The effect of photoperiod and temperature on ovarian development and fat production in Culex peus Speiser (Diptera:Culicidae)

Abstract

Graduation date: 1983The effect of photoperiod and temperature on ovarian\ud follicle development and fat production was studied\ud in a colonized population of CuZex peus Speiser from\ud Philomath, Oregon.\ud Females were subjected to simulated fall conditions\ud of photoperiod and temperature. Under a combination of\ud short photoperiod and low temperature, there were various\ud effects on their physiological activities such as\ud the retardation of follicular development, a reduction\ud in the blood-feeding rate and the occurrence of hypertrophic\ud fat. In the laboratory, conditions of a short\ud day length photoperiod (8hL:16hD) and cool temperatures\ud (15°C) to which females were subjected from the\ud pupal stage to eight days after emergence influenced the\ud development of follicles, and resulted in the ovaries\ud remaining in a diapause condition. Under conditions of\ud 16 hour photophases and 25°C, females showed an increase\ud in follicle size over time. Females exhibited a marked\ud reduction of blood-feeding activity in response to a\ud combination of short photophases (8 hours) and cool\ud temperatures (15°C). Blood-fed females held under simulated\ud fall conditions developed a considerable amount\ud of fat reserve while non-blood-fed females, maintained\ud under the same conditions, and females taking a bloodmeal\ud at warmer temperatures had significantly less fat.\ud It was concluded that daylength is an important\ud factor controlling the follicular development of females\ud of C. peus. Pupae and adults were exposed to combinations\ud of 12 photoperiods (photophases of 9.5, 10, 10.5,\ud 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5 and 15 hours) and\ud a temperature of 18°C. Follicle size gradually increased\ud as photophase was lengthened. At photophases between\ud 9.5 and 12.5 hours the follicles remained small\ud and the sharp increase was seen at photophases of 13\ud hours or more. Experimental study showed that less than\ud 13 hours of light per day stimulated the entire population\ud to enter ovarian diapause.\ud Field collections of larvae made in 1981 showed\ud that adult activity decreased in September. With the\ud retardation of follicle development, suppression of bloodfeeding\ud drive and formation of hypertrophic fat in response\ud to simulated fall conditions, it was concluded\ud that the northern population of C. peus undergoes\ud ovarian diapause each fall as inseminated adult females