Impacts of Storicide II on internal feeders of brown rice

Authors: Scully, Erin; Gerken, Alison; Fifield, Adriane; NGUYEN, VALERIE - Kansas State University; VAN PELT, NICHOLAS - Kansas State University; ARTHUR, FANKLIN - Retired ARS Employee

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2020
Publication Date: 1/15/2021
Citation: Scully, E.D., Gerken, A.R., Fifield, A.N., Nguyen, V., Van Pelt, N., Arthur, F.H. 2021. Impacts of Storicide II on internal feeders of brown rice. Journal of Stored Products Research. 90:101758. https://doi.org/10.1016/j.jspr.2020.101758.
DOI: https://doi.org/10.1016/j.jspr.2020.101758

Interpretive Summary: Protectant insecticides are applied to stored grains such as wheat and can reduce damage caused by insect feeding. Although these protectants are often effective against insects that feed on the external surface of the grain, they may be less effective against species that develop internally in grain kernels. Although internal feeding insects such as the lesser grain borer, rice weevil, and Angoumois grain moth spend most of their life inside the grain, they can encounter the exterior surface of the grain during limited periods so grain protectant insecticides might have some efficacy against these important pests. The impact of grain protectant Storicide II was evaluated against three internal feeders at different temperatures and different percentages of treated and untreated grain. Overall, the lesser grain borer was the most susceptible as mortality was observed in mixtures containing 10% Storicide II treated grain and the number of offspring was reduced relative to untreated controls. Angoumois grain moth was the least susceptible species since mixtures containing 50% or more treated kernels were required to reduce number of offspring. Grain when stored is often very warm, with temperatures above 85°F. Lowering the storage temperature can reduced insect damage by itself but it also improved the effectiveness of Storicide. For example, 75% of treated grain was required to reduce Angoumois grain moth offspring at 80°F, but by lowering temperature to 72°F, reductions in offspring were noted with 50% treated grain. Similar temperature effects were observed for rice weevil and lesser grain borer. Overall, these findings suggest that Storicide II can provide some protection against these three species and that combining this protectant with cooler temperatures can improve efficacy.

Technical Abstract: Protectants applied to grain can reduce damage caused by insect feeding during storage. Although these protectants are effective against many external feeders, they may also reduce damage caused by internal feeders as they often interact with the exterior surface of the grain during their larval or adult stages to feed or oviposit. For this study, we investigated impacts of Storicide II applied to brown rice on three different internal feeders: Rhyzopertha dominica (Fauvel) (Coleoptera: Bostrichidae), Sitophilus oryzae (L.) (Coleoptera: Curculionidae), and Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae). We also investigated the effects of this protectant at three different temperatures and when it was combined with different percentages of untreated brown rice. Time-series clustering was also performed to determine whether treatments caused disruptions to the timing of progeny emergence. Overall, R. dominica was the most susceptible as mortality and knockdown were observed in mixtures containing 10% treated brown rice. In contrast, S. cerealella was the least susceptible as mixtures containing at least 50 to 75% treated brown rice were required to reduce progeny production. However, lowering the temperature to 22 °C did reduce the amount of treated brown rice required to reduce progeny emergence and also reduced the number of progeny that emerged synchronously, which would likely reduce mating and reduce population levels over time. Similar effects were observed for S. oryzae. Overall, these findings suggest that Storicide II can reduce population levels of internal feeders and that combining this protectant with cooler temperatures can provide additional protection.