No abstract

Under controlled laboratory conditions of 28-30 degrees C and 16:8 L:D photoperiod, an attempt was made to develop an age-grading technique for Anopheles culicifacies males. Mating activity was maximal when females were 5-12 days old males were 5-7 days old. The numbers of total and mature spermatocysts declined significantly with age, and the proportion of the testes occupied by the sperm reservoir increased as virgin males grew older. Mating resulted in the loss of spermatozoa and accessory gland substance from the reproductive system. Loss of mating ability of older virgin males seemed to be age-related, because the reproductive system contained ample supplies of accessory gland substance and spermatozoa. Morphological changes of the reproductive system, due to mating and age, were used to infer the age and reproductive history of unknown males in a laboratory evaluation.

The vector competence of Culex tarsalis Coquillett for the BFS 1703 strain of western equine encephalomyelitis virus (WEEV) changed significantly as a function of time after infection, mosquito genotype, and infectious virus dose. After ingesting a high virus dose (5 log10 plaque-forming units [PFU]/0.1 ml), female of the susceptible high virus producer (HVP) strain rapidly amplified the virus, developed a disseminated infection, and efficiently transmitted WEEV by 4 days postinfection (dpi). The quantity of virus expectorated peaked at 4 dpi (mean 3.4 log10 PFU), and the percentage of females transmitting per os peaked at 7 dpi (80%); both measures of transmission subsequently decreased to low levels throughout the remainder of infected life. HVP females imbibing a low virus dose (3 log10 PFU/0.1 ml) were infected less frequently and took longer to amplify virus to levels recorded for the high virus dose group and did not transmit virus efficiently, thereby indicating midgut infection and escape barriers were dose and time dependent. These data emphasized the importance of elevated avian viremias in Cx. tarsalis vector competence. Females from the WEEV-resistant (WR) strain and two wild-type strains from Kern and Riverside counties were significantly less susceptible to infection at both high and low doses than was the HVP strain. Overall, females with a high virus titer more frequently had a disseminated infection, but there did not seem to be a distinct threshold demarcating this relationship. In marked contrast, all infected females transmitting virus had body titers >4.3 log10 PFU, and most had titers >4.8 log10 PFU. These data indicated that not all females with a disseminated infection transmitted virus because of the presence of one or more salivary gland barriers.

A preliminary survey of natural populations of Anopheles stephensi Liston in Pakistan has uncovered the presence of 16 autosomal paracentric inversions. Twelve previously undescribed inversions were observed in the field populations and an additional new one was seen in a laboratory colony. A comparison of urban and rural populations showed striking differences in the kinds and frequencies of paracentric inversions.

The life table attributes of Culex tarsalis Coquillett females infected experimentally by feeding on 4 and 6 log10 plaque-forming units (PFU) of western equine encephalomyelitis virus (WEEV) per milliliter of heparinized chicken blood were compared with an uninfected control group. Females continually were offered 10% sucrose and an oviposition substrate and daily a blood meal through a biomembrane feeder. Mortality (dead females) and fecundity (female eggs per female) were monitored daily until all females died. Overall, 94% of 198 females in the two virus-infected groups were positive for WEEV at death when tested by plaque assay; the average body virus titer at death did not differ between groups. WEEV infection significantly altered the life table characteristics of Cx. tarsalis. Life expectancy at infection in days (ex), reproductive effort in female eggs per female per generation (Ro), and generation time (T) in days for the infected cohorts were significantly lower than for the uninfected controls, whereas the reproductive rate (rc) in female eggs per female per day was higher for infected than uninfected cohorts. In agreement with the WEEV infection data that showed similar body titers, there were few differences between the life table parameters for the 4 and 6 log10 PFU treatment groups. Greatest differences were observed for survivorship between days 17-40 when virus titers in infected dying females were greatest. Our data extend recent studies that indicate mosquito infection with encephalitis viruses has a cost of reduced life expectancy and fitness.