Effects of low temperature on various biological stages of cowpea weewil (Callosobruchus maculatus, Coleoptera: Chrysomelidae: Bruchinae)

Cowpea weevil, [Callosobruchus maculatus (F.), Coleoptera:Chrysomelidae: Bruchinae] is an important pest of stored legumes, mainly cowpea and chickpea. This insect pest reproduces several generations in the field and in storage during the year and can cause substantial damage in terms of both quantity and quality. Alternative approaches to chemical control are needed in storages. Low temperature disinfestation is one of the means of physical insect control. In this study, the effects of three low temperatures (-25 °C, -16 °C, +4 oC) were investigated to control the egg, larva, old larva, pupae and adult stage, on chickpea. These biological stages of the pest were exposed to -25 oC and -16 o C for 20, 40, 60, 80, 100 and 120 min., exposed to +4 oC for 24, 48, 72, 96, 120 and 144 hours thus mortality ratios were determined at each temperature and duration combination, after exposure. The adults survived from treatments were mated and number of egg, egg hatching, longetivity of adult were also examined. The results showed that low temperature treatments had significant effects on the life variables of cowpea weevil. 80 minutes at 25 oC and 120 minutes at -16 oC resulted in 100% mortality for each biological period. At +4 o C, the highest mortality rate was found to be 67.5% in the egg treatment. It was found that the most tolerant stage to -25 oC, -16 oC and +4 oC for all stages was pupa and the most sensitive period was the adult period. The lowest number of eggs of surviving adults after the treatment was 13.7 in the egg stage -16 oC 80 min treatment. The lowest egg hatching rate was 42% in the -16 oC 80 min treatment for mature larvae. The shortest adult longetivity was 2.6 days in the -16 oC 40 min treatment.