Evaluation of variety alone or in combination with diatomaceous earth or pyriproxyfen (an insect growth regulator) for managing plodia Interpunctella (hubner) (lepidoptera; pyralidae) on stored groundnuts (arachis hypogaea L.)

Abstract

In storage, insect pests cause considerable losses to stored groundnut (Arachis hypogaca L.) and one of the major storage pests worldwide is Plodia interpunctella (Hubner). Two experiment were conducted to evaluate the effects of interactions between host plant resistance and naturally occurring diatomaceous earth (DE) and pyriproxyfen (insect growth regulator) on reducing damage on stored groundnut by P. interpunctella. In the first experiment, biological fitness parameters were used to evaluate 10 varieties (Tsosabana, Peolwane, Nakwana, Sellie, GO74; GO15; GO73; BMM188; GO64-B and BMM268) for resistance against of P. interpunctella based on two generations. The result showed that the lowest fecundity occurred on variety BMM 268. The survival rates of P. interpunctella was significantly lower on varieties BMM268 and Sellie on both first and second generations. The lowest percentage of seed damaged occurred on variety G064-B, followed by Sellie, then BMM268 and the highest occurred on Nakwana. BMM 268 had the lowest susceptibility index and Nakwana had the highest susceptibility index amongst varieties. A significant reduction in mean net reproductive rate and associated fecundity ofP. interpunctella feeding on these variety indicated that antibiosis may be mediating resistance associated with these varieties. The second experiment evaluated efficacy of DE and pyriproxyfen against P. interpunctella. Four varieties (Peolwane, Nakwana, Sellie, and GO 15) were selected and one mutant entry MIT200-2 was included. Pyriproxyfen became more effective regardless of concentration used as time of exposure to treatment increased. Significant increase in mortality was observed on eggs, larvae and pupae. Adult emergence from pupae treated pupae was also significantly reduced compared to control. Diatomaceous earth (DE) becomes more effective as time of exposure to treatment increased. Adequate larval mortalities (LD90) were achieved with application of 0.91 and 0.82g/kg of DE when assessed 16 days after application on MIT 200-2, lower than on other varieties assessed on the same period. The results show that using variety MIT 2002 in combination with DE will be more effective in controlling P. interpunctella. A combination of Sellie and BMM 268 with either pyriproxyfen or DE will reduce damage caused by P. interpunctella on groundnuts in storage.