Interactions Among Allelochemicals and Insect Resistance in Crop Plants

Abstract

Many crop plants may have the genetic potential to cut production costs, not only of their own allelochemical defense systems against insect enemies, but also of the synthetic insecticide defense systems humans have devised for plant protection. Common among crop plants are allelochemicals which act as synergists, or chemicals that themselves lack toxicity to insects but can enhance the toxicity of a co-occurring chemical.Most widespread among these synergists are inhibitors of mixed-function oxidases, the membranebound metabolic enzymes responsible for the detoxification of a wide variety of xenobiotics. These inhibitors include methylenedioxyphenyl (MDP) compounds. Myristicin, a common constituent of many umbelliferous crops, is as effective a synergist for carbaryl as is piperonyl butoxide, a commercial synergist of synthetic insecticides. Also ubiquitous are synergists that inhibit glutathione-S-transferases, soluble enzymes involved in a number of xenobiotic transformations. These endogenous allelochemicals can synergize both cooccurring toxicants and exogenous synthetic organic insecticides. Such synergists in leaf tissue can significantly increase the toxicity of an insecticide; carbaryl toxicity is thus greatly influenced by the chemistry of the plant on which it is applied. While there are possible complications involved in the use of endogenous synergists to potentiate chemical control of insects, there is great potential for using these chemicals to reduce the impact of synthetic insecticides on nontarget organisms and on the environment without compromising insect control.