New Zealand has a wasp problem. In the beech forests of the north-west of the South Island, wasps feed on the honeydew exuded by the trees. In some areas, their combined biomass has been estimated at nearly 4 kg/hectare – more than that of the birds and mammals in the same area.
Wasps compete with native birds, such as rifleman, fantail, whitehead, and yellowhead, for food, insects as well as honeydew. Wasps eat 99% of the available honeydew, leaving none for native fungi, microbes, insects, and birds. They even attack hatchlings.
The context for our wasp problem is that our current set of tools to control them is not working. Indeed, most of the tools we use to control invasive pests are becoming less effective – except 1080 poison, used for possums, which is effective but excites a good deal of public anxiety. If we can’t control invasive pests, we will see native bird and other animal species becoming extinct.
The targets the world set for the year 2020 in the 1992 Convention on Biodiversity (not signed by the US) have not been achieved. Globally, species are becoming extinct at an unparalleled rate, due to the impact of humans on fragile ecosystems. What is to be done?
Entomologist Professor Phil Lester, and colleagues from one of the National Science Challenges, NZ’s Biological Heritage, is working on New Zealand’s wasp problem, investigating the potential of a novel control for wasps based on gene editing. One of the Science Challenge’s goals is to develop new pest controls that can be used at landscape scale. Of these, gene drives to control wasps are looking promising.
Sadly, current regulations prevent turning this idea into a reality. However The Opportunities Party is proposing to change that, allowing gene editing where no new genetic material is added to an organism. The outcome is just like selective breeding, only faster. This would allow us to tackle some of our trickiest environmental challenges; including wasps.
A gene drive is a genetic modification to a target genome, such as the wasp genome, that consists of three parts: an enzyme to cut the DNA (known as CRISPR-Cas 9), a short strand of guide RNA, and a target gene. The team’s target genes for wasps are those used in spermatogenesis. Once the target gene has been altered, rendering the male wasp infertile, the modification will surge through the population, with nearly 100% penetration.
There are lots of opinions about gene drives. Some people think they have no place in conservation. Others, like Professor Lester, think the benefits could be huge (potentially the eradication of wasps in New Zealand within a few years), but we still need more research before any conclusion about their potential or effects can be made. For instance, it’s possible that in some species wild populations will develop some resistance making gene drives ineffective. In that case the gene drive wouldn’t work. Unfortunately, there’s not enough evidence yet to support either case.
Phil Lester and his team have worked on the genomes of three wasp species in New Zealand (common wasp, German wasp, and Western yellowjacket) to identify the genes responsible for spermatogenesis, and understand the range of variation in specific genes.
Highly variable genes would enable us to develop gene drives that target a specific genotype. Targeting a highly conserved gene (with little variation), on the other hand, would be more effective in eradicating an entire population.
The next step was to design guide RNA for a CRISPR-Cas 9 transformation, and test it in vitro. Once tested, the team designed a precision drive targeting some New Zealand gene variants that are not found in the European wasp. They also looked at the potential for off-target effects. In the case of their target wasp spermatogenesis gene, they are very different to those in other species, such as the honey bee. There is no possibility that the modified gene could jump from the wasp into bee species.
The next stage was to do some modelling to understand the effect once deployed in a landscape. The findings were surprising. Complete gene sterility doesn’t work (because it is too devastating for reproduction in the wasps), but partial drone sterility would substantially lower populations. Eradication might be possible when gene drives are combined with pesticide. Although pesticides are not very effective on their own, the modelling shows that, if used in conjunction with a gene drive, they could knock out a wasp population in 20 years.
Are there risks? Phil Lester says that there is a risk that the gene drive might fail and disappear. But as far as our native forests are concerned, there is a greater risk – that of doing nothing. More work investigating the potential of gene drives is needed. This technology is definitely a tool worth investigating.