Molecular Biotechnology: Principles and Applications - Glick B., Pasternak J. 2002

Molecular Biotechnology of Microbial Systems
Microbial Insecticides

Of all animal classes, the insect Class is the most numerous, with the number of described species approaching 1 million. Insects can cause massive damage to agricultural crops, and some of them serve as vectors for Human and Animal diseases. In the 1940s, numerous chemical insecticides were synthesized to control pest insect populations. The most famous of these was dichlorodiphenyltrichloroethane (DDT). This organochlorine compound was first synthesized in the 1870s, but it was not used as an insecticide until the late 1930s. DDT proved to be a highly effective agent for controlling many insect pests. Like other organochlorines, it exerts a paralyzing effect on The Nervous system and Muscle Tissues of insects. To date, other organochlorine compounds have been synthesized and widely used, including dieldrin, aldrin, chlordane, lindane, and toxaphene.

Another class of chemical insecticides consists of organophosphates, which include malathion, parathion, and diazinon. First-generation organophosphate insecticides were originally developed as chemical warfare agents. Today, they are used for insect population control. Their action is based on the inhibition of acetylcholinesterase, which hydrolyzes the neurotransmitter acetylcholine. Insecticides of this class disrupt the functioning of motor Neurons and Brain neurons in insects.

By the early 1960s, about 50 million hectares of agricultural land in the United States were treated with chemical insecticides. Around this time, it was demonstrated that organochlorine (to a greater extent) and organophosphate (to a lesser extent) insecticides have harmful effects on humans, animals, and ecosystems. These effects can manifest immediately or over the long term. Organochlorine compounds (specifically DDT) persist in the environment for 15 to 20 years and accumulate in ever-increasing concentrations. The bioaccumulation of chemical insecticides in the fatty tissues of many organisms has already led to disastrous consequences. For instance, in North America, many bird species were nearly driven to extinction, including peregrine falcons, sparrowhawks, bald eagles, brown pelicans, and double-crested cormorants.

Over time, major insect pests became increasingly resistant to many chemical insecticides, which meant that by the 1950s, higher concentrations of insecticides had to be used to control their populations. Furthermore, chemical insecticides were shown to act non-selectively; that is, alongside pest insects, they also destroy beneficial insects, and in some cases, they are far more effective at eliminating the natural enemies of pests than the pests themselves. This often led to highly unexpected outcomes, where chemical Treatment actually triggered an increase in pest populations.

In light of this, the past 20 years have seen intensive efforts to find alternative Methods for controlling pest insect populations. First and foremost, researchers turned to natural insecticides synthesized by various microorganisms and plants. These compounds are typically highly specific and undergo rapid biodegradation, meaning that resistance to them develops slowly. Unfortunately, they are often not very effective and are expensive to produce, which limits their widespread application. There is hope that Recombinant DNA technology will help overcome these challenges. To enhance the efficacy of Microbial Insecticides, researchers can now manipulate the genes encoding their Biosynthesis. Specifically, this involves genes for insecticides produced by the bacterium Bacillus thuringiensis or insect Baculoviruses; these insecticides are safe, specific, and highly effective.

The pesticide market is enormous: currently, more than 20 billion dollars are spent annually on their production worldwide, and this figure is growing rapidly. Yet, biopesticides—primarily B. thuringiensis insecticides—account for only 1% of this total, though future progress in this field is projected to be driven precisely by biopesticides.