Wednesday, August 21, 2013

Fighting foreigners with foreigners: aphid vs. vine

Apparently the NYC Department of Parks and Recreation is releasing thousands of weevils originally from Asia to fight mile-a-minute, an invasive vine also native to Asia, which has taken over parts of the city.
I want your MAM(my)! 

When I first read this, it immediately triggered alarm bells to go off in my head. I don't know if it is the combination of quasi-hippie environmentalist and old-school naturalist professors I had during my undergraduate, which insisted on letting things be, or my mother's insistence that two wrongs don't make a right, but I thought this would be yet another human manipulation destined for failure. Think cane toads, native to central America and introduced to sugar cane fields in the Caribbean and Australia to keep down pests, but now spreading well beyond its range and killing off many of its would-be predators with its poisonous skin. Or, the story (for which I can find absolutely no evidence for now) that rats were introduced to an island, then snakes were introduced to eliminate the rats, and the plan backfired and the snakes have taken over the island, killing much of the native wildlife (it almost sounds like the story of Guam and brown tree snakes, but isn't).

However, I am glad to learn that we have learned from our mistakes, and when we say that extensive research was done to evaluate both safety and efficacy of the aphids in targeting mile-a-minute, hopefully we mean it (see references here). As with most pest invasion studies, potential control mechanisms were identified by looking for the herbivores which keep the plant in check in its native environment. Researchers identified Rhinoncomimus latipes aphids (they really need a good common name - can we nickname them munch-a-minutes?) as good potential targets for further research, and their breeding began in controlled environments in the US.

The potential heroes of the story...

Of course, organisms don't always behave the same in a new environment as they did in their original environment (this is why things may be minor members of a diverse community in their native habitat, and invade in another), so the next step was to evaluate whether they still feed primarily (or ideally uniquely) on mile-a-minute. Researchers at the University of Delaware dusted these aphids red, and placed them at the base of non-target plants, or yellow, and placed them at the base of mile-a-minute, and followed them through time to see where they ended up. The researchers found that aphids which originally started on mile-a-minute did not stray onto non-host plants, and those on non-host plants found their way onto mile-a-minute more and more as time went on. This is all good.

However, there are still other questions which remain unanswered. For example, do the aphids have natural predators? If mile-a-minute declines, or is in low density in some places, will the aphids switch to other food sources (like us and previously disregarded fish)? Will they reproduce with native mites and make new, super cabbage-eating mites which will upset community gardeners? And, as far as I can tell, although we know it munches on the weed, we don't know whether the mite occurs in sufficient density to have a noticeable impact on mile-a-minute population.

While some of these worries may seem a little far-fetched, all have previously emerged as problems. That said, we cannot be frozen by fear; we live in a dynamic world we change for better or worse.  We don't have enough knowledge to predict the future, so we should try and balance gathering enough information to make an informed decision, and making a decision in a timely manner. After all, researchers need results for grant applications or to appease investors, and some are willing to release their experimental creatures into the wild without full ecological impact assessments in order to undercut scientists with possibly more ethical methods.

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