Resource Book on Horticulture Nursery Management

Male moths attempting to locate the point-source attractiveness of female lose the ability
to find mates, resulting in far fewer eggs laid and hence significantly reduced pest
populations.
Biological control is the use of natural enemies of insect pests to regulate their
numbers below a level where damage is economically important. It is a very useful
strategy. More host-specific parasites (parasitoids) in the insect orders of Hymenoptera
and Diptera can reduce the densities of pests considerably.
The biocontrol insects and biopesticides (fungal and bacterial based) are important
tools to break/interrupt the continuous presence and activity of the pests present in the
nursery. These normally act on the young stages of the pests (nymphal /larval /grub) and
minimize the damage. The friendly biocontrol insects are natural parasites and predator.
Trichogramma species are egg parasites while Bracon, Encarsia and Apanteles are larval
parasites and Coccygominus is a pupal parasite. The predating insects voraciously feed
upon the eggs, larvae and adults of various pests. Larvae of Chrysoperla and the adults of
Coccinella, Chrysopa, Cryptolaemus, Amblyseus and spiders eliminate aphids, jassids,
whiteflies, mites and Helicoverpa larvae through predation.
Microbial biopesticides are based on the organism, by-product produced by
the organism or a mixture of organisms which are applied periodically to control nursery
seedling pests. The most commonly used microbial pesticides are based on Bacillus
thurigiensis (Bt). ‘Bt’ acts mostly on caterpillars and other insects, generally polyphagous
and resistant to traditional chemical pesticides such as, Helicoverpa, Spodoptera,
bollworms, hairy caterpillars and Plutella. Some Bt strains are active even on beetles and
flies.
Baculoviruses, including Nuclear Polyhedrosis Virus (NPV) and Granulosis Virus
(GV) are also important biopesticides which are highly host specific. The NPVs and
GVs act through oral infection and multiplication of virus particles in infected cells in the
gut and septicemia leading to death in 5-20 days. Normally the death of larva due to
Bt/NPV/GV results in depletion of pupa and adults. The surviving pupa/adults are often
deformed, infected and incapacitated to carry out normal lifecycles.
Fungal biopesticides based on Beauveria are highly effective on lepidopterans,
whiteflies, hoppers, borers and also aphids and red spider mites. Verticillium is most
effective on aphids, jassids & whiteflies. Entomophtorales are effective against
whiteflies and Metarhizium on white grubs and locusts. These fungi mostly act on the
pests through enzymes and toxins. Fungal agents like Trichoderma are highly potential
seed treatment agents to control wilts and rots etc.
The botanical pesticides based on extracts of leaves, kernels or seeds of neem,
karanja, chillies, garlic are equally efficacious insecticides. Neem is the most promising
and widely used against a number of insect pests due to its versatile mode of action. It has
a broad spectrum action on insects and is very useful. However, the problems of quality,
shelf life, presence of aflatoxins and phytotoxicity limit its efficacy and eco-safety.
Formulations based on sound technology would have a promising future.
Note: Chemical industries play a very important role in supplying various chemicals
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