Silent Spring Redux

Rachel Carson wrote her now famous book Silent Spring fifty years ago. In her book she documented the unintended effect of the use of persistent insecticides such as DDT. DDT (Dichloro Diphenyl Trichloroethane) when introduced was heralded as a tremendous advance in technology in the battle between humans and insects for our food supply.

Previously available insecticides were toxic to all forms of life. The so called first generation pesticides include agents such as Lead Arsenate which contain both Lead and Arsenic. Nicotine from tobacco plants also has historical use. These substances are acutely toxic to humans and pests alike.

DDT and other second generation pesticides were thought to be much safer as they have much lower toxicity to mammals and birds compared to insect toxicity. Further, these substances were persistent meaning that insecticide application occurred less frequently. An unintended consequence of the use of these insecticides was their bioaccumulation.

The littlest critters are eaten by little critters, who are in turn eaten by slightly bigger ones. The higher up in the food chain, the higher the accumulated dose of insecticide. The problem with birds, raptors in particular is not acute toxicity but an effect on egg shell thickness. Eagles, hawks, and some sea birds weren’t killed directly by the pesticides, but rather had trouble reproducing because the thin egg shells broke.

When the problem of bioaccumulation was recognized a new generation of pesticides was developed. The third generation of insecticides are of a relatively low toxicity to non-target organisms, but more importantly much less stable in the environment. But once again unintended consequences rears its head.

This third generation of insecticides includes a class of compounds called neonicotinoids. As their name implies they are structurally related to nicotine but have more specificity in their toxicity towards insects. Imidacloprid is an example and is in widespread use around the world. It is used against many insect species especially agricultural pests.

The neonicotinoids were developed and put to use in the middle of the 1990s with considerable success. It has only recently come to notice that a connection exists between these compounds and a condition called colony collapse disorder (CCD). Around 2005 it was noticed that wild honey bees were disappearing. Bee keepers also noticed that the number of bees in their hives were decreasing to the point of collapse hence the name. What was happening was poorly understood as there weren’t any dead bodies and as every murder mystery follower knows it’s hard to get a conviction without a dead body. The only thing known about CCD was that bees went out in the morning but didn’t come back in the evening.

Two recent studies published in Science have made the connection. Using the equivalent of radio collars for bees, scientists were able to show that bees exposed to minute quantities of neonicotinoids were not killed outright. They essentially were made stupid, too stupid to find their way back to the colony. The insecticide is taken up into the tissues of plants where it finds its way to the nectar and pollen. Bees collect the nectar and pollen, are intoxicated and get lost. It’s as simple as that. But that is a big deal, as over thirty percent of food crops worldwide require pollination by bees.

Originally published in the Russellville Courier, August 2012

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