ABSENCE OF FATTY ACID GERMINATION INHIBITORS FOR CONIDIA OF BEAUVERIA BASSIANA ON THE INTEGUMENT OF THE BARK BEETLE DENDROCTONUS PONDEROSAE (COLEOPTERA: SCOLYTIDAE)

Abstract

Ether extracts from Eurygaster integriceps (Evlakhova and Chekhourina 1962) and Bombyx mori (Koidsumi 1957) have been found to inhibit germination of conidia of the white muscardine fungus, Beauveria bassiana, and of Aspergillus flavus, respectively. Free fatty acids, such as caprylic acid, which inhibit the germination of B. bassiana conidia (Smith and Grula 1981), have been found on the cuticle of several insects (Smith and Grula 1982; Saito and Aoki 1983). However, Smith and Grula (1982) found that the toxicity of free fatty acids to B. bassiana conidia in vitro is dependent on the nutritional conditions present. The germination of B. bassiana conidia onthe integument of the mountain pine beetle, Dendroctonus ponderosae, is seldom observed without nutrient enhancement (Hunt et al. 1984). My objective was to determine whether the relative absence of conidial germination on D. ponderosae cuticle is due in part to the action of toxic free fatty acids.