Is Nemasys harmful to bumble bees?

Recent study finds consumer biological control lethal to bumble bee Bombus terrestris in laboratory tests

For many years, gardeners and horticulturists have been using biological control products as a means to eradicate garden pests such as weevils, carrot root fly, thrips and slugs. Many gardeners, including myself, have used these products as a more natural pest control over ‘nastier’ chemical alternatives, but a recent study has shown that these seemingly harmless nematodes could pose a threat to the invertebrates gardeners do like to see and actively encourage – such as bees.

Scientists at Liverpool John Moores University, found that entomopathogenic nematodes in two Nemasys products; ‘Grow Your Own’ and ‘Vine Weevil Killer’ were lethal to the bumble bee Bombus terrestris in controlled laboratory experiments. Results showed high mortality in bees exposed to soil containing nematodes from each of the products. These products are both currently widely available and largely unregulated.

Entomopathogenic nematodes are a parasite, causing death in their hosts through an association with bacteria. Juvinile nematodes are infected with bacteria in the soil then seek and enters it’s host, such as a weevil or moth larvae. The bacteria causes septicemia and kills the host, providing a food source for the nematodes before they proliferate, sending more infected parasites out to find their next victim.

This study has highlighted the potential threat that these methods of biological control could have on our wild bee species, especially those such as Bombus terrestris in which the queen often overwinters under the soil. Worryingly, due to the delay between infection and mortality, if the nematodes are able to proliferate in the dead bees, there is a risk the whole colony could become infected.

Further field research is definitely needed into the safety of available biological control products on non-target species, and the effect that such products have on species outside of the laboratory.

The full article can be found here  in the open access journal PeerJ. Thank you to Steve Head from the Wildlife Gardening Forum for sharing this in the latest newsletter.

-Larissa

Header photo taken in the Natural History Museum’s Wildlife Garden.

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