Bees for Development Journal 129 December 2018
Pesticides and bees – an overview Janet Lowore, Programme Manager for Africa, Bees for Development The FAO Code of Conduct on the Distribution and Use of Pesticides defines as pesticides, ‘any substance or mixture of substances of chemical or biological ingredients, intended for repelling, destroying or controlling any pest or regulating plant growth’. Pesticides are used to kill fungi, weeds and animal pests, especially insects and mites. Pesticides contain more than 1,000 active ingredients. These ingredients make pesticides effective killers of different living organisms. Many pesticides are designed to kill insects, and this means that in addition to killing the target insect species, it is inevitable that other insects including bees are also harmed.
Our modern era of pesticide use stems from the 1940s. Concern over the unintended negative consequences of pesticide use was flagged in 1962 with the publication of the famous book Silent Spring by Rachel Carson. Carson wrote about how a single application of DDT could continue killing for months and years. This led to an era of greater control and regulation in some countries, but the problem is still with us. The companies that produce pesticides try to downplay the negative impact and spend considerable effort in ‘proving’ their safety. This is not surprising given the amount of money at stake in the industry. There are different broad groups of pesticides. The older-type pesticides, such as DDT were widely used until the full extent of their harmful consequences caused them to be banned or heavily controlled, along with many other Persistent Organic Pollutants (POPs). A new class of pesticides, neonicotinoids came into widespread use in the 2000s. Following increasing concern about the impact of neonicotinoids on bees,
Types of pesticides Type
Examples
In brief
Organochlorines
DDT
DDT was widely used in the 1940s to 1970s. It caused widespread and catastrophic harm to wildlife because it does not biodegrade and instead accumulates through the food chain. DDT is now banned for most uses in most parts of the world but is used to kill malaria-spreading mosquitos in some countries.
Organophosphates
Malathion
Highly toxic and widely used insecticides used in agriculture, gardens, homes and veterinary practices. Highly toxic to all insects, including bees. Interferes with insects’ nervous systems preventing them from moving or breathing. Malathion is applied in dusts and sprays and is harmful to people if inhaled or comes into contact with their skin.
Carbamates
Sevin
Carbamates are heavily used in agriculture as fungicides, herbicides and insecticides. Carbamate insecticides vary in their spectrum of activity, mammalian toxicity and persistence. Used as either dusts or sprays. Carbamate pesticides kill insects in a similar fashion as organophosphate insecticides but some carbamates are less toxic and degrade faster than organophosphates. Sevin (one example) is moderately toxic to mammals, but highly toxic to honey bees.
Pyrethroids
Neonicotinoids
Pyrethroids are a group of man-made pesticides similar to the natural pesticide pyrethrum. Pyrethroids are a broad-spectrum insecticide and widely used to control insects in agriculture. Considered less toxic to mammals than organophosphates and relatively cheap. Sub-lethally toxic to honey bees and harmful to aquatic wildlife. Imidacloprid
First used commercially in the 1990s, ‘neonics’ are now among the most popular insecticides in the world. They are coated onto crop seeds and – being water soluble – are taken up and dispersed throughout the plant. This mode of action is called systemic and explains how the toxin enters the nectar and pollen. Sometimes they are sprayed onto foliage. They are especially effective against sucking pests (such as aphids). Increasing evidence that neonics are sub-lethally toxic to honey bees led to a partial ban in the EU in 2013.
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