Entomopathogenic Nematodes- bioagents for management of insect pests Introduction Biology of EPNs Advantages over chemical pesti...
Entomopathogenic
Nematodes- bioagents for management of insect pests
Use of
chemical pesticides in agriculture posed a concern about hazardous effects of
pesticides on environment. There is an urgent need for methods that are
eco-friendly. Development of resistance and emergence of new biotypes is
another concern about using chemical pesticides which drive us for a change in
pest management methods. Biological control is an attractive alternative which
is environmentally safe and feasible in crop protection. Understanding the
biology and adaptability of bio-control agents has an important role in
successful application of bio-agent based products in different crop ecosystems.
Entomopathogenic Nematodes (EPNs) are effective bio-control agents for the
management of insect pests, especially soil dwelling insects. Two genera, Steinernema and Heterorhabditis are
highly virulent EPNs, killing the insect host within 1-2 days. Steinernema and Heterorhabditis has
symbiotic bacteria Xenorhabdus and Photorhabdus respectively in
their guts which they will release upon entering the insect.
Third
stage juvenile of the EPN species are infective. They are free-living,
non-feeding and possess highly sensitive chemoreceptors which can detect host
cues. When a insect has been located, the nematodes enter into the insect
body cavity via natural body openings (mouth, anus, spiracles) or
cuticle. After entering the insect haemolymph, bacteria released produceds
toxins with insecticidal properties and the insect gets killed with 24-48 h due
to septicemia (blood poisoning). In the dead insect , nematodes
and bacteria feed on insect body contents and reproduce inside the
cadaver. After completing several generations, thousands of
infective juveniles emerge out of cadaver and search for a fresh host.
- Highly lethal to
important insect pests with least off-target effects.
- Highly safe to humans and
environment. No safety equipment required, no residual effects, no
groundwater contamination and are safe to pollinators.
- Kills insects within 24-48
hours
- Easy to mass produce and are
compatible with standard agrochemical equipment and irrigation systems for
application.
There are
two methods of mass production, In vivo and In vitro mass
production methods s. In vivo mass production is done using
greater wax moth larvae or rice moth larvae. It is oriented for small
scale production.This method is more laborious. In vitro mass
multiplication is done using solid or liquid media. Bacteria from EPNs is
isolated and inoculated in media.After 2 days incubation at 27 degrees, fresh
IJ are inoculated.After 2-3 weeks, newly emerged IJs can be harvested
through white's trap. This method is used for large scale production.
Formulation
plays a significant role in commercialization of bioagents. EPNs can be
formulated either with active nematodes in various substrates or with reduced
or arrested mobility(partial of complete anhydrobiosis). A number of
formulations are available with good nematode storage and application including
activated charcoal, alginate and polyacrylamide gels, baits, clay, paste, peat,
polyurethane sponge, vermiculite, and water-dispersible granules. The
shelf-life is variable among the formulations and it mainly depends on the
activity of infective juveniles.EPNs are highly sensitive to temperature
fluctuations and soil moistures in environment. So researchers has to
keep this problem in mind and develop suitable EPN formulations which improves
the shelflife and protection from environmental fluctuations under field
conditions.
Source:
B.Gayatri and P Duraimurugan, ICAR-Indian Institute of Oilseeds Reserach,
Telangana, Hyderabad
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