When people discuss the decline in insect populations, the biggest culprit, unsurprisingly, is the over-use of insecticides. Agriculture isn’t the only area where that’s a problem, but it’s probably the biggest. Farmers around the world have developed alternative methods of pest control, including the nurturing of predators and parasitoids. Probably the most infamous failure of this method has been the Australian cane toad debacle, but I think my favorite version comes from cranberry bogs:
I’m sure PZ has been tempted to take up cranberry farming, but I dunno how well I’d fare with wolf spiders on my face. This post really gets at the essence of the technique – the spiders are fellow workers. That attitude is very much how I think we should be viewing most of the rest of life on this planet, so while it needs to be done carefully (see the cane toad documentary I linked above, if you haven’t), I think it’s a brilliant technique.
The problem (you knew there was going to be a problem, didn’t you?) is that unless we actually take a systemic approach to change, those people trying to do better in the context of our current, destructive system, are being undermined by that system. I’ve talked before about how air pollution is bad for humans, so it shouldn’t be a surprise that it’s bad for other critters. Specifically, diesel exhaust and ozone cause problems for parasitoid wasps used to protect plants grown for vegetable oil (apologies in advance for this article being about the worst-named plant in existence):
The team, led by scientists from the University of Reading, used special equipment to deliver controlled amounts of diesel exhaust and ozone to oilseed rape plants. They also added aphids to the plants and measured the reproductive success of parasitic wasps that habitually lay their eggs inside a freshly stung aphid.
Dr James Ryalls, University of Reading said: “Even at the levels we used, which were lower than safe maximums set by environmental regulators, the overall numbers of parasitic insects still fell. This is a worrying result as many sustainable farming practices rely on natural pest control to keep aphids and other unwelcome creatures away from valuable crops.
“Diesel and ozone appear to make it more difficult for the wasps to find aphids to prey upon and so the wasp population would drop over time.”
Fortunately, this study has two bits of good news. The first, which is more an implication, is that efforts to decrease air pollution – which are already necessary for other reasons – will increase the effectiveness of wasp-based pest control. The other is that this doesn’t seem to be a problem for all of the wasps:
While the majority of parasitic wasp species decreased in polluted environments, one species of parasitic wasp appeared to do better when both diesel and ozone were present. However, the researchers found that this combination of pollutants also correlated with changes in the plants that might explain the finding.
With both pollutants present, oilseed rape plants produced more of the compounds that give brassica family crops, including mustards and cabbages, their distinctive bitter, hot and peppery flavour notes. These usually repel insects but in the case of Diaretiella rapae wasps, there was greater abundance and reproductive success associated with diesel exhaust and ozone together.
Dr Ryalls said: “Diaretiella rapae particularly likes to prey on cabbage aphids, which love to eat brassica crops.
“We know that some of the flavour and smell compounds in oilseed rape are converted into substances that do attract D.rapae. So, we could speculate that the stronger smell attracts the wasps and they are more successful in finding and preying upon aphids, that way. It could be that D.rapae is a good choice for pest control in diesel and ozone polluted areas.
“This really goes to show that the only way to predict and mitigate the impacts of air pollutants is to study whole systems.”
As transport shifts away from diesel and towards electric motors, air pollution will change. Knowing how pest-regulation service providers, such as parasitic wasps, respond to these progressive changes, will be essential to planning mitigation strategies to ensure sustainable food security now, and in the future. This research shows that we also must consider the impact of pollution on the plants, wasps, and prey insects, and the interactions between all three.
I think this last point is an important one to end on. In building a better society, we’re not looking to abandon technology. That means, as I’ve said before, that we will keep engaging in resource extraction that is destructive to the environment, and we will keep creating poisonous industrial byproducts. Our project, at this stage, is one of changing which pollutants we create most, and how we manage them. Creating an economic system that does not require infinite growth will help reduce all pollutants, but we will still have to contend with that which is unavoidable. That means that, unlike the present arrangement, we will need to actually clean up the messes we make through industry, just as we do with human waste. In that case, the time and energy put into sewage treatment helps everyone by making the world more pleasant to live in, and by reducing disease outbreaks. Getting a better handle on industrial pollution will yield similar results.
Healthy ecosystems that are beneficial to humans, like food forests and other “edible ecosystems”, is a goal worth working towards, but it’s not something that’s likely to work if don’t actually commit to it. Rising temperatures, pollution, and direct habitat destruction currently keep that future out of reach, which is why it’s so important to maintain a holistic perspective on the situation.
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