Campbell Vaughn: Consider the mode of action when killing bugs

There are a lot of folks who don’t like bugs at all. Count the number of exterminator trucks out on the road and you can see that people don’t mind paying to get rid of insects. I admit that I am squeamish when it comes to roaches. You can call them palmetto bugs all you want, but I call them roaches and I don’t want them in my house. There are numerous insecticides available to dispose of these creepy crawlers, but the different ways they attack insects are what I find fascinating.


Insecticides disrupt the insect’s ability to live long and prosperous in a variety of ways. The methods for harming the pest are referred to as “mode of action or MOA.” Insecticides don’t just kill by causing a tiny bug heart attack. Different insecticides do a mixture of things to insects and ultimately result in mortality. Mixing the modes of action on insecticides helps to prevent insects from building immunity to a particular product.

The most common MOA is to affect the insect’s nervous system. To understand this mode of action, it is important to have a basic understanding of how the nervous system operates. In insects, the nervous system is composed of a series of highly specialized, interconnected cells, along which travel electrical charges called impulses. The uninterrupted transmission of impulses along this series of cells is required for a nervous system to function properly. When exposed to these type MOA chemicals, the result is that the nervous system becomes overexcited resulting in tremors and uncoordinated movement. In insects, prolonged or irreversible disruption of a normal functioning nervous system will result in death. Rest in peace, palmetto bug.

Insect growth regulators (IGRs) used by the pest management industry disrupt critical physiological functions associated with normal insect growth, development and reproduction (egg production). IGRs are typically not immediately toxic to adult insects. The juvenile insects are the ones harmed by these types of insecticides. So timing of application is essential. One way IGRs work that is interesting is they will tell the insect to skip a phase of development or not mature at all. Vamoose, no more insect.

Some insecticides inhibit energy production. These chemicals cause insects to die on their feet. They essentially run out of gas.

Other chemicals affect a thin covering of wax on an insect’s body. This waxy substance helps to prevent water loss from the surface. When an insect comes in contact with one of these chemicals, it is absorbed in the protective waxy covering on the insect resulting in rapid water loss and eventual death from dryness. Think Tybee Island on the Fourth of July. Insecticidal soaps also have this mode of action.

There are some other environmentally friendly options for insecticides that have unique modes of action. Azadirachtin is the active ingredient in neem extracts and has a mammal toxicity. It acts as a feeding deterrent and starves the insect. Death by dieting.

Horticulture oils are some of my favorites for scale on camellias. When applied, they cover the insect and smother them. No air, no bug.

So when treating for insect pests, consider the mode of action. Try and diversify the ingredients and modes of action to avoid resistance and to maximize kill rate. The insects may not appreciate it, but who wants palmetto bugs in the house?

Reach Campbell Vaughn, the UGA Agriculture and Natural Resource agent for Richmond County, by e-mailing