An organism becomes a pest only when we perceive a conflict between ourselves and the normal activities of the organism. This conflict can develop in many ways.
For example insects are considered pests if they :
- feed on us or our livestock, (e.g. biting flies)
- transmit pathogens to us or our livestock ( e.g. mosquitoes and malaria)
- poisons us (e.g. hornets)
- feed on crops (e.g. locusts)
- it transmit pathogens to crops (e.g. aphids)
- feed on stored products (e.g. grain moths)
- damage renewable resources (e.g. forest defoliating caterpillars)
- damage wooded structures (e.g. termites)
- produce a smelly mess (e.g. many short lived mayflies that have a mass emergence)
- regularly invade houses (e.g. earwigs) or
- are simply annoying (e.g. house crickets)
Plants are considered pests if they:
- displace other desirable plants (e.g. purple loosestrife)
- serve as a host for a pathogen or pest of a desirable plant (e.g. wild mustard for the cabbage butterfly)
- have spines, burs or toxic properties (e.g. thistle, burdock, and poison ivy) or
- are simply growing in the wrong place (e.g. roadside weeds).
Origin of new pests
The majority of new pest situations are largely the result of modification of the environment, transportation, and changes in human attitudes.
Modifying the environment can eliminate the original host species of an organism resulting to a shift to a new host species, often a species introduced during the process of modification (e.g. introduction of cucumbers to North America provided a leaf beetle with a new host).
Modern transportation can easily introduce pest species from one part of the world to another (e.g. cabbage butterfly brought to North America from Europe). Desire for blemish-free produce has elevated many previously unimportant species to pest status.
Methods to control pest species
Chemical control. Natural or synthetic pesticides can be used to reduce the population of a pest species, at least for a time. Most are effective, act within a short time, can work against large populations, and readily available, when needed. On the other hand, pesticides have many drawbacks. They can be very hazardous to apply, difficult to store safely, leave long term residues, affect non-target organisms, accumulate in the food web, and lead to the evolution of pesticide resistant varieties of target organisms. Despite all of these concerns, modern levels of agricultural production would be impossible without use of pesticides.
Genetic Control. Breeding resistant host species is a time-honored method of control, particularly for pathogenic bacteria, fungi, and viruses (e.g. silkworm disease, potato blight, and many leaf mosaic viruses). Releasing sterilizing males into the population has had at least one spectacular success with the eradication of the screwworm, a serious pest of cattle that sapped their strength and damaged the hides. Genetic engineering of resistance is a new method that, in principle, is the same as breeding resistance but has the potential of being more precise and gives greater scope of raw material (e.g. transferring gene for production of natural pesticide from one species to another.
Ecological Control. Adjusting the environment so that pest species are disadvantages is another tried and true method. By eliminating refuges or over wintering sites, by adjusting planting time, by avoiding large mass collections of host species, by shifting fields or pastures, by removing alternate host species, by providing more attractive alternate hosts that are later destroyed, by altering water management practices, and by appropriate tillage, are among the many methods by which pest populations may be kept below problem levels.
Biological Control. Although introduction of predators has had spectacular success, this technique far more often has only limited effect or is judged a failure. Examples include the Australian ladybird beetle that saved the citrus industry in California by controlling an accidentally imported scale insect, the cactoblastis moth that eliminated the introduced prickly pear cactus from the range land of Australia.
Some of the advantages of biological control include :
- potential to target one pest
- non toxic
- self perpetuating, and
- lower possibility that target species will develop resistance
Some of the disadvantages of biological control include:
- the need to have a comprehensive understanding of the biology of both the control species and the target species
- relatively slow acting
- lack of appropriate control species
- high initial costs
- low rate of success
Integrated Pest Management
Philosophy. Integrated Pest Management (IPM) is an attempt to blend more recent chemical, genetic, ecological, and biological techniques into a single system to suppress pest populations while minimizing costs and environmental damage. In other words, IPM attempts the impossible task of satisfying everyone.
There are three phases to the program, pesticide management, ecological management, and biological control. Pesticide management phase requires determining the appropriate pesticide schedule to reduce damage at the lowest cost. In other words, using exactly as much as needed and no more(e.g. not applying pesticides during periods when host is not susceptible to pest species).
Ecological management stage involves learning enough about the interaction between the pest and the host to alter rearing or planting practices to minimize loses (e.g. later planting dates may avoid most infestation). Biological control phase is the most difficult and involves further altering of practices to increase natural populations of predators and parasites, importing and establishing control agents where appropriate, and in the future, genetic engineering of new control agents.