Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Frequently asked questions

What is it?

The Trojan Female Technique is a new idea for managing pest organisms (including vertebrates such as possums and stoats, and invertebrates such as weevils and fruit flies) that cause losses to both our agricultural sector and native biodiversity. It would also be applicable in other countries to managing vectors of disease threats to human health (such as mosquitoes). We are currently in the middle of a two year project working with fruit flies and mice in the lab, to demonstrate that the idea is actually feasible to develop for the ‘real’ pests impacting New Zealand’s agricultural sector.

How does it work?

The idea is based on the mitochondria that occur in the cells of all animals. These are the ‘batteries’ of the cell, providing the energy needed to carry out all of its essential processes. We have discovered that inherited variation, causing a decrease in the energy output of these batteries, occurs naturally among individuals. Most cells have low energy requirements and lots of mitochondria, so such variation doesn’t normally affect them. However, a unique exception is sperm. Sperm have high energy requirements and very few mitochondria, so that males with such variation can have compromised (or no) fertility. This effect has previously been recognised as a potential threat to small populations of endangered species, and is a known cause of human male infertility. We want to turn this concept on its head, and purposefully use it to reduce the breeding output of pests and thus the size of the populations that they can grow to.

What’s behind the name?

In addition to being a catchy title, the name refers to two key elements of this new idea. First, as noted above, the idea is based on variation that compromises fertility in male pests but has no effect on females (or, indeed, any other effect on males). Second, all animals inherit their mitochondria from their mothers (in the egg) and not from their fathers (with the few mitochondria in sperm being left behind upon fertilisation of the egg). So, similar to how the Trojan Horse was used to smuggle Greek fighters into Troy to sack the city in ancient history, here the females themselves of the pest species targeted would carry the agent of its decline.

What could we use it on?

Since all animals have mitochondria, this idea is potentially applicable to the full range of vertebrate and invertebrate pest species impacting agriculture, conservation, and human health.

Why do we need it?

Vertebrate and invertebrate pests cause output losses of $885 million p.a. to New Zealand’s primary sector. Application of this idea thus has the potential to not only eliminate a substantial proportion of these losses (and associated pest management costs), but also provide a basis for control development to combat new incursions. In this manner it will support sustainable productivity growth in New Zealand. Beyond the current project, the idea is also applicable to controlling the animal pests (such as stoats, possums and rats) that continue to decimate our native biodiversity.

What advantages does this idea have over similar existing approaches?

The Trojan Female Technique is a novel twist on an existing paradigm used to manage insect pests worldwide, called the Sterile Male Technique. This technique, involving the yearly mass release of large numbers of males that have been irradiated to sterilise them, has proven highly successful. For example, it has been used to eradicate the parasitic screwworm fly from multiple countries with an estimated $1 billion p.a. saving to the agricultural sector of the USA alone. Unlike the Sterile Male Technique, where the population suppression effects of releases are transient (necessitating the yearly release of large numbers), the effects of Trojan Female Technique population suppression are persistent (because the females carrying the variation compromising male fertility are not themselves affected by it). Models thus predict the same eradication effect at much lower effort and cost, such that this approach could even be applied to suppressing vertebrate pest populations.

How could it be applied?

For managing invertebrate pests, large number of females carrying the Trojan Female Technique variation could be released into the target populations that we want to control. After an initial increase in pest population size, the population would reduce and be held at a lower level. Further releases could be conducted to reduce even lower, or even eradicate, the target pest populations. For situations where large releases are undesirable due to the impact that they might have in the initial ‘increased population’ phase, or if it’s not feasible or economic to rear such large numbers, standard methods of population control could be applied first, after which the release of far fewer Trojan Female Technique females would limit the size to which the post-control population grows back (including eradication). Such an approach would also be applicable to vertebrate pest control.

Does the Trojan Female Technique involve GMO?

Our goal for the Trojan Female Technique is the ability to use the variation in male fertility that naturally occurs in animal populations to control those populations, by identifying the mitochondrial variation that has the desired effect (compromised male fertility only) and selectively breeding females for release that carry that variation. However, to be able to do this we need to know what type of variation in the mitochondrial genome that we are looking for. To gain this understanding for vertebrates, we are working with GMO mice in the lab in the two years of the current project. After this, further GMO use, either in the research development phase or for the actual application of the Trojan Female Technique to the control of real pest populations, will not be necessary.

Who is developing this?

The current project is being conducted through a joint venture combining scientific experts from Landcare Research, the University of Otago, and Monash University, with independent sociologists and agricultural consultants. Project governance is provided by a cross-stakeholder Advisory Group and the project is funded by an MBIE Biological Industries ‘Smart Ideas Phase I’ grant.

How long might the Trojan Female Technique take to develop?

If this work continues, we would hope to be conducting the first applications of the Trojan Female Technique to real pests (both vertebrate and invertebrate) in a real-world situation before 2020.