Management
Last Review/Updated: May 31, 2002
Management of Invertebrates
People have tried to "manage" invertebrates by attempting to reduce or control numbers of pests. Pests are those organisms that cause disease (including parasites), which compete with people for food, or cause discomfort. Although people have tried to eliminate many of these species, they have had little success.
People have tried to control pests by the use of chemical poisons (pesticides). In the past, chemicals have been used on pests with little regard as to how they might affect other non-pest organisms. For example, when lakes and ponds are sprayed with pesticide to kill mosquito larvae, the pesticide may kill other invertebrates, like freshwater shrimp, water beetles, and dragonfly nymphs. These animals are important in lake or pond food chains. Their removal affects the survival of other members of the chain. Fish, frogs, and ducks are some of the animals that depend upon aquatic invertebrates for food. When someone says "fishing used to be good here," the lack of fish may indicate that a particular lake or pond has been sprayed with pesticide.
Similarly, pesticides sprayed on crops and forests to reduce pest species may also kill invertebrates that are important in field and forest food chains. Populations of vertebrate wildlife, such as songbirds, hawks, mice and shrews, may be reduced.
When a pesticide is used repeatedly, the pest species may develop a resistance to it. People then develop more powerful pesticides to kill the resistant pests. These in turn cause a development of populations resistant to the new pesticides. It seems that man cannot stay ahead of the pests. Although the use of pesticide has greatly increased over the last decades, the damage caused by pests is about the same as it was before the use of chemical pesticides.
Many pesticides remain in soil or water long after they are used or needed. Invertebrates, resistant to the pesticide, take it in, and when they are eaten, pass the pesticide along. If an animal eats enough invertebrates containing a pesticide, it may eventually die or be unable to reproduce. The peregrine falcon almost became extinct in Alberta because of use of the pesticide DDT. The presence of this pesticide in the falcon's body caused the eggs of the bird to be infertile or thin-shelled. These thin-shelled eggs break before the young could hatch. DDT was banned in Alberta when it was discovered that the pesticide was causing the disappearance of peregrine falcons and other birds of prey. Introduction programs over the years have re-established the peregrine population in the province.
Chemical pesticides are not the best solution to pest control. Their use has created many additional problems. Today, scientists are developing methods of control that are not as dangerous or as damaging to the environment. Some of these methods include the use of natural predators, specific pest diseases, and chemicals that affect only some pest species. Combinations of these methods will probably be the most effective.
