The hormetic effect is a bi-phasic, dose-dependent response to an external stimulus. It has been primarily studied in pharmacology in the context of dose-dependent responses to medicinal drugs. The general idea stems from the observation that along a spectrum of doses there exists a therapeutic window where the drug will be most beneficial and outside this window, the drug may be harmful or neutral. However, this concept has not yet been extensively studied outside pharmacology and a handful of papers in the plant defense literature. In this study, we asked whether there is a so-called therapeutic window with an insect virus, the Junonia coenia densosvirus, and the host lepidopteran, Vanessa cardui (Nymphalidae). Caterpillars were reared on two different host plants (Plantago major and Plantago lanceolata), then infected at 4th instar with one of five doses of the virus. Following infection, development time, pupal mass, survivorship, and adult longevity were recorded. Consistent with hormesis, we found that at low to intermediate doses, adult longevity increased by as much as 5 days, particularly on P. lanceolata. Pupal mass and development time were also improved with intermediate doses of the virus. Nonetheless, survival was highest in the uninfected control group. We conclude that this virus can have beneficial effects for the host insect, however, the outcome for survival was still detrimental. Future studies will focus on fecundity of infected and uninfected females to further understand the full outcome of infection and possible hormetic effects.
