Management of the yam moth, Dasyses rugosella Stainton, a pest of stored yam tubers (Dioscorea spp.) using plant products

Yams are members of the genus Dioscorea, which produce bulbils, tubers or rhizomes that are of economic importance. West Africa accounts for 90-95% of world production, Nigeria being the major producer. In 2004, the total world production of yam was about 47 million metric tonnes (MT), with 96% of this coming from Africa. Nigeria accounts for about 70% of world production. In spite of the great economic importance of this food item, 20-30% (about 9.4-14.1 million tonnes) is lost during storage. Storage losses of the order of 10-15% after the first three months and approaching 50% after six months have been observed. Yam tubers in storage are attacked by several moth and beetle pests. The moth pests include Dasyses rugosella Stainton, Euzopherodes vapidella Mann and Decadarchis minuscula Walsingham. Dioscorea alata L. (water yam) was found to be the most susceptible species of yam to infestation by these moths. The plant powders tested for their efficacy against D. rugosella included Capsicum frutescens L. (fruit), C. annum Miller (fruit), Piper guineense Schum and Thonn (seed), Aframomum melegueta Schum (seed), Allium cepa L. (scale), A. sativum L. (scale), Citrus sinensis Osbeck (peel) and Azadirachta indica A. Juss (leaf). In another experiment, the oil extracts of the following plants were tested against D. rugosella, Jatropha gossypifolia L. (fruits), Arachis hypogaea L. (seeds), Citrus sinensis Osbeck (seeds), Elaeis guineensis Jacq (kernel), Piper guineense Schum and Thonn (seeds), Aframomum melegueta Schum (seeds) and Adansonia digitata L. (fruits). Results showed that powders of C. annum and C. frutescens were effective against the adult moth producing 100% mortality within 24hrs of application of powder. In addition, P. guineense, A. cepa and A. sativum were effective against D. rugosella within 3 days of application of plant powder. However, C. annum and C. frutescens were able to effectively persist for 14days after application of plant powders. There was no fecundity of the moth in sample treated with C. annum and C. frutescens while fecundity was reduced in others. The survival of the moth from eggs to adults when treated with the plant powders showed that there was significantly (PArachis hypogaea and E. guineensis were effective in preventing adult emergence. This study showed that some plant products (powders of C. annum and C. frutescens and oils of A. hypogaea, P. guineense and E. guineensis) were toxic or very effective against the yam moth, D. rugosellaand the powders can be applied on cut or damaged surfaces of yam tubers to prevent hatching of the eggs of the moth there by helping in their management and also minimize rotting.Keywords: Toxicity, Dasyses rugosella, Management, Mortality, Powder extrac

Resistance of strains of rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae) to pirimiphos methyl

Insecticidal resistance of five strains of Sitophilus oryzae (L.) to pirimiphos methyl (Actellic®) was investigated in the laboratory at 28 ± 2oC and 89 ± 5% relative humidity. Rice infested by S. oryzaewas sampled from Nigerian stores in Akure (Ondo state), Ibadan (Oyo state), Ikotun (Lagos state) and Ilesha (Osun state) and a laboratory culture (in Akure). Twenty adult weevils from each location were exposed to filter papers impregnated with liquid pirimiphos methyl at one of seven concentrations ranging from 0.0 to 5.0%. Mortality rates of the rice weevils were observed at 3, 6 and 24 h after treatment. The mortality of weevils increased with increasing concentration and period of exposure. Irrespective of the strain, 100% mortality was observed in all the treatments at 24 h after exposure to pirimiphos methyl. Weevils sampled from Ibadan were the most resistant, while laboratory strains were the least resistant at 2 and 5% concentrations.Keywords: Strains, insecticide, Pirimiphos methyl, Resistance, Sitophilus oryzae

Resistance of Seven Biscuit Types to Infestation by Tribolium castaneum (Herbst)(Coleoptera: Tenebrionidae)

Seven biscuit types namely, Okin, Digestive, Cabin, Peanut, Cream crackers, Hobnobs and Glucose and wheat flour were screened for their resistance to Tribolium castaneum   (Herbst) at ambient temperature of 28±2 °C and 78±2% relative humidity in the laboratory. 50 g of each biscuit sample were infested with four female and two male adult beetles and left for 15 days then remove for a resistant experiment and 70 days for a mortality experiment. Each treatment and the control without beetles were replicated three times. Results showed that there was significant difference (P<0.05) in the mortality rate of T. castaneum in the biscuit types and wheat flour samples,while there was no significant difference (P>0.05) in the weight loss of biscuit types. The highest adult mortality of beetles (100%) was obtained from Peanut biscuits at 28 days after infestation while there was only 5.5% adult mortality in wheat flour at 70 days after infestation. The susceptibility index was 0 for all the biscuit types since there was no adult emergence indicating that they were resistant to T. castaneum infestation. Resistance in the biscuit types could be due to chemical additives (e.g. sodium chloride and sodium bicarbonate) used in the production of biscuits, which may have inhibitory effect on the development of T. castaneum and also the low moisture content of the biscuits. Packages that can easily be perforated or damaged to allow absorption of moisture from the environment should not be used in packing biscuits