Effects of 50°C temperature on Sitophilus granarius (L.), Sitophilus oryzae (L.) and Sitophilus zeamais (Motsch.)

Adults of laboratory populations of granary weevil (S. granarius), rice weevil (S. oryzae)and maize weevil (S. zeamais) were exposed at the temperature of 50°C to determine lethal time (parameters LT20, LT50 and LT99) and progeny production/reduction in F1 generationat mentioned temperature. For each exposure and each species 25 adults aged 2-5 weeks, in four replicates, were used. In the first treatment, the insects were exposed for 6, 10, 14, 16, 18, 20, 22, 26 and 30 min in plastic dishes (V=200 cm3) with 1.8 ± 0.2 g of untreated coarse wheat. In the second treatment, in dishes with 100 g of untreated wheat grain the adults were exposed for 90, 100, 110, 120, 130, 140, 150, 165 and 180 min. After the exposure, the adults were placed in 100 g of untreated wheat grain, in four replicates,at 25 ± 1oC and 60 ± 5% r.h., for recovery. After one, two and seven days of recovery, the weevils were separated by sifting of wheat, and the mortality was determined, and after total period of eight weeks from the exposure of parents, the effect on progeny in F1 generation was determined. Lethal time for weevils was determined by probit analysis, and progeny production/reduction by analysis of variance. After weevils exposure in coarse wheat and after one, two and seven days of recovery, S. oryzae adults were the most susceptible (LT50 12.48-13.68 min), and the most tolerant were adults of S. granarius (LT50 17.79-20.89 min). After insects exposure in wheat grain, the most susceptible were S. granarius and S. oryzae (LT50 107.11-120.73 min), and the most tolerant S. zeamais(LT50 139.90-155.35 min). After exposure of parents of all three weevil species, in coarse wheat, progeny reduction at 100% level is after 22 min. However, after exposure of parents of all three weevil species in wheat grain, progeny reduction at 100% level in S. granarius is after 130 min, in S. oryzae after 150 min, and at 99.7% level in S. zeamais after 180 min. The investigations indicated that short-term exposure of weevils from Sitophilus genus at the temperature of 50°C adversely affects their survival and progeny production,as well as that there is a potential for its successful use as a physical measure in control of storage pest insects.