The Rural Voice, 1988-07, Page 20worms are free-living in the soil and
enter the insects through natural
openings. Once inside, they mature,
multiply, and reproduce more
"immatures" which leave the insect
for the soil again. The bacterial
infection caused by the nematodes
kills the insect. The nematodes have
shown some effectiveness against
cutworms in lab and greenhouse
studies, Dr. Morris says, but have not
yet been effective in field trials.
An entirely different form of bio-
logical control attempts to use a pest's
own chemicals to kill it or to disrupt
the life cycle enough that the popula-
tion will fall. The chemicals, princi-
pally hormones and pheromones, have
been synthesized artifically for some
time and were thought to be good can-
didates for controlling insects. They
were completely specific for the target
species and ineffective against any-
thing else. But they have not proven
very practical. Pheromones are now
used almost exclusively as monitoring
agents, and the big hormonal hope of
the 1960s, juvenile hormone, is pretty
well finished as a control agent,
according to Dr. Robert Bodnaryk, an
insect biochemist at the Agriculture
Canada Research Station in Winnipeg.
Dr. Bodnaryk says that an inter-
esting prospect for hormonal control
involves prothoracic tropic hormone
(PTTH), which is made in the insect
brain and affects the production of
other hormones responsible for as-
pects of moulting. New technological
developments in Japan have meant
that enough PTTH has been isolated to
allow the structure to be worked out.
It is hoped that through genetic engi-
neering plants can be convinced to
make PTTH, so that when an insect
eats the leaves it will get a dose of
hormone and die.
This manipulation of plants, either
by breeding resistant varieties or by
using genetic engineering, is enjoying
a high profile in biological control.
Resistant plants are not new. The
wheat stem sawfiy, for example, was
controlled in the early part of this
century by breeding a wheat variety
that had a stem unsuitable for the
insect. What is new is the range of
possibilities brought to the field by
genetic engineering. Now, by using
gene splicing and viral vectoring
agents, characteristics from one group
of plants can theoretically be inserted
into another unrelated group. Even
non -plant material can be looked upon
as potential plant material. For ex-
ample, a great effort is being made to
get the genes that produce the Bt toxin
inserted into plants so that the plant
itself will produce the toxin and
protect itself from insect damage.
Some of the methods of plant
protection being considered by genetic
engineers are nearly unbelievable. A
British study is looking at whether Bt
toxin genes can be inserted into an
insect virus in order to make it more
toxic to insects. Another British study
is looking at whether a bacterium can
be used to carry a fungicide to plant
roots. An interesting aspect of this
study is that the bacterium will only
produce the fungicide when the plant
is injured and most vulnerable to
fungal infection. The bacteria con-
gregate around the wounds and their
combined numbers cause the produc-
tion of the chemical. When the wound
heals up, the bacteria disperse and stop
producing the fungicide.
It is evident from this brief outline
of methods and ideas that biological
control is a vibrant and thriving field.
Yet, despite its advantages, biological
control is not being used at the farm
level. Biological control systems or
disease sprays have not been devel-
oped for the major agricultural pests
in Canada.
The reasons this is so are complex
and diverse. Dr. Laing says there are
three primary explanations. In the
first place, it is difficult to make any
money from biological control, so
companies do not get involved. The
problem for industry is that when a
biological control method is perfected,
it enters the public domain. Industry
cannot patent the control organism or
govern it in any other way to get a
return on its investment. Dr. Laing
says that it is the nature of biological
control to be self-perpetuating and a
public enterprise. This is both its
beauty and its downfall, for without
industrial involvement there is no
promotion of the product.
A second factor is that chemicals
are largely successful, cheap, and
effective. In spite of the long-term
problems with chemicals, they have
done their job, Dr. Laing says, so there
has been no incentive to look for new
techniques.
The third factor relates to the first.
Governments and universities are the
main source of funds for biological
control. There are only a few ento-
mologists working in the field in
Canada, and governments are reluctant
to increase funding to such a low -
profile area.
Dr. Morris also points to econo-
mics as the reason why microbial
insecticides will never completely
replace chemicals in agriculture. He
says they are too specific for their
target pests, making commercial
production unprofitable. The cost of
application is higher too. Dr. Morris
thinks it will be a while before micro-
bial insecticides will compete with
chemicals even in terms of propor-
tional use (i.e., a 50-50 split) but is
optimistic that the problems will be
worked out.
On top of all these economic
problems, there is the problem of
public attitudes to the compounds and
methods used. Despite the general
desire for safer methods of pest
control, Dr. Laing says the public has
a funny perception of biological
control, especially when it comes to
pathogens. People hear of a virus
being sprayed onto cabbage and panic,
even though they have been eating
that same virus (which is on the leaves
from natural infections) for years.
Dr. Laing speaks with some anger
about an editorial in the Windsor Star
recently (March 14, 1988) that
criticizes the release of the parasite
Trichogramma. The editorial worries
that "history is full of examples of
shortsighted experiments with nature
that have backfired." It then goes on
to use as examples the release of
starlings to North America and rabbits
in Australia.
This editorial, Dr. Laing says,
represents the public's general lack of
understanding about biological con-
trol. The writers failed to realize that
Trichogramma is not an exotic para-
site, but is native to Canada. Even if it
had been an imported parasite, Dr.
Laing says, insect parasites are biolo-
gically tuned in to their hosts, and will
live only in the target species or one
closely related. He stresses that insect
18 THE RURAL VOICE