RAPID ASSESSMENT OF THE INSECTICIDAL VALUE OF DIATOMACEOUS EARTH WITHOUT CONDUCTING BIOASSAYS

The efficacy of diatomaceous earth (DE) against insects depends greatl y on several physical properties of the diatom particles. Ideally, act ive DE should have an high amorphous silicon dioxide content with a un iform particle size (less than 10 mu m), a high oil sorption capacity, a large active surface, and very little clay and other impurities. Th e analysis of physical and chemical properties of DE is time-consuming and expensive, and ran be conducted only by experts at specially equi pped laboratories. Therefore, in the past, bioassay was considered the most important criterion for the assessment of the efficacy of DE aga inst insects. These methods are relatively expensive and time-consumin g also, since they require an expert and a well-equipped entomological laboratory. After conducting numerous experiments with 36 different d iatomaceous earths or formulations collected from the U.S.A., Mexico, Canada, Australia, Japan, China, and Macedonia (Europe), results indic ate that the efficacy of DE against insects depends on different prope rties of the diatom particles. Properties include the ability of DE pa rticles to reduce bulk grain density (test weight), DE tapped and loos e density, the tendency of DE particles to adhere on the grain surface , particle size distribution, diatom shape, and pH. It is possible to evaluate and to predict the insecticidal value of diatomaceous earth m ainly by very simple and low-cost analysis of these properties of DE w ithout bioassays or extensive physical and chemical analyses. (C) 1997 Elsevier Science Ltd.