There are 167 species and subspecies of mosquitoes in North America north of Mexico. Of these, 28 species have been found, under laboratory conditions, to support the growth of dog heartworm (Dirofilaria immitis). For various reasons, which include host preference (which animals female mosquitoes will or will not bite) and longevity, only the fifteen species listed below are thought to transmit dog heartworm in nature. Each species name is a link to a page giving, among other things, bionomic information (where the females lay their eggs, when the eggs hatch, when the females bite) and a distribution map.
Species of four genera are implicated in the transmission of Dog Heartworm. Aedes, Anopheles, Culex and Ochlerotatus. Aedes and Ochlerotatus species generally utilize temporary water habitats such as rain pools, stream flood pools, artifical and natural containers, habitats which periodically dry. Their eggs are adapted to drying and lie dormant, waiting for the next rain to reflood their habitat. Not all eggs from each female hatch with the next flooding. Some are programmed to hatch on the second flooding, a smaller portion on the third, etc. Should wet conditions persist, many eggs will hatch without drying. Some species of these genera utilize the rot cavities in trees almost exclusively. Some species will use only temporary pools in open situations, such as grasslands; others only bogs or habitats in wooded areas. A few will tolerate brackish water and are may be found near the seashore in saltmarshes. Others are restricted to fresh water only.
Anopheles and Culex species tend to utilize more permanent bodies of water such as slow moving streams, pond margins, and fresh water marshes, particularly those with submerged, emergent and floating vegetation. The eggs of these two genera are not resistant to drying.
Aedes and Ochlerotatus species overwinter in the egg stage. Anopheles and Culex overwinter as hibernating adults. In the extreme south some species are active all year.
Not only do mosquitoes exhibit a specificity for larval habitats but also for which animal host species females will bite to obtain a blood meal. Aedes and Ochlerotatus species tend to be mammal feeders, as do Anopheles. Culex species feed on a wider variety of animals including mammals, birds and reptiles. There is also a wide range of times when females seek their blood meal. Some species seek hosts in daylight, some only after dark, and some only at morning and evening twilight.