The response of phosphine-resistant lesser grain borer rhyzopertha dominica and rice weevilsitophilus oryzae in mixed-age cultures to varying concentrations of phosphine

摘要

The response of Rhyzoprtha dominica and Sitophilus oryzae (both phosphine-resistant) in mixed-age cultures to phosphine at fixed concentration-time products (CT) of 10 500 to 168000 #mu#l litre~(-1)h (ppmh) with either constant, rising or falling concentrations for 7 days were studied at 27(+-2) deg C. At lower CT products, rising cvoncentrations of phosphine led to sngnificantly fewer survivors of R dominica and S oryzae. Conversely, exposure to falling concentrations of phosphine resulted in significantly more survivors. The influence of changing concentrations of phosphine was more pronounced in S oryzae than in R dominica. In the latter, at the lower CT products of 21000 and 42000 #mu#l litre~(-1)h, the adult stage proved to be most tolerant, contrary to the accepted belief that the egg or pupal stage are always more tolerant to phosphine. The results indicate that application of phosphine in rising concentrations is more effective than in constant or falling concentrations.