Anopheles sergentii (Diptera: Culicidae): seasonal variation in the development rates of immatures from El Faiyum and Siwa Oasis, Egypt.

Three colonies of An. sergentii from El Faiyum (Tersa and El Nazlah) and Siwa oasis were maintained for one year under the circulating room conditions to examine the rates of immature development and survival. For each colony, the egg incubation periods and immature developmental periods (P 50 and E 50) were significantly longer at low temperatures (mean = 13.4 degrees C) during winter. Egg hatch rates and survivorships of the different immature stages did not significantly differ among seasons except for Siwa colony where rates of immature survival decreased during summer (mean = 28.5 degrees C). No differences in such estimates were observed among the three colonies. With the exception of Tersa eggs, the developmental velocity (V = 1/period)--temperature relationships were linear (r2 = 0.94-0.98). The temperature thresholds (to) were 8.64 and 7.35 degrees C with thermal constants (K) of 38.61 and 42.74 degree--days (DD) for eggs of El Nazlah and Siwa, respectively. For adult emergence (male or female) of the three colonies, the to's were 8.02-9.41 degrees C and K's were 212.34-223.71, DD required above the to to complete development. The study indicated that seasons of higher temperatures (mean = > 20 degrees C) are optimal for the development and survival of An. sergentii immatures.