Lethal doses and Bees

By Peter Dearden 30/07/2013

Peter K. Dearden

More bad news for bees this week. Honeybees around the world are struggling in the face of disease and insecticide threats. In New Zealand we have Varroa mite, that increases costs for beekeepers, destroys unmanaged beehives and vectors viruses, making them more virulent. Overseas, Colony Collapse Disorder and pesticide-threats are adding to the woes Varroa brings, meaning bee numbers appear to be declining.

The loss of pollination capacity due to the loss of bees should be a big issue for all of us. In New Zealand, honeybees are estimated to support 35% of our primary sector, contributing $5.1 billion in export revenues (Laas, F., Foster, B. & Newstrom-Lloyd, L. Report to the Select Committee on Pollinator Security in New Zealand. (2011)).  Beyond this, the pollination of the beans and fruit trees in your garden and parks, is dependent to some extent on bees. New Zealand would be poorer, both environmentally and economically, without bees.

A paper published this week adds to the problem. It finds that bees that consume pollen with high fungicide levels have an increased probability of high rates of infection of Nosema ceranae (Pettis et al, PLOS One 8:7 e70182). Nosema is a unicellular parasite (microsoporidian) of honeybees, and have been linked to Colony Collapse Disorder. High rates of Nosema are detrimental to bee and hive health. The finding that fungicide dose affects Nosema infection is surprising, because fungicides should be perfectly safe for bees. The doses here are not high, but they seem enough to disrupt hive health, perhaps producing honeybee declines.

The bad news is that all but one of the fungicides found to have an association with Nosema are used in New Zealand. We also have Nosema.

Let’s be clear here; this is not a black and white issue. Agrichemicals are key parts of our production systems, and are not, in the main, used indiscriminately.  Now there is a balancing act: ensuring bee health while maintaining efficient production. This is not going to be an easy equilibrium to maintain.

Perhaps more pressing is the need to investigate more sensibly the affect of agrichemicals on bees. Determining the lethal dose (the dose at which a bee dies) of a chemical, does not determine if sub-lethal does have effects on the behaviour or health of the whole hive. Bees are incredible animals because of their hive behaviour, their division of labour and their sociality. This also makes them sensitive in ways that non-social insects are not. We need to know more about the impacts of agrichemicals, used validly to improve our primary production output, on the remarkable super-organisms that are bees.

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