Stimuli associated with viburnum leaf beetle ( Pyrrhalta viburni ) aggregative oviposition behavior

Viburnum leaf beetle, Pyrrhalta viburni (Paykull) (Coleoptera: Chrysomelidae), oviposits in terminal twigs of Viburnum spp. shrubs (Caprifoliaceae). Twigs react to oviposition by producing neoplasm that overgrows the egg mass. Pyrrhalta viburni oviposition behavior is aggregative: females prefer to lay egg masses on twigs previously infested by other females and to position their egg masses adjacent to existing ones. Female oviposition preferences were studied in a series of choice tests under laboratory conditions. The three components of the egg mass (cavity, eggs, and egg cap) were not sufficient to elicit complete aggregation oviposition response when presented separately. Cavity and egg cap elicited positional preference, but not the artificial cavity, artificial egg cap, or frass, suggesting that stimulatory cues might be associated with insect saliva and egg cap secretion. Females preferred to lay eggs on twigs that had produced wound tissue in response to previous oviposition. We conclude that twig choice and positional preference for oviposition are likely to be dissociated, and that twig wound response might be used by P. viburni females to locate twigs already infested and possibly less defended against subsequent oviposition. Pyrrhalta viburni females preferred to lay egg masses on heavily infested twigs rather than on lightly infested twigs. Females did not show preference for twigs infested with their own egg masses, but laid more egg masses on twigs infested by multiple females than on twigs infested by single females. We conclude that both egg mass and conspecific density affect oviposition preferences of P. viburni and discuss the possible ecological implications of this behavior.