Short-Exposure Biological Activity of Dichlorvos Insecticide Strips on Coleopteran Storage Pests under Two Evaporation Regimes: Can Slow-Release Dichlorvos Formulations Replace Aerosols?

Because of new restrictive DDVP regulations we investigated efficacy of short exposures of slow- release DDVP strips from the perspective of increasing the human safety. Therefore, we determined efficacy of 1-, 6-, and 24-h DDVP (evaporation rate: 0.15 +/- 0.02 g.day(-1)) strip exposures on 5 stored-product pests, namely, Tribolium castaneum, Oryzaephilus surinamensis, Cryptolestes ferrugineus, Rhyzopertha dominica and Sitophilus granarius in an experimental chamber. We tested two DDVP evaporation regimes from the strips, namely, "preventive" and "repressive". In the "preventative" regime, the strips are introduced 168 h before pest exposure whereas in the "repressive" regime strips are introduced concurrently with pests. Based on our data, mortalities ranged from 0 to 100% depending on species. The most sensitive species was O. surinamensis whereas the most tolerant was R. dominica. At 1- and 4-h exposure periods, there were significant differences in mortality between repressive and preventive regimes. However, no differences between regimes existed for 24-h exposure. Our data show that short term exposure to DDVP strips have suppression effect for O. surinamensis but cannot fully replace long term exposure of strips or high dose DDVP aerosols for T castaneum, C. ferrugineus, R. dominica and S. granarius.