert infections were up to 2 orders of magnitude commoner tha n patent infections, but the prevalence of covert infections did not appear to be related to virus inoculum concentration. Exposure of larvae to virus inoculum resulted in extended juvenile development times. A reduction in t he mean and an increase in the variability of fecundity and adult progeny p roduction was observed in females exposed to an inoculum challenge, althoug h formal analysis was not possible. Males appeared capable of passing virus to uninfected females during the mating process. Covertly infected females were smaller and had shorter lifespans than control or virus-challenged fe males. A conservative estimate for the reduction in the net reproductive ra te (Ro) of such insects was calculated at slightly more than 20% relative t o controls.