Insecticidal efficacy of natural diatomaceous earth deposits from Greece and Romania against four stored grain beetles: the effect of temperature and relative humidity

In two separate experimental bioassays, the efficacy of diatomaceous earth (DE) deposits from Greece and Romania, as well as two DE commercial formulations were evaluated against four stored-product beetle species. In the 1(st) experiment, four doses (100, 300, 500 and 900 ppm) of two Greek (Elassona 1 and Elassona 2), two Romanian (PatRom and AdRom) DEs and two commercial DEs (SilicoSec and PyriSec) were tested against adults of Tribolium castaneum (Herbst) (Coleoptera Tenebrionidae) and Oryzaephilus surinamensis (L.) (Coleoptera Silvanidae) in wheat and barley. In the 2(nd) experiment, the effect of temperature (20, 25 and 30 degrees C) and relative humidity (RH) (55 and 75%) on the efficacy of DEs from Greece (Elassona 1), Romania (PatRom) and the commercial DE SilicoSec at three doses (300, 600 and 900 ppm) in wheat was investigated against adults of Sitophilus oryzae (L.) (Coleoptera Curculionidae) and Rhyzopertha dominica (F.) (Coleoptera Bostrychidae). Mortality of the exposed adults in both experiments was assessed after 7, 14 and 21 days of exposure. In the 1st experiment, the most effective DE was PyriSec which caused complete mortality of O. surinamensis adults at 300 ppm after 7 and 14 days of exposure in wheat and barley respectively. In both commodities, the Greek (Elassona 1) and Romanian (PatRom) DEs had the same performance with SilicoSec at 500 ppm. Complete mortality of T. castaneum adults was recorded after 21 days at the highest dose in both commodities treated with PyriSec. Greek and Romanian DEs caused low mortality (< 25%) even after 21 days of exposure at the highest dose. T. castaneum was less susceptible than O. surinamensis, especially to Greek and Romanian DEs. Results from the 2nd experiment indicated that S. oryzae adults were more susceptible than R. dominica adults to the tested DEs. Mortality levels for both species were high, but only at 900 ppm. The increase of temperature, increased the efficacy of the tested DEs against adults of both species. Higher mortality levels were recorded in the low RH for both species. The Romanian DE PatRom was more effective compared with SilicoSec and the Greek DE Elassona 1 against S. oryzae and R. dominica adults at 900 ppm and 25 degrees C.