ARS | Publication request: Residual activity of methoprene and novaluron as surface treatments to manage the flour beetles, Tribolium castaneum and Tribolium confusum

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2012
Publication Date: August 15, 2012
Citation: Arthur, F.H., Fontenot, E.A. 2012. Residual activity of methoprene and novaluron as surface treatments to manage the flour beetles, Tribolium castaneum and Tribolium confusum. Journal of Insect Science. 12:95. Available: http://insectscience.org/12.95..

Interpretive Summary: Insect growth regulators are insecticides that inhibit insect development but do not kill adults, and historically these insecticides are evaluated by incorporation into the diet of an insect, which may not reflect how they would be exposed in actual field situations. We tested different methods to assess susceptibility of the red flour beetle and the confused flour beetle, two common pests of stored products. Exposing larvae directly on plywood, floor tile, and concrete treated with methoprene showed that the red flour beetle was the more susceptible of the two species, as determined by whether or not the larvae were able to reach the adult stage. Control was poorest on concrete. We then exposed larvae on concrete treated with a new insecticide, novaluron, and the confused flour beetle was again more difficult to kill than the red flour beetle. In our final test, we exposed adult confused flour beetles with flour on concrete treated with both insecticides, gave the adults the opportunity to lay eggs, and determined production of offspring. Novaluron provided better control than methoprene. Results show that evaluating an insect growth regulator by allowing flour beetle larvae to be exposed on a treated surface or by letting adult flour beetles lay eggs on a treated surface and examining progeny production would be effective methods for assessing susceptibility of different insect species.

Technical Abstract: The juvenile hormone analog methoprene and the chitin synthesis inhibitor novaluron were evaluated by exposing late-stage larvae of Tribolium castaneum (Herbst) or Tribolium confusum (Jacqueline DuVal), with food material on concrete, plywood, and floor tile. Larvae of T. castaneum were more susceptible than T. confusum larvae to both methoprene and novaluron on all surfaces. A further evaluation was done exposing adults of T. confusum only with food on concrete treated with methoprene and novaluron, and then assessing resulting progeny production. Emergence of adults with normal morphology was reduced for both insecticides, with more malformed adults appearing in the methoprene treatment, and fewer adults of any form emerging in the novaluron treatment. Results show direct exposures of larvae or determining progeny production from exposed adults are valid methods for assessing susceptibility of flour beetles to insecticides.