Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 27, 1999
Publication Date: N/A
Interpretive Summary: The development of new, ecologically sound methods for termite control must take into account the compatibilities of current pesticides and biological control agents such as the fungus METARHIZIUM ANISOPLIAE. Failure to show compatibilities between such disparate control strategies jeopardizes the search for alternative control strategies that can be used even more effectively in combinations rather than singly. This study tested effects to M. ANISOPLIAE by imidacloprid, one of the most powerful and popular of new insecticidal compounds. It was shown very effectively that in both sterile test soils that common insecticidal levels of imidacloprid enhanced the susceptibility of eastern subterranean termites (RETICULITERMES FLAVIPES) to fungal infections (due, apparently, to pesticide impairment of the routine grooming by treated termites, thus allowing fungal spores more time to infect the insects). Joint treatment with imidacloprid and fungus did not harm the fungus, and caused termites to die sooner than either fungus or insecticide alone would do. However, the presence of normal populations of bacteria and fungi in non-sterile soil compete with and lower the effectiveness of the applied fungal pathogen. There is great promise for the possible use of fungal biocontrols against termites, either alone or in concert with chemical insecticides. This study indicates that there is an encouraging degree of compatibility in the possible co-application of both the only commercialized fungal biocontrol registered for use against termites and one of the most powerful and widely used among all available chemical insecticides.
The effect of imidacloprid and the entomopathogen METARHIZIUM ANISOPLIAE (Metsch.) Sorok. on eastern subterranean termite, RETICULITERMES FLAVIPES (Kollar), mortality were simultaneously evaluated in a 4x3 factorial experiment in both sterile and non-sterile loam soil. Termites were not susceptible to M. ANISOPLIAE when assays were conducted in non-sterile soil, but were highly susceptible in sterilized soil. For example, termite mortality after 21 d of continuous exposure to 10(4) conidia/g soil was 0 and 41.6% in non-sterile and sterile soil, respectively. Termites were significantly more susceptible to sterile soil containing 10(7) conidia/g than the same soil containing 10(4) conidia/g. In continuous exposure assays, termites were highly susceptible to imidacloprid-treated (5, 10 and 20 ppm) non-sterile and sterile soil containing no experimentally- introduced M. ANISOPLIAE. Exposure of termites to imidacloprid enhanced their susceptibility to introduced M. ANISOPLIAE in both non-sterile and sterile soil. Mortality of termites concurrently exposed to imidacloprid and M. ANISOPLIAE was significantly greater than the mortality caused by either treatment alone. Native entomopathogens recovered from termites exposed to imidacloprid treated, nonsterile soil i.e., no introduced M. ANISOPLIAE) included CONIDIOBOLUS CORONATUS (Costantin) Batko, CUNNINGHAMELLA ECHINULATA Thaxter, FUSARIUM spp., ASPERGILLUS spp, and a naturally occurring strain of M. ANISOPLIAE var. MAJUS.