Evaluating Spinosad for use as a contact insecticide in grain bins and warehouses – A 12-month study

Abstract: Contact insecticides are chemical products applied to surfaces to adversely affect
insects upon direct contact with the treated area. They can be effective on all life stages of
insects either by quick knockdown and mortality and/or through disruption of development.
Tempo® SC (β-cyfluthrin), is registered in the United States for empty bin treatment, while
Sensat™ (Spinosad), is registered for use on stored grain. However, there has been no work
investigating the effect of the Sensat™ (spinosad) formulation’s use as a contact insecticide
inside grain bins, processing or storage facilities. The objective of this research study was to
compare the efficacy of β-cyfluthrin and spinosad applied to concrete, metal and painted
concrete surfaces stored in an empty grain bin and storage warehouse, compared to laboratory control, over a 12-month period on Sitophilus oryzae (L.), rice weevil, and Rhyzopertha dominica (F.), lesser grain borer, adults. Adult beetles were exposed to the treated surfaces held in each location at months 0, 1, 2, 3, 6, 9 and 12 and observed for mortality at 1, 3 and 7 d. Sitophilus oryzae and R. dominica were highly susceptible to both β-cyfluthrin and spinosad over the length of the study. Highest mortality was achieved after 7 d of exposure among all locations and surfaces. Bioassay arenas stored in the empty grain bin demonstrated the greatest reduction in 7 d mortality, while arenas stored in the lab had maintained the highest mortality rates among both species. Minimal differences in mortality rates were observed across the different surfaces. In conclusion, Sensat™ could be a viable option as a contact insecticide for controlling R. dominica and S. oryzae in empty grain bins or storage facilities.