How do chemical pesticides work?

The most widespread method of keeping pests at bay is by chemical intervention. Created with the ultimate goal of killing the invading pests, there are many different branches of toxins used on crops. Currently, more than 1,000 pesticides are used around the world to prevent food damage, each with varying properties and toxic effects.

The majority of insecticides are chemically engineered or naturally affect the nervous systems of an array of pest insects. Most of the pesticides used today affect the way insect neurons receive instructions to function by changing the sodium and potassium balance between the nerve cells. They either prevent a signal being generated or overstimulate the nerves so that they misfire. Either of these malfunctions of the nervous system will paralyse and then kill the pest.

Using chemical insecticides has been a controversial endeavour for some years, with their risk to human health being a major issue. In larger quantities pesticides can cause serious health issues, or even be fatal to someone that is exposed to them, which is why farmers must wear protective gear when spraying down their crops. However, pesticides in the past have caused larger scale problems in the surrounding ecosystem. Developed as the first modern synthetic pesticide in the 1940s, dichloro-diphenyl-trichloroethane (DDT) is now remembered as the biggest mistake in the history of agricultural pest control.

Created to combat pestborne diseases like malaria and typhus, the use of DDT quickly became its own health hazard. When exposed to high doses, it could cause vomiting, tremors and even seizures. Although highly effective as a pesticide, DDT was also very good at bioaccumulating, whereby an animal, such as a bird, eats the pest killed by DDT and accumulates it in their bodies, leading to a whole host of health issues. This includes making the shells of birds’ eggs so thin that they break during incubation, destroying their population. As a result of the health hazards to both humans and wildlife, DDT was banned in the UK in 1984, but some countries still use it.

Today’s harvested foods that have been treated with pesticides are rinsed and cleaned before they reach your plate. Regular pesticide residue testing is also done to ensure that any remaining pesticides are at a low and safe enough level for human consumption.

The bee debacle 

It’s safe to say that bees are the backbone of our ecosystem, and are vital for successful harvests for some crops. As keen pollinators, honey bees are free labour for farmers, with over one-third of the food we eat depending on bee pollination. However, bees are being put at risk by a group of chemical insecticides called neonicotinoids. This synthetic chemical treatment is very effective at killing pests. However, it’s not targeted towards unwanted insects, and so bees are also placed in the firing line.

Neonicotinoids work by compromising the insects’ nervous systems and ultimately killing them. The chemicals also persist on the pollen of plants, thus finding their way onto a bee’s body and resulting in their inevitable death. Studies have also shown that even a close proximity to neonicotinoids can disrupt a bee’s ability to navigate and reproduce.

The use of neonicotinoids has been banned in part across all European Union member countries since 2013, and as of 2018 the ban extended to all outdoor use of the chemical. However, countries such as the US have not adopted the same ban on the controversial insecticide, but the Environmental Protection Agency persists to introduce measures to manage the risks they cause.

Read more about different methods of pest control in issue 143 of How It Works magazine