Neonicotinoids and fipronil are both systemic chemicals that are absorbed by plants, commonly after seed treatment or soil application.
However, laboratory research has found that they can also have a direct toxic effect on nontarget species, such as birds and mammals, resulting in reduced growth and reproduction, or even death.
They can also have indirect effects on these animals in the wild, for example, by reducing the amount of insect prey available, which in turn may affect their growth, breeding success and survival.
The researchers reviewed 150 studies on the direct and indirect effects of fipronil and the neonicotinoids imidacloprid and clothianidin, on vertebrate species, i.e. mammals, birds, fish, amphibians and reptiles. The researchers classified the effects of the insecticides on different vertebrates using the US Environmental Protection Agency’s ecotoxicity classification system.
All three insecticides were directly toxic to vertebrates, the results showed. Imidacloprid, for example, was moderately to highly toxic to many birds. Clothianidin was moderately to practically nontoxic to rats, mice and birds and practically non-toxic to fish. Fipronil was highly toxic to game birds and fish.
Furthermore, all three insecticides had sub-lethal effects, impairing growth, development and reproduction of mammals, birds, fish and amphibians. Other sub-lethal impacts found included damage to genetic material and cells and abnormal behaviour.
Levels of imidacloprid and clothianidin likely to be found in freshwater are not high enough to kill fish and amphibians, the researchers found. However, sub-lethal effects could still occur, including damage to DNA and the immune system.
A small number of studies reviewed also show the indirect effects of imidacloprid or fipronil on mammals, birds, fish and reptiles. For example, in one study, fipronil and imidacloprid affected the growth and development of the fish medaka (Oryzias latipes) in rice fields, most likely by reducing populations of insects that the fish feed on.
In another study, fipronil used to kill locusts in Madagascar also killed harvester termites, a non-target species. This significantly reduced prey for lizards and led to their population decline. The authors of this study call for greater consideration of systemic insecticides’ effects on birds, mammals and fish.
