Effectiveness of spinosad and spinetoram against three Sitophilus species: Influence of wheat endosperm vitreousness

Abstract

The influence of wheat endosperm vitreousness on the effectiveness of spinosad and spinetoram against lab populations of Sitophilus granarius, Sitophilus oryzae (from Serbia) and Sitophilus zemais (from Serbia and Slovenia) were evaluated in a laboratory conditions. Characteristics of two test wheat varieties were determined, i.e. a variety with high (HVWG) and another with low (LVWG) endosperm vitreousness. Spinosad and spinetoram were applied at the doses of 0.5, 1 and 2 mg/kg (ppm) to both wheat varieties. Mortality was assessed after 7, 14 and 21 days, while impact on progeny production/reduction PR (%) was assessed after 8 weeks. All doses of spinosad applied to the HVWG variety and 1–2 mg applied to the LVWG variety achieved high mortality (93–100%) of S. granarius after 14 days, while high mortality of the other test species (97–100%) was achieved by 1–2 mg doses on the HVWG and 2 mg on LVWG varieties. After 14 days, all doses of spinetoram achieved high mortality (96–100%) of S. granarius on both wheat varieties, while high mortality of S. oryzae (97–100%) and both populations of S. zeamais (93–100%) was achieved using 1–2 mg doses on the HVWG and 2 mg dose on the LVWG variety. The highest S. granarius PR (>90%) was found in both wheat varieties treated with 2 mg/kg of spinosad or spinetoram, while the highest PR of S. zeamais was observed in HVWG treated with 2 mg/kg of spinosad and 1–2 mg/kg of spinetoram, and in LVWG treated with 2 mg/kg of spinetoram. The greatest PR (91–94%) of S. oryzae in both wheat varieties was observed only in grain treated with 2 mg/kg spinetoram. In general, endosperm vitreousness was found to influence the effectiveness of spinosyns to all Sitophilus species, especially their doses not causing high mortality.