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20 August 2015

The department of parasitic wasps: why has the government lifted a ban?

Scientists argue they do damage to bees and other native insects. So why is the government lifting the restrictions on the parasitic wasp?

By Michael Brooks

It is a triptych of horror. First, it involves our culture’s current bogeyman: zombies. It also has wasps, which we all hate, and spiders, which we see as a necessary evil at best. Read on if you dare.

Research published in the Journal of Experimental Biology explores how a parasitic wasp takes over the brain and body of a spider. First comes the wasp sting, which occurs in a dive-bomb attack. The spider is paralysed and helpless to stop the wasp injecting it with an egg. When the wasp larva hatches, it feeds on the spider’s blood. Then, for no apparent reason, the spider – now little more than a “drugged navvy”, according to the researchers – builds the larva a cocoon.

The cocoon, it seems, is a reinforced version of the webs spiders build as a protective habitat when moulting. Somehow, the wasp larva flips switches in the spider’s brain to trigger a moulting instinct, but with a modification that makes the web stronger and the dying spider uninterested in occupying the cocoon.

It’s a clever manipulation and scientists confess that there’s a lot they don’t understand. That is partly because it’s not easy finding out what is happening inside a zombie spider’s brain. It’s a bit like trying to understand the astonishing decision to lift a ban on chemicals that seem to be disruptive to our bee population. Experiment after experiment has demonstrated that the pesticides known as neonicotinoids can destroy bees’ ability to navigate. Bees are the main pollinators of agricultural crops, making this a grave threat to the future of agriculture (the EU banned neonicotinoids for this reason).

Now the UK government has lifted the ban temporarily for reasons scientists can’t explain. It is particularly difficult to understand, as the government department involved has been instructed not to publish the minutes of its discussions on the matter. According to Christopher Connolly of the University of Dundee, “there has not been any change in the balance of scientific evidence to warrant the reintroduction of the neonicotinoids”.

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Barbara Knowles, a senior science policy adviser at the Royal Society of Biology, is equally puzzled. “The science case is now much stronger that neonics harm bees and other wildlife, increase slug damage, and accumulate and persist in the environment,” she wrote in a blog post on the society’s website. The economic case for lifting the ban – 3.5 per cent lower yields – “seems weak”, she wrote, and “surely we can easily live with these marginally lower yields as a small price to pay for protecting bees”.

Especially worrying are reports that recently one of the newly permitted chemicals has been shown to diminish severely the number of queen bees. A paper published in the journal Nature in May showed that treating rape seed with clothianidin leads to landscapes with a third the normal number of queens. The lifting of the ban could lead some areas of the country to lose two-thirds of their wild bumblebee queens by the end of next autumn.

Lynn Dicks of the University of Cambridge has asked Bayer and Syngenta, two leading agrochemical companies that will benefit from the government’s decision, to fund independent monitoring of the effects of reintroducing the chemicals. But really it’s like watching more spiders die. We need to dig deeper to uncover the mechanisms. Maybe the parasitic wasp research can help. Maybe the Department for Rural Affairs has been infected with something. But what? There are some areas where scientists can only make an educated guess. 

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