Insects in Flooded
Rice Fields-94



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Project Leader and Principal UC Investigators

Rachel Emerson O'Malley, doctoral candidate, Biology Board, UC Santa Cruz

Daniel F. Doak, assistant professor, Environmental Studies Board, UC Santa Cruz

Joshua Garr, undergreaduate research assistant, UC Santa Cruz

Jennifer Kluse undergraduate research assistant, UC Santa Cruz

Catherine Wilewski, undergraduate research assistant, UC Santa Cruz


The vast majority of entomological research funded by the Rice Research Board has focused on the population biology of the rice water weevil at the Rice Experiment Station. Interactions between the rice water weevil, the rice environment and other insects in this complex ecosystem have been little studied until now. Researchers from the University of California, Santa Cruz, initiated this study in 1993 to learn-more about these interactions and how they change when farmers' fields are flooded through the winter for straw management

Last year's research focused on the effects of winter flooding on natural enemy efficiency and rice water weevil and other pest population levels during the regular growing season. Historically, outbreaks of insect pests in California have rarely been serious. Currently, only the rice water weevil and a few other herbivorous pests such as seed midges, armyworm and leafhoppers sporadically cause problems. In many parts of the world, however, where fields are flooded year-round, these pests cause more significant economic damage both by feeding and by vectoring viruses. Widespread changes in the crop environment, such as winter flooding, could strongly influence the biology of these and other potential pests.

These scientists worked with five growers at 15 on-farm sites, and an additional eight plots at another site where a straw management study is under way. The sites were sampled every two weeks from May through October. To date, 271 species of insects and spiders have been identified in the rice fields. Many of them have never before been reported in rice.

Of the potentially beneficial species, 21 are spiders, 29 are predatory and parasitic wasps, 15 are predatory bugs, 47 are beetles and 18 are ants, predatory flies and other occasional beneficial insects. On the flip side of potentially harmful species were 12 plant-sucking bugs (such as leafhoppers and aphids), 14 species of midges, 10 different cricket species and six weevil species, including the rice water weevil. - The remaining species are mostly scavengers, serving as general prey for some beneficials but not necessarily affecting rice production to any degree.

Researchers were still sorting through the large number of samples taken as this report was prepared. However, preliminary analyses indicate that overall levels of both pest and natural enemy species were higher in the winter-flooded fields. Full details will be published in next year's annual report.

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This research will have significant applied value for rice management in the Sacramento Valley by contributing much needed information on the effects of new management techniques - particularly winter flooding - on natural enemy efficiency and non-chemical pest control potential in this important California crop. Researchers hope to quantify and analyze the reasons behind changes in beneficial and pest insect food webs resulting from changing off-season farm management techniques.

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