Improving efficacy of the sterile insect technique by incorporation of hormone and dietary supplements into adult holding protocols

Full text: One of the most effective and environmentally sound methods for suppression or eradication of pest insects is the Sterile Insect Technique (SIT) pioneered by E. F. Knipling. It was first implemented effectively to eradicate the screwworm fly from Florida and since has been used to control numerous lepidopteran and dipteran pests. Control is achieved in SIT by mass-release of sterile males who mate with wild females. Females that mate with sterile males do not produce viable eggs that over time, results in population decline and suppression or eventual eradication. The key to optimising efficacy of SIT is to produce sterile males that compete as well as, or out-compete, wild males in mating opportunities with wild females. Although SIT is an effective control tool, it is expensive in terms of both money and time, thus cost benefits must be clearly defined in order to balance the needs for effective control with funding constraints. One of the more significant costs associated with SIT protocols is that frequently males require many days to become sexually mature. For example males of many of Tephritid and tsetse fly species require 7 days to become fully mature. If males are held for several days prior to release, costs of holding are high and mortality prior to release and mating reduces the effective number of sterile males available. One way of improving efficacy of SIT management protocols is to develop methods to accelerate reproductive development in sterile males, while still optimising reproductive performance. Developing ways to effectively accelerate reproductive development of sterile males while insuring that males are capable of competing effectively against wild males for mating with wild females requires a thorough knowledge of the endogenous mechanists that regulate reproductive development and sexual signaling. However, few studies have been conducted on the endogenous regulation of sexual maturity and signaling in male insects. Our recent research on the Mediterranean, Caribbean, Mexican, and West Indian fruit flies has documented conclusively that juvemile hormone (JH) is a crucial hormone regulating development of reproductive competence and sexual signaling. We demonstrated that topical application of JH or the JH mimics, methoprene and fenoxycarb, to newly enclosed adults or late stage pupae induced precocious reproductive development. Thus, males treated with hormone on the day of adult emergence mate 5-7 days earlier than untreated males. Additionally, treatment of sterilised pupae of Mediterranean fruit flies induced males to release pheromone earlier in the day than untreated flies. Thus, treated flies began sexual signaling during the same period of the day that wild males release pheromone. The crucial role of JH in coordinating reproductive maturity with sexual signaling in these flies has allowed us to develop hormone supplement therapy techniques for accelerating reproductive maturity and improving reproductive competence in sterilised males of these Tephritid flies. (author)