Attracting or repelling insects

To an insect, some things are tasty and some things are repulsive. Of course that depends on which kind of insect is deciding what to eat. This can be important to us humans, because some insects are pests to us. We can trick insects into eating pesticide. We can repel insects from eating crops.

Here’s an example of tricking insects into eating pesticide. People put down poisoned bait for cockroaches. But insects are clever little creatures, quick to evolve. My fellow blogger Charlotte Elson at Plantwise tells us that some populations of a common and widespread pest, the German cockroach (Blattella germanica), have evolved ‘glucose aversion’. To these cockroaches, sweet-tasting baits are no longer attractive. Here’s the science about that.

This story got me wondering what Bt crops taste like to insects. Bt crops are genetically modified (GM, also called genetically engineered, GE) to produce an insecticide which originated in a bacterium called Bacillus thuringiensis.

In countries where GM crops are permitted, many farmers choose Bt crops. You can follow my ‘Bt toxin’ tag for more about these crops. Sometimes they affect organisms which rely on insects, or which are harmed by insects. Sometimes insects evolve resistance to the Bt insecticide. Here’s the science about that. When Bt crops succeed – when they kill pests – it’s because they’ve tasted good enough for insects to eat some parts of the crops.

A completely different, but still GM, approach could be inspired by the glucose-averse cockroaches. Crops can be modified to taste or smell repulsive to pests.

Here’s an example of repelling insects so that they’ll leave crops alone. We don’t like most aphids (Hemiptera) because they’re pests on crops. John Pickett at Rothampstead Research Institute modified wheat (Triticum aestivum) to produce a pheromone (that is, a smelly signal) which originated in peppermint (Mentha piperita).

This minty pheromone is called E-beta-farnesene (EBf). As well as being part of peppermint oil, EBf is released by aphids when they’re in danger. Therefore when aphids smell EBf they fly away. As an added bonus for us, some of the aphids’ natural enemies can smell EBf too. These insects are parasitoids (like parasites, but fatal to their hosts) called lacewings (Neuroptera). Lacewings use the smell of EBf to find aphids. When they find aphids, they lay eggs inside them.

Nick Collins at the Telegraph tells us about the subtly minty GM wheat. I say ‘subtly minty’ because there’s not enough EBf to spoil the flavour of the wheat grain for human consumers. Here’s Prof Pickett’s summary of the ongoing EBf wheat project.

If EBf wheat performs well, its seeds might be offered to farmers. Here in Britain and in the rest of Europe, that would mean permitting farmers to grow a GM crop. I wonder how long it would take for aphids to evolve EBf indifference.


About argylesock

I wrote a PhD about veterinary parasitology so that's the starting point for this blog. But I'm now branching out into other areas of biology and into popular science writing. I'll write here about science that happens in landscapes, particularly farmland, and about science involving interspecific interactions. Datasets and statistics get my attention. Exactly where this blog will lead? That's a journey that I'm on and I hope you'll come with me.
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