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Why do we study insects?
- Insects spread disease. Malaria, which is a disease carried by
Anopheles
mosquitoes, kills over 1.5 million people in Africa every year, most of them
children. Simulium
flies in West Africa spread a disease to people called onchocerciasis which
makes them go blind. Tsetse flies (Glossina spp.) infect people with
sleeping sickness which left untreated can result in death. If you swallow a
flea in your house you run the risk of being infected with tapeworm. There
are many other diseases transmitted between humans and between humans and
animals by insects and in order to control the spread of these diseases we
need to study the vector insects that spread them.
- Insects eat our crops. Millions of rand are spent annually in South
Africa controlling insects that eat our crops. Insecticides are the one way
of controlling pests but they have undesirable side-effects on our health
and the environment so the preferred method is biological control where
entomologists find beneficial parasitic and predatory insects such as
parasitic wasps and ladybird beetles that can be released to control the
pests.
- Insects eat our stored food. The large grain borer, Prostephanus
truncatus, has recently spread through subsaharan Africa and is causing
value and weight losses to stored maize approaching 60%. There are many
other stored product pests that can cause serious food losses and some of
these you will have encountered in your kitchen if dry foods are left
unprotected in your cupboard for too long.
- Insects maim and kill our livestock. About 10 million km2
of Africa is affected by animal trypanosomiasis (nagana), spread by Tsetse
flies (Glossina
spp.), which seriously limits farming efforts. For cattle to thrive in these
areas, they need to be given drugs and/or the tsetse need to be controlled.
The sheep blowfly Lucilia cuprina causes about a R20 million loss to
the South African wool and mutton industries per year. Ticks (which are
arachnids not insects) spread many livestock diseases and farmers in South
Africa spend millions annually on pesticides to control them.
- Insects provide us with food. Honeybees (Apis mellifera)
provide us with honey. Many people in Africa feed on insects directly:
grasshoppers, flying termites and ants, mopane caterpillars are common food
items. For a review of the insects eaten by people in Africa, see
van Huis (1996).
- Insects recycle waste.
Dung beetles bury dung and prevent it from building up and acting as a
breeding site for flies. Flies and beetles breed in dead animals and consume
the flesh and skin resulting in nutrient recycling and cleaning up of the
landscape. Termites eat dead plant material, so the nutrients in the plants
are returned to the soil. There are numerous other insect groups that make
their living on decaying organic matter.
- Insects pollinate flowers. The deciduous and citrus fruit
industries depend upon honeybees to pollinate flowers on fruit trees and
without this pollination we would have no fruit. Bees, beetles and other
insects are also essential in the pollination of most wild flowers.
- Insects provide food to other animals. Birds such as robins,
white-eyes and warblers feed mainly on insects. Antbears and pangolins have
become specialists in feeding on ants and termites.
- Insects control weeds. Leaf, wood and seed-feeding insects prevent
particular plant species from taking over the land surface and becoming
weeds. A plant often becomes a weed when it is introduced to a foreign
country without the insects that feed on it. Entomologists return to the
country of origin and find these insects and after checking that the insects
do not feed on beneficial plants, they are introduced to control the weed.
See also: Bugs: the
good, the bad and the ugly (USDA Systematics Laboratory)
References
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