Bt in insects

April 2011

Many of these are our pollinators

Bees

Recent years have seen waves of massive bee decline around the globe. Some of these can be traced to infection or infestation, but others are a complete mystery. However, the finger is being increasingly pointed at agri-pesticides in and on the flowering crops from which the bees gather their food.



Two forms of colony collapse are being seen. One involves “piles of dead bees at the entrance of hives”, the other involves the sudden disappearance of adult bees from the hive, leaving behind intact food stores and broods, and is referred to as 'Colony Collapse Disorder'. The first problem suggests the bees are being directly exposed to a lethal toxin. The second problem suggests foraging bees have become disoriented by damage to their nervous system and have been unable to find their way back to the hive.

Bayer CropScience, which is a major global supplier of suspect, 'neonicotinoid', insecticides insists that:
“Extensive internal and international scientific studies have confirmed that (the insecticide) does not present a hazard to bees.” 
The Company may well be telling the truth.

The scientific studies cited as safety assessments of the toxins look only at the lethal dose of an isolated substance given to healthy bees. Neonicotinoids and Bt-toxins tested this way show no adverse effect.
Unable to identify any single causative agent for CCD, the US Department of Agriculture, has finally begun long-overdue studies of the interactions between pesticides and bee pathogens. This is a good start, but also needs to be extended beyond the recording of 'death' to the study of behavioural disruption.

The successful life-cycle of bees is highly dependent on behaviour, such as food gathering followed by returning to the hive, to support the whole colony. Moreover, it's beginning to emerge that bees have very little physiological immunity: their avoidance of disease, again, depends on behaviour, such as hive cleaning. Neurotoxic effects of insecticides may not be lethal but will disrupt normal behaviour, leading to the collapse of the hive. Insecticides, especially Bt-toxins which react with insect gut cells, can also suppress the bees' limited immune system still further, making it supremely vulnerable to pathogens.

Sources
  • Adapted from 'BT is a TOXIN' which first appeared on GM-free Scotland in September 2008
  • Dr. Mae-Wan Ho and Prof Joe Cummins, Emergency Pesticide Ban for Saving the Honeybee, Institute of Science in Society, 39 Autumn 2008
  • German Coalition Sues Bayer Over Pesticide Honey Bee Deaths, Environment News Service, http://www.ens-newswire.com//, 25.08.08
Moths

Cabbages genetically transformed to produce Bt toxin worked as intended for a while: the novel insecticide killed the targeted moth larvae. However, when the insects started to become resistant to the toxin, the increased protein in the GM plants became a food supplement and made the pests thrive. Resistant larvae of the diamondback moth (a major problem in the USA) grew twice as fast after eating the GM cabbage leaves. (Cabbage is a traditional staple green vegetable in many countries.)
Sources:
  • Adapted from 'NON-TARGET EFFECTS' which first appeared on GM-free Scotland in July 2009
  • Bugs can feed on 'pest-proof' genetic crops, The Sunday Sun, 13.04.03

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