SUSCEPTIBILITY TO CHALKBROOD OF ALFALFA LEAFCUTTER BEES, MEGACHILE-ROTUNDATA, REARED ON NATURAL AND ARTIFICIAL PROVISIONS

Chalkbrood susceptibilities of leafcutter bees reared on either natural or artificial provisions were compared. The dose-mortality responses of larvae reared on artificial diet were similar to those reported earlier; the LD50 was estimated to be 100 spores/larva with a probit slope of 1.13. Larvae reared on natural provisions showed different dose-mortality responses; mortality increased with an increase in dose up to 101 spores/larva. Above this dose, mortality decreased linearly with increasing dose. Differences in disease symptomatology were also detected; larvae reared on artificial diet had decreased numbers of sporulating cadavers at doses greater than 103 spores/larva. In contrast, such an effect was not apparent when larvae were reared on natural provisions; percentage sporulation was little affected by dose. It is concluded that diet has a profound influence on susceptibility of leafcutter bees to chalkbrood. © 1993 Academic Press. All rights reserved.