Pollution and Pollution Control - Environmental Biotechnology: Theory and Application - page 83

Semiochemicals are natural messenger substances which influence growth,
development or behaviour in numerous plant and animal species and include
the group known as pheromones, a number of which are responsible for sexual
attraction in many insects. This has been successfully applied to control various
forms of insect pests, either directly to divert them from crops and trap them, or
indirectly to trap their natural enemies in large numbers for introduction into the
fields for defence.
For example, crops worldwide suffer severe damage as a result of a number of
pentatomid insects, amongst which are several of the common brown stink bugs
of North America ( Euschistus spp.). They arrive late in the growing season and
often cause major harm before detection. A major part of bio-control involves
obtaining a thorough understanding of their migration patterns and to help achieve
it in this case, a pheromone, methyl 2E,4Z-decadienoate, has been produced
commercially to aid trapping. The early success of this is being developed to
extend its scope in three main directions. Firstly, to capture and eliminate the
pests themselves, secondly, to harvest predatory stink bugs for bio-augmentative
control programmes and thirdly, to identify more pheromones to widen the num-
ber of phytophagous stink bug species which can be countered in this way.
As something of an aside, one interesting and somewhat unusual use has
been proposed for this technology. The Siberian moth Dendrolimus superans is
a vigorous defoliating pest of northern Asian coniferous forests and, though it
does not presently occur in North America, its arrival is much feared. In an
attempt to provide a first line of defence against this potential threat to native
woodlands, it has been suggested that a blend of Z5,E7-dodecadienal and Z5,E7-
dodecadienol, which has been shown to act as a powerful sex attractant for male
Siberian moths, be deployed at US ports of entry.
However, as illustrated by the case of another pentatomid, Nezara viridula ,
the southern green stink bug, the use of this approach to biological control is
not universally applicable. These insects are major agricultural pests affecting a
variety of field crops, vegetables, fruits and nuts. While it has been known for
some time that sexually mature males produce an attractant pheromone, the active
ingredients of which have been identified, early attempts to use this knowledge to
exclude them from crops have been of only limited effectiveness. As a result, an
alternative method of Nezara control has been suggested involving the genetic
engineering of its gut symbionts to produce a reduced tolerance of environmental
stress. Preliminary work at the Agricultural Research Center, Beltsville, US has
isolated and cultured in vitro a gram-negative bacterium from the mid-gut of
the pest insect, which appears to be a specific symbiont and has been putatively
identified as a species of Yokenella . This kind of application of transgenic tech-
nology may increasingly be the future of biological control for species which do
not respond favourably to pheromone trapping.
Not all approaches to bio-control truly qualify as environmental biotechnolo-
gies, at least not within the frame of reference used in this topic. However, where