ABC Transporters and Their Role in Protecting Insects from Pesticides and Their Metabolites

Insects are frequently exposed to toxic compounds either naturally produced by host plants to prevent feeding damage or artificially manufactured by man to control herbivores and vectors of diseases. As a result from co-evolutionary adaptation, many of these insects have developed strategies to avoid exposure or eliminate toxic effects by biotransformation and/or reduction of the effective cytosolic concentrations. The elimination of toxic compounds frequently involves phase I and phase II reactions which functionalise the molecules and increase their solubility in water. Excretion in turn may rely on the activity of ATP-binding cassette (ABC) transporters, integral membrane proteins of the ABC superfamily that utilise the energy derived from ATP hydrolysis to translocate a variety of different physiological metabolites and xenobiotics. In recent years, ABC transporters have raised special interest, because multidrug resistance-associated ABC genes particularly of subfamilies B and C have been linked with insecticide resistance. In addition, some ABC transporters have been shown to directly mediate toxic effects of insecticides and biopesticides, and several inhibitors may prove useful in potentiating insecticide toxicity. Increasing the knowledge on the specific physiological functions of ABC transporters and elucidation of ABC-mediated resistance mechanisms may help to identify novel compounds for insect control that are highly selective and environmentally safe.