Effect of ultra violet irradiation on egg hatching of Callosobruchus maculatus (F.)(Coleoptera: Bruchidae)
Abstract: The cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) is aserious cosmopolitan pest of stored products, especially seeds of Leguminosae, and is to be foundthroughout the tropics and subtropics. In this research, the effect of ultraviolet irradiation (UV)on egg hatching of C. maculatus was evaluated at temperature of 25±5ºC and a photoperiod of10:14 (L:D), without humidity control. Three age groups of eggs (1-, 2- and 3-day old eggs),were exposed to UV-irradiation (254nm wavelength). In each group 120 eggs were irradiated for2, 4, 8, 16, 24, 32, 40 min. The results indicated that all exposure periods of UV-irradiation,reduced the hatching of eggs in comparison to control. An increase in time of exposure toirradiation caused a gradual decrease in percentage of hatching of eggs in all age groups of eggs.However, for each exposure duration, the hatching rate was decreased as the age of irradiatedeggs increased from 1 to 3 days. The percentage of egg hatching was determined to be 95% incontrol treatment. In one-day-old eggs, egg hatching was 71.93, 64.92, 37.72, 28.95, 22.81, 10.53and 7.89% at 2, 4, 8, 16, 24, 32 and 40 min exposure time, respectively. Irradiation of 2-day-oldeggs at 2, 4, 8, 16, 24, 32 and 40 min exposure duration resulted in 43.86, 18.43, 9.65, 5.27, 7.03,6.15 and 5.51% egg hatch, respectively. Irradiation of 3-day-old eggs at the same exposureduration resulted in 40.36, 21.93, 9.65, 7.89, 5.27, 2.64 and 1.86% egg hatch, respectively. The 1-day-old eggs were less sensitive to irradiation than 2- and 3-day old eggs. It may be concludedthat UV-irradiation is a safe and clean method for stored product preservation and pest control.However, much more comprehensive studies on demographic parameters of C. maculatus areneeded.