Efficacy of selected fungicides against chalkbrood of the leafcutting bee

Nine fungicides were tested for efficacy against chalkbrood (Ascosphaera aggregata) and for toxicity to larvae and prepupae of the leafcutting bee Megachile rotundata. Only Benlate at 1.0% active ingredient (a.i.) and carbendazim at 1.0 and 0.1% a.i. in the diet reduced the incidence of chalkbrood in larvae challenged with lOs spores while exhibiting no toxic effects on larval or prepupal survival. Captan (Orthocide) was lethal at 1.0% a.i. and significantly reduced survival to prepupae at 0.1% without reducing the incidence of chalkbrood significantly. Captan at 0.1% a.i. also extended the number of days required for development of larvae to prepupae by over 40%.