Ultraviolet light induced autophototoxicity and negative phototaxis in Reticulitermes termites (Isoptera: Rhinotermitidae)

Reticulitermes tibialis Banks, R. flavipes (Kollar) and R. virginicus (Banks) termites contain the phototoxic alkaloid norharmane, and ultraviolet light exposure experiments (60 and/or 30 W/m(2)) caused high autophototoxic mortality in all three species. This may be the first known instance of autophototoxicity in nature. Norharmane has been previously reported as a phototoxin when fed to other insects, and this termite endosymbiont-produced beta-carboline may be the causal agent in Reticulitermes spp. autophototoxic mortality. Regardless of mechanism, the observed UV-induced termite mortality suggests novel pest control possibilities. UV exposure bioassays with half-covered arenas showed that Reticulitermes termites are negatively phototactic to ultraviolet light. Additionally, mortality was significantly reduced in half-covered arenas compared to uncovered controls and this may be a mechanism by which the termites avoid autophototoxicity. Norharmane transfer between trophic levels was observed in saprophagous Tyrophagus sp. mites, associated with laboratory colonies of Reticulitermes, which become fluorescent after ingesting norharmane from termite cadavers. In contrast to termites, these mites showed no mortality when exposed to UV light. No UV-mediated mortality was observed in pavement ants, Tetramorium caespitum L., fed on sucrose and norharmane, discounting the hypothesis that norharmane may play a role in predation protection.