frequent applications and a movement to more expensive formulations. Pesticides are formulated 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. The widely used neonicotinoids have been banned on flowering crops in some countries because of their effects on bees. 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. Hunting 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