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Bumblebees unknowingly poisoning their broods

Bumblebees fail to recognise some toxins in lupins and other flowers they visit for nectar and pollen - unwittingly weakening or even killing their broods, according to new research published by the University of Greenwich.

The university’s chemical ecology research group says more work is needed to discover if this previously unknown problem is affecting other pollinators such as honeybees.

Professor Phil Stevenson and Research Fellow Dr Sarah Arnold, of the university’s Natural Resources Institute (NRI), used insectories - a suite of temperature-controlled rooms which are home to insects, such as bumblebees, mosquitoes and grain storage pests - to explore the chemicals produced by plants, examining their ecological roles and any effects they have on visiting pollinators.

Professor Stevenson, an expert in plant chemistry, says: “Many plants produce a wide range of toxins which we know deter or are poisonous to herbivores. What has not been examined in depth before is how these toxins may affect the plants’ major pollinators.

“Many of the toxins are present at low levels and therefore do not kill insects, such as bumblebees, outright.

“However, they can have sub-lethal effects that affect the whole colony, if individual bees collect nectar or pollen from toxin-containing flowers and bring it back to feed the brood.

“Sub-lethal doses of toxins weaken individual bees and their broods, making them more susceptible to other stresses such as pesticides, parasites and viruses.

“Our research shows that bumblebee broods fed with low level toxins in their pollen, such as lupanine from lupins, produce fewer males and these individuals are smaller than those in broods not exposed to the toxins.”

Dr Arnold adds: “This work has implications in agriculture and horticulture more widely, as breeding plants to produce natural defensive chemicals is one possible alternative to pesticide use to reduce damage from insect pests. But we now need to consider whether crops containing natural toxins could cause negative effects for the pollinators they rely on when they are grown on a large scale. We need to find out much more about what roles plant chemicals play in pollinator behaviour and ecology.”

Professor Stevenson and Dr Arnold’s research into the effect of plant toxins on bumblebees has been published in the Journal of Experimental Biology and the Journal of Chemical Ecology.

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