Laboratory colonization of Toxorhynchites brevipalpis*

Brief communications Laboratory colonization of Toxorhynchites brevipalpis* MILAN TRPis 1 & EUGENE J. GERBERG2 Abstract Toxorhynchites brevipalpis, apredator on larvae of Aedes aegypti and other mosquitos, was successfully colonized in the laboratory. At 25°C, embryonic development was completed within 50 hours of ovi- position, while larval andpupal development together took a further 27-41 days. The adult mosquitos mated in cages as small as 15 x 15 x 15 cm, and the embryon- ated eggs were obtained 6-31 days after the adults emerged. Since the predacious larvae of the non-biting mosquitos in the genus Toxorhynchites could be valuable agents for the biological control of larvae of biting and disease-carrying mosquitos (Swezey, 1931; Paine, 1934; Steffan, 1968), a sample of a field population of T. brevipalpis from an automobile dump in Dar es Salaam, Tanzania, was collected and taken to the laboratory there for colonization. The adult females were placed in a large cage meas- uring 80 x 60 x 60 cm. Absorbent cellulose (Cellu- cotton) soaked in honey and water was used to provide food. Several 100-ml beakers filled with water were placed inside the cage to serve as sites for oviposition. Embryonic development The eggs laid on the water surface were placed with the beakers into incubators at 25°C. The dura- tion of embryonic development was found to be 50-52 hours. * This study was supported by US Public Health Service research grant No. CC 00261 from the Center for Disease Control, Atlanta, Ga., USA, and the World Health Organ- ization. 1 Entomologist/Ecologist, WHO East Africa Aedes Research Unit, Dar es Salaam, Tanzania. Present address: Department of Biology, University of Notre Dame, Notre Dame, Ind., USA. 2 Acting Project Leader, WHO East Africa Aedes Research Unit, Dar es Salaam, Tanzania. Present address: Director, Insect Control and Research Inc., Baltimore, Md., USA. Larval development As the larvae of T. brevipalpis are said to be cannibalistic, the freshly-hatched larvae were sep- arated and reared individually in small Petri dishes (diameter 50 mm) containing 13-20 ml of water. The water depth was 7-10 mm. Every day, 10 freshly- hatched larvae of Aedes aegypti were given to each T. brevipalpis larva as food. Since the lst-instar larvae of T. brevipalpis are not able to kill 3rd- instar larvae of A. aegypti, it was necessary to supply Ist-instar larvae until the T. brevipalpis larvae reached their 3rd instar. It was found that each of the first 3 instars was completed in 2 days. A further 16-23 days elapsed before the 4th-instar larvae pupated, the pupal stage lasting 5-12 days. The total time from hatching to emergence ofadults was 27-41 days. Mating and oviposition Freshly-emerged adults of T. brevipalpis (10 males and 13 females) that had been kept individually in vials were released into a plastic cage measuring 20 x 20 x 20 cm, and kept at a temperature of 25°C. Cellucotton soaked in honey and water and one 100-ml beaker filled with water were placed in the cage. The first batch of 63 eggs was found in the beaker after 30 days. When a new beaker with water was placed in the cage a fresh batch of 12 eggs was found after a further period of 7 days. All the eggs hatched after 50 hours at 25°C. In a second experiment one virgin female and one male were placed in a cylindrical cardboard cage 180 mm high and 180 mm in diameter. The same source of food was used as in the previous experi- ment. After 29 days a batch of 16 eggs was found in the beaker of water provided. All the eggs had hatched after a further 50 hours. In a third experiment, a cage made from a wire frame covered with nylon screening and measuring 15x15x15 cm was used. Five virgin females and 3 newly-emerged males of T. brevipalpis were placed 3060 -637- 638 BRIEF COMMUNICATIONS in the cage. After 6 days the first batch of 15 eggs was found in the oviposition beaker. The next batch of 15 eggs appeared 3 days later, and a third batch of 25 eggs was collected after another 3 days. Mating was observed several times during the daytime in all the types of cage. At the end of each experiment, all the remaining females were dissected and their spermathecae were checked for the presence of live spermatozoa; every insect was found to have been inseminated. REFERENCES Paine, R. W. (1934) Bull. ent. Res., 25, 1 Steffan, W. A. (1968) J. med. Ent., 5, 310 Swezey, C. H. (1931) Rep. Comm. exp. Sta. Hawaii. Sug. Pirs' Ass., 1929-1930, pp. 23-30