The synergistic effects of Metarhizium anisopliae (Metschikoff) with the acyl urea insecticides teflubenzuron and diflubenzuron for Schistocerca gregaria (Orthoptera: Acrididae)

Abstract

The acyl urea insecticide teflubenzuron (=Nomolt -) caused loss of appetite, ecdysial failure and eventual death in 4th instar Schistocerca gregaria. The entomopathogenic fungus Metarhizium anisopliae also caused mortality due to mycosis among nymphs of the locust. Enhanced mortality occurred following dual application of the growth regulator and the fungus, which at one combination was synergistic. In another experiment, the fungus was exposed to cuticle treated with acetone (the carrier for the insecticide). This reduced the effectiveness of the fungus. An ultrastructural study showed the effect of the joint application of another acyl urea diflubenzuron (= Dimlin-) and Metarhizium anisopliae on locust cuticle. Disruption of the lamellae pattern was observed in some areas of cuticle. This is consistent with localised disruption of chitin synthesized during treatment with Dimlin. This compound, that has a short half-life in the locust, was applied to the food at 5 day interval over a 15 day period. Clearing zones in the cuticle around penetrant hyphae suggested action of cuticle degrading fungal enzymes. These zones were more extensive around gyphae in Dimlin-affected cuticle suggesting possible enhanced hydrolysis of cuticle protein by fungal proteases in the absence of chitin. SINET: Ethiopian Journal of Science Vol. 24, No. 1 (June 2001), pp. 113-125 Key words/phrases: Diflubenzuron, Metarhizium anisopliae, Schistocerca gregaria, teflubenzuron