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The developmental times, eclosion to emergence, of 18 broods of Psorophora confinnis Lynch Arribalzaga, observed in irrigated date groves in the Coachella Valley, Calif., ranged from 78 to 126 hours with a mean of 97 hours at average water temperatures of 77–88°F. In 38% of the broods, all pupae were stranded on mud by the disappearance of open water, but 50%–95% of these metamorphosed successfully although stranded for as much as 15 hours. Thus, at summer temperatures, irrigation water needs to persist only 3–3.5 days to permit emergence. At constant water temperatures of 65°–95°F, developmental time varied inversely with temperature, but the effect of a 5° increase was progressively less as temperature increased. Total development was fastest (86–89 hours) at 90°–95°F. Survival, from second-instar larva to adult, was maximum at 75°–85°F. For each immature stage there is agreement between the constant temperatures which allowed good survival in the laboratory and the range of water temperatures encountered in nature. The first- and second-instar larvae were most susceptible to temperature extremes; later stages were progressively more resistant. Pupae appeared normal at 115°F and metamorphosed after such exposure. The rapid development from eclosion to emergence and the high tolerance of the pupae, together with their ability to metamorphose on mud, are significant adaptations of the Coachella Valley populations of P. confinnis .

Nerves connecting larval and pupal setae of prepupal mosquitoes were used to establish the homologies of the abdominal setae. Both larval and pupal setal patterns were then utilized to deduce serial (segment to segment) homologies. The chaetotactic system proposed is based on previous ones but contains several modifications suggested by the present work. The studies described were clone with prepupae of Culiseta inornata (Williston), Culex pipiens quinquefasciatus Say and Psorophora confinnis (Lynch Arribalzaga).

The seasonal hatching of the eggs is controlled by the annual cycle of temperature. Preflooding temperatures control the hatchability of the eggs by exerting a conditioning or deconditioning effect. The eggs are conditioned by an increase in temperature and deconditioned by a decrease. All eggs are conditioned when held at 90°F for 1–2 weeks and deconditioned after 4 weeks at 60°. Intermediate temperatures may either condition or decondition the eggs, depending upon the previous temperature of exposure, since conditioning occurs only at temperatures higher than the prior deconditioning temperature. Thus, temperatures of 70° and 80° condition eggs in late spring and early summer, and decondition eggs in late summer and early autumn. The percentage of conditioned eggs that hatch when flooded varies directly with the temperature of the medium. The combined effects of preflooding and flooding temperatures upon the hatching of the eggs control the seasonal occurrence of adults. Deconditioned eggs do not hatch during the winter, although repeatedly flooded by irrigation water.