Mortality and survival patterns for the immature stages of Psorophora columbiae

Abstract

To determine the patterns of Psorophora columbiae survival and mortality, methods were employed that involved the simultaneous use of laboratory-reared cohorts, predator-exclusion cages, and field estimates of larval dynamics. Laboratory studies indicated that the maximum daily survival averaged from 0.92 for day-old larvae to 1.0 for the older age classes with no significant differences (P greater than 0.05) in survival among days. Data from predator-exclusion cages indicated that mortality inflicted by factors other than predation was significantly (P less than 0.05) more intense in the younger age classes and the relatively few individuals that survived to the older age classes had a high expectation of successful emergence. A quantitative estimate of the mortality inflicted on Ps. columbiae larvae by all indigenous natural enemies indicated that mortality rates were higher in the older age classes. This supports the view that the predator complex is a major source of irreplaceable mortality for immature mosquitoes inhabiting Louisiana rice fields.