The investigation of the combined effects of gamma irradiation and environmental manipulation on mortality and sterility of Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae)

Abstract

Abstract With respect to the limitations use of methyl bromide and phosphine, employing ionizing radiation to control stored product pests has attracted great attention. The aim of this study is the investigation of the combined effects of gamma irradiation as viable alternatives to synthetic insecticides and environmental management on mortality and sterility of Rhyzopertha dominica (Fabricius) in a wheat cultivar (Gascogen). The effect of doses range from 30 to 2000 Gy gamma irradiation in combination with manipulation of temperature (15, 21, 27 and 32 °C) and relative humidity (20%, 50%, 65% and 85%) on 5–10 days old adults of R. dominica in Gascogen cultivar of wheat were explored. The experiments were repeated three times and conducted in The Nuclear Agriculture Research School in Karaj and laboratory of shahid steki silo in shahre-kord. Probit analysis revealed that both temperature and relative humidity had combined effects when used with gamma irradiation. The lowest doses of gamma ray required to kill 25% (14.2 Gy) and 50% (610.8 Gy) of the population (LD25 and LD50) were recorded at 21 °C and 85% relative humidity respectively. The low dose for 99% mortality (LD99; 2386.7 Gy) was recorded for beetles maintained at 21 °C and 50% relative humidity. The effect of temperature (15, 21, 27 and 32 °C) on sterility caused by gamma irradiation was also investigated. The results showed that the F1 generation emerged only when the beetles were treated with doses of 0–100 Gy at 32 °C and 0–70 Gy at 27 °C. These results indicate that temperature and relative humidity play an important role in the susceptibility of the lesser grain beetle to gamma irradiation. The results suggest that controlling the efficiency of gamma radiation through environmental control allows the use of low doses of gamma radiation that have a less harmful effect on human health, non-target organisms and seed agronomic features.