Pest control, a process that maintains nuisance organisms below economic thresholds, is a complex ecological process often mediated by biodiversity. Agricultural intensification results in widespread losses of biodiversity, with important implications for pest control.

Types of Pests

Types of physical pest control methods include:
Insects, such as roaches, termites, mosquitoes, aphids, beetles, fleas, and caterpillars.
insect-like organisms, such as mites, ticks, and spiders.
microbial organisms, such as bacteria, fungi, nematodes, viruses, and mycoplasmas,
weeds, which are any plants growing where they arc not wanted.
mollusks, such as snails, slugs, and shipworms, and
vertebrates, such as rats, mice, other rodents, birds, fish, and snakes.

Most organisms are not pests. A species may be a pest in some situations and not in others. An organism should not be considered a pest until it is proven to be one. Categories of physical pest control methods include:
continuous pests that arc nearly always present and require regular control.
sporadic. migratory, or cyclical pests that require physical pest control methods occasionally or intermittently.potential pests that do not require control under normal conditions. but may require control in certain circumstances.

Recognizing the role of natural enemies of physical pest control methods insects

Pests are those species that attack some resource we human beings want to protect, and do it successfully enough to become either economically important or just a major annoyance. They are only a tiny fraction of the insect species around us. Even many of the species we would recognize as important pests only occasionally do significant damage to us or our resources.

Natural enemies play an important role in limiting the densities of potential pests. This has been demonstrated repeatedly when pesticides have devastated the natural enemies of potential pests. Insects which were previously of little economic importance often become damaging pests when released from the control of their natural enemies. Conversely, when a non-toxic method is found to control a key pest, the reduced use of pesticides and increased survival of natural enemies frequently reduces the numbers and damage of formerly important secondary pest species.

The three categories of natural enemies of insect pests are: predators, parasitoids, and pathogens.

Using biological control in the field

There are three primary physical methods of pest control of using biological control in the field:
1) conservation of existing natural enemies,
2) introducing new natural enemies and establishing a permanent population called “classical biological control
3) mass rearing and periodic release, either on a seasonal basis or inundatively.

1.Conservation of existing natural enemies
Reducing pesticide use: Most natural enemies are highly susceptible to pesticides, and pesticide use is a major limitation to their effectiveness in the field. The original idea that inspired integrated pest management (IPM) was to combine biological and chemical control by reducing pesticide use to the minimum required for economic production, and applying the required pesticides in a manner that is least disruptive to biological control agents. The need for pesticides can be reduced by use of resistant varieties, cultural methods that reduce pest abundance or damage, methods of manipulating pest mating or host-finding behavior, and, in some cases, physical pest control methods. Many IPM programs, however, have not been able to move beyond the first stage of developing sampling methods and economic thresholds for pesticide application.

Several USDA and EPA surveys of pesticide use in major crops indicate that the quantity of pesticides used in the U.S. has been stable or increasing since the late 1980’s. Although there are variations by crop and class of pesticide, the overall trend is that previous reductions, due to the substitution of economic thresholds for calendar spraying and the use of pesticides effective at lower dosages, are being reversed by increases in acreage treated and number of treatments per season. This stagnation of physical method of pest coontrol management has resulted in calls for IPM to be re-focused toward preventing pest problems by greater understanding of pest ecology, enhancing the ability of plants and animals to defend themselves against pests, and building populations of beneficial organisms. This strategy is sometimes called “biointensive IPM.

The effect of a pesticide on natural enemy populations depends on the physiological effect of the chemical and on how the pesticide is used how and when it is applied, for example. While insecticides and acaricides are most likely to be toxic to insect and mite natural enemies, herbicides and fungicides are sometimes toxic as well. A database has been compiled on the effects of pesticides on beneficial insects, spiders and mites .This database compares the toxicity of different pesticides and the “selectivity ratio” — the dose required to kill 50% of the target pest divided by the dose that kills 50% of the affected natural enemy species. Among the insecticides, synthetic pyrethroids are among the most toxic to beneficials, while Bacillus thuringiensis and insect growth regulators were among the least toxic. In general, systemic insecticides, which require consuming plant material for exposure, and insecticides that must be ingested for toxicity affect natural enemies much less than pests.

Pesticides may also have more subtle effects on the physiology of natural enemies than direct toxicity. Several fungicides, such as benomyl, thiophanate-methyl, and carbendazim, inhibit oviposition by predacious phytoseiid mites. Certain herbicides diquat and paraquat make the treated soil in vineyards repellent to predacious mites.

The impact of pesticides on natural enemies can be reduced by careful timing and placement of applications to minimize contact between the beneficial organism and the pesticide. Less persistent pesticides reduce contact, especially if used with knowledge of the biology of the natural enemy to avoid susceptible life stages. Spot applications in the areas of high pest density or treatment of alternating strips within a field may leave natural enemies in adjacent areas unaffected. The effectivenss of limiting the areas treated may depend on the mobility of the natural enemy and the pest.

Natural enemies are generally not active during the winter in the Northeast, and thus, unless they are re-released each year, must have a suitable environment for overwintering. Some parasitoids and pathogens overwinter in the bodies of their hosts which may then have overwintering requirements of their own), but others may pass the winter in crop residues, other vegetation, or in soil. A classic example is the overwintering of predacious mites in fruit orchards. Ground cover in these orchards provides shelter over the winter, refuge from pesticides used on the fruit trees, and a source of pollen and alternate prey.