Effects of rice straw and water management on riceland mosquitoes

Rice fields are important sources of mosquitoes in many regions, and rice (Oryza spp.) growing practices can affect mosquito populations. Rice straw incorporation and winter flooding have become common methods to prepare seedbeds, largely replacing burning of straw. These methods increase nutrients during the growing season. We sampled mosquito larvae during 1999-2001 in 16 0.72-ha plots where straw was either burned or incorporated into soil after the previous growing season; these treatments were crossed with either winter flooding or no winter flooding. In 2000, all fields were drained mid-season for an application of herbicide, and then they were reflooded. Mosquitoes responded positively to straw incorporation and winter flooding, especially in combination. The mid-season reflood in year 2 was associated with an order of magnitude increase in Culex tarsalis Coquillett larvae. Results confirm that rice straw and water management can strongly influence mosquito populations.