Growth and development of geographic and crossbred strains of colonized Simulium decorum (Diptera: Simuliidae)

Abstract

The developmental times from larval hatch to adult emergence were computed for strains of Simulium decorum from Warm Springs, Georgia (GA), and Dryden Lake, New York (DL). Rearings were conducted at several constant temperatures. Differences between geographic strains and between sexes within strains were significant in nearly every instance (P < 0.01). At cool temperatures (13 to 17 °C), the GA strain developed more quickly; however, this trend was reversed at intermediate temperatures (18 to 20 °C), and at 21 °C only GA males developed faster than DL males. With few exceptions, both sexes of the GA strain required more cumulative degree-days for development than their northern counterparts.The number of instars was determined for each strain by measuring the length of the postgena of head capsules collected during warm (21 °C) and cool (13 °C) rearings. Although both strains pass through seven stadia, differences between strains were noted in the size of middle instars. In all rearings sexual dimorphism was evident in the morphology of last-instar head capsules; in rearings conducted at cool temperatures (13 °C), sexes could also be separated by the size of last-instar head capsules.Strains were crossed and their progeny reared. High values for net reproductive rate (R0), fecundity, and adult survival suggest that heterosis resulted from crossbreeding the two geographic strains.