Biopesticides - Pesticides: Evaluation of Environmental Pollution - page 591

19.3 Bacteria Biopesticides
Biopesticides based on bacteria have been used to control plant diseases, nematodes,
insects, and weeds. Bacteria are present in all soils and are the most abundant microorgan-
isms in soil samples. Many spore forming and nonspore forming bacteria are known to
be effective against a wide spectrum of insects and diseases (Garczynski and Siegel 2007).
The most well-known and widely used of all biopesticides are insecticides based on
Bacillus thuringiensis , commonly referred to as “Bt.” During spore formation, Bt produces
insecticidal proteins (known as δ-endotoxins) that kill caterpillar pests, fly and mosquito
larvae, or beetles (depending on the subspecies and strain of Bt) that ingest them through
feeding in Bt-treated areas. The highly specific δ-endotoxins bind to and destroy the cel-
lular lining of the insect digestive tract, causing the insect to stop feeding and die. Bt has
been in continuous commercial use for over 50 years, a record not exceeded by any other
insecticide active ingredient. Bacillus sphaericus is another insecticidal bacterium that has
been used successfully to control certain mosquito species (Copping 2009).
Bt is registered for use against 90 different insects as Bt formulations listed in Table 19.4.
Bt can be used at any time, upto harvest, and is also used as a cleanup spray before taking
the produce to market. Bacillus thuringiensis israelensis (Btl) is another strain of BtI isolated
from Israel and extremely lethal to insects belonging to Diptera. This Btl strain will find
increasing use in future.
Other bacteria are used for the control of plant pathogens. Certain strains of Bacillus
subtilis , Bacillus pumilus , Pseudomonas spp., and Streptomyces spp. increase yield and prevent
plant diseases by outcompeting plant pathogens in the rhizosphere, producing antifungal
compounds, and by promoting plant and root growth.

19.4 Fungal Biopesticides
Different fungal biopesticides can be used to control plant diseases (caused by other fungi,
bacteria, or nematodes), as well as some insect pests and weeds. Fungi are a diverse group
of organisms and can be found in almost every environment on the Earth. Most have com-
plex lifecycles, and some are parasitic to various eukaryotes, including plants and insects.
Some species have proven useful as microbial biopesticides. However, because they are
living organisms, they do require specific environmental conditions to proliferate (Hibbett
et al. 2007; Humber 2007, 2008).

TABLE 19.4
Some Commercially Available Bt Formulations

Product Producer Trade name

Bacillus thuringiensis HD-1 1. Abbott Dipe** HG & 4L

2. Biochem products Bactospeine, Novabac

3. Sandoz Thuricide + HP, HPCL 32B & 16B

4. Upjohn SOK-BT

5. Agriculture & Nutrition Co. Bactur TH

6. Pennwalt, Holland N.V. Tribactur

**Copping 2009.