Michael J. Stout
The rice stink bug is the most important late-season insect pest of rice in Louisiana. This insect feeds on rice grains as they develop. Feeding by this insect reduces both grain yield and grain quality. The rice stink bug is probably present in nearly all rice fields in Louisiana every year, and one or more applications of insecticides are often required to control this insect in fields. Guidelines for managing this insect are well-established, but efforts to improve the current management program continue.
Rice stink bugs have piercing/ sucking mouthparts and damage rice by removing the liquid contents of grains as the grains mature. The consequences of rice stink bug feeding depend on the stage at which the grain is attacked. The entire contents of rice grains may be removed at anthesis (flowering stage) and during the early milk stages of grain development, resulting in empty or atrophied grains and in reduced yields. Feeding during later stages of grain development (late milk and dough stages) can also result in reduced grain size. More importantly, however, attack during the late milk and dough stages often results in chalkiness and discoloration around the feeding site.
Microorganisms (bacteria or fungi) introduced into the grain during feeding are involved in causing this chalkiness and discoloration. Rice grains so affected are referred to as “pecky” and have a lower market value. Pecky rice often breaks during milling, further reducing the market value of the grain. Pecky rice shows reduced viability and does not germinate well when planted.
Before moving into rice fields, the rice stink bug can be found feeding on grassy weeds in or around rice fields. Keeping fields and field margins free of weeds may reduce the severity of stink bug infestations.
Scientists are investigating the factors that attract rice stink bugs to rice fields. Recent research in Texas suggests that rice at the milk and soft dough stages of development is more attractive to rice stink bugs than rice at anthesis. Current research in Louisiana is focused on identifying volatile compounds involved in attracting bugs to heading rice. This research may lead to improved methods for monitoring this insect.
These insects are called “stink bugs” because they emit an odor when disturbed. We have characterized the chemical components of this odor, again as part of an effort to develop ways of more effectively monitoring this insect in rice fields.
Management guidelines call for monitoring this insect using a standard insect sweep net. Sweep sampling should begin at or before 50 percent heading. Applications of insecticides are recommended when stink bug densities exceed three bugs per 10 sweeps during the first two weeks of heading or 10 bugs per 10 sweeps during later stages of grain development. The action threshold increases during later stages of grain development because rice in the dough stage of development is more tolerant of stink bug feeding.
A number of insecticides are labeled for use against the rice stink bug: methyl parathion, malathion, lambdacyhalothrin (Karate), gamma-cyhalothrin (Prolex) and zeta-cypermethrin (Mustang Max). The major problem with these insecticides is that they have short residual activities, although the pyrethroid insecticides (Prolex, Mustang Max and Karate) probably have longer residual activities than the other two insecticides. Malathion has shown lower efficacy than the other insecticides in small-plot studies conducted at the LSU AgCenter’s Rice Research Station
in Crowley. Alternative insecticides are being evaluated. Michael J. Stout
, Associate Professor, Department of Entomology, LSU AgCenter, Baton Rouge, La. (This article was published in the summer 2007 issue of Louisiana Agriculture.)