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Diatomaceous earth (DE) is a desiccant insecticide and most efficacious in low humidity. It acts on insect cuticle by absorbing lipids, and perhaps by cuticular abrasion. Beauveria bassiana (Balsamo) Vuillemin, an entomopathogenic fungus, is most efficacious in high humidity and has a complex interaction with cuticular lipids. Interaction between these materials may enhance insect control performance. Assays with stored-grain beetles were conducted with B. bassiana at rates of 11, 33, 100, and 300 mg of conidia per kilogram of grain with and without single rates of DE that killed 10% or less of the target beetles. The assays revealed synergism in effects on adult Rhyzopertha dominica (F.) and Oryzaephilus surinamensis (L.) at all doses. There was statistically significant synergism for adult Cryptolestes ferrugineus (Stephens) and larval R. dominica but at only one B. bassiana rate for each target. Both amorphous silicon dioxide, a sorptive dust, and diamond dust, an abrasive, showed synergistic interaction with B. bassiana on adult R. dominica. These results may provide a basis for a least-toxic approach to control of stored-product beetles and for efficacy-enhancing formulation of entomopathogenic fungi.

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In 125 years since MetchnikoV proposed the use of Metarhizium anisopliae to control the wheat cockchafer and brought about the Wrst Weld trials, microbial control has progressed from the application of naturalists' observations to biotechnology and precision delivery. This review highlights major milestones in its evolution and presents a perspective on its current direction. Fungal pathogens, the most eye-catching agents, dominated the early period, but major mycological control eVorts for chinch bugs and citrus pests in the US had questionable success, and interest waned. The discoveries of Bacillus popilliae and Bacillus thuringiensis began the era of practical and commercially viable microbial control. A program to control the Japanese beetle in the US led to the discovery of both B. popilliae and Steinernema glaseri, the Wrst nematode used as a microbial control agent. Viral insect control became practical in the latter half of the 20th century, and the Wrst registration was obtained with the Heliothis nuclear polyhedrosis virus in 1975. Now strategies are shifting for microbial control. While Bt transgenic crops are now planted on millions of hectares, the successes of more narrowly deWned microbial control are mainly in small niches. Commercial enthusiasm for traditional microbial control agents has been unsteady in recent years. The prospects of microbial insecticide use on vast areas of major crops are now viewed more realistically. Regulatory constraints, activist resistance, benign and eYcacious chemicals, and limited research funding all drive changes in focus. Emphasis is shifting to monitoring, conservation, integration with chemical pesticides, and selection of favorable venues such as organic agriculture and countries that have low costs, mild regulatory climates, modest chemical inputs, and small scale farming. Published by Elsevier Inc.

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