TOXIC AND ANTIFEEDANT ACTION OF NUTMEG OIL AGAINST TRIBOLIUM-CASTANEUM (HERBST) AND SITOPHILUS-ZEAMAIS MOTSCH

The essential oil extracted from nutmeg seeds using steam distillation was tested against the stored product insect pests, Tribolium castane um (Herbst) and Sitophilus zeamais Motsch., for contact toxicity, fumi gant toxicity and antifeedant activity. Filter paper impregnation was employed for contact and fumigant toxicity studies, whereas a flour di sc bioassay was used to investigate antifeedant effects. Adults of S. zeamais were about ten times more susceptible than T. castaneum adults to contact action (LC50 values of 1.7 mg/cm(2) and 18 mg/cm(2) respec tively). However, S. zeamais adults were only 1.7 times more susceptib le than T. castaneum adults to fumigant action (LC50 values of 4.5 mg/ cm(2) and 7.7 mg/cm(2) respectively). Furthermore, the larvae (10-16 d ays old) of T. castaneum were more susceptible than the adults, but th e susceptibility of the larvae decreased with age. Nutmeg oil also sig nificantly (P < 0.05) affected the hatching of T. castaneum eggs and t he subsequent survival of the larvae in the concentration range 1.4-3. 2 mg/cm(2). The production of F1 progeny of both T. castaneum and S. z eamais exposed to media treated with nutmeg oil was significantly (P < 0.05) reduced at all concentrations tested. F1 progeny production was totally suppressed at nutmeg oil concentrations of 1.05 g/100 g rice for T. castaneum and 0.35 g/100 g wheat for S. zeamais. Nutritional st udies showed that nutmeg oil significantly (P < 0.05) affected the gro wth rate and food consumption of both insect species, depending on the concentrations used, but the antifeedant activity was more pronounced against S. zeamais than against T. castaneum. At 20 g nutmeg oil/100 ml, the feeding deterrence index of T. castaneum was only about 7%, wh ereas that of S. zeamais was 33%. These results suggest that nutmeg oi l may be useful as a grain protectant with contact, fumigant and antif eedant activities against these insects. (C) 1997 Elsevier Science Ltd . All rights reserved.