Herbicide induced effects on oviposition of the rice water weevil (Lissorhoptrus oryzophilus)

The area of induced host plant resistance is currently garnering a great deal of attention. While biotic factors are most well studied, abiotic inducing agents are deserving of attention as well. There is evidence that herbicides may induce plant defense to insects. One report involving 2, 4-dichlorophenoxyacetic acid, showed herbicide induced resistance in rice to the striped stem borer Chilo suppressalis. We intend to expand upon this area by looking at an array of herbicides, and how they affect a major Louisiana rice pest. Lissorhoptrus oryzophilus, the rice water weevil, is the most economically important pest of rice in the U.S. This insect has spread from its native region in North America and has become a global pest. We hypothesize that herbicides will affect ovipositional behavior of the weevil.

In order to investigate, we used Clearfield rice variety CL111. The chosen herbicides included 2, 4-dichlorophenoxyacetic acid, Command, Newpath, and Ricebeaux. We applied each at the highest label rate during the four leaf stage. Two days after application the field was flooded, and rice water weevils allowed to naturally infest. We hypothesized that the herbicides would induce hormonal defenses in the rice, potentially reducing insect oviposition. In order to measure this we sampled for rice water weevil eggs, counted larval emergence from collected roots in test tubes, and did core samples for each plot. Our results indicate that there were differential effects on weevil oviposition, depending upon the herbicide.