Modern pest management and control is an increasingly diverse science with thousands of different management strategies. Synthetic chemical pesticides, which appeared in our arsenal around World War II, are a relatively new development in an epic battle against pests and parasites. Prior to the development of synthetic pesticides, there was a perpetual and slow battle of simple tools and natural chemicals against the incessant onslaught of pests.
As long as there have been producer/consumer, predator/prey or parasite/host relationships, there have been attempts at pest control. The need to control pests is not only a human pursuit; many animal and insect groups have pest control behaviors or mechanisms to reduce the effect of parasitism. Bird species have been observed to crush ants on the surface of their feathers to discourage other pests. Higher order animals, such as bears and primates, create pest deterrents from natural products such as roots and plants which then are applied to their coats.
Pest control needs increased as humanoids began gathering food stuffs and branched into agriculture. Attempts at pest control developed into management strategies. Pest control strategies are generally grouped into three basic categories: Biological controls, Mechanical or Physical controls and Chemical controls.
Biological pest control is a method of pest management which uses other living organisms to control the population of the predator or parasite. There is often an exploitation of an existing predator-prey, parasite-host or pathogenic relationship, which is then implemented and managed by humans.
There are three types of biological control strategies: Importation, Augmentation and Conservation.
Importation involves introducing either a native or non-native predator to an environment which previously did not contain that predator. In some cases, non-native species of predators are used due to their predation on similar or related species. An example of this type of importation occurred when the Chinese wasp was imported into North America to control the borer beetle population.
Traditionally, biological controls had the benefit of being relatively inexpensive to implement, but carried the danger of adding an uncontrolled and invasive predator into an environment. Modern biological controls attempt to limit the environmental impact of the release to just the targeted prey species. The importation of predators is most successful in the control of invasive or non-native introduced species of parasites or pests.
Augmentation pest control involves increasing the population of a natural native predator population to control the prey species. An example of commonly used augmentation pest management with a native species is when gardeners purchase lady bugs, or other native predators, for release in their gardens. Even the domestication of dogs and cats can be considered, in terms of pest management, as an early implementation of biological controls to reduce pests and discourage other predators.
Conservation pest control implements the advancement and propagation of the native predator species by increasing habitat or optimizing conditions for population growth of those predators, over the prey species. An example of one such management strategy is planting varieties of plants which encourage or host the predators.
Mechanical or Physical pest controls are one of the simplest forms of pest control. These include barriers (i.e. fences, traps, crop barriers, tilling); removal of pests (i.e. weeding, hand-removal); and environmental changes (i.e. fire, smoke, temperature control). The earliest methods of pest control, which persist into modern times, started with just the removal of the pests and using simple tools such as fire, smoke, mud, animal fats and dung as deterrents or barriers to pests.
Chemical pest control methods encompass a large range of strategies from companion planting to chemical sterilization agents. The most common forms of chemical pest controls are pesticides.
Pesticides are chemical or biological agents which deter, discourage, incapacitate or kill a pest. Early pesticides included the use of botanicals and simple elements or compounds. With scientific and cultural development, more pesticide agents were discovered and utilized. Early Romans discovered that crushed olive pits produced oil called Amurea which could kill pests.
The earliest documented chemical pesticide compounds were elements such as sulfur, heavy metals and salt. The use of elemental compounds for pest control started at the dawn of agriculture and has continued, in some cases, through the present day.
Elemental sulfur is believed to be one of the earliest chemical pesticides. Solutions of lime sulfur were used as dips to destroy lice, sulfur dioxide was generated by burning elemental sulfur, and was used to inhibit the respiration of insects and other small pests. Acidic solutions of sulfur, applied as a liquid or powder discouraged the growth of molds. Even today, the use of sulfur as a pesticide continues in modern pest management.
Sodium chloride, or Salt, was a very important commodity throughout history. Its value as a preservative was recognized early on, and it became a traded commodity and currency. Early Romans also discovered that salt could kill their enemies’ crops and caused fields to go fallow, making it an early herbicide.
The heavy metal compounds were probably first used due to their high toxicity. Arsenic compounds (particularly Arsenic (III) oxides) were found to be highly toxic to insects, bacteria and fungi. Arsenic (III) oxides combine rapidly with thiols found in biologically important molecules such as cysteine and coenzyme A, and interrupt enzymatic activities including ATP production. Modern use of Arsenic compounds is still found in wood treatment and preservative processes, as well as some arsenate pesticides. Similarly to Arsenic compounds, Mercury compounds (primarily organic mercury compounds) also have a high affinity for thiols and can disrupt biological and enzymatic processes. Lead compounds act as a calcium analog and cause incomplete heme synthesis leading to anemia.
The benefit of these inorganic pesticides, at the time, was that they lasted a long time and were not easily degraded. Unfortunately, they often leached into the ecosystem, wreaking havoc on local wildlife and posing a health threat to its human inhabitants.
During the course of the Middle Ages to the Victorian era, science moved from the realm of religion and magic to practical study. The disciplines of chemistry and biology were embraced, opening up studies into chemical compounds, reactions, and chemical synthesis. Pest control methods benefited from this pursuit of knowledge. Older methods of pest control were still in use (removal, barriers, botanicals, and elemental salts) but the mechanisms behind the efficacy of these methods were being discovered.
The nineteenth century was the dawn of the manufactured chemical pesticides. Chemicals were extracted from their botanical sources and purified in laboratories. By the 1800’s, nicotine compounds were purified from tobacco, pyrethrums were extracted from flowers and rotenone isolated from roots. Cyanides were recognized as the toxic compounds in pits of some fruits.
During this time, chemical compounds were blended and produced for the purpose of pest control. In 1814, an inorganic compound of copper (ii) acetoarsenite called “Paris Green” was introduced as a pigment. By 1867, Paris Green was widely sold as an insecticide and rodenticide. Paris Green paints were produced up until the 1960’s.
Similarly, the Bordeaux Mixture was developed in the late 19th century to fight the Great French Wine Blight. The mixture of copper (ii) sulfate and calcium hydroxide was designed to combat fungal and mildew infections in vineyards.
The Victorian era was the time when the traditional methods of pest control were formally investigated and put to the scientific method. All of the chemical compound that were historically available in their botanical forms (i.e. rotenone in roots and pyrethrums in chrysanthemums) now were purified for commercial and home use. Elemental compounds were blended to create more efficient pesticides. The humble beginnings of simple, natural repellents and physical pest controls grew into chemical and agricultural industries seeking out new and improved methods.
The primitive tools now had scientific reasoning behind their efficacy and identifying chemical formulations, moving them from the realms of natural extracts to synthesized pesticides, signaling the rise of the chemical pesticide revolution.