Age and Body Size Influence Male Sperm Capacity of the Dengue Vector Aedes aegypti (Diptera: Culicidae)

Abstract

Understanding mosquito mating biology is essential for studies of mosquito behavior, gene ßow, population structure, and genetic control. In the current study, we examine the effect of age and body size on spermatozoa number in two laboratory strains of the dengue vector, Aedes aegypti (L.), Thailand and Rockefeller (ROCK), and in wild-collected mosquitoes from Thailand. Body size was a major predictor of total spermatozoa number, with signiÞcantly greater sperm numbers in large (2.27-mm wing length) versus small males (1.85-mm wing length) within the same age group. Total sperm capacity also varied by male age. Spermatozoa numbers in virgin Ae. aegypti males increased signiÞcantly up to 10 d after emergence and then leveled off until 20 d. SigniÞcant variations in sperm number were detected among Ae. aegypti strains, with wild-collected mosquitoes having the greatest total number of sperm. Our study provides the Þrst evidence of spermatogenesis in adult mosquitoes and indicates high rates of spermatogenesis in male mosquitoes up to 10 d of age (3.3 degree-days). Our results emphasize the potential role of body size and age on the mating capacity of this important vector of dengue and yellow fever viruses. KEY WORDS Aedes aegypti, sperm capacity, mating, age and body size effect Reproduction is one of the important characteristics of evolution and life history for all organisms, including insects (Emlen and Orings 1977, Thornhill and Alcock 1983). However, not all males experience equal reproductive success. For mosquitoes, many factors could potentially inßuence male reproductive success, including age, body size, sperm quantity, and sperm quality. Previous studies have reported an age-related effect on male mating capacity as measured by the presence of spermatozoa in cohabited females. For example, peak Anopheles culicifacies Giles male mating behavior occurred when males were 5Ð7 d old, and mating ability decreased by age 10 Ð12 d (Mahmood and Reisen 1994). Mating success inßuenced by the maturation of accessory glands and testes morphology of male Anopheles stephensi Liston reached a peak 3Ð7 d after eclosion (Mahmood and Reisen 1982). Female Anopheles gambiae Giles exposed to 2-d-old males were more likely to oviposit than those held with 6-d-old males (Chambers and Klowden 2001). Hauser-mann and Nijhout (1975) demonstrated an inßuence of male age of Aedes aegypti (L.) on successful mating by comparing morphological traits of testes and sem-inal vesicles from 0-to 30-d-old males. Mosquito insemination studies conducted with Ae.