Rice culture, as well as other irrigated agricultural situations, can provide a suitable environment for mosquito breeding. In cases where these agricultural lands interface with urbanized or public areas, mosquitoes can be a public nuisance, and certain mosquito species can create health problems for humans and livestock. Culex tarsalis and several other species can transmit the viruses that cause encephalitis, including West Nile Virus. Anopheles freeborni can transmit the pathogens that cause malaria.
Mosquito control in rice fields is often carried out primarily by mosquito abatement or vector control personnel who are authorized to visit rice fields and treat for mosquito infestations. Mosquito Abatement or Vector Control Districts combine a variety of methods to manage mosquitoes in rice fields including insecticide application and stocking fields with the mosquito-eating fish, Gambusia affinis. Some mosquito control agencies use the bacteria Bacillus thuringiensis israelensis (Bti) and B. sphaericus (Bs), which are effective in killing mosquito larvae, yet have low toxicity to other organisms. Agencies also use ultra-low volume pesticide fogs to control flying adult mosquitoes in rice-growing areas (usually pyrethroids or malathion). These fogs do not kill the fish, insects, and some of the other invertebrates in the water.
In addition to the control measures taken by mosquito abatement districts, there are numerous cultural practices growers can take to reduce the rice field's desirability as a mosquito-breeding site.
- Construct access roads around each field for checking and repairing levee breaks and for mosquito abatement personnel to use to check fields.
- Drain and eliminate borrow pits and seepage areas external to the field.
- Seek assistance of your local mosquito abatement district staff to develop the best possible abatement program for a field.
- Check with abatement district personnel to find out how to minimize impacts of pesticides used in your pest management program on mosquito-eating fish, and notify them if disruptive pesticides are used later in the season than May so that they can monitor the fish populations.
Preserving Mosquito Predators
Many insects occurring naturally in rice fields are predators of mosquitoes. These include backswimmers, scavenger beetle larvae, giant water bugs, predaceous diving beetles and their larvae, and damselfly and dragonfly nymphs. While these useful predators consume the majority of mosquito larvae, supplemental mosquito control is usually necessary because the low percentages that survive still represent very large numbers. It is very important, however, to conserve the natural predators that accomplish most mosquito control. Whenever possible, follow good integrated pest management practices for invertebrate pests so that the use of broad-spectrum pesticides can be minimized. This will facilitate the survival of mosquito fish and other natural enemies of mosquitoes and help to minimize buildup of mosquito populations.