A SYNOPSIS OF 

 THE MOSQUITOES 

 OF ILLINOIS 



(Dip+era, Culicidae) 



Herbert H. Ross 

 William R. Horsfall 



Fig. 1. — Adult of Aedes aej^ypti. (From photo.uraph. lent hy the U. S. 

 Health Service, of model in the American Museum of Natural History.) 



Publii 



TO ALL OF US WHO LIVE IN ILLINOIS, mos- 

 cjuitoes are familiar as pests that attack persons and live- 

 stock out of doors from spring to fall. 



They may be of greater consequence than simply 

 as biting pests. Some kinds are solely responsible for 

 transmitting certain parasites to man and domestic ani- 

 mals. Blood parasites such as those that cause malaria, 

 yellow fever, dengue, and filariasis must have mosquitoes 

 to take them from sick to well persons. Several of the 

 encephalitis-producing ultramicroscopic viruses that at- 

 tack the brain and spinal cord are carried solely by mos- 

 quitoes from wild animals to man or from man to man. 

 Past control efforts against mosquitoes have reduced 

 some of these diseases to insignificance. Other diseases 

 carried by mosquitoes still rise at times to plague us. 



To date, mosquitoes of 55 different species have been 

 taken in Illinois. Seven additional species, known in 

 neighboring states from situations similar to those in 

 this state, may also occur in Illinois and arc included in 

 this synopsis. These 62 species, along with se\cral hun- 

 dred more in other parts of the world, constitute the 

 family Culicidae. This family and a hundred or more 

 additional families of two-winged flies together comprise 

 the order Diptera. 



The Illinois species of mosquitoes differ from each 

 other in the habitats they frequent and in many details 



This paper is piiiitwl t>.v juithnrit.v of the State of llli 

 IKS Ch. 127. I'ar. 5S.22. U is a contrilnition from tlie Se' 

 of Faiiiii.stii- Surveys and Insert Identification of the 111 

 Natural Histor.v Survey. Dr. lioss is head of that section. 

 Horsfall is a Professor of ICntomoloc.v. Department of li 

 moloiiy. University of Illinois. 



The authors wish tf) express special thanks t() Jame 

 Ayars. the Survey's Technical I'Mitrir, for the i-reative wa 

 which he has contrihuted to the production of this Sifiirt 

 His unstinting and understanilini? help in siniplifyitin term 

 OK.v. rephrasing couplets, and clarifying concepts has made 

 publication u.serul to a much wider circle. 



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of their life histories. All of them, however, have many 

 characters and habits in common. The immature form 

 or larva (known as a wriggler) is aquatic, that is, it 

 lives in water. This form requires several to many days 

 to become a full-grown lar\ a. At this time, it transforms 

 into the next life history stage, the pupal (as pupae, 

 mosquitoes are called rumblers ) , and this stage also is 

 aquatic. The pupal stage, which lasts only a few days, 

 is a transformation stage; within the pupa the tissues of 

 the larva are transformed into those of the adult mos- 

 t|uito. When the transformation is complete, the pupa 

 floats at the surface of the water, its shell cracks and 

 breaks the surface film, and the winged adult emerges. 



Adult mosquitoes (I'ig. 1) are entirely aerial and 

 never enter the water. After a period of feeding and 

 mating, the females lay eggs either on the surface of 

 the water or in soil that will be flooded at a later date. 

 Eggs laid on the water hatch in a few days; each small 

 larva emerges directly into the water from the end of 

 the egg that sticks into it. Eggs laid in soil hatch when 

 the soil is flooded and the eggs are covered by the right 

 kind of water. 



This synopsis pro\ides means tor idcntilying the 

 mosquitoes likely to be found in Illinois. It contains 

 keys to eggs, larvae, and adults, because the sanitarian, 

 ecologist, and collector working with mosquitoes will 

 find all stages of the insects and may not have the time 

 or means to rear the insects to other stages. It is an 

 extension of the original report. The Mosquitoes of Illi- 

 nois (Ross 1947) in that it includes more species and 

 presents a key to eggs of floodwater mosquitoes. Most 

 of the keys in this synopsis have been enlarged from the 

 original report; some of the illustrations are from the 

 original report and some are new. 



