Developmental factors for different strains of medically important mosquitoes

Abstract

Competition between northern sympatric mosquitoes, Culex restuans and Culex pipiens pipiens, was evaluated in Illinois using different ratios of the two species. Similarly, competition between southern sympatric species, Culex restuans and Culex pipiens quinquefasciatus, was evaluated in Alabama. Species ratios were repeated at biologically relevant temperatures and densities. Results for the northern study suggested that Cx. restuans survival was greater than Cx. pipiens across all treatment variables, whereas survival did not differ between the southern strains. Survival of both northern and southern strains of Cx restuans increased with increasing competition, but southern strains of this species had poor survival in high temperature, high density treatments. By comparison, survival peaked at intermediate temperatures for only northern strain of Cx. pipiens, while survival of both northern and southern strains of this species was independent of the competition. Body mass increased with increasing competition only for the northern strain of Cx. pipiens, whereas competition did not affect body mass of either Cx. restuans strains. Temperature was inversely related to body masses of both species only for the southern strains. Development times were shorter for Cx. restuans strains than for Cx. pipiens complex. Competition reduced development times but only for the southern strains of the species. Overall results suggest that interspecific competition (between species) may reduce intraspecific competition (within species).

In separate studies, northern and southern strains of Aedes albopictus were compared with distinct strains of sympatric species Aedes aegypti to determine life history characteristics of the egg stage and larval stage. Egg hatch of Ae. albopictus was regulated by temperature and photoperiod, but not for Ae. aegypti. Notably, egg diapause of the southern strain was less complete than for the northern strain of Ae. albopictus. Egg diapause was completely negated when exposed to high temperatures only for the southern strain. In larval studies, Ae. albopictus life history characteristics were more closely associated with sylvan strains of Ae. aegypti than urban strains. Since Ae. albopictus has more recently shifted from forest to urban niches than Ae. aegypti, it is reasonable to believe that urban strains of this species may retain sylvan characteristic which allow for greater plasticity in larval habitat niche.

Keywords: Culex restuans, Culex pipiens, Culex quinquefasciatus, Aedes albopictus, Aedes aegypti, and development