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CHIRONOMID MIDGES -- Biological Control

(Chironomus spp. -- Diptera, Chironomidae)

Although usually not of public health importance, chironomids are often bothersome pests in recreation and urban areas, and also may be economically important when huge numbers threaten food processing industry or contaminate hospital environments. The public often perceives chironomids as mosquitoes which stimulates a psychological fear of them. Thus, they must frequently be controlled by abatement agencies. In the early 1960\'s chironomids of the genus Chironomus began to show resistance to insecticides that were used for their control in urban storm drain channels and recreational lakes of southwestern California. The Southeast Mosquito Abatement District in Los Angeles subsidized a study with University of California, Riverside scientists to investigate biological control alternatives.

Research on the biological control of Chironomidae has been in conjunction with mosquito control, because the breeding habitats are often the same or similar. The same natural enemy groups were investigated, which includes fish, hydra, planaria and various aquatic insect predators. As with mosquitoes, fish have given the most significant levels of control, with cichlids of the genera Tilapia and Oreochromis being most important. A permanent classical biological control has been achieved in the principal storm drain channels of Los Angeles with the establishment of Oreochromis mossambica (Peters) and Oreochromis. hornorum Trewazas there. Persistence of these subtropical cichlids is facilitated by areas of warm water effluent that is discharged into the storm channels from electrical power plants in winter.

Benthic species of Chironomidae are grazed to control levels in these channels, and the cichlid populations annually reach very dense populations, which by early autumn show signs of starvation. Pelagic Chironomidae have increased in abundance with reduced competition for food in the absence of benthic forms. Fortuitously, pelagic species pose no public nuisance. Research revealed that densities of principally Chironomus decorus Johannsen larvae, declined markedly in detritus habitats of the urban drainages of the Los Angeles basin, with the establishment of the cichlids. However, density changes in another group of non-annoying midges, Cricotopus and Tanypus species, were not pronounced over a 9-yr study period. The effective foraging on Chironomidae in certain substrates by very dense populations of the species of cichlids influences the phenotypic characteristics of such substrates to produce chironomids. Typically the insect-produced fish biomass in autumn can exceed 4 x 10⁵ kg over a distance of 18 km of paved river channel, a phenomenon apparently dependent indirectly on the availability of warm water effluent from a power generating plant. The cichlids now range in the neritic zone along the southwestern California coast, and their contribution to enhancing predatory marine fish biomass may be significant.

A native species of pupfish, Cyprinodon macularius Baird & Girard, has also been shown to be an effective predator of chironomid midges. This species might be superior to Gambusia for mosquito abatement as well, being able to rely on other than mosquito food in periods of low mosquito abundance (Walters & Legner 1980).

Details of biological control efforts against Chironomidae may be found in the following references.

REFERENCES:

Legner, E. F. 1973. Book Review, "Biologische Sch�dlingsbek�mpfung." by J. M. Franz. Paul Parey-Verlag, Berlin. 298 pp., 16 fig. Bull. Entomol. Soc. Amer. 19(2): 126.

Legner, E. F. 1983e. Imported cichlid behaviour in California. Proc. Intern. Symp. on Tilapia in aquaculture, Nazareth, Israel, 8-13 May, 1983. Tel Aviv Univ. Publ. 59-63. (CLICK to view details)

Legner, E. F. 1995. Biological control of Diptera of medical and veterinary importance. J. Vector Ecology 20(1): 59-120. . (CLICK to view details)

Legner, E. F. & E. C. Bay. 1970a. The introduction of natural enemies in California for the biological control of noxious flies and gnats. Proc. Calif. Mosq. Contr. Assoc., Inc. 37: 126-129. . (CLICK to view details)

Legner, E. F. & R. A. Medved. 1972. Predators investigated for the biological control of mosquitoes and midges at the University of California, Riverside. Proc. Calif. Mosq. Contr. Assoc., Inc. 40: 109-111. . (CLICK to view details)

Legner, E. F. & R. A. Medved. 1973b. Influence of Tilapia mossambica (Peters), T. zillii (Gervais) (Cichlidae) and Mollienesia latipinna LeSueur (Poeciliidae) on pond populations of Culex mosquitoes and chironomid midges. J. Amer Mosq. Contr. Assoc. 33(3): 354-364. . (CLICK to view details)

Legner, E. F. & R. A. Medved. 1974b. The native desert pupfish, Cyprinodon macularius Baird and Girard, a substitute for Gambusia in mosquito control? Proc. Calif. Mosq. Contr. Assoc., Inc. 42: 58-59. . (CLICK to view details)

Legner, E. F. & F. W. Pelsue. 1977. Adaptations of Tilapia to Culex and chironomid midge ecosystems in south California. Proc. Calif. Mosq. & Vect. Contr. Assoc., Inc. 45: 95-97. . (CLICK to view details)

Legner, E. F. & F. W. Pelsue, Jr. 1983. Contemporary appraisal of the population dynamics of introduced cichlid fish in south California. Proc. Calif. Mosq. & Vect. Contr. Assoc., Inc. 51: 38-39. . (CLICK to view details)

Legner, E. F., R. A. Medved & W. J. Hauser. 1975b. Predation by the desert pupfish, Cyprinodon macularius on Culex mosquitoes and benthic chironomid midges. Entomophaga 20(1): 23-30. . (CLICK to view details)

Legner, E. F., R. A. Medved & F. Pelsue. 1980b. Changes in chironomid breeding patterns in a paved river channel following adaptation of cichlids of the Tilapia mossambica-hornorum complex. Ann. Entomol. Soc. Amer. 73(1): 293-299. . (CLICK to view details)

Walters, L. L. & E. F. Legner. 1980. Impact of the desert pupfish, Cyprinodon macularius, and Gambusia affinis on fauna in pond ecosystems.� Hilgardia 48(3): 1-18. . (CLICK to view details)