Effects of Ultraviolet Irradiation on Life Table of Cowpea Weevil, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)
The cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) is a serious cosmopolitan pest of stored products throughout the world. In this research, effect of UVC irradiation on egg-hatching, reproduction and population growth parameters of this pest were determined. In the experiments 1, 2 and 3-day-old eggs of C. maculatus were exposed to 254nm wavelength (UVC) for different durations at 25±5 ºC and a photoperiod of 10:14 (L: D). The results showed that an increase in time of exposure to UVC-irradiation caused a gradual decrease in the percentage of eggs hatch in all age groups. In all treatments, the older eggs were more sensitive than younger ones. The percentage of hatched eggs was determined to be 95 % in control treatment, while in 1, 2 and 3-day-old eggs it was 7.5, 1.67 and 0.83 %, respectively, at 40 min of exposure to UV- irradiation. All exposure periods of UVC-irradiation in all group of ages caused reduction of reproduction of subsequent adults significantly. The net fecundity rate was estimated to be 79.98±2.34 eggs/female for control and it was lowest (11.07±0.42 eggs/female) in 2-day-old eggs treated by 4 min irradiation. Intrinsic rate of increase (rm), was 0.14±0.001 day-1 in control and decreasing with increasing irradiation time. The lowest value of rm was observed in 2-day-old eggs treated by 4 min exposure (0.05±0.0012 day-1). Finite rates of increase (λ) decreased with increasing exposure time from 2 to 4 min. The doubling rime (DT) and mean generation time (T) increased with increasing time of exposure time from 2 to 4 min. The longest mean generation time was recorded in 3-day-old eggs treated for 4 min exposure time (31.72±0.06 days). It may be concluded that UVC-irradiation is a safe and clean method for stored product preservation and storage pest control.
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