Larvivorous fishes fail to control mosquitoes in experimental rice plots |
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Authors: | Leon Blaustein |
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Institution: | (1) Ecology Program, Department of Entomology, University of California, 95616 Davis, CA, USA;(2) Ben Gurion University of the Negev, Blaustein Institute for Desert Research, Mitrani Center for Ecology, 84990 Sde Boker, Israel |
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Abstract: | The individual and interactive effects of mosquitofish (Gambusia affinis Baird and Girard) and green sunfish (Lepomis cyanellus Rafinesque) populations on densities of mosquito immatures and other aquatic fauna were assessed in experimental rice plots
over a 12 week period. Mosquitofish, stocked at a much higher rate (2318 per ha) than is usually used in commercial rice fields,
increased 88-fold in numbers per minnow trap over a ten week period. Adult green sunfish (7–10 cm TL), stocked at the same
rate as mosquitofish, reproduced in the rice plots, but reproductive success was strongly associated with plot depth. Mosquitofish
numbers were significantly lower in plots stocked with green sunfish early in the season but this difference soon disappeared.
Significant reductions in densities of the immature stages of the mosquito, Culex tarsalis Coquillet, by the fishes were not demonstrated by analyses of variance and covariance (mosquitofish may have provided some
control during the very last week Blaustein, 1990]). Populations of the mosquito, Anopheles freeborni Aitken, were not significantly reduced by mosquitofish except during the last week. A. freeborni populations were significantly higher in the green sunfish treatment than in the control and mosquitofish treatment.
Numbers of notonectids (predators of mosquitoes) were depressed in all fish treatments. This may have indirectly contributed
to the ineffectiveness of the fishes to control mosquitoes. Other invertebrate predators of mosquitoes were not reduced significantly
by the fishes. Similarly, these fishes had little effect on microcrustaceans and chironomids. These fauna, by serving as alternative
prey, may have reduced predation intensity on mosquitoes.
These results demonstrate that high stocking rates and high population growth of mosquitofish will not necessarily provide
control of mosquitoes in rice fields. |
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Keywords: | Anopheles freeborni biological control Culex tarsalis Gambusia affinis Lepomis cyanellus mosquitoes mosquitofish predation rice fields |
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