Pesticides

Chemical insecticides are used extensively in crop production today as a means of eliminating insect pests, but there are major problems associated with these chemicals. Pesticides are rarely selective, thus killing many insects, including the beneficial and indispensable ones. Numerous pesticides have built up a resistance to insecticides, thus requiring more intense applications of these chemicals.

Many scientists suggest that pesticides are linked to the decline of bee populations. Neo-nicotinoid pesticides are a class of neuro-active insecticides chemically related to nicotine, and they are systemic, meaning that they diffuse all throughout the tissues as plants grow up, eventually contaminating nectar and pollen[1].

Poncho owned by Bayer (also known as clothianidin) is a neonicotinoid insecticide currently registered for use as a seed treatment on corn, canola seed and rapeseed[2]. The most common effects to honey bees exposed are sub-lethal in nature, meaning that the bees will not die from exposure to the chemical alone, but that it will injure them to a degree which makes it difficult or impossible for them to perform essential tasks.

Poncho actually coats the crop seeds before they are planted. Then, when they germinate, the pesticide literally becomes part of the plant pollen. When the bees land on the plant and gather the pollen, they are exposed to the chemical, and if they bring the pollen back to their hive, the rest of the colony becomes exposed as well.

The neonicotinoid imidacloprid is a very commonly used insecticide worldwide. Imidacloprid has been shown to impair olfactory memory of honeybees[3].  When honey bees are reminded of a smell, they can find their way back to the food using visual clues to guide them. Therefore, olfactory memory is crucial for honey bees to locate valuable food sources again and again, and with increased usage of pesticides, their foraging ability could be jeopardized.

Neonicotinoids can alter learning and memory skills, navigational skills, and even mortality in bees. For instance, nonlethal exposure of honey bees to neonicotinoid caused high mortality due to homing failure at levels that could put a colony at risk of collapse[1]. Therefore, even at nonlethal doses, neonicotinoids can decrease foraging success in honey bees. Foragers are directly exposed and are negatively affected, but so is the rest of the colony when returning foragers store or exchange contaminated material with hive conspecifics.

There has also been evidence suggesting that bees exposed to pesticides have weaker immune systems, and are thus more susceptible to disease, especially at a young age. Higher proportion of bees reared from a high pesticide residue brood comb became infected with the parasite N. ceranae, and at a younger age, compared to those reared in low residue brood combs. These data suggest that developmental exposure to pesticides in brood comb increases the susceptibility of bees to N. ceranae infection[4].

Therefore, even nonlethal exposure to pesticides can have serious consequences for bees’ memory and navigation skills, as well as their immune systems. Over a long period of time, regular exposure to these chemicals could lead to mortality and even colony collapses.

What can you do to help?

  • Buy organic: purchase locally grown foods that do not contain pesticides.
  • Go native in your garden: since native plants are already adapted to the local environment, they require less maintenance. This way, you’ll reduce the need for fertilizer, pesticides and extra water.

[1] Mickaël, H., M. Béguin, F. Requier, O. Rollin,J.F. Odoux, P. Aupinel, J. Aptel, S. Tchamitchian, A. Decourtye. 2012. A common pesticide decreases foraging success and survival in honey bees. Science 336: 348-350.

[2] Feldman, Jay. “Why New Pesticides Are Putting Bees at Risk”. EarthShare.  2012. 14 November 2012 <http://www.earthshare.org/2012/05/pesticides-and-honeybees.html>.

[3]A. Decourtye. C. Armengaud,M. Renou, J. Devillers, S. Cluzeau, M. Gauthier, M.H. Pham-Delegue. 2004. Imidacloprid impairs memory and brain metabolism in the honeybee (Apis mellifera L.).Pesticide Biochemistry and Physiology 78: 83-92.

[4] Wu, J. Y., M.D. Smart, C.M Anelli, W.S. Sheppard. 2012. Honey bees (Apis mellifera) reared in brood combs containing high levels of pesticide residues exhibited increased susceptibility to Nosema (Microsporidia) infection. Journal of Invertebrate Pathology 109: 326-329.

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