Control methods Biological pest control :
parasitoid wasp (
Cotesia congregata) adult with pupal cocoons on its host, a tobacco hornworm
Manduca sexta (green background) Biological pest control is a method of controlling pests such as
insects and
mites by
using other organisms. It relies on
predation,
parasitism,
herbivory,
parasitody or other natural mechanisms, but typically also involves an active human management role. Classical biological control involves the introduction of natural enemies of the pest that are bred in the laboratory and released into the environment. An alternative approach is to augment the natural enemies that occur in a particular area by releasing more, either in small, repeated batches, or in a single large-scale release. Ideally, the released organism will breed and survive, and provide long-term control. Biological control can be an important component of an
integrated pest management programme. For example: mosquitoes are often controlled by putting
Bt Bacillus thuringiensis ssp.
israelensis, a bacterium that infects and kills mosquito larvae, in local water sources.
Cultural control exposes insect pests to predators such as
black-headed gulls. (adult and pupa shown), a serious pest of forests, can be monitored using
pheromone traps. Mechanical pest control is the use of hands-on techniques as well as simple equipment and devices, that provides a
protective barrier between
plants and
insects. This is referred to as
tillage and is one of the oldest methods of weed control as well as being useful for pest control; wireworms, the larvae of the
common click beetle, are very destructive pests of newly ploughed grassland, and repeated cultivation exposes them to the birds and other predators that feed on them. Crop rotation can help to control pests by depriving them of their
host plants. It is a major tactic in the control of
corn rootworm, and has reduced early season incidence of
Colorado potato beetle by as much as 95%.
Trap cropping A
trap crop is a crop of a plant that attracts pests, diverting them from nearby crops. Pests aggregated on the trap crop can be more easily controlled using pesticides or other methods. However, trap-cropping, on its own, has often failed to cost effectively reduce pest densities on large commercial scales, without the use of pesticides, possibly due to the pests' ability to disperse back into the main field. The efficacy of chemical pesticides tends to diminish over time. This is because any organism that manages to survive the initial application will pass on its genes to its offspring and a
resistant strain will be developed. In this way, some of the most serious pests have developed resistance and are no longer killed by pesticides that used to kill their ancestors. This necessitates higher concentrations of chemical, more frequent applications and a movement to more expensive formulations. Pesticides are intended to kill pests, but many have detrimental effects on non-target species; of particular concern is the
damage done to
honey-bees, solitary bees and other
pollinating insects and in this regard, the time of day when the spray is applied can be important. Some pesticides may cause
cancer and other health problems in humans, as well as being harmful to wildlife. There can be acute effects immediately after exposure or chronic effects after continuous low-level, or occasional exposure.
Maximum residue limits for pesticides in foodstuffs and animal feed are set by many nations.
Genetics Using crops with
inheritable resistance to pests is referred to as host-plant resistance and reduces the need for pesticide use. These crops can harm or even kill pests, repel feeding, prevent colonization, or tolerate the presence of a pest without significantly impacting yield. Resistance can also occur through
genetic engineering to have traits with resistance to insects, such as with
Bt corn, or papaya resistance to ringspot virus. When farmers are purchasing seed, variety information often includes resistance to selected pests in addition to other traits.
Hunting s, a varmint species that was known to damage crops.
Overhunting resulted in complete extinction of the species.Pest control can also be achieved via
culling the pest animals — generally small- to medium-sized
wild or
feral mammals or birds that inhabit the
ecological niches near
farms,
pastures or other
human settlements — by employing human
hunters or
trappers to physically track down, kill and remove them from the area. The culled animals, known as
vermin, may be targeted because they are deemed harmful to agricultural crops, livestock or facilities; serve as
hosts or
vectors that
transmit pathogens
across species or
to humans; or for
population control as a mean of
protecting other
vulnerable species and
ecosystems. Pest control via hunting, like all forms of harvest, has imposed an artificial
selective pressure on the organisms being targeted. While varmint hunting is potentially selecting for desired
behavioural and
demographic changes (e.g. animals avoiding human populated areas, crops and livestock), it can also result in unpredicted outcomes such as the targeted animal
adapting for
faster reproductive cycles.
Forestry Forest pests present a significant problem because it is not easy to access the canopy and monitor pest populations. In addition, forestry pests such as bark beetles, kept under control by natural enemies in their native range, may be transported large distances in cut timber to places where they have no natural predators, enabling them to cause extensive economic damage.
Pheromone traps have been used to monitor pest populations in the canopy. These release volatile chemicals that attract males. Pheromone traps can detect the arrival of pests or alert foresters to outbreaks. For example, the
spruce budworm, a destructive pest of
spruce and
balsam fir, has been monitored using pheromone traps in Canadian forests for several decades. In some regions, such as New Brunswick, areas of forest are sprayed with pesticide to control the budworm population and prevent the damage caused during outbreaks. ==In homes and cities==