Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2016
Publication Date: 6/21/2016
Publication URL: http://handle.nal.usda.gov/10113/62725
Citation: Arthur, F.H. 2016. Efficacy of methoprene for multi-year protection of stored wheat, brown rice, rough rice and corn. Journal of Stored Products Research. 68: 85-92. doi: 10.1016/j.jspr.2016.04.005.
Interpretive Summary: A new formulation (Diacon IGR) of the insect growth regulator methoprene was introduced into the stored product market several years ago, but there have been no long-term studies of efficacy with this insecticide on different grains. Over a 24 month period, both the high and low insecticide rate completely suppressed progeny production of the lesser grain borer on wheat, rough rice, and brown rice and red flour beetle on wheat and corn. There was some progeny production of Angoumois grain moth on the treated rice and corn, especially after 12 months, but it was far less than what occurred in untreated controls. Overall there was little difference between the two label rates for any insect species on any commodity. However, there was more progeny production and feeding damage on brown rice relative to the other commodities, especially in untreated controls. Feeding damage, commodity weight loss, and insect-damaged kernels increased with the number of progeny produced in all the grains. Results show that Diacon IGR even at the low label rate can give multi-year protection against stored product beetles, with suppression of Angoumois grain moth but not complete control.
Technical Abstract: Hard red winter wheat, brown rice, rough rice, and corn were treated with the insect growth regulator (IGR) at rates of 1.25 and 2.5 ppm, held for 24 months at ambient conditions at the floor of a grain bin, and sampled every two months. Bioassays were done by exposing 10 mixed-sex adults of Rhyzopertha dominica (F.), the lesser grain borer and Tribolium castaneum (Herbst), the red flour beetle on wheat, R. dominica and Sitotroga cerealella (Oliver), the Angoumois grain moth on brown rice and rough rice, and T. castaneum and S. cerealella on corn. Sample size for all commodities was about 80 g, and these samples were held for 3 months at 27°C-60% r.h. Both rates of the IGR completely suppressed adult progeny development of R. dominica with little resulting feeding damage, sample weight loss, or insect damaged kernels (IDK). Some adult progeny production of S. cerealella and resulting IDK occurred at both rates on rough rice, brown rice, and corn, but was far less than in untreated controls. There was little adult progeny production but some feeding damage caused by larval T. castaneum in the IGR treatments on wheat and corn but again far less than in untreated control. Allowing continual exposure of parental adults on grains treated with an IGR, rather than exposing those parental adults for a short time period, may give more accurate evaluations of residual efficacy of IGRs. Results show that methoprene used as a grain protectant will give residual control of stored product beetles for 24 months, but complete control of S. cerealella may require inclusion of a contact insecticide.