Augmentative biological control: research and methods to help make it work.

Augmentative biological control, especially in field situations, can be complex but there are novel or incompletely explored directions for research and methods development that may lead to improved future performance. At the fundamental level, augmentation faces inherent ecological/behavioural challenges such as enemy dispersal, pest refugia and deleterious interactions within predator/parasitoid guilds. However, these may be addressed by the choice of natural enemies with specific or manipulatable dispersal capabilities which attack hosts when most vulnerable. Integration of augmentative biological control with other control methods has not been sufficiently explored. One promising partner is the sterile insect technique (SIT) and related technologies such as conditional-lethality and genetic-drives that perform best at low and declining pest densities and should interact well, even synergistically, with natural enemy augmentation. Other candidates for integration with augmentative biological control include the addition of plants that support natural enemies, infochemicals such as kairomones that could lead pests to occupy more vulnerable microhabitats and even certain pesticides. At the production level, new or not widely adopted technologies for mass-rearing can lower costs. For example, host irradiation simplifies the handling of parasitoids, improves sanitation, facilitates the movement of natural enemies across borders and allows hosts to be exposed in sentinel-traps. Parasitoid rearing expenses could be halved by using thelytokous strains such as those resulting from <i>Wolbachia</i> infections. In some cases, hosts for specialist parasitoids can be obtained inexpensively from the unwanted sex of mass-reared pests: another advantage of integration with SIT. While many innovations are now costly, scientifically sophisticated and planned for use in regional-scale projects, new techniques and genetic modifications could become widely available to the agricultural industry.