Fumigant toxicity of neem formulations against Sitophilus oryzae and Rhyzopertha dominica

Abstract

Fumigation toxicity of two neem formulations viz. Ware house neem I (mist and spray) and Ware house neem II (thermal fog) (Azadirachtin-1500 ppm in both) were studied against two major storage pests of maize, the rice weevil, Sitophilus oryzae and the lesser grain borer, Rhyzopertha dominica under laboratory conditions. The insects were confined in vials covered with cloth net (25 mesh) and were placed inside the fumigation chamber of 250 ml capacity. The lid was sealed by adhesive tape to create an air tight condition in the chamber. The adults were exposed to fumigants with and without grains. When the adults alone were exposed to WHN I, complete mortality of Sitophilus oryzae and Rhyzopertha dominica was observed at 15 µl and 30 µl / 250 ml and above doses, respectively at both the exposure periods (48 and 72 hours). Whereas in the case of WHN II, complete mortality of Sitophilus oryzae as observed at 50 µl in both exposure period and 93.33 per cent mortality of Rhyzopertha dominica observed at 250 µl with 72 hours exposure periods. Fumigation with grains required higher doses to cause the same level of mortality to that of fumigation with insects alone. Complete mortality of Sitophilus oryzae and Rhyzopertha dominica with WHN I was observed at 20 and 50 µl, respectively in 10 days of exposure period. In the case WHN II 100% mortality of Sitophilus oryzae was observed at 50 µl with 10 days exposure period, however only 50 per cent mortality of Rhyzopertha dominica was observed with 250 µl, which was five times higher than the former. Thus, Sitophilus oryzae was found more susceptible than Rhyzopertha dominica to fumigation of both formulations. The progeny emergence, percent damage and per cent weight loss were less in different doses of fumigants to both the pests when compared with untreated control. WHN I has more fumigation potential than WHN II to the test insects.