Pollution and Pollution Control 83insects. Despite much research and development effort, the results were largely
unpredictable, with success against many of the target species, like wireworms
and root maggots, proving elusive. One avenue of potential application for this
technology may, however, lie in the control of cockroaches, which have been
found to be the most vulnerable species to augmented nematode attack (Georgis
1996). However, there still remain some technical problems to overcome in terms
of ensuring a level of parasite delivery before widespread uptake is likely. Aug-
mentation is, obviously, a highly interventionist approach and relies on a regime
of continual management to ensure its effectiveness.
There is also a role for the engineered application of biologically derived chem-
icals in this sector. One example of this is the growing interest inAzadirachta
indica, the neem, a plant which is found naturally in over 50 countries around
the world including India, where its medicinal and agricultural value has been
known for centuries. The compound azadirachtin has been identified and isolated
from the plant and it has been shown to have broad spectrum insecticidal proper-
ties, acting to disturb larval moults and preventing metamorphosis to the imago.
Additionally, it also seems to repel many leaf-eating species, and trials involving
the direct foliar application of azadirachtin has shown it to be an effective way
of protecting crop plants (Georgis 1996). This duality of action makes it a par-
ticularly appealing prospect for wide-scale applications, if suitable methods for
its production can be made commercially viable.
Semiochemical agents
However, perhaps one of the best examples of the use of such biological technolo-
gies in pest control is the development of isolated or synthesised semiochemical
agents.
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 (Euschistusspp.). They arrive late in the growing season
and often cause major harm before detection. A major part of biocontrol 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 bioaugmentative control