Population dynamics of some Pakistan mosquitoes: temporal changes in reproductive status, age structure and survivorship of Anopheles culicifacies, An. stephensi and Culex tritaeniorhynchus

Abstract

The reproductive biology and age-structure of female Anopheles culicifacies, An. stephensi and Culex tritaeniorhynchus were studied at rural Punjabi villages near Lahore, Pakistan, during 1976–1980. Both Anopheles remained gonotrophically active throughout the year with blood-fed, gravid, parous and virgin females collected during all months. Culex tritaeniorhynchus populations bifurcated into reproductively active, non-overwintering and reproductively inactive, overwintering populations in October and/or November. Most female Cx. tritaeniorhynchus overwintered as inseminated nullipars with ovaries arrested at follicular State I; however, host-seeking and parous females were collected during every month of the year.

Survivorship was calculated for each species by three methods and was negatively correlated with mean monthly ambient temperature. The ovarian tracheolation method provided inadequate estimates of parity for females collected at diurnal resting sites which refed the night of oviposition, but was suitable for Cx. tritaeniorhynchus females captured at bovid baits. The dilatation method of Polovodova was applied to all three species and yielded survivorship patterns which were constant with age and agreed well with a log-linear model. Anopheles culicifacies survived longer than did An. stephensi and thus was considered a better vector of malaria. Age-specific survivorship tables were constructed for all three species for those periods of the year when the gonotrophic rhythm was constant and generations were overlapping.