Celli gives thirty days as the time that elapses between the egg stage and that of the perfect insect (Anophelince) at a temperature of 20° to 25° C. These, after another twenty days, lay eggs, so that fifty days is the extent of a generation, or, at higher temperatures, as little as forty. Meinert considers that there are two or three generations of the Anophelince annually, according to the temperature. In the tropics, however, the duration of the larval and pupal stage is much less. Thus for M. rossii in India Christophers gives fourteen days as the minimum time, and about the same for M. culicifacies and for Ce. argyrotarsis; Taylor in Havana gives also fourteen days.
The pupa of the Anophelince is not so readily distinguished from that of other Culicidce as is the larva by a naked eye examination. The attitude, according to Howard, is more horizontal than that of other pupae. A closer examination with a low power of the microscope reveals an easy mode of distinction in the respiratory trumpets. In the Anophelince they have a square, truncated end, and project from about the middle of the thorax. In Culex they are long and narrow and have a slit like opening. In Stegomyia and other genera they are again different. Whether differences occur in the different genera of the Anophelince has not so far been established. The pupal or nymphal stage in the tropics lasts for about forty eight hours. The change from the larval to the nymphal stage is a sudden one, but its details have not been minutely studied.
The change from the nymph to the imago we have already described. Various factors besides temperature influence the emergence of the imago. Thus, Howard found that creasote oil added to the water caused a violent struggling of the pupae and the escape of the imagos, the pupal stage in this case lasting only fifteen hours. Pupae taken out of the water and placed upon moist blotting paper hatch out after a variable time, but if placed upon a dry surface, so that they become shriveled, flies rarely emerge. The pupal stage is the one that is most sensitive to excessive motion, so that the conveyance in tubes, etc., is difficult; but they may be subjected to the concussions of a railway journey of some hundred miles if they are given fresh air at each halt at a station.
We may now proceed to consider, as a group, the Anophelince, their distribution, habits, etc., and their relationship to malaria .