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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.

During a 2-year study (1969-70), Psorophora confinnis (Lynch-Arribalzaga), Anopheles quadrimaculatus Say, and A. crucians Wiedemann populations caused statistically significant and economically damaging reductions in the average daily gain of feedlot steers. Steers on a high-energy-level ration (20% roughage) and steers on a low-energy-level ration (60% roughage) that were protected from mosquito attack gained significantly more ( P ‘0.01) during certain periods than steers on the same rations exposed to mosquito attack in 1969 and 1970. During these periods of loss in weight-gain efficiency, 6.8-114.7 blood-fed mosquitoes/ft2 wall were observed in the unscreened barn from 30 to 120 min after official sunset. Steers on the low-energy-level ration which were protected from mosquito attack gained in 1969 18.2 lb/head and sold for $5.78/head and in 1970 gained 45.5 lb/head and sold for $13.12/head more than unprotected steers on the same ration. Mosquito attack did not reduce the economic value of the steers on the high-energy level ration in 1969 and reduced their value only by $0.35/head in 1970 No overall significant difference was found between the average daily feed intake of the steers which were exposed to mosquito attack and those protected by screen wire. Larger numbers of blood-fed mosquitoes were observed in the barn 60, 90, and 120 min after official sunset than at 30 minutes after sunset ( P ‘0.01). However, the rate of increase from 90 to 120 minutes after official sunset was much less than that observed during the 1st 90 minutes.

Small-plot and outfield tests were conducted to determine the amount required and best method of FLIT® MLO application to control Psorophora confinnis (Lynch-Arribalzaga) in Louisiana. Larval mortality was determined 24 hours following application. At the 0.5 gal/acre rate, the spray and pour-on applications of the material caused 97% mortality to first-stage larvae, while the drip-bucket and capsule applications effected 94 and 90% mortality, respectively. In small-plot tests, the film caused 96% or greater larval mortality at the 2.0 gal/acre rate regardless of the method of application. Spray and capsule application of the material at 0.5 gal/acre resulted in 99% larval mortality in the outfield tests, while 1.0 gal/acre rates were necessary to achieve the same degree of control with the drip-bucket and pour-on methods. The yields of rice in 1968 and 1969 for each method and rate of application indicated that no reduction occurred through use of the surface film. FLIT MLO was not detected in rice grain or straw from plots which had been sprayed with 2.0 gal/acre. An LC50 of 0.34 gal/acre equivalent and an LC90 of 0.53 gal/acre equivalent were determined for P. confinnis pupae.

Newly emerged females of 11 species of Florida mosquitoes were flown in sound-recording boxes at 27°C under LD 12:12 to investigate the effects of temporary crowding during larval stages on the spontaneous flight activity patterns. None of the species investigated exhibited the migratory type flight activity pattern which could be attributable to temporary crowding rearing conditions. Only 4 species, Psorophora confinnis, Culex nigripalpus, Culex Pipiens quinquifasciatus, and Anopheles quadrimaculatus distinctly showed increased flight activity during the first 3 days after emergence when reared under temporary crowding rearing conditions. Seven other species showed at most a very slight increase in flight activity which could be attributed to temporary crowding rearing conditions. The duration of teneral period appears to be species specific and affected by the larval rearing conditions. Most of the species investigated did not show entrainment to light and dark cycles before 48 hr after emergence.

Massive populations of the dark rice field mosquito, Psorophora confinnis (Lynch-Arribalzaga), are produced in southwestern Louisiana by the water management methods used in the cultivation of rice.