Imidacloprid-enhanced Reticulitermes flavipes (Isoptera: Rhinotermitidae) susceptibility to the entomopathogen Metarhizium anisopliae

Abstract

The effects of imidacloprid and the entomopathogen Metarhizium anisopliae (Metsch.) Sorokin on the eastern subterranean termite, Reticulitermes flavipes (Kollar), were evaluated in a 4 x 3 factorial experiment in both sterile and nonsterile loam soil. Termites were not susceptible to M. anisopliae when assays were conducted in nonsterile soil but were highly susceptible in sterile soil. Termite mortality after 21 d of continuous exposure to 104 conidia per gram of soil was zero and 41.6% in nonsterile and sterile soil, respectively. Termites were significantly more susceptible to sterile soil containing 107 conidia per gram than to the same soil containing 104 conidia per gram. In continuous exposure assays, termites were highly susceptible to imidacloprid-treated (5, 10, and 20 ppm) nonsterile and sterile soil containing no experimentally introduced M. anisopliae. Exposure of termites to imidacloprid enhanced their susceptibility to introduced M. anisopliae in nonsterile and sterile soil. Native entomopathogens recovered from termites exposed to imidacloprid-treated, nonsterile soil (i.e., no introduced M. anisopliae) included Conidiobolus coronatus (Constantin) Batko, Cunninghamella echinulata Thaxter, Fusarium spp., Aspergillus spp., and a naturally occurring strain of M. anisopliae variety majus.