Foreword - CCS HAU, Hisar

on roots as in wireworms, weevil grubs and chafers (white grubs) while in the case of the flea
beetle Longitarsus belgaumensis the grubs bore or tunnel. Sometimes it may be seen that
the seeds sown do not germinate as they have been eaten away by insects like ants in the
soil. The tubers of the sweet potato crops in the fields are sometimes riddled with holes by
the larvae of the weevil Cylas formicarius and the gelechiid moth Phthorimaea operculella,
respectively.
Injury to stored products
In three ways the stored products are attacked by insects.
It may be a continuation of a field attack as in sweet potato weevil and potato tuber moth.
The eggs may be laid in the field itself and the damage may occur in storage as in
redgram infested by the bruchid beetle.
The infestation may continue from the material stored earlier and be carried over to fresh
material stored later in a godown or storage house as in the grain weevil, Sitophilus
oryzae, which infests single grains and the flour moth, Cadra cautella which webs together
the grains with silken threads and feeds on them. Apart from this type of attack the
occasional damage to food material in the stores by cockroaches may also be considered.
INDIRECT EFFECTS OF FEEDING
Making the harvest more difficult
Heavy incidence of some pests on crops makes the harvest of the crop more difficult. It
may be very difficult to harvest cabbage or Lab-lab pods infested heavily with aphids or
kapas from cotton bolls damaged by bollworms.
Causing contamination and loss of quality of produce
Due to insect attack the final produce may show loss of quality by reduction in nutritional
value or in marketability. In the case of cardamom the berries infested by thrips become poor in
quality due to scaly patches on the rind. Other examples are sweet potato tubers riddled with
holes by the weevil Cylas formicarius, brinjal fruits bored by larvae of Leucinodes orbonalis,
amaranthus leaves skeletonised by larvae of Hymenia recurvalis and cabbage riddled with shot
holes by the semilooper Trichoplusia ni.
Disseminate plant diseases
Insects are responsible for spreading many plant diseases caused by bacteria, fungi
and viruses. Though bacteria and fungi have alternative methods of dispersal, many plant
viruses are mostly dependent upon their insect vectors for dissemination.
INJURY BY OTHER METHOD
Injury by egg-laying
Insects take a great deal of care in laying their eggs at the right place so that the young one
will have enough food material for its development, and thus survive. By the act of oviposition
sometimes a few species of insects have been observed to inflict injury to crops. It is a wellknown
fact that the periodical cicada, also known as “seventeen year locust”, splits the wood
severely on twigs of one year old growth for egg laying as a result of which the portion beyond
that dries up. In the case of cow bugs (Membracidae), they insert their eggs in rows into the
tissue of the tender stem and thus cause injury. The grapevine stem girdler, Sthenias grisator,
which attacks a number of plants in South India, chews off the twig by ringing and then inserts
the eggs into the distal portion of the twig so that the larvae may have wood in a suitable condition
of moisture and decay for its development.
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