Combining the Incompatible and Sterile Insect Techniques for Pest and Vector Control

Abstract

The Incompatible Insect Technique (IIT) is a Sterile Insect Technique (SIT)-related approach that uses the reproductive parasitism caused by infection with maternally-inherited bacterial endosymbionts to make released males reproductively incompatible with the wild-type females of the target population. The most common and widespread of such endosymbionts is Wolbachia, which is found throughout many insect orders, and often causes cytoplasmic incompatibility (CI), a form of conditional sterility where the fertilized eggs of females not infected with the same Wolbachia strain as the males with which they are mated undergo embryonic death. An advantage of IIT is that the incompatibility induced by Wolbachia often has either no or only minor effects on the quality of infected males. In addition, such endosymbionts can also have other desirable phenotypic effects on their hosts, such as reducing the ability of target species to act as disease vectors, thus allowing the undesirable sex(es) to be tolerated among the sterile insects to be released. However, an inherent problem with IIT, which has so far restricted its operational use, is that, unlike SIT, the accidental release of endosymbiont-infected females may prevent further population suppression by causing unintended population replacement, whereby the original target population is replaced with individuals infected with the same endosymbiont strain as the released males. A solution to this problem, at least for the majority of insects whose females are more sensitive than males to radiation, is to combine IIT with SIT, such that all endosymbiont-infected individuals destined for release are also first subjected to low-dose radiation, which completely sterilizes any contaminant females without affecting the incompatibility or quality of the irradiated males. Here, we discuss the biology and general theoretical principles underlying the use of IIT alone, and the rationale and necessity of combining IIT with SIT, as well as the logistical problems encountered, and technological developments required, for the mass-production and release of irradiated endosymbiont-infected individuals as part of area-wide integrated pest control programmes. We primarily illustrate our discussion with examples involving mosquitoes, for which the majority of the relevant research has been conducted, including the first open-release field trial of combined IIT/SIT application against the important arboviral vector Aedes albopictus (Skuse). However, 368the combined IIT/SIT approach should be broadly applicable to a wide range of other insect pests and vectors, and so of interest to entomologists in general.