Study on 300 t of wheat stored in corrugated steel bin for two years in Canada. Part II – Movement and distribution of Cryptolestes ferrugineus (Stephens) and Tribolium castaneum (Herbst)

Abstract

Movement and distribution of Cryptolestes ferrugineus and Tribolium castaneum inside a 10 m diameter corrugated steel bin containing 300 t of wheat (initial moisture content of 12.5 ± 0.1%), were monitored by using Insectors® (electronic traps) installed at 65 locations, from September 6, 2019, to October 31, 2021, in Winnipeg, Canada. The data from only 38 locations were available throughout the experimental period due to the failure of some Insectors®. During the first and second week of September 2019, C. ferrugineus adults (combined insect density of 0.25 A/kg) were introduced on the centre grain surface in two equal batches. During the second week of September 2020, the same number of T. castaneum adults (insect density of 0.25 A/kg) were introduced at the same location in two batches. The temperature inside the bin was higher than 7.8 °C, at least at one location throughout 26 months. At the end of the study, both C. ferrugineus and T. castaneum survived inside the bin. Cryptolestes ferrugineus activity was not recorded near the sidewalls at 0.1 m depth from the grain surface, from February to April 2020, when the temperature dropped below 2.5 °C. Cryptolestes ferrugineus activity was recorded when the temperature increased above 4.5 °C. Tribolium castaneum activity was not recorded near the sidewalls at 0.1 m depth when the temperature dropped below 22 °C (mid-October 2020) and the activity was recorded when the temperature increased above 22 °C (mid-July 2021). Although adult T. castaneum were mainly captured at top grain layer (about 1 m depth from the grain surface), they could be captured at any place in the bin. The insect activity near the sidewalls reduced drastically because of the temperature drop. The insect counts and insect activity increased with increase in temperature. Therefore, highest insect counts were recorded inside and around the hot spot for both insects.