BIOLOGY OF THE HORSE CHESTNUT SCALE, PULVINARIA REGALIS CANARD (HEMIPTERA: COCCOIDEA: COCCIDAE), IN SWITZERLAND.

Abstract

BIOLOGY OF THE HORSE CHESTNUT SCALE, PULVINARIA REGALIS CANARD (HEMIPTERA: COCCOIDEA: COCCIDAE), IN SWITZERLAND. In 1997, many lime (Tilia spp.) and horse chestnut (Aesculus hippocastanum) trees in the centre of Zurich were found to be heavily infested by the horse chestnut scale, Pulvinaria regalis Canard. The biology of this introduced coccid was studied for one year. Crawlers hatched from the end of May and moved to the leaves of their host plants. There the nymphs settled and fed until Sept./Oct., when they migrated to adjacent twigs to overwinter as the 3rd-instar females. After the final nymphal moult in the spring, the adult female went through a period of rapid growth. Adult males appeared for a short period at the beginning of May but were rare. At this time, the females began to move to the main branches and the trunk of the tree, where they secreted a white ovisac consisting of wax filaments. Shortly after oviposition, the females died but remained attached to the ovisac. Two species of aphelinid (Coccophagus lycimnia (Walker) and, much less commonly, C. semicircularis (Forster)) emerged from parasitised scale nymphs in May (on twigs) and at the beginning of September (on leaves). The average rate of parasitisation of P. regalis was low (≤5%). No dipteran and only a few coccinellid predators were found during the sampling period. Key words: sex ratio, plant stress, Pseudaulacaspis pentagona, Coccophagus obscurus, C. scutellaris, Exochomus quadripustulatus, Leucopis silesiaca, urban environment, parasitoids.