Toxorhynchites
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Toxorhynchites speciosus |
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| Theobald , 1901 |
Toxorhynchites (from ancient Greek toxon , bow 'and rhýnchos , beak') is a genus of mosquitoes thatoccurlargely in the tropics , in which the females do not suck blood, but like male mosquitoes only feed on nectar and other sweet plant juices. The mosquitoes have a strongly curved proboscis, are usually large, colorful and diurnal. The larvae feed predatory and mainly on other mosquito larvae. They have therefore been used with some success in the control of disease-carrying mosquitoes .
Characteristics and biology
Adults / adults
Adult Toxorhynchites are easy to recognize by their size and their strongly curved trunk. Her body is covered in iridescent green, purple and red scales. The different species are very similar and sometimes difficult to distinguish. In contrast to all other genus of mosquitoes, in which the females ingest blood, both sexes of Toxorhynchites feed exclusively on flower nectar and other sugary plant juices. They are diurnal and occur primarily in forests.
Larvae
The larvae of Toxorhynchites are also large and can be pink, red, or purple in color. They can be found in small pools of water, for example in knotholes, open bamboo stems, leaf axils, bromeliads or in containers, vessels or car tires that are thrown away or standing around. They colonize similar biotopes like the yellow fever mosquito or the Asian tiger mosquito .
All larval stages are predatory, usually from the mosquito larvae predominantly found in their larval waters. The prey is not actively sought or pursued, but rather grasped with the mouthparts when it comes within range. Mechanoreceptors play the most important role in their perception, since the eyes of Toxorhynchites larvae are still underdeveloped. Once captured, the catch is usually eaten within minutes. In the course of its larval life, a single Toxorhynchites larva can eat large numbers of other larvae. For example, T. brevipalpis larvae killed up to 358 yellow fever mosquito larvae during their developmental period. In this and another species ( T. amboinensis ) it has also been observed that larvae kill other larvae that remained shortly before pupation, but do not eat them, probably to protect themselves during their pupal phase. In addition to mosquito larvae, other water-bound insect larvae, small tadpoles and wriggling flying insects caught on the water surface are also eaten. The size of the prey can be up to twice your own body size. Cannibalism occurs, especially in small containers with little food and little hiding place.
The larval development takes between three and thirteen weeks, depending on the food supply and temperature. Above all, the fourth and last larval stage before pupation is also resistant to lack of food and partial dehydration. Toxorhynchites splendens can go months without food in the fourth larval stage. T. brevipalpis can be kept without food and only in a humid atmosphere for more than three weeks and then develops normally again in the water and supplied with food.
The subsequent development time of the doll is between three and twelve days.
distribution
The species within the genus are largely restricted to the tropics . Some species occur in the eastern fringes of Asia and North America . Three species apparently introduced to control other mosquitoes are found in Fiji and Samoa in the southern Pacific . The subgenus Toxorhynchites exists only in the Old World , the subgenus Afrorhynchus in Africa , the subgenus Ankylorhynchus and Lynchiella exclusively in the New World .
meaning
The usual methods of control against growing up in small water tanks disease-carrying mosquitoes (especially the yellow fever mosquito and the Asian tiger mosquito ), the fight against adult animals with adulticide and the destruction or treatment of Larvalgewässer with chemical or biological larvicides. When using insecticides, however, there is a risk of resistance building up . In addition, the methods mentioned are labor-intensive and must be repeated regularly. An automatic and continuous control through the use of natural enemies like Toxorhynchites would not have these disadvantages; However, the circumstances under which such a strategy can be successful are not yet fully understood.
As early as 1911, the possibility of using Toxorhynchites to combat mosquitoes was pointed out . The first practical experiment took place in Hawaii in 1929 , but the species released in the process ( T. inornatus from New Britain ) could not establish itself permanently. In the 1950s, more species were introduced, two of which ( T. amboinensis and T. brevipalpis ) were able to establish themselves. However, the success in the control of the Asian tiger mosquito was not satisfactory, possibly because the less effective species T. amboinensis got out of hand in the resulting competitive situation.
The introduction of the same species to American Samoa , for example, was more successful, in which T. amboinensis also established itself, but successfully controlled the Polynesian tiger mosquito, Stegomyia polynesiensis , a carrier of filariasis .
When combating disease-transmitting mosquitoes with Toxorhynchites , it is particularly important to use species that colonize the correct larval waters in the target biotope. So it is important to understand the biology and the interaction of the species involved. There is still a need for research here.
In addition, it must be taken into account that the generation time of Toxorhynchites is about three times longer than that of their prey, whose population initially grows faster when the larval waters are colonized at the same time. Immediate success with the use of Toxorhynchites is therefore not to be expected, but if it is established it should be possible to achieve adequate control of the target species over longer periods of time.
Systematics
Toxorhynchites is the only genus of the tribe Toxorhynchitini. It contains 90 species from four subgenera:
- Subgenus Afrorhynchus (18 species)
- Subgenus Ankylorhynchus (4 species)
- Subgenus Lynchiella (16 species)
- Subgenus Toxorhynchites (52 species)
supporting documents
- ^ A b c d Genus TOXORHYNCHITES Theobald, 1901. RE Harbach: Mosquito Taxonomic Inventory, accessed on August 6, 2012 .
- ↑ a b c d e f g Collins LE & Blackwell A. (2000) The biology of Toxorhynchites mosquitoes and their potential as biocontrol agents In: Biocontrol News and Information 21 (4) ISSN 0143-1404 , pp. 105N-116N ( PDF -File; 0.16 MB )
- ^ Tribe Toxorhynchitini Lahille, 1904. RE Harbach: Mosquito Taxonomic Inventory, accessed on August 6, 2012 .
- ↑ a b c d e f Steffan WA & Evenhuis NL (1981) Biology of Toxorhynchites In: Annual Review of Entomology 26 ISSN 0066-4170 , pp. 159-181
- ↑ Steffan WA (1975) Systematics and Biological Control Potential of Toxorhynchites (Diptera: Culicidae) In: Mosquito Systematics 7 (1), pp. 59-67
- ↑ Toxorhynchites . (No longer available online.) Walter Reed Biosystematic Unit: Mosquito Genera, archived from the original on August 14, 2013 ; Retrieved August 18, 2012 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
