The Trojan Female Technique: a novel nonlethal approach for pest control
Although there are substantial gains in efficiency to be made from the more refined and coordinated application of existing pest control technology, the general consensus at the Pest Summit convened by the Department of Conservation in December 2012 was that the use of cutting-edge science to develop new tools and approaches is also needed to protect both agriculture and biodiversity in New Zealand. To this end, a research consortium comprised of Landcare Research, the University of Otago and Monash University have proposed a novel and cost-effective technology platform for the specific (i.e. no potential for non-target effects), persistent, non-lethal and non-GMO (genetically modified organism) control of vertebrate and invertebrate pests (i.e. the Trojan Female Technique or TFT).
Naturally occurring mutations that cause male infertility have now been identified in the maternally inherited mitochondrial DNA (mtDNA). These have little or no impact on females, and hence are minimally or not selected against (i.e. are self-perpetuating in nature). While these mutations have thus far only been identified in model systems such as fruit flies and mice, they are likely to be widespread in nature where they may pose a threat to the viability of small populations of endangered species. The consortium aims to harness these mutations to develop a widely applicable capability for pest control, through the release of Trojan females carrying the mutations.
Reproductive management is an effective approach to pest control. For example, the Sterile Male Technique (SMT), commonly applied to invertebrates, has eradicated the parasitic screwworm fly from multiple countries, with an estimated $1 billion p.a. saving to the USA alone. However, the SMT requires large quantities of sterile males to be produced and released each year in a costly process that can limit its use. The TFT, a novel twist on the SMT paradigm, could provide similar control at greatly reduced effort; large potential cost savings of the TFT arise from it being self-perpetuating in nature, making it economically viable to apply to a wider range of invertebrate species under a wider range of contexts than the SMT, and even to vertebrates (for which the SMT is not cost-effective).
The Trojan Female Technique is thus relevant across the animal pest spectrum (i.e. from possums, rabbits, stoats and rats, to mites, aphids, moths and weevils). It will be applicable to both reducing current pest impacts (and associated management costs) and combating new pest incursions. Once developed, TFT application to new species would be inexpensive. For example, naturally occurring mutations appropriate for use in TFT were identified by screening just 55 male brown hares. Successful application of the TFT would thus allow substantial reductions in both the current losses of $885 million p.a. in New Zealand’s agricultural sector caused by invertebrate and vertebrate pests, and pest impacts to native biodiversity. The TFT would both support New Zealand’s economy and enhance protection of the natural environment, while avoiding concerns over non-target effects, GMO, welfare issues, environmental contamination and toxin resistance.
The TFT would be highly complementary to and most effective when combined with conventional control (e.g. population reduction obtained with conventional control, and then maintained by the release of Trojan females into the residual population). Depending on the desired outcome, the TFT could be used to decrease pest populations from high levels, drive populations to extinction, or maintain populations at desired levels. In addition, low-density populations with high mutant frequencies could be used as ‘wild nurseries’: sources of individuals for introduction to other populations or natural dispersal into adjacent inaccessible areas. This strategy would generate significant cost savings. The TFT is thus a strong candidate for the effective, persistent and specific reproductive control of multiple pests, providing synergies with conventional control that allow extension to the landscape scale.
The proposed technology platform is the topic of a current ‘Smart Ideas’ grant application to the Ministry of Business, Innovation and Employment Biological Industries fund, for its application to agricultural pests. Funding applications to develop this technology for the protection of biodiversity (in alignment with the remit of Predator-Free New Zealand) are pending.
Neil Gemmell (University of Otago)
Damian Dowling (Monash University)