Lecture 17: How Insects Get Around
is the capacity of an insect to move from its birthplace to new areas. This movement
can be multidirectional or unidirectional. The consequences of the two are quite different.
Unidirectional dispersal occurs when individuals in a species, like monarchs, migrate on a
seasonal basis. They move in a focused manner in one direction. This makes it possible for
species to leave habitats when conditions become too harsh to survive. Multidirectional
migration occurs when individuals move away from their birth place. Dispersal is usually, but
not always confined to the adult stage in insects, although there are many examples of juvenile
stages that disperse. Dispersal is the normal part of the life cycle in many insects. Dispersal also
occurs in response to habitat modification caused by natural or unnatural (human) processes.
Dispersal is primarily an
process. Natural selection generally favors individuals that
move away from their parents. By moving away from their birth site individuals avoid the
potential competition between offspring and parents and among offspring that occurs close to the
birth site. Dispersal can also be caused by changes in the environmental quality of the birth site,
which may occur because of the numbers of individuals concentrated in that area.
Major dispersal events also occur on a
scale, although these are far less common. The
most obvious examples involve colonization of "new" habitats, like oceanic islands, areas wiped
clean by tsunami waves, or volcanoes, like Mt. St. Helens after it erupted.
Mechanisms of dispersal
There are two basic ways that insects disperse,
. Active movement
is done under the insect’s own muscular output, and consists of walking, running, jumping,
flying and swimming. Passive movement involves the insect taking advantage of another animal
or components of the physical environment to move, including.
(phoresy). Phoresy involves the use other organisms to move from place to
place, without actually harming it. For example hummingbirds carry mites from flower to flower
on their feathers. Booklice (Order Psocoptera) have been found clinging to the feathers of
migratory birds. Cockleburs have specially barbed seeds that cling to fur or clothing and end up
dislodged when the animal or person grooms.
. Aerial plankton consists of tiny animals, spores, tiny seeds and pollen,
which are passively carried by air movement from one place to another, often at high altitudes.
Tiny organisms are readily carried through the atmosphere by air currents because they are so
light they can be moved by simple air currents. Examples of organisms that become aerial
plankton include aphids, mites, thrips, spores, pollen, parasitoid wasps and orchid seeds.
Sampling from jets flying 15,000 ft above Louisiana yielded 210 families and 18 orders of