BiocontrolNews and Information 2000 Vol. 21 No. 4 105N – 116N The biology of Toxorhynchites mosquitoes and their potential as biocontrol agents Larissa E. Collins 1 and Alison Blackwell 2 Department of Biological Sciences, University of Dundee, UK Abstract Toxorhynchites spp. mosquitoes are recognised as potential biological control agents of pest and vector species of mosquito. There have been many attempts to use them for this purpose since the beginning of the twentieth century, although with relatively low levels of success, which has been attributed to a lack of knowledge of the general biology of Toxorhynchites mosquitoes. Increasing resistance of vector mosquitoes to traditional chemical pesticides and the expansion of the ranges of these vector mosquitoes have made the search for alternative methods of mosquito control imperative. This review draws together the current knowledge of both the taxonomy and the general biology of Toxorhynchites mosquitoes and details previous attempts to use this group as biocontrol agents and in integrated control programmes. In addition, it makes recommendations for further study of this group in order to facilitate their successful utilization against vector mosquitoes. Introduction Mosquitoes (Dipt., Culicidae) are responsible for the transmission of the pathogens causing some of the most life-threatening and debilitating diseases of man, including malaria, yellow fever, dengue fever and filariasis. In many areas the incidence and geographical distribution of these diseases have expanded, largely as a result of decreased efficacy of vector-control programmes and subsequent increases in vector mosquito populations. Mosquitoes are also becoming increasingly resistant to traditional chemical pesticides and there is growing concern about the potential health and environmental risks surrounding these products. Environmental protection agencies have banned or placed severe restrictions on the use of many pesticides which were formerly used in mosquito control programmes and there are now fewer adulticides available than there have been for the last 20 years (Rathburn, 1990). Furthermore, manufacturers themselves have withdrawn some insecticides due to the high cost of carrying out the additional tests now required by governments, in addition to the fact that the production of crop pesticides for the agricultural market is much more lucrative (Rathburn, 1990). It is likely, therefore, that mosquitoes will very quickly develop high levels of resistance to the remaining available adulticides, leading to concern among operational mosquito control personnel that effective insecticides may not be available in the near future (Kline, 1994). Hence, it is imperative that novel mosquito control methods are developed and put into general use as soon as possible. One potential alternative approach to the use of chemical pesticides is the use of Toxorhynchites spp. mosquitoes as biological control agents of pest mosquitoes. This was suggested as early as 1911 by W. R. Colledge in an address to the Royal Society of Queensland and since this time there have been many attempts, some successful and some not. Toxorhynchites mosquitoes have an unusual life cycle in that they are not capable of blood feeding and, therefore, are not pests or vectors. In addition, their larvae are predatory on other mosquito larvae. In the development of any biological control strategy it is imperative that the biology and taxonomy of both the target species and the potential biological control agent are understood fully, which has not been the case for most Toxorhynchites species. Due to their lack of importance as pest species, their general biology and taxonomy have been largely neglected. Exceptions have been many isolated descriptions of particular aspects of the biology of some Toxorhynchites spp. mosquitoes, in addition to a small number of taxonomic studies. This review draws together the current knowledge of the general biology and taxonomy of Toxorhynchites spp. mosquitoes. It also describes previous attempts to use these mosquitoes as biological control agents of vector mosquitoes and makes recommendations for further studies of this group. Review Article 1 Present address: Dr L.E. Collins, Central Science Laboratory, Ministry of Agriculture, Fisheries and Food, Sand Hutton, York YO41 1LZ, UK. 2 Present and correspondence address: Dr A. Blackwell, Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian, EH25 9RG, UK.