Biomedical Engineering Reference
In-Depth Information
coding for proteases and chitinases, osmosensors, peptide transporters, carbon
and nitrogen repressors, toxin synthesis and regulators of signal transduction
pathways.
INTRODUCTION
About 700 species of fungi belonging to ~90 genera have been identifi ed
with an entomopathogenic habit (Roberts and Humber 1981). Fungi are
highly diverse spanning all the major taxonomic groups of fungi except
the higher Basidiomycetes. Some of these species cause disease epidemics
in insect populations leading to their mass knockdown, a phenomenon
technically described as 'epizootics'. Epizootics on insect pest populations
in standing crops are a respite to the farmers. Impressive natural
epizootics wiping out insect pests in crop fi elds have been extensively
reported. Emulating the natural phenomenon, artifi cial induction of
epizootics through formulations made from fungal propagules has been
attempted in numerous instances with reports of varied success. These
mycopesticides utilized in biological control of insect pests are few
compared to the number of fungi with entomogenous habit. Only fi ve
species of Ascomycetes with a predominantly mitosporic life cycle have
been registered as biopesticides (Butt et al. 2001). Fungi include
Beauveria
bassiana (
Bals.) Vuillemin
, Metarhizium anisopliae
(Metsch.) Sorokin
,
Nomuraea rileyi
(Farlow) Samson
, Verticillium lecanii
(Zimmermann)
Viegas and
Paecilomyces fumosoroseus
(Wize) A.H.S. Br. and G. Sm. Thus,
there is a large yet to be tapped potential of entomogenous fungi in insect
pest management. Realizing their potential is a priority to censor the
unwarranted loss world-wide of more than 30% of agricultural produce
to insect pests. In addition to fungi, bacteria, viruses, nematodes and
protozoa are among the list of insect pathogens. Bioinsecticides based
on the bacterium
Bacillus thuringiensis
Berliner 1915
(Bt) are a paradigm
of success of microbial biopesticides and also in transgenic approach for
development of insect resistant plants. Entomopathogenic fungi infect
insects through their cuticle and cause death of the insect by systemic
infection and parasitization unlike the bacterial entomopathogens like
Bt which kill through a toxin. Therefore, built up of resistance in insect
populations to fungal pathogens is diffi cult if not impossible unlike the
case of Bt where resistance to the transgenic plants with the
cry
toxin gene
of Bt has been recorded.
None of the fungal based biopesticides have yet captured a share
equal to Bt in the biopesticide market. The mycopesticides still remain to be
exploited on a large scale. The problems holding back their wide application
are: (a) inconsistency in fi eld performance—a feature common to all types of
microbial biopesticides due to sensitivity of the active living component to
