Persistence and efficacy of spinetoram against three major stored grain beetle on wheat

Abstract

The insecticidal efficacy of spinetoram at concentrations of 0.1, 1 and 5 ppm on wheat was investigated against adults of three major stored-grain species, Sitophilus oryzae (L.), Rhyzopertha dominica (F.) and Tribolium confusum Jacquelin Du Val on a monthly basis for a period of 8 months in laboratory conditions. Bioassays were conducted with treated or untreated samples that were taken from lots stored in continuous darkness, and additional wheat samples were taken from the 5 ppm treatment for residue analysis. Mortality in the bioassays was assessed after 7, 14 and 21 days of exposure while progeny emergence was recorded 65 days later. R. dominica was the most susceptible species and was totally controlled even at the lowest concentration of 0.1 ppm after 14 days of exposure, while progeny production was also suppressed in comparison with untreated wheat. On the other hand, S. oryzae was effectively controlled only at the two higher concentrations for the same exposure interval while progeny production was reduced only at 5 ppm. T. confusum was the least susceptible of the species tested. Additionally, for all species, mortality levels remained stable for the whole 8-month testing period. The residue analysis results showed that spinetoram was stable throughout the entire experimental period (8 months), without a noticeable degradation with time.