Pollen protects honeybees against pathogens

Rebecca Nesbit, press officer at the Society of Biology, reports on Professor May Berenbaum’s talk at the Impact of Pesticides on Bee Health conference organised by the Biochemical Society, the British Ecological Society and the Society for Experimental Biology.

In 2006, American beekeepers were alarmed by sudden losses of hives to colony collapse disorder, where worker bees suddenly disappear leaving the queen and brood in the hive.

Many factors were put forward as potential causes, including GM corn pollen, mobile phones, elevated UVB light, and Soviet Russian mind control experiments. These ones, however, have been put in the ‘less likely’ category along with alien abduction.

The most likely factors contributing to colony collapse disorder include pathogens and parasites, declines in the nutritional quality of their diets, and exposure to pesticides. Pesticides potentially affect immune responses, navigation ability, learning and memory.

Professor Berenbaum’s recent work looks at the honeybee genome, which was sequenced in 2006. The honeybee has unusually few genes associated with detoxification, and detoxification is exactly what they need to do to deal with pesticides. Notably, most insect species have around 80 genes for P450 detoxification enzymes but honeybees have only 46.

We know that pollen ingestion can reduce honeybee susceptibility to pesticides and pathogens, which may be partly because pollen can increase the expression of particular genes. A compound within the cell wall of pollen is thought to increase the expression of certain genes required for defence against pesticides and pathogens.

This compound is present in honey, which is made using pollen, but not in sucrose and high-fructose corn syrup. These are used by as honey substitutes by commercial bee keepers. This became common after laboratory experiments suggested that they were nutritionally equivalent. However, these experiments were done before the arrival of varroa mites, which increased the number of pathogens bees are exposed to. It also led to an increased exposure to pesticides as beekeepers add pesticides to the hives to control the mite.
Professor Berenbaum’s work starts to explain the complex interactions which make bees susceptible to different environmental factors. It also raises questions about bee management.

Videos of some of the talks will be available online, and tune in from 10.45 today (24th January) to see the live webcast.

Mao W, Schuler MA, & Berenbaum MR (2013). Honey constituents up-regulate detoxification and immunity genes in the western honey bee Apis mellifera. Proceedings of the National Academy of Sciences of the United States of America, 110 (22), 8842-6 PMID: 23630255