Location: Crop Protection and Management Research
Title: Integrating augmentative biocontrol and inherited sterility for management of lepidopteran pests Author
Submitted to: International Symposium on Biological Control of Arthropods
Publication Type: Proceedings
Publication Acceptance Date: December 12, 2012
Publication Date: March 4, 2013
Citation: Carpenter, J.E. 2013. Integrating augmentative biocontrol and inherited sterility for management of lepidopteran pests. Prceedings of the 4th International Symposium on Biological Control of Arthropods, March 4-8, 2013, Punco, Chile. p.380. Technical Abstract: Insect pest management can benefit from the integration of biological control agents and the release of sterile insect pests (hosts). Released sterile or semi-sterile insects and their sterile progeny may augment natural enemies by serving as hosts for build-up of the natural enemies prior to the time the target pest has reached the economic threshold, and as hosts for natural enemy survival during critical times of low pest populations. Conversely, periodic releases of a natural enemy for the control of a pest population can enhance the efficacy of sterile insects being deployed in a Sterile Insect Technique (SIT) program by reducing the number of pests reaching the adult stage, and thereby increasing the sterile : fertile overflooding ratio. These synergistic effects realized when integrating augmentative biocontrol and sterile insects have been examined with population models (Barclay 1987, Carpenter 1993, Knipling 1992). The results from these models suggest that although releasing only natural enemies or only sterile insects would be effective, combined releases of both natural enemies and sterile insects would require fewer released insects overall but provide superior control of the pest population. Because lepidopteran females generally are more sensitive to radiation than are males of the same species, the dose of radiation used in a SIT program is usually set to fully sterilize the females but allow males to remain only partially sterile. When partially sterile males mate with fertile females the radiation-induced deleterious effects are inherited by the F1 generation. As a result, egg hatch is reduced and the resulting offspring are both sterile and predominately male. Therefore, as a result of this inherited sterility, F1 sterile progeny (eggs – adults) produced in the field can be used to augment the production of natural enemies. Successful integration of inherited sterility and parasitoid augmentation into a management approach should consider whether or not parasitoid strategies negatively impact irradiated insects and their progeny more than that of the wild population, and whether or not inherited sterility negatively impacts the efficacy and reproduction of parasitoids. Knowledge of any negative impact of inherited sterility on parasitoids would be important before implementing an area wide management program that combined these two tactics. For example, if parasitoids that attack the F1 sterile progeny are unable to develop normally, and most of the hosts present are F1 sterile progeny, then there could be a negative impact on subsequent parasitoid populations. Conversely, if parasitoids develop normally on F1 eggs, larvae, and pupae, then the greater number of hosts available would allow for an increase in the parasitoid population. Because many hosts of the F1 generation would experience genetically-induced mortality before they reached the adult stage, any parasitoids completing their development in these hosts would result in a positive and synergistic increase in the efficacy of an area wide management program (Carpenter 2000). Laboratory and field trials with several different lepidopteran species have indicated that F1 sterile progeny were acceptable and suitable as hosts for egg and larval parasitoids, and female parasitoids demonstrated no ovipositional preference for progeny from female moths paired with either irradiated or un-irradiated males (Carpenter et al. 2005, Hendrichs et al. 2009). Other studies have revealed that releases of egg parasitoids along with releases of irradiated moths have provided synergistic suppression of moth pest populations (Carpenter et al. 2004, Saour 2009) as predicted by population models. Although the synergistic effects realized through the simultaneous release of irradiated lepidopterans and their parasitoids are quite intriging, there are other scenerios in which inherited sterility could be integrated with natural enemies to suppress pest populations. The release of partially sterile males and females could produce large numbers of sterile F1 eggs and larvae that could be field-reared on early season host plants. Natural enemies (native and/or released) could use the F1 eggs, larvae and pupae as hosts and thereby substantially increase the natural enemy population for the next generation of the pest insect (Proshold et al. 1998). Any surviving sterile F1 progeny would produce sterile adults that would negatively impact the next generation of the pest insect. Similarly, another management option could be the establishment of host plants for the pest in insecticide-free nursery crops adjacent to the crop to be protected. Nursery plants could be artificially infested with pest larvae to provide natural enemies (native and/or released) with an adequate supply of hosts. If the pest larvae used in the artificial infestations (nursery crops) are sterile (i.e., the progeny of irradiated parents), then non-parasitized larvae would not contribute to the increase of the wild pest population, but would produce sterile adults that would negatively impact the next generation of the pest insect (Carpenter 2000).