The following is part of a report I wrote on Anopheline and Culicine mosquitoes, it is aimed at a more academic audience but I think it is accessible to all. Any questions/comments please post them in the comments section and I will get back to you.
Anopheles stephensi obtaining a blood meal
The mosquito is an insect which is apart of the Culicidae family and of the order of true flies, Diptera. The taxonomic classification for the mosquito is in the table below-
Mosquitoes are believed to have evolved around 50 million years ago and consist of three subfamilies two of which Anophelinae and Culicinae I am going to discuss in this article and the third Toxorhynchitinae. The females of most mosquito species are haematophagic meaning they feed on blood. They have evolved great senses to aid in the acquisition of a blood meal, for example they have heat sensors which can detect endothermic animals such as humans and cattle. Mosquitoes also have chemical sensors which can detect carbon dioxide and lactic acid which are also both produced by respiring and aid in the mosquito detecting its blood meal source. The mosquito’s final adaption is that of visual sensors which allow the mosquito to detect movement and then combined with its other sensors allows for its meal source to be found. As with all members of the Insecta class the mosquito’s body is segmented consisting of the head, thorax and abdomen. Unlike other members of the order Diptera the wings of the mosquito have scales on the veins. The head being the segment responsible for obtaining the blood meal in females; it is here that the palpus and proboscis are found which allow the mosquito to penetrate the epidermis of an animal and withdraw a blood meal.
Life cycles of Anopheline and Culicine mosquitoes
Mosquitoes of the genus Anopheles lay their eggs (40-400) singularly at the waters surface after consuming a blood meal. As with all mosquito species they undergo complete metamorphosis starting at the egg instar and moving on to the larval and pupae stages before becoming an adult, which emerges on the fourth instar, from the pupa the adult mosquito rests on the waters surface while it dries and blood flows to its wings. The Anopheles larvae do not possess a breathing tube called a siphon, which other mosquito larvae use to respire, so they have to lie parallel to the waters surface (Fig1.1), they do however possess spiracles which are located on the 8th abdominal segment, so they have to be in contact with the surface of the water regularly to breathe. The larvae spend most their time feeding on algae and bacteria, as well as other micro-organisms in the water. When the larvae form a pupa the head and thorax are combined into a cephalothorax with the abdomen curving underneath. The pupa also respires and achieves this through a pair of respiratory tubes on the cephalothorax. The pupa does not feed during the pupa instar and remains at the surface unless disturbed. After around 10-14 days (in tropical regions, it is longer in more temperate regions) the dorsal surface of the cephalothorax splits open and the adult mosquito emerges and then rests on the surface of the water for a while as it dries and blood flows to the wings allowing it to fly. The males will go in search of nectar or fruit as well as a mate and the females will go in search of a mate and a blood meal so she can produce eggs. Without a substantial blood meal she will die without having produced any eggs. The malarial parasite has an advantage here as the female will take 4-5 days before being able to produce eggs meaning the malarial parasite has time to get to its intermediate host (mosquito) and then go through the second half of its life cycle within the mosquito before the mosquito bites its primary host (human in the case of Anopheles). The female adult anopheles mosquito has a long palpus which is as long and straight as the proboscis, where as culicine mosquitoes have shorter palpi, which is useful when identifying the genus to which the mosquito belongs to before more extensive identification can take place. The anopheles mosquitoes are the only mosquitoes which can transmit malaria to humans.
Fig1.1 Anopheles larva on left, Culicine larva on right
Culicine mosquitoes lay eggs in rafts (clumped together) which is different from the singular egg laying of the anopheles mosquito. The larvae of the culicine mosquito possess a breathing tube called a siphon which as described earlier is not present in the anopheles mosquito. The culicine larva does not have palmate hairs which can aid in identifying the genus to which larva belong. The life cycle is the same as all mosquitoes; Egg-Larva-Pupa-Adult. The adult culicine mosquito can act as a vector for the parasitic disease filiariasis so although not a malarial vector it can still act as a parasitic vector. The difference between the anopheles and culicine mosquitoes is not in the larval stages themselves but rather the physical characteristics at the different instars and of the adult mosquito. The life cycle for a mosquito can be seen in fig.1.2
Fig1.2 life cycle of a mosquito