Predator control by poisons is considered a must by many in New Zealand. This is a touchy subject to approach as people’s opinions tend to be polarised with arguments for and against. These are particularly focused on how humane these controls are, and the risk to non-target species, especially birds. But without sufficient predator control we will not only be left with a deafening silence in our forests but also vacancies in insect motels.
The importance of keeping our birds safe has always been top priority. The Department of Conservation (DOC) has been heavily involved in protecting birds, including running a predator control programme called the Battle for our Birds which primarily uses poisons to knock back predatory mammal numbers. It has been encouraging to find that over the last couple of years this control programme has been successful. Birds and livestock commonly are the non-target species studied. This I believe is due to public awareness on this issue. What about the other animals like insects? Birds are more likely to be highlighted on the news, rather than insects. The exception being the fear and revulsion of bugs: bed-bugs invading hotel beds or pests in horticultural crops. Unfortunately insects have a bad rap and are commonly referred to as “creepy-crawlies” or “mini monsters“. Perhaps not surprisingly, few studies have explored the impacts that mammalian predator control poisons have on native New Zealand insect populations.
Mike Bowie and James Ross , researchers at Lincoln University conducted a study in 2006 which focused on the impact of weta foraging on poison (brodifacoum bait) and the secondary risks it had on the birds that ate these weta. This study was done on Quail Island in Lyttelton harbour. They found weta were eating the bait, but fortunately did not die from eating it. Instead, they even put on weight! Ground weta (Hemiandrus n. sp.) and cave weta (Pleioplectron simplex) were at lower risk of secondary poisoning, while tree weta (Hemideina ricta) were estimated to be at higher risk as they have larger bodies. These estimates are to be treated with caution as they are based on the wetas consuming the baits in one sitting. The results also showed that birds were more susceptible to poisoning by directly eating the bait rather than eating the insects which had eaten the poison. These results are limited as the brodifacoum levels were not directly measured in birds, therefore we cannot definitively predict the continuing exposure of eating insects that have been exposed to the poison.
James Ross, when asked about the possible implications of this result, replied, “What could we leave out on the island to prevent rodent re-invasion and not present a risk for non-target bird species?” Although this research considered the secondary risk of poisoning, its primary interest was on birds rather than insects. But what are the impacts to weta with continuous exposure, the sub-lethal affects, and are there any changes to their behaviour? Interestingly there have been many studies on the sub-lethal impact on insects with agrichemicals (for example, see here and here). There are few studies that focus on the primarily risk of poisoning insects shown here. Mike Bowie took the same line: “Many species of invertebrates are found feeding on poison baits used for mammalian pests – it would be interesting to know how significant the secondary poisoning issue is in ecosystems.”
Bugs may not pull at our heartstrings because they don’t have fur or fluffy feathers and big brown eyes. Nevertheless, they play an important roles in ecosystems. They play an essential role in pollinating our flowers, and they produce usable items we use daily such as honey, beeswax, and silk. They also decompose plant and animal materials. As gross as maggots are they actually speed up the process of decomposition and can be used in forensic science. Insects play other vital roles in our ecosystems.
DOC and universities often provide the research into environmental impacts, including poisons, and public pressure can often influence the type and scope of the research they do. At present, public awareness around the impact of environmental changes on insects is poor. One of the many reasons is the public’s lack of education around insects. For example, on DOC walkways there may be information about birds and trees but little or no information about insects. Not everyone has to be an expert in this area, but some basic common knowledge may raise public awareness to the issues faced by our insects.
My personal opinion as a budding entomologist is that there needs to be more research into the effects that these poisons have on invertebrates. It’s hard not to be biased towards this but the lack of studies is evident. Birds and insects should have equal importance and, although this is yet to be the case, people should be more aware of the smaller living things around them. At the beginning of my studies I admit having seen bugs as creepy crawlies, things to be killed on sight. However, the more I’ve learnt about them, the more I’ve seen their beauty, and their characters. They have gone from yuck to remarkable, from disgusting to fascinating. So next time you are in your home or garden, instead of being revolted, or scared of the bugs, stop even for a moment to be curious. You might be surprised at what you see.
The author Kate Curtis is a postgraduate student in the Master of Science taught at Lincoln University. She wrote this article as part of her assessment for ECOL 608 Research Methods in Ecology.
The author acknowledges the following peer review article:
Bowie, M. H., and Ross, J. G. (2006). Identification of weta foraging on brodifacoum bait and the risk of secondary poisoning for birds on Quail Island, Canterbury, New Zealand. New Zealand Journal of Ecology 30 (2). 219-228.