Integrated Environmental Biotechnology - Environmental Biotechnology: Theory and Application - page 252

each one producing a toxin active against a limited number of insect species; a
relationship which is continuously evolving. Already successful and on sale to
the public for domestic use, it continues to be a leading candidate for develop-
ment into an even more generally useful and effective biopesticide thus reducing
the dependence on chemical pesticides.
There are limitations associated with its use, all of which are being addressed
in active research. These include a limited range of insects susceptible to each
toxin, requiring dosing with multiple toxins, insufficient ingestion by the insect to
prove lethal in a usefully short time, stability of the toxin when sprayed on crops
and the development of resistance by the insect. The last stumbling block has
attracted particular interest (Roush, 1994; Gould,1994; Bohorova et al ., 2001).
The genes coding for the toxins have been isolated opening the way to their
alteration and introduction into suitable 'delivery systems', either bacterial or into
the plant itself, offering the plant inbuilt protection, thus attempting to overcome
the various limitations introduced above.
However, even without genetic engineering, Bacillus thuringiensis in its native
form, remains a widely used and successful product for commercial crop pro-
tection especially in 'organic' farming. In practice, the only major developments
found to be necessary, are improvements to the physical formulation of the crop
spray; dry, flowable formulations being an advance on the original wettable pow-
ders. Increasingly, nematodes especially Steinernema sp, are demonstrating great
potential as biological control agents applied as sprays. It is anticipated that
they will complement Bacillus thuringiensis in extending the spectrum of pests
controlled by 'environmentally friendly' means (Knight, R, Koppert Biological
Systems, personal communication).
There are other Bacillus species which have also been used effectively as
microbial insecticides. These are Bacillus sphaericus which produces a toxin
more potent but more specific than Bt, and Bacillus popillae which although not
producing a toxin, kills its host by weight of bacterial numbers. The latter is active
against the Japanese beetle, while the former is quite specific against mosquito lar-
vae. Both the mosquito larvae and Bacillus sphaericus abound in heavily polluted
water such as cesspits where the bacterium may exert control on the proliferation
of mosquitoes. A different approach to microbial pesticides has been to examine
the exploitation of Baculoviruses. The drive to use Baculoviruses as a means of
biological pest control has dominated its research for some time but also, these
viruses are recognised as vectors capable of expressing proteins of various ori-
gins at a very high level indeed and so have become enormously useful tools in
the major branches of biotechnology. Several 'wild type' (not been GM) Bac-
uloviruses are registered for use in the USA as insecticides, for example against
maize bollworm ( Heliothis zea SNPV), gypsy moth ( Lymantira dispar MNPV),
Douglas fir tussock moth ( Orgyia pseudotsugata MNPV) and in the UK against
pine sawfly ( Neodiprion sertifer MNPV) and pine beauty moth ( Panolis flam-
mea MNPV). Their use as natural insecticides is now worldwide (van Beek and
Davis, 2007) however, attempts to develop new, improved recombinant strains
have hit licensing problems (Inceoglu, Kamita and Hammock, 2006). Members of