ARS | Publication request: Mechanisms by which pesticides affect insect immunity

Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2011
Publication Date: December 20, 2011
Citation: James, R.R., Xu, J. 2011. Mechanisms by which pesticides affect insect immunity. Insect Molecular Biology. 109: 175-182.

Interpretive Summary: We ask the question here, what is known about how pesticides affect insect immunity. Pesticides, especially insecticides, are generally designed to kill insect pests. Thus it is not surprising that many pesticides affect the health of beneficial insects, such as bees. However, considerable research has gone into designing pesticides that are environmentally friendly, including the development of ones that have low toxicity to mammals, birds, and bees. More recently, people have become concerned that even some of these pesticides (both insecticides and fungicides) are harmful to bees, even when they do not cause immediate death. Bees are constantly exposed to low levels of pesticides when they visit flowers in farm fields and home gardens. Does this low level of exposure causes the bees to be more susceptible to disease? We show here that some insecticides (but not all) do affect insect immunity. In particular, both artificially and naturally based pesticides have been found to affect the cellular immune response (phagocytosis). In addition, insects produce a variety of proteins for fighting invading pathogens, and little research has been conducted to determine how pesticides might affect the chemical pathways that produce these proteins, but research does show that pesticides can affect one especially important compound, melanin. Pesticides can also affect behaviors, such as grooming, that insects use to prevent infections. Little is known about how insects defend against viruses, but from what is known, pesticides probably do not affect an insect’s ability to fight off viruses. More research is needed to evaluate synthetic pesticides. Also, insects have mechanisms for detoxification of pesticides, and more research is needed to determine how these mechanisms affect immunity.

Technical Abstract: The known effects of pesticides on insect immunity is reviewed here. A basic understanding of these interactions is needed for several reasons, including to improve methods for controlling pest insects in agricultural settings, for controlling insect vectors of human diseases, and for reducing mortality in beneficial insects. Bees are particularly vulnerable to sublethal pesticide exposures because they gather nectar and pollen, concentrating environmental toxins in their nests in the process. Pesticides do have effects on immunity. Organophosphates and some botanicals have been found to impact hemocyte number, differentiation, and thus affect phagocytosis. The phenoloxidase cascade and malanization have also been shown to be affected by several insecticides. Many synthetic insecticides increase oxidative stress, and this could have severe impacts on the production of some antimicrobial peptides in insects, but research is needed to determine the actual effects. Pesticides can also affect grooming behaviors, rendering insects more susceptible to disease. Despite laboratory data documenting pesticide/pathogen interactions, little field data is available at the population level.