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. (C) 2015 Elsevier Ltd. All rights reserved

651-966_Proceedings

Abstract In order to mitigate the effect of diatomaceous earth (DE) on bulk density and grain flowability, during the recent years, two new enhanced DEs with synergistic mode of physical and chemical actions have been developed; one with the addition of the soil bacteria metabolite abamectin (DEA) and the other with the addition of the plant extract bitterbarkomycin (DEBBM). Both formulations have very low mammalian toxicity with the oral LD50 for rat higher than 4,500 mg/ kg. The insecticidal effects of both formulations have been extensively evaluated under laboratory conditions. Against the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrychidae) and the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) 75 ppm of DEA on maize and wheat, respectively, provided 100 % parental mortality after 14 days of exposure. In the case of R. dominica, 75 ppm of DEA provided complete progeny suppression. Similar results were produced in the case of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae); however but 125 ppm were required to provide complete progeny suppression. In the case of P. truncatus, it was found that DEA performance remained unaffected in all combinations of the temperature 20, 25 and 30 o C and of the relative humidity (r.h.) levels 55 and 75 %, while mortality was 100 % after only 7 days. For DEBBM, 75 ppm provided 100 % mortality of R. dominica and of the rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae) after 14 d, and complete suppression of progeny production. For a 100 % mortality of S. oryzae and of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) 100-125 ppm was required, but progeny production was extremely low. Based on these results, it becomes evident that these two formulations could be used with success against stored-grain beetle species, at very low application rates