Reproduced from Wing Beats of the AMCA, the official publication of the Florida Mosquito Control Association. Please use the following citation when referring to this article:
Kaiser, P. 1994. The "Quads," Anopheles quadrimaculatus Say. Wing Beats, Vol. 5(3):8-9.
This mosquito was the most important vector of malaria in the southeastern United States and today is a major host of the nematode that causes dog heartwortn. Large populations are found in rice fields, reservoirs, lakes and rivers which makes this mosquito a significant pest of man and livestock. Anopheles quadrimaculatus (Say) has recently been described as a sibling species complex composed of five valid, yet unnamed, species. Generally accepted dogma concerning this mosquito should be broadened to include new information regarding the sibling species.
All five sibling species can be distinguished by the following methods: (1) enzyme electrophoresis, (2) polytene chromosome analysis, (3) DNA restriction patterns and (4) egg morphology.
Anopheles quadrimaculatus (in the strict sense), which is species A, has a distribution that covers much of the eastern United States. Its range extends from southern Canada to the Florida Everglades, and to the west from Minnesota to Mexico. Species B and D have been found in states south of Kentucky and east of Texas. Species C, and C 2 populations are limited to coastal areas, predominantly along Florida's Gulf coast and the Atlantic coast of Georgia.
Adults of the An. quadrimaculatus complex, which are morphologically indistinguishable from each other, are large dark-brown mosquitoes with four dense patches of scales on each wing. Resting adults stand more parallel to surfaces than do other anophelines. Larvae have hairs on the head capsule that are more widely spaced than other anophelines. Species B larvae are always green. Eggs from sp. A and B can be separated from eggs of sp. C,, C 2 and D because in the latter three the upper surface of the egg is almost completely covered by exochorion.
Species A generally breeds in large bodies of water such as rice fields, reservoirs, lakes and canals that have established surface vegetation or emergent vegetation. Species B breeds in permanent-water swamps that have filtered sunlight and limited aquatic fauna. Eggs of these two species hatch within 36-48 hours after being deposited on the surface of the water. Species C, and C 2 are found in swwnps that have temporary water and dense overhead canopy allowing little sunlight; larvae are found in leaf litter and floatage. Eggs from these two species can resist drought conditions for weeks, and then hatch when the swamp is reflooded. Typical habitat for sp. D is similar to sp. C, but is found further inland.
In cooler months, or in moving streams, An. crucians or An. punctipennis may be found breeding with sp. A. In rice fields, sp. A breeds with Psorophora columbiae. The two C's are commonly associated with Aedes and Psorophora species.
Larvae are surface feeders that ingest microorganisms and detritus. They associate themselves with aquatic vegetation or floatage to avoid predation. They also change color to mimic that of their breeding habitat.
Host preferences of the five sibling species are not known. But in areas with large populations of sp. A and B, some favorite hosts include cattle, horses, pigs, deer and, to a lesser extent, man. In one Florida park, sp. A was much more likely to feed on man than sp. B or C,. Females typically fly less than I mile for a blood meal; sp. A, with fewer breeding restrictions, probably reaches a broader range. Females deposit eggs 3-4 days post feeding.
In northern climates, sp. A is active during the warm summer months and overwinters as an adult female. In more temperate regions, sp. A, B and D have a 6 month breeding season. In Florida and along the Gulf coast, all 5 species breed throughout the year.
Paul Kaiser is a Research Entomologist, Medical and Veterinary Entomology Research Laboratory, U.S. Department of Agriculture, Gainesville, FL.