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:
Jones, C. and E. Schreiber. 1994. The carnivores, Toxorhynchites. Wing Beats, Vol. 5(4):4.
DR. CARL JONES and DR. ERIC SCHREIBER
Predatory mosquitoes in the genus Toxorhynchites are the most common arthropods which have been used for control of "container-breeding" mosquitoes. The combination of carnivorous larvae and innocuous adults is very attractive in biological control. Successful biological control has been reported usingToxorhynchites species from Japan, Southeast Asia, the Caribbean and the United States.
Most of the 71 species of Toxorhynchites are found in forested tropical regions throughout the world. At least one, Toxorhynchites rutilus, has a subspecies (septentrionalis) that is found as far north as 40 degrees N latitude in Connecticut and southern New York. The other subspecies of Toxorhynchites rutilus found in mainland United States, Tr. rutilus, has been reported only from Florida, Georgia and Louisiana. Although successful introduction of Southeast Asian species has occurred in Hawaii, continual introduction of exotic species at sites in the southern U.S. has not resulted in their establishment.
Toxorhynchites are unusually large mosquitoes; the wingspan may exceed 12 mm; the body length may exceed 7 mm. Adults are frequently covered with iridescent scales and the proboscis has a pronounced 90 degree downward curve. Larvae are generally dark brown or reddish in appearance, with very conspicuous hairs on the abdomen. The head capsule is quite thick and contains powerful mandibles. Fourth instar larvae may be more than 2 cm in length.
Adults feed on plant nectars, which most species require for egg development. A few species are precocious and do not need nectar to initiate oviposition. Protein used in reproduction is apparently entirely derived from larval feeding, although some nectars may provide modest amounts of some amino acids. Cumbersome in flight, they are most frequently seen resting near treeholes or engaging in their characteristic elliptical oviposition flight patterns at the mouth of natural and man-made containers. They are not known to oviposit in small ponds or other open water such as ground pools.
Larvae feed on the living macroinvertebrates inhabiting flooded treeholes, bromeliads and man-made containers. They are dependent on movement for prey location. Although they are more successful in feeding on mosquitoes, eating as many as 400 larvae during their larval development periods, they can successfully complete larval development with artificial protein sources such as water fleas (Daphnia) or brine shrimp. Cannibalism is not uncommon, especially in small containers, but containers such as tires with ample food supplies may support half a dozen or more similarly sized larvae. Larval behavior is especially intriguing with feeding dependent on prey size and availability. Wanton killing of prey without feeding has been reported.
All known species are multivoltine. In the United States, Toxorhynchites generally overwinter as late larval instars. Diapause is controlled by day length, rather than temperature.
Although the use of Toxorhynchites alone is unlikely to reduce pest or vector species below operational thresholds, they can be a valuable tool in areas where containers and treeholes contribute substantially to the standing crop of mosquitoes. However, they are highly susceptible to insecticides, and care has to be exercised in the timing of release of Toxorhynchites and application of insecticide sprays. Their large size and docile appearance create the opportunity for them to serve as focal points for public awareness campaigns aimed at the cleanup of man-made containers that are used as breeding sites by pest mosquitoes.
Dr. Carl Jones is with the College of Veterinary Medicine, Department of Veterinary Pathobiology at the University of Illinois In Urbana-Champaign, Illinois.
Dr. Eric Schreiber is with the John A. Mulrennan, Sr. Research Laboratory at Florida A&M University in Panama City, Florida.