Arthropods, 2012, 1(1): 24-34
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Effects of irradiation on the cowpea weevil (Callosobruchus maculates F.) and moisture sorption isotherm of cowpea seed (Vigna unguiculata L. Walp)

B. Darfour1, F.C.K. Ocloo1, D.D. Wilson2
1Radiation Technology Centre, Biotechnology and Nuclear Agriculture Research Institute of Ghana Atomic Energy Commission, P.O. Box LG 80, Legon, Accra, Ghana
2Department of Animal Science, University of Ghana, Legon, Accra, Ghana

Received 23 November 2011;Accepted 31 January 2012;Published online 10 March 2012

Cowpeas during storage may be attacked by a number of biological agents (microorganisms, rodents, and insects) which results in losses in the quality and quantity of the stored seeds. One of the means of reducing these losses is through the application of radiation processing. The aim of this study was to determine the effects of gamma irradiation on a major storage insect pest, Callosobruchus maculatus F. and on moisture sorption isotherms of cowpea seeds in storage. The cowpeas were infested with adults C. maculatus and then irradiated at doses of 0.0, 0.25, 0.5, 0.75, 1.0 and 1.5 (kGy) at a dose rate of 1.074 kGyhr-1. Samples were stored for 1 month under controlled temperature (27.3-30 oC) and humidity (70-85 %) during which counting of the insects was done every 48 hours and those alive or dead noted. Moisture sorption isotherms of the cowpea samples were equally determined by establishing equilibrium relative humidity (ERH) of 55, 65, 75, 85 and 95 % using a formulation of glycerol-water mixture at temperature of 301 and the weight (loss or gain) of the samples was determined every 2 days. Irradiation at a dose of 0.25 kGy killed the C. maculatus within eight days and therefore 0.25 kGy would be economically beneficial as a control dose. There was significant difference (p < 0.05) in the percent mortality between the irradiated and the non-irradiated weevils, and the percent mortality increased with increase in the radiation dose. At moisture content of 14 % the irradiated cowpea samples were safely stored for one month at an equilibrium relative humidity of 60-75 % at a temperature of 292 oC.

Keywords irradiated cowpea;radiosensitivity;Callosobruchus maculatus;moisture sorption isotherms;percent mortality.

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