The Mosquito as a Laboratory Animal

Buzz-z-z-z-z-z-z Swat! How often these sounds are re-enacted during warm summer evenings, together with a condemnation of mosquitoes in general and the ones at hand in particular. Although mosquitoes long have plagued mankind as vectors of disease and just plain spoilers of outdoor fun, there is one area in which they can be of some value. This is in the high school biology laboratory. Using the mosquito has several important advantages. Its short life cycle makes it possible to study complete insect metamorphosis usually within the time spent in class on insects. Ten to 14 days is enough time to obtain adults from eggs. By using a hand lens or microscope, the student can watch the larvae wriggling free of the egg cases during hatching. The development of the larvae through the four larval stages can be observed, as can the process of pupation. During the pupal stage the development of the adult structures can be seen through the cuticle. By watching from the first day of pupation, the formation of the adult can be followed. At the end of this stage it is a fascinating sight to see an adult mosquito emerge from its pupal case, dry its wings, and leave the water. All this in two weeks or less. Almost any species of mosquito will do. In the spring students can collect eggs and larvae of several species of Culex and Aedes. Through most of the United States, the most commonly found are Culex pipiens, Aedes vexans, and Aedes stimulans. Culex pipiens, the common house mosquito, breeds in stagnant water almost anywhere. The latter two are floodwater mosquitoes-the eggs being laid on land, and hatching when rising water covers them. Woodland pools are common collecting places for these species. Rafts of Culex eggs can be obtained commercially from any one of several biological supply houses any time during the year. The illustration shows the chief differences between A edes and Culex, as well as the main characteristics of the Anophelines. The mosquito is a useful animal in studying genetics. It is larger than Drosophila and has a high spontaneous mutation rate. Many of these mutants are visible with the naked eye. Although most mutations have been found in adults, some can be observed in the larvae. Mendel's Laws can easily be demonstrated with the mosquito, and long term genetic studies by individual students can produce excellent projects. Probably the best laboratory species is the yellow fever mosquito, Aedes aegypti. Its use should be confined to the northern states, however, as the south is its natural habitat. Eradication is the order of the day in that area. In the laboratory A. aegypti has the advantage of laying its eggs on paper towelling which can be stored. Hatching and rearing then can take place at any time. This species is commonly reared in medical schools and biological laboratories. In rearing mosquitoes the temperature should be between 70-90?F with 80?F producing the best results. Humidity should be between 50 and 95%o. At 80?F and 80% relative humidity adults can be produced in 7-9 days with proper feeding (see Table 1). At ordinary room temperature it takes closer to two weeks. Lighting is not a factor, as development will take place in total darkness or 24 hour light. Under laboratory conditions A. aegypti will lay its eggs in a container just above the water line-not on the water. The container should be lined with paper towelling to provide a place for oviposition. This will usually be completed four days following the blood meal. The towelling is then removed from the container and allowed to dry slowly. The eggs can be stored and will stay viable for several weeks. The eggs of