Larviposition Response of Myiopharus doryphorae (Diptera: Tachinidae) to Colorado Potato Beetle (Coleoptera: Chrysomelidae) Larvae Treated with Lethal and Sublethal Doses of Bacillus thuringiensis Berliner subsp. tenebrionis

Abstract

Larviposition response of Myiopharus doryphorae (Riley) toward Colorado potato beetle, Leptinotarsa decemlineata (Say), host larvae fed for periods of 1 or 24 h on lethal and sublethal doses of Bacillus thuringiensis Berliner subsp. tenebrionis was studied under greenhouse conditions. A significantly shorter delay occurred before the 1st larviposition in hosts fed for 1 h on lethal and sublethal doses of B. thuringiensis compared with the time before larviposition in hosts fed untreated foliage (control). Time before 1st larviposition in hosts fed for 24 h on sublethal doses of B. thuringiensis was also significantly shorter than that for hosts fed lethal doses and control. A substantially lower total number of parasitoid larvae were deposited in hosts fed foliage treated with lethal doses of B. thuringiensis for 24 h than in those fed for 1 h; the lowest rate of parasitization occurred in the hosts fed for 24 h at the lethal dose level. Parasitoid acceptance of sublethally intoxicated Colorado potato beetle larvae and their ability to overcome weaker defensive reactions of these hosts, together with their rejection of lethally infected hosts, indicated that host selection may be based more on manifestations of host vigor and defense than a direct reaction to the presence or absence of B. thuringiensis toxin.