The Potential of Using Hydrothermal Treatment for Protection of Stored Cowpeas against Callosobruchus Maculatus (F.)
Date
1998-01
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Publisher
University of Ghana
Abstract
Laboratory experiments were carried out to evaluate the effect of steaming cowpeas on the oviposition and larval development of the cowpea beetle, Callosobruchus maculatus (F.). The possibility of oven and solar drying as well as the effect of the initial temperature of the cowpeas on the steaming effect were also investigated. Samples of four cowpea varieties (Soronko, Asontem, Amantin and US Blackeye) were steamed for 10 and 15 minutes and solar or oven dried. Some initially stored at 4°C or at room temperature were steamed for ten minutes while other samples were oven dried, solar dried, treated with Actellic super dust or untreated. The results showed that when Soronko, Asontem and Amantin cowpeas were steamed for 15 minutes and oven dried at 70°C for 8 hours, oviposition by C. maculatus was not significantly different from unsteamed beans. Of the four cowpea varieties tested, US blackeye cowpeas were most preferred as oviposition substrate and also for larval development followed by Soronko, Asontem and Amantin. The drying method (solar or oven drying) did not affect oviposition of the bruchids. Significantly fewer eggs were laid on steamed beans compared with unsteamed beans. When US blackeye were steamed for 10 or15 minutes and solar dried, the grains were protected against the development of bruchid larvae comparable to Actellic Super Dust insecticide. In contrast, steaming blackeye cowpeas for 10 or 15 minutes and oven drying delayed adult bruchid emergence for about 4-5 days due to starch gelatinization and protein denaturation. Furthermore, steaming cowpeas initially at a lower temperature of 4°C significantly reduced oviposition in gravid C. maculatus compared to beans at room temperature. Fifteen or ten minutes steaming did not affect damage to the beans so long as the seeds were solar dried to attain safe shelf moisture levels before storage. Microscopic examination of hatched eggs in steamed cowpeas which failed to develop into adults showed death of larvae due to non-utilization of the normal nutrition. All seeds of the four varieties of cowpeas that were steamed lost the ability to germinate.