The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice, Oryza sativa L. in the United States. Larval feeding causes stunted root systems and reduced grain yields. In spring, adults initiate flights from overwintering sites and move into rice fields. Proper timing of insecticide applications is critical for the exclusion of adults before they lay eggs. An accurate prediction of the emergence date of adults from overwintering sites will facilitate successful use of insecticides. Previous studies showed that flight activity of rice water weevils is dependent upon development of flight muscles, which in turn is a function of accumulated heat units. In order to predict the emergence date, a degree-day model was developed using C programming. Light trap catches and weather data from 14 years from the Rice Research Station, were used to develop the model. The parameters of the model are: starting date for accumulation of heat units; temperature threshold, and cumulative catches of weevils. An iterative procedure was used to determine the combination of parameters that minimized the difference between predicted and actual dates of emergence using the sine wave method. The parameters of the best fit model were as follows: starting date, Feb 2; temperature threshold, 60°F; cumulative catches of weevils, 6. Using these parameters, emergence of weevils occurred after accumulation of 250.5 degree-days. The differences were 4, 7 and 1 days for 2001, 2002 and 2003 flights. In typical year, the emergence date is at middle of April.
Species 1: Coleoptera Curculionidae Lissorhoptrus oryzophilus (rice water weevil)
Keywords: phenology, degree day
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