WHAT WE SHOULD KNOW ABOUT MOSQUITO BIOLOGY 267 



in our own country. One traveling in other countries must guard 

 against entirely different species. 



OVIPOSITION AND THE EGG STAGE 



Mosquitoes lay their eggs in various ways. The mode of deposition 

 best known is that of laying all the eggs at once in a so-called raft. 

 The eggs are cylindrical, rounded at the ends and tapering toward the 

 upper end. They are placed in an upright position and fastened together 

 by a viscous secretion. They are deposited upon the water or near it. 

 Such is the type of oviposition of Culex and several other genera. 



Some mosquitoes, as Culex jenningsi, surround the eggs with a gelat- 

 inous mass which furnishes the first food to the newly-hatched larvae. 



The various species of Anopheles deposit the eggs separately in small 

 numbers on the surface of the water. The eggs lie upon their sides and 

 are kept afloat by a peculiar hydrostatic organ, a partial envelope which 

 is more or less expanded, particularly along the median portion of the 

 egg. This organ is variously shaped in the different species of Anopheles 

 and is called a float. 



Of the mosquitoes which lay single eggs, some fasten them by a 

 gelatinous substance at the margin of the water, others lay them on 

 the ground where they remain until rains provide sufficient moisture for 

 hatching. Some of these eggs are enabled to float because of spinose 

 tubercules which hold the air between them. The species of Aedes lay 

 their eggs singly and not all at once. It often happens that eggs laid 

 in the summer in northern latitudes lay over to the next spring. 



Aedes argenteus Poirret, the yellow fever mosquito, lays eggs meas- 

 uring 0.53 mm. long and 0.15 mm. in diameter. They are black, fusiform, 

 very slightly flattened on one side, slightly more tapered toward the 

 micropylar end ; sculptured with rough, somewhat irregular rhomboidal 

 callosities forming spiral rows. Under natural conditions the eggs are 

 laid singly in small irregular groups some distance above the margin 

 of the water. They are laid in from one to seven da3's after the female has 

 fed upon blood, and usually at intervals after successive blood meals. 



Culex quinquefasciatus Say, the dengue fever mosquito, la3^s its eggs 

 in boat-shaped masses floating on the surface of the w^ater. It may lay 

 from 180 to 350 in a mass in 7 to 11 rows. The eggs hatch after one to 

 three days. An egg mass of a Culex mosquito is shown in fig. 48. 



Anopheles crucians Wiedemann has an elongate fusiform egg 

 (fig. 49c) slightly more tapered toward one end, both ends rounded. 

 The dorsal surface is granular, the ventral surface coarsely hexagonally 

 reticulate. The floats occupy about half the sides in top view, and arc 

 separated at the middle by nearly one-third the diameter of the egg. 



