Rice Water Weevil (Coleoptera: Curculionidae) Population Dynamics in Louisiana

Abstract

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, has long been an important pest of rice in the U.S. and has recently emerged as a pest of rice in Asia. A systematic study of the life history and population dynamics of this insect was conducted during the 2002 growing season at the Louisiana State University Rice Research Station, Crowley, Acadia Parish, LA, an area where it is a particularly severe pest. By monitoring weevil populations using collections from overwintering sites, from plots of rice planted throughout the growing season, and from light traps, and by dissecting collected weevils to assess the conditions of their fat bodies, flight muscles and ovaries, we concluded that a portion of the weevil population in Louisiana is univoltine, another portion is bivoltine, and another portion may pass through multiple generations if young rice is continually available. However, only one generation of weevils developed in a single rice field. Adult weevils invaded rice fields in apparently large numbers prior to flooding. Weevils possessing both well-developed ovaries and well-developed flight muscles were found in both light traps and rice plots, suggesting that adults were capable of seeking new habitats by flying if rice plants were not suitable for oviposition. Weevils were able to complete a generation on ratoon-crop rice. The emergence of overwintered weevils started in late March, with peak emergence occurring during April and May. Return to overwintering sites began in early June and continued until October. Weevils appeared to move among overwintering habitats. A comparison of weevil population dynamics in rice plots planted on different dates supported the use of early planting as a management strategy.