Uptake and development of Wuchereria bancrofti in Culex pipiens L. and Aedes caspius pallas

Studies were conducted to compare early phenomena associated with W. bancrofti infection and further development in the filaria vector Culex pipiens and the refractory mosquito Aedes caspius. Ingestion rates evaluated immediately after simultaneous feeding on an infected human were 69.1% for 43 Cx. pipiens and 35.7% for 28 Ae. caspius. The observed number of mf ingested by either mosquito did not vary significantly (2.7 +/- 1.4, and 2.3 +/- 0.9, respectively) and, based on the size of the blood meal ingested (2.8 and 2.3 microliters respectively), a two-fold mf concentration factor was recorded for both species. Blood ingested by Cx. pipiens (N = 16) and Ae. caspius (N = 10) clotted within 120 and 90 min post-feeding respectively. The time difference observed, however, did not affect significantly the rates of migration into the hemocele (56 and 67% respectively). Comparison of initial infection rates with those obtained after the extrinsic incubation period of the parasite was completed, indicated that the proportion of infected Cx. pipiens was reduced by 3.9% and that of Ae. caspius by 30.0%. Furthermore, the observed infectivity ratio of 265 Cx. pipiens that had an infective blood meal was 0.74 and only 0.009 for 70 Ae. caspius. It is concluded that refractoriness of Ae. caspius to W. bancrofti is expressed through the feeding mechanism itself, by severely limiting the mf ingestion rate, and through physiological processes that inhibited the development of ingested worms.