Role of Entomopathogenic fungi in insect pest management Host range Mode of action and host reaction Symptoms Commercial produ...
Role of
Entomopathogenic fungi in insect pest management
- Host range
- Mode of action and host reaction
- Symptoms
- Commercial production of EPF
- Use of EPF in Pest Management
A group
of fungi that kill an insect by attacking and infecting its insect host is
called entomopathogenic fungi.
Entomopathogenic
fungi is identified as a promising biocontrol agent in the regulation of insect
pest population without harming the non-target insects. Over 800 species of
entomopathogenic fungi and 1000 species of protozoa pathogenic have been
described and identified. Most research on entomopathogenic fungi has been
aimed at developing them as inundative biological control agents of insects,
mites and ticks, despite the great potential for use in conservation and
classical biocontrol strategies.
In 1980s,
the first insect pathogenic studies were carried out and their focus was to
find the methods of disease management of the silkworm. Bassi in 1835, first
time formulated the germ theory by the use of white muscardine fungus on the
silkworm that was then named in his honor as Beauveria bassiana.
Gilbert and Gill (2010) described that this silkworm disease gave the idea of
using insect infecting fungi for the control of insect pest management.
Fungal
diseases are common in Lepidoptera (particularly larvae), Homoptera
(particularly aphids, whiteflies, cicadas, scale insects), Hymenoptera (bees),
Coleoptera (beetles) and Diptera (flies and mosquitoes).
The mode
of action of insect pathogenic fungi varies and kills the insect by different
ways such as causing starvation to toxin production. These insect pathogenic
fungi produce many toxins and extracellular enzymes such as proteases and
chitinases which aid penetration of the host physical defenses. Cuticle is the
main hurdle to infection in insects as it is the main path of fungus
penetration. Hence, it needs some physical or enzymatic means to pierce the
hard cuticle.
The
infective unit in most fungi is a spore, usually a conidium. In many cases, the
conidia are adhesive to the cuticle, or secrete adhesive mucus as the conidium
swells during pregermination. In favourable conditions, the conidium,
germinates into a short germ tube which gives out small swellings called
appressoria. The appressorium attaches itself to the cuticle and sends out an
infection peg which provides a firm attachment that the fungus needs to
physically force its way into the host. The hyphae then penetrate the layers of
the integument by enzymatic dissolution of chitin and protein, ramify first in
the cuticle and then reach the haemocoel and internal organs. The invasion by
the fungal mycelium continues until the insect is virtually filled with the
fungus and becomes quite firm to touch. Conidiophores are then produced which
erupt through the cuticle and produce spores on the outside of the insect,
infecting nearby healthy insects also. Death of the host is by obliteration
(choking) of the tissues and also by the toxins produced by the fungus.
Loss of
appetite and an attempt to climb higher up are the early symptoms of the fungal
disease. They are followed by decreased irritability, general or partial
paralysis, discoloured patches on integument and increased acidity in the blood.
The body hardens and the insect in upright on its legs at the time of death.
Death occurs within a week or even within 24 hours. The causes of death may be
as follows: hyphae may force apart muscles, blood cells may stop circulating
due to increased hyphae, blockage of the gut and by the toxin produced by the
fungus.
Most of
the commercially produced fungi are species of Beauveria, Metarhizium and Lecanicillium that
are relatively easy to mass produce. Attention has focused predominantly on the
technical aspects of biopesticide development, such as mass production and
formulation, and the selection of strains with rapid kill (Shahid et
al., 2012).
Production
requirements include reasonable cost, long-term stability, and, most
importantly, consistent efficacy under field conditions. The prevalent methods
involve the production of diaspores (dispersal units) by induction of aerial
conidiation on solid growth media, production of blastospores by yeast-like
growth in liquid media or growth of hyphal biomass in liquid or solid media
(Faria and Wraight, 2007).
EPF are a
major component of integrated pest management techniques as biological control
agents against insect pests and other arthropods and are an integral part of
myco-insecticides in horticulture, forestry and agriculture.
Some of
the commonly used EPF are as follows.
- Beauveria bassiana – These enter the host insects body through food
or in contact with the host cuticle and reproduce inside the insect body.
It produces toxins namely beauvericin, bassianocide etc. inside the host
body causes paralysis of the host insects and ultimately kills the insects
within four or five days. They are used particularly to control sucking
pests and caterpillars infesting crop plants. These fungi are used to
control the caterpillars of yellow stem borer and leaf folder of rice,
white grub of groundnut, sugarcane pyrilla, coconut rhinoceros beetle, caterpillars
of pulses, tomato and cotton, diamond back moth, leaf eating caterpillars
of tobacco and sunflower etc.
- Lecanicelium lecanii – This beneficial fungus is mainly used to
control whiteflies, aphids, thrips, brown plant hopper, scale insects,
mealy bugs and other sucking insect pests of crop plants.
- Metarrhizium anisopliae – This pathogenic fungus is used to control
mainly coconut rhinoceros beetle, groundnut cut worm, rice brown plant
hopper, diamond back moth and early shoot borer, top shoot borer and
internode borer of sugarcane.
- Nomuraea rileyi – It is used to control pod borers, cut worms, cabbage
borers etc.
- Hirsutella thompsonii – These fungi are used to control different hoppers and
bug pests, whiteflies, red mites etc.
- Paecelomyces fumosoroseus – This fungus is used to control yellow and red
mite, whiteflies etc.
References
- Gilbert, L.I. and S.S. Gill.
2010. Insect control: biological and synthetic agents. Academic Press,
Elsevier, London, pp. 1-5
- Faria, M.R. and S.P. Wraight.
2007. Mycoinsecticides and mycoacaricides: A comprehensive list with
worldwide coverage and international classification of formulation
types. Biological Control, 43: 237-256
- Shahid, A.A., A.Q. Rao, A.
Bakhsh and T. Husnain. 2012. Entomopathogenic fungi as biological
controllers:New insights into their virulence and pathogenicity. Archives
of Biological Science, Belgrade, 64(1): 21-42.
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