Management Information
Preventative measures: Reducing the number of potential water catchments (mosquito breeding sites) helps reduce populations of mosquitoes, and reducing pig numbers reduces potential mosquito populations. In Hawaii, the introduction of pigs into forest areas has increased the number of potential breeding areas for mosquitoes. In foraging pigs will often fell tree ferns and create trough-like depressions that fill with rainwater. Mosquitoes have been found in greater abundance in these pig-infested areas than elsewhere. Thus, excluding pigs from conservation areas or eradicating them from forested areas reduces the number of potential mosquito breeding areas.Chemical: The approach most commonly used to control mosquito vectors is the application of insecticides (McCarroll and Hemingway 2002, in Liu et al. 2005). However, diverse resistance mechanisms and multiple mechanisms acting in concert often evolve in mosquitoes, making them resistant to insecticide (Brengues et al,. 2003, in Liu et al. 2005). Members of the Cx. pipiens complex have a notorious reputation for developing resistance to insecticides, including organophosphates (OPs), carbamates (Hemingway and Karunaratne 1998), pyrethroids (Bisset et al. 1991, Ben Cheikh et al. 1998, Chandre et al. 1998, Kasai et al. 1998), and Bacillus sphaericus (Nielsen-Leroux et al. 1997, Yuan et al. 2000). Where the control of mosquitoes via insecticide application (of OPs or pyrethroids) has proved insufficient to manage them effectively (due to the evolution of resistant strains) it has been found that increasing the dosage and frequency of insecticide applications and/or changing to different insecticides may help (Liu et al. 2005). Biological: Given their ability to develop insecticide resistance, the evolution and spread of resistance genes among members of the Cx. pipiens complex across continents has become a topic of considerable applied and basic scientific interest (Raymond et al. 1991, Callaghan et al. 1998, Small et al. 1999, in Cornel et al. 2002).
The bacterium Bacillus thuringiensis subsp. israelensis was discovered in the mid-1970s in Israel (Goldberg and Margalit 1977), and was shown to be highly effective in controlling the larvae of numerous species of mosquitoes. This high efficacy quickly led to development of BTI as the active ingredient for commercial bacterial larvicides (Mulla 1990). These larvicides are now used routinely in vector control programs around the world. Despite its intensive use in many control programs, there are no reports of resistance to BTI (Wirth Walton and Federici 1999).
Bacterial larvicides based on commercial formulations of B. sphaericus 2362 are used in several countries and resistance in field populations of Cx. quinquefasciatus has been reported in France, Brazil and India (Sinègre et al. 1994, Silva-Filha et al. 1995, Rao et al. 1995, in Wirth Walton and Federici 1999). Wirth Walton and Federici (1999) found that adding Cyt1A (from Bacillus thuringiensis subsp. israelensis) at a ratio as low as 1:10 to B. sphaericus larvicides restored most of the toxicity against even highly resistant populations of Cx. quinquefasciatus. Therefore, Cyt1A provides a practical tool for managing B. sphaericus resistance. The observation that Cyt1Aa from BTI can reduce resistance to B. sphaericus (as well as the ability of Cyt1A to suppress resistance to other mosquitocidal B. thuringiensis strains) indicates that other mosquitocidal cytolytic toxins also may prove useful in resistance management. Cyt proteins vary in their toxicity to mosquitoes and they may find different roles in managing resistance to B. thuringiensis and B. sphaericus in mosquito populations.
Management Resources/Links
2. Harding., Jon S., Culum Brown, Felicity Jones, & Russell Taylor., 2006. A preliminary assessment of the distribution of mosquitoes in the kingdom of Tonga: potential threats to biodiversity through invasive pathogens. University of canterbury. School of Biological Sciences Research Report
Summary:
Report of a study which involved a preliminary survey of mosquito species and larval habitat preferences in the kingdom of Tonga in order to assess the possible risk to indigenous wildlife from mosquito-borne diseases. 3. Liu, H., Xu, Q., Zhang, L. and Liua, N. 2005. Chlorpyrifos Resistance in Mosquito Culex quinquefasciatus, Journal of Medical Entomology 42(5). 4. Lounibos, L.P. 2002. Invasions by Insect Vectors of Human Disease, Annual Review of Entomology 47. 6. Whitman, N.K., Goodman, S.J., Sinclair, B.J., Walsh, T., Cunningham A.A., Kramer, L.D. and Parker, P.G. 2005. Establishment of the avian disease vector Culex quinquefasciatus Say, 1823 (Diptera: Culicidae) on the Galápagos Islands, Ecuador, Ibis 147(4). Results Page: 1
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