Pollution and Pollution Control - Environmental Biotechnology: Theory and Application - page 82

dynamics, as examined in other sections of this topic, has a supportive role to
play in the overall management regime and, thus, there exists an environmental
dimension to its general use in this context.
Biological control methods can provide an effective way to mitigate pesticide
use and thus the risk represented to the environment and to public health. In
addition, unlike most insecticides, biocontrols are often highly target-specific
reducing the danger to other nonpest species. Against this, biological measures
typically demand much more intensive management and careful planning than
the simple application of chemical agents. Success is much more dependent on
a thorough understanding of the life-cycles of the organisms involved and can
often be much more of a long-term project. In addition, though high specificity is,
generally, a major advantage of biocontrol measures, under some circumstances,
if exactly the right measure is not put in place, it may also permit certain pests to
continue their harmful activities unabated. Considering the huge preponderance
of insect species in the world, a large number of which pose a threat to crops or
other commodities and thus represent an economic concern, it is small wonder
that the global insecticide market has been estimated at over $8 billion (US) per
year. Accordingly, much of the biological control currently in practice relates to
this group of animals.
Whole-organism approaches
There are three main ways in which whole-organism biological pest control may
be brought about. Classical biological control, as with the previously mentioned
Cane Toad, requires the importation of natural predators and is principally of use
when the pest in question is newly arrived in an area, often from another region
or country, having left these normal biological checks behind. Another form of
control involves conservation measures aimed at bolstering the predatory species,
which may be a valuable approach when natural enemies already exist within
the pest's range. However, the third method, augmentation, is more relevant to
the concepts of biotechnology and refers to means designed to bring about the
increase in effectiveness of natural enemies to a given pest. This may consist
simply of artificially rearing them in large numbers for timed release or may
extend to more intensive and sophisticated measures like the modification, either
by selective breeding or genetic manipulation, of the predator such that it is better
able to locate or attack the pest.
One attempt at augmentation which has been tried commercially is the pro-
duction of parasitic nematodes. Juvenile stages of the nematodes, which are then
only around 500 µ m long and 20 µ m wide, can enter soil insects and many carry
pathogenic bacteria in their guts. Once ingested, these bacteria pass out of the
nematode and multiply inside the insect, typically causing death within a few
days. Five species of nematode were made available on the US agricultural mar-
ket, namely Steinernema carpocapsae , S. riobravis , S. feltiae , Heterorhabditis
bacteriophora and H. megidis , each being effective against different groups of