Allyl isothiocyanate as a fumigant in the cowpea and its effect on the physical properties of the grain

Abstract

The cowpea is subject to both quantitative and qualitative loss during storage due to attack by the insect pest Callosobruchus maculatus (Fabricius) (Coleoptera: Chrysomelidae). There is a growing interest in controlling the pest using insecticides that result from the reactions of secondary metabolites produced by plants, due to their high efficiency, wide availability and selectivity for the target organisms. The present study aimed to evaluate the fumigant activity of allyl isothiocyanate (AITC) on the development of C. maculatus and its effect on the physical properties of the cowpea. To evaluate the instantaneous population growth rate (r), the insects were exposed to concentrations of 3.81, 5.71, 7.67, 9.41 and 17.85 mL AITC m-3 cowpea (corresponding to LC1, LC10, LC30, LC50 and LC95) for 40 days, after which the physical properties of the cowpea were analyzed. The degree of infestation increased considerably with the reduction in AITC concentration, as did the water content and electrical conductivity. The germination percentage and apparent density decreased with the reduction in AITC concentration. The LC10 sublethal concentration reduced reproduction in C. maculatus and the degree of infestation of the cowpea after 40 days of storage. AITC inhibits the development of C. maculatus and helps maintain the physical properties of the cowpea, thereby representing an alternative to the use of traditional insecticides and showing potential for the control of insect pests in stored grain.