DR. BUGS | BY RAYMOND A. CLOYD Can Plants Influence Susceptibility to Insecticides? Question: I have read that plants fed upon by insect pests can affect their susceptibility to insecticides. Can you explain? Answer: You ask a great question. The primary mechanism by which plants can affect insect pests susceptibility to insecticides, or influence the toxicity of insecticides to insect pests, is by inducing a high level of activity of metabolic detoxifying enzymes in insect pests because of exposure to plant allelochemicals when feeding. Plant allelochemicals or secondary metabolites are considered nonessential to plant growth but are responsible for producing plant defensive compounds to avert insect pest feeding. However, insect pests have evolved the ability to metabolize and/or detoxify plant allelochemicals through the induction or activity of certain metabolic detoxifying enzymes. The variability associated with insect pest susceptibility to insecticides on certain plants is related to different levels of metabolic detoxifying enzymes, which can be induced by the plant. There are a number of enzymes involved in detoxification or metabolism that are active on a diverse array of substances, including naturally occurring plant allelochemicals and insecticides. Insect pest responses to Sucking insect pests develop resistance at a slower rate than chewing insect pests. 12 JANUARY 2024 GPNMAG.COM Plants produce defensive compounds called plant allelochemicals that provide protection from insect pest feeding. Photos by Raymond Cloyd. plants may result in enhanced metabolism of insecticides because the mechanisms responsible for the detoxification of plant allelochemicals by insect pests may also be effective in detoxifying insecticides. Furthermore, the selection pressure affiliated with exposure to plant allelochemicals when insects feed on plants may promote or induce the activity of metabolic detoxifying enzymes. The primary metabolic detoxifying enzymes are cytochrome P450 monooxygenases, glutathione S-transferases and esterases. Cytochrome P450 monooxygenases, glutathione S-transferases and esterases are common enzymes that metabolically detoxify insecticides. These enzymes convert plant allelochemicals and insecticides into non-toxic metabolites. The enzymes remove lipophilic (substances that dissolve in lipids) compounds that may be toxic to insect pests by converting these compounds into metabolites that are excreted or removed from the insect pest body.http://www.GPNMAG.COM