Eradication And Management

Eradication is one possible response to an introduced species, particularly one that has not dispersed widely. Many introduced insects have been eradicated, some from substantial areas. Perhaps the most impressive is the chemical eradication of the African malaria mosquito A. gambiae from 31,000 km2 of northeastern Brazil in 1939-1940. The Mediterranean fruit fly (Ceratitis capitata) was eradicated over 18 months from a 20-county region of Florida by a strict quarantine, destruction of produce and plants, trapping, and insecticide sprays. More recent attempts to eradicate C. capitata in both Florida and California may not have been as successful. Although victory has been declared repeatedly, reappearances are frequent and may constitute either new invasions or simply recovery by uneradicated remnant populations.

The development of the sterile-male technique in the United States against the New World screwworm gave tremendous impetus to the eradication approach. Release of massive numbers of sterile males so reduced the probability of fruitful mating by females that this species disappeared totally from the island of Curaçao in 1954-1955, and this method greatly aided eradication of this fly from the southeastern United States in 1958-1959. The melon fly (Bactrocera cucurbitae) was eliminated from Rota Island by this method. The male annihilation method, in which males are attracted and destroyed, has also succeeded in eradicating introduced fruitfly populations from islands, including the Oriental fruit fly (Dacus dorsalis) from Rota and Guam and the melon fly from Nauru. Male annihilation followed by release of sterile males eradicated the melon fly from the entire Ryukyu Archipelago. The white-spotted tussock moth (Orgyia thyellina) was eradicated from greater Auckland, New Zealand, by pheromone lures plus spraying of Bacillus thuringiensis.

There have also been disastrous failures of expensive eradication campaigns, such as the $200 million attempt to eradicate chemically the red imported fire ant from the southeastern United States, an effort that imposed greater mortality on native insects than on the invader. Quick detection, rapid response, sufficient resources to finish the project, and adequate regulatory power to enforce cooperation have proven most conducive to successful eradication.

If eradication fails or is not attempted, chemical and biological control are the two methods most commonly attempted to manage introduced insects. There are successes and failures for both methods. The nontarget and human health impacts of early generation insecticides such as DDT are legendary. Though more recent chemicals minimize or eliminate this problem, chemical control frequently is problematic for two main, related reasons. First, insects evolve resistance to chemicals; second, expense can be far too great, especially when ever larger amounts must be used because of resistance. For large natural areas, expense of continued chemical applications can be particularly prohibitive.

Biological control is attractive because the expense of development and deployment is lower, and because, although a host may evolve resistance, the biological control agent itself can evolve countermeasures (as witness B. curculionis, discussed earlier). However, the success rate of biological control is rather low. For instance, for parasitoids introduced for insect control, only 10% have been effective. Furthermore, biocontrol agents can affect nontargets, as the sevenspotted lady beetle has done, and these nontarget impacts can be generated by established biocontrol agents that are not even effective against their targets (about three times as many biocontrol parasitoids establish populations as actually control the target pest). The tachinid fly Compsilura concinnata has failed to control gypsy moths in North America, but it is believed to be responsible for the decline of several large native moths.

See Also the Following Articles

Conservation • Fire Ants • Gypsy Moth • Island Biogeography and Evolution • Neotropical African Bees • Regulatory Entomology

Further Reading

New, T. R. (1994). "Exotic Insects in Australia." Gleneagles, Adelaide. Sailer, R. I. (1983). History of insect introductions. In "Exotic Pest Plants and North American Agriculture" (C. Graham and C. Wilson, eds.), pp.

15—38. Academic Press, New York.

Simberloff, D. (1986). Introduced insects: A biogeographic and systematic perspective. In "Ecology of Invasions of North America and Hawaii" (H. A. Mooney and J. A. Drake, eds.). pp. 3—26. Springer-Verlag, New York. Simberloff, D. (1989). Which insect introductions succeed and which fail? In "Biological Invasions. A Global Perspective" (J. A. Drake, H. A. Mooney, F. diCastri, R. H. Groves, F. J. Kruger, M. Rejmanek, and M. Williamson, eds.), pp. 61-75. Wiley, Chichester. Williams, D. F. (ed.). (1994). "Exotic Ants. Biology, Impact, and Control of

Introduced Species." Westview, Boulder, CO. Williamson, M. (1996). "Biological Invasions." Chapman & Hall, London.

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