06-12-2012, 12:44 PM
BIOPESTICIDE PRODUCTION
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Introduction
For the past five decades humans have almost been wholly dependent upon
synthetic/organic insecticides. Agriculture has been revolutionized by the use of
chemicals for crop protection, which started in the last 1800 with the introduction of
arsenical insecticides and Bordeau mixtures as grape fungicide, and progressing to the
very sophisticated compounds available now. Today, fewer people produce more food
at less cost than ever before. The effect of synthetic chemicals on agriculture has been
so dramatic that conventional agriculture now means using chemicals. Despite the immense benefits, they are used in increasing quantities designed to kill living
organisms. However, the very properties that give these chemicals useful-long residual
action and high toxicity for a wide spectrum of organisms, have given rise to serious
environmental problems. Furthermore, the emergence and spread of increasing
resistance in many vector species, concerns over environmental pollution, and the ever
increasing cost of the new chemical insecticides, make it apparent that vector and pest
control can no longer be safely based upon the use of chemicals alone.
Biological Control
Of the nearly one million known species of insects, about 15,000 species are considered
pests and about 300 require some form of control. Fortunately, most insect pests have
pathogenic microorganisms associated with them.
Entomopathogens have been suggested as controlling agents of insect pests for over a
century, and belong to species of fungi, viruses, bacteria, and protozoa.
Insect pathology per se probably had its beginning in the nineteenth century under the
stimulus of Bassi and Pasteur. A significant contribution to microbial control of insects
was made by Mechnikoff in 1879 and Krassilnikow in 1888, who were the first to
document that an entomopathogen, a muscordine fungus, Metarrhizium anisopliae
could be mass produced and applied as a microbial insecticide to control the grain and
the sugar beet pests. The control of insect pests with bacteria was probably first
attempted by d'Herelle in 1914, approximately 35 years after Pasteur's description of
silkworm diseases. Apparently the control was not consistent and therefore interest in
bacterial pathogens was curtailed.
Microbial Insecticides
Microbial insect control utilizes pathogenic microorganisms isolated from diseased
insects during naturally occurring epidemics. Typically, such epidemics only occur
when pest population densities are high and usually after appreciable damage have been
done to crops. Over 400 species of fungi and more than 90 species of bacteria which
infect insects have been described including Bacillus thuringiensis, varieties of which
are manufactured and sold throughout the world primarily for the control of caterpillar
pests and more recently mosquitoes and black flies.
Among fungal pesticides, five have been introduced since 1979, and three in 1981.
Many countries with centrally planned economies have been using fungal pesticides
successfully for many years. Sofar, more than 40,000 species of Bacillus thuringiensis
have been isolated and identified as belonging to 39 serotypes. These organisms are
active against either Lepidoptera, or Diptera or Coleoptera.
Bacillus thuringiensis
Maximizing the potential for successfully developing and deploying a biocontrol
product begins with a carefully crafted microbial screening procedure, proceeds with
developing mass production protocols that optimize product quantity and quality, and
ends with devising a product formulation that preserves shelf-life, aids product delivery,
and enhances bioactivity. Microbial selection procedures that require prospective
biocontrol agents to possess both efficacy and amenability to production in liquid
culture increase the likelihood of selecting agents with enhanced commercial
development potential. Scale-up of biomass production procedures must optimize
product quantity without compromise of product efficacy or amenability to stabilization
and formulation. Formulation of Bacillus spp. for use against plant pathogens is an
enormous topic in general terms but limited in published specifics regarding
formulations used in commercially available products. Types of formulations include
dry products such as wettable powders, dusts, and granules, and liquid products
including cell suspensions in water, oils, and emulsions.