human history, as silk-driven trade established relationships between China and the rest of
the world.
Fly larvae (maggots) were formerly used to treat wounds to prevent or stop gangrene, as they
would only consume dead flesh. This treatment is finding modern usage in some hospitals.
Adult insects such as crickets, and insect larvae of various kinds, are also commonly used as
fishing bait.
In some parts of the world, insects are used for human food, while being a taboo in other
places. Some people support this idea to provide a source of protein in human nutrition.
Insects also have a role in controlling insect pests, as we will see in the next section.
Controlling Insect Pests
Insects commonly regarded as pests include those that are parasitic (mosquitoes, lice, bed
bugs), transmit diseases (mosquitoes, flies), damage structures (termites), or destroy agri-
cultural products (locusts, weevils). Many entomologists are involved in various forms of
pest control, often using insecticides, but more and more relying on methods of biocontrol.
Biological control of pests in agriculture is a method of controlling pests that relies on
predation, parasitism, herbivory, or other natural mechanisms. Insect predators, such as
lady beetles and lacewings, are mainly free-living species that consume a large number of
prey during their lifetime.
Parasitoidsare species whose immature stage develops on or within a single insect host,
ultimately killing the host. Most have a very narrow host range. Many species of wasps
and some flies are parasitoids. Both of these types of predators and parasitoids are used to
control insect pests. Pathogens are disease-causing organisms including bacteria, fungi, and
viruses, which kill or debilitate their host and are specific to certain insect groups.
Most of the insecticides now applied are long-lasting synthetic compounds that affect the
nervous system of insects on contact. Agricultural pesticides prevent a monetary loss of
about $9 billion each year in the U.S. These benefits, however, must be weighed against
the costs to society of using pesticides, which include human poisonings, fish kills, honeybee
poisonings, and the contamination of livestock products.
Lesson Summary
- InsectsarethemostdiversegroupofanimalsonEarth; theyarefoundinnearlyallenvi-
ronments. They have segmented bodies with an exoskeleton; the nervous, respiratory,
and circulatory systems are fairly simple. Insects are the only invertebrates to have
developed flight. Insects have very sensitive and/or specialized organs of perception,
including visual, chemical, heat-sensitive, and auditory. Some insects, like termites,
ants, and many bees and wasps, are social and live together in large well-organized