ENTOMOLOGY

'VHAT WE SHOULD KNOW ABOUT MOSQUITO BIOLOGY 267in our own country. One traveling in other countries must guardagainst entirely different species.OVIPOSITION AND THE EGG STAGEMosquitoes lay their eggs in various ways. The mode of depositionbest 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 theupper end. They are placed in an upright position and fastened togetherby a viscous secretion. They are deposited upon the water or ncar it.Such is the type of oviposition of Culex and several other genera.Some mosquitoes, as Culex jenningsi, surround the eggs with a gelatinousmass which furnishes the first food to the newly-hatched larvae.The various species of Anopheles deposit the eggs separately in smallnumbers on the surface of the water. The eggs lie upon their sides andare kept afloat by a peculiar hydrostatic organ, a partial envelope whichis more or less expanded, particularly along the median portion of theegg. This organ is variously shaped in the different species of Anophelesand is called a float.Of the mosquitoes which lay single eggs, some fasten them by tI.gelatinous substance at the margin of, the water, others lay them onthe ground where they remain until rains provide sufficient moisture fl)rhatching. Some of these eggs are enabled to float because of spinosetubercules which hold the air between them. The species of Aedes laytheir eggs singly and not all at once. It often happens that eggs laidin the summer in northern latitudes layover to th~ next spring.Aedes argenteua Poirret, the yello,v fever mosquito, lays eggs measuring0.53 mm. long and 0.15 mm. in diameter. They are black, fusiform,very slightly flattened on one side, slightly more tapered toward themicropylar end; sculptured with rough, somewhat irregular rhomboidalcallosities forming spiral rows. Under natural conditions the eggs arelaid singly in small irregular groups some distance above the marginof the water. They are laid in from one to seven days after the female hasfed upon blood, and usually at intervals after successive blood meals.Culex quinque{asciatus Say, the dengue fever mosquito, lays its eggsin boat-shaped masses floating on the surface of the water. It may layfrom 180 to 350 in a maf!.s in 7 to 11 rows. The eggs hatch after one tothree days. An egg mass of a Culex mosquito is shown in fig. 48.AnoplU!les cTUcians 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 hexagonallyreticulate. The floats occupy about half the sides in top view, and arcseparated at the middle by nearly one-third the diameter of the egg.