commonly used by the military: methyl bromide and aluminum phosphide. Methyl
bromide was used almost exclusively until the cheaper, safer, and more effective
aluminum phosphide was developed. Methyl bromide is very effective against stored
grain and enclosed subsistence items due to its good penetrating ability. Toxic
concentrations are usually produced quickly; however, death in insects is delayed for
several minutes. The gas diffuses into the respiratory system and finally affects the
nervous system. The compound is extremely toxic to man also; therefore, gas masks
are a necessity when applying it. Methyl bromide is a colorless, noncorrosive and
non-flammable gas having an odor similar to chloroform. It is usually applied by forcing
the gas into a grain storage area or confined storage areas. The chemical leaves no
harmful concentration of residue because, when aerated, the gas diffuses readily. The
other fumigant, aluminum phosphide, will be discussed in detail later in Section III of this
lesson.
4-10. BIOLOGICAL CONTROL
A third phase of insect control is a separate process from the previously
discussed phases. Biological control is relatively new and at present not widely used. It
appears to be an exciting development to be exploited in the future. Biological control
could also be termed "natural control," for it utilizes natural ecological principles.
Biological control involves predator-prey and parasite-host relationships.
a. Any specific environment with all of its naturally occurring species of life is
termed an ecosystem. Ecosystems all have an equilibrium position of populations with
minor fluctuations occurring from time to time either up or down from this position.
Many of these fluctuations are predator-prey or parasite-host oriented. If the number of
a given predator species is lower than normal for some reason, the prey species of the
relationship will eventually rise somewhat. The same holds true for parasite populations
and their hosts. Man is responsible many times for a decline in a predator species and
finally an increase in the prey species will become manifested, sometimes way out of
proportion to the natural fluctuation. It is easy to see why the "balance of nature" is a
critical matter and, frequently, changes, which man considers insignificant, can
mushroom into significant problems.
b. Many of the species of insects causing problems, as far as man is concerned,
were brought to an area within the US with no knowledge of the insect's arrival;
that is, on imported products. If the species survives and becomes established, it
will usually develop into a large population, often times infesting areas of concern in
man's environment. Most of the time when such an occurrence happens, the particular
exotic species has no natural enemy; the predator or parasite did not make the move to
the new environment; hence, the population of the new species will rise above the
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