The medical importance of riceland mosquitoes and their control using alternatives to chemical insecticides.

Abstract

The medical importance, ecology and control of riceland mosquitoes using alternative strategies is reviewed. Over 135 pest and vector anopheline and culicine mosquito species found in association with riceland habitats and their medical importance are presented. Malaria and Japanese encephalitis are the two most serious human diseases transmitted by riceland mosquitoes, but they have been incriminated as vectors of dozens of arboviruses and other parasites and pathogens including the causal agents of West Nile and Rift Valley Fevers and lymphatic filariasis. Control of vector and pest mosquitoes using chemical pesticides has generated several problems including: insecticide resistance, safety risks for humans and domestic animals, and other environmental concerns. These problems and the high cost and sustainability of programs based predominantly on conventional insecticides have stimulated increased interest in integrated control measures in ricelands. The integrated pest management (IPM) strategy for mosquito control, also known as integrated vector control (IVC), is an ecologically based approach that may involve several complementary interventions used in combination or singly. Environmental management, and chemical, biological and mechanical control, comprise the elements of IVC proposed for use in or near riceland habitats. Some of the elements of environmental management include the use of intermittent irrigation; flushing of fields; use of rice cultivars that require less water; shifting of planting schedules to avoid optimal mosquito breeding conditions; relocation of communities or use of dry belt farming around them; and zooprophylaxis and other personal protection methods, especially use of insecticide-impregnated bed nets. Biological control agents that have been used successfully in rice fields include several species of larvivorous fish, a mermithid nematode (Romanomermis culicivorax), a fungus (Lagenidium giganteum) and bacteria (Bacillus thuringiensis var. israelensis and Bacillus sphaericus). The mermithid and the entomopathogens have demonstrated little or no adverse effects on populations of vertebrate and invertebrate nontarget organisms. The successful use of any particular method or combination of interventions for the control of riceland mosquitoes will depend on in-depth ecological studies on the target species and nontarget organisms, sound geographic reconnaissance and effective routine sampling and evaluation. When biological control agents are considered, additional background on the environmental factors limiting their efficacy will also be needed. In addition to the technical components of the various interventions employed in integrated control, sustained suppression of riceland mosquitoes and the diseases they transmit will require a greater sociocultural supportive background, particularly in developing countries.(ABSTRACT TRUNCATED AT 400 WORDS)