Evaluation of three novel diatomaceous earths against three stored-grain beetle species on wheat and maize

The insecticidal effect of three diatomaceous earths (DEs), that contained different active ingredients, was evaluated under laboratory conditions for the control of adults of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). The tested DEs were DEBBM, which is a mixture of two natural compounds: bitterbarkomycin (BBM) and DE, DEA which is a mixture of abamectin and DE and DESgBAIT which is a mixture of DE, silica gel Sipernat 50S and food grade bait. They were tested at 200, 400, 600, 800 and 1000 ppm on wheat, Triticum durum Desf., and maize, Zea mays L. DEA and DEBBM were generally more effective than DESgBAIT, for all species and commodities. For R. dominica, mortality was high and exceeded 90% for both commodities treated with DEA even at 200 ppm, after 14 d of exposure. Similarly, for the same DE, all adults of S. oryzae were dead on wheat after 14 d for all doses, but mortality was considerably lower on maize. T. confusum was the least susceptible species to all three DEs, as compared with R. dominica and S. oryzae. For this species, doses >400 ppm were needed to obtain a satisfactory level of control. The results of the present study indicate that the simultaneous use of a low mammalian toxicity active ingredient with DEs are notably effective against major stored-product insect pests.