To study insect pests with respect to identification marks, nature of damage and economic importance.

Aim : To study insect pests with respect to identification marks, nature of damage and economic importance.

1)Jowar stem borer (Chilo zonellus) :- 

Distribution - It occurs throughout India. The jowar stem borer is commonly called as spotted stalk borer or pink borer.

Identification marks - The adult moth is a medium sized insect with 3 cm wing span. Its forewings are straw or light brown in colour with numerous shining brown spots on the margin and hindwings are white and papery. Head of caterpillars are dark brown and with mandibulate type of mouth parts. Mature caterpillars are measured about 12-20 mm in length and shows four broad and patchy strips on the body.

Nature of damage - Newly hatched caterpillars initially feed on the leaves causing numerous small holes in the leaf lamina and attack all parts of jowar plant except the roots. The larvae on entering the leaf, whorl and cut the leaves, which on emergence manifest characteristic pin holes, shoot holes and longitudinal streaks. At times the growing point is cut which results in drying of the central shoots and subsequently formation of dead-heart. The larvae after entering the stem, feed on the tissues (pith) and tunnels of galleries are formed.

•Control Measures :-

1)Cultural method : 

i)Hand picking or light trapping of adult moths and collection of their eggs for destruction.

ii)Burning of stubbles and trash which harbour borers and act as source of infestation for the next crop.

2)Chemical method -

i)0.05% should be sprayed for chilo on sorghum. Lindane or 0.1% endosulfan has been found effective on 15-day-old plants.

Third application with 0.2% Carbaryl can be sprayed if needed.

ii)In case of early infestation, dusting of 10% BHC at the rate of 25 kg per hectare or spraying of 350-400 ml of Aldrin or Dieldrin in 200 liters of water helps control the pest.

3)Biological method -

i)The hymenopteran, Trichogramma minutum is employed as egg parasite.

ii)Apanteles flavipes and Bracon brevicornis as larval parasites.

iii)Sexmaculata have been recorded predating on early stages of the larvae of this pest.

2)Red cotton Bug (Dysdercus cingulatus) :-

Host Plants - Cotton, bhendi, ambadi, hollyhock and 

several other malvaceous plant.

Identification marks - The adult bug is about 12-15 mm in length. Females are longer (15 mm) than males (12 mm). This is blood red in color except eyes, scutellum and antennae which are black coloured. Mouth parts are adapted for piercing and sucking. They form a straight beak or rostrum. The nymphs are smaller than adults and are wingless.

Life cycle -

The mature female lays eggs during spring in clusters of 70-80 eggs each under the moist soil surface; fallen leaves and in crevices. Eggs are spherical, yellowish white, about 1.2 mm long. After 7 days of incubation period and moist weather, eggs are hatched into active 1mm long red coloured nymphs which are resemble the adult except size and absence of wings. The nymphs undergo 5 moults within 49-89 days to reach adult stage. The life cycle of bug is completed within six to eight weeks.

Nature of Damage -

Both nymphs and adults absorb cell sap from Leaves and tender shoots and impair the vitality of the plant. If the attack is severe, bolls open badly and the lint is of poor quality. In addition they also feed on the seeds and lower their oil content and low percentage of germination; such seeds are unfit for sowing. The lint is stained by the excreta of bugs or by their body juice as they are crushed in the ginning factories.

Control measures - 

1)Cotton field should be ploughed to expose eggs to sunlight.

2)Insects should be hand picked and killed in kerosinised water.

3)Moistened cotton seeds should be hunged, they may get killed in the kerosinised mix water.

4)Spraying of malathion 0.05% is effective to control pest.

3)Brinjal Fruit Borer (Leucinodes orbonalis) :-

Common Name - Brinjal shoot and fruit borer.

Host plants - Brinjal shoot and other solanaceous plants and peas (alternative).

Identification Marks -

The moths are medium sized of about 20 mm across the spread wings. The head and thorax are blackish brown. The wings are whites provided with small hairs along the apical and anal margins. A number of black, pale and light brown spots are found on the fore and hindwings of the moth.The caterpillars are pale white and about 12 mm long when fully grown.

Life cycle - The moth lays elongated eggs singly or in small batches, on the leaf surface, shoots and fruits. They hatch in 3-5 days. In about 10-15 days larva undergoes for 5th moults. The fifth instar larva is stout pink and measures about 1.6 cm in length. Pupation takes place in a cacoon on the plant and lasts for 6-8 days. Moth lives 2-5 days and the female lays upto 250 eggs. 

Nature of damage - The only destructive stage is the larval. In the early stages the larvae bore into tender shoot as a result the infested shoots droop down and ultimately dry up. The 70%. loss of crop is caused by this pest. It forms zig-zag tunnels in fruits and fruits holed.

Control measures -

i)The affected fruits and drooping shoots, containing caterpillars inside, should be clipped off and destroyed.

ii)The crop should be sprayed with suspension / emulsion, sevin.

iii)The biological agencies like, Braconid wasps and Inchenumonid wasps parasitize the larvae of this pest.

4)Mango stem borer :-

Host plant - This pest is found on the planted plants like mango, fig, rubber and jack.

Identification marks - The adult beetles are well built, large sized, measuring about 5 cm long in length and brownish yellow/grey coloured. It has orange yellow spots on thorax and has hard forewings (elytra); lateral spines on prothorax and long antennae and legs.The grubs are large, yellowish white in colour, fleshy in appearance and measures about 100×10 mm with black head and bearing strong mandibles.

Life cycle - The female beetle lays single egg under loose bark or in a diseased part of trunk. After incubation Period of 14 to 17 days - eggs hatched out. Feeds on stem or root and woody tissue. It remains 3-6 months in pupation and make tunnels. Adult emerge during the mansoon.

Nature of Damage - The grubs make zig-zag galleries beneath the bark and tunnel into trunks or main stems. As a result of feeding on the internal tissues, the attacked branches and stem die and wither away. In severe cases af attack, the branches may collapse and tree may die.

Control Measures - 

1)The Population of grubs and pupae of stem borer can be reduced by cutting and destroying infested branches.

2)The best way to control the grubs is to just inject borer solution (i.e 2 parts of carbon disulphide + one part of chloroform and cresole) in the holes after which it should be closed by mud.

5)Lemon Butterfly (Papilio demoleus) :-

Host plant - Citrus is the only host plant of this pest.

Identification marks - It is a beautiful butterfly of large size measuring about 2.8 cm in length and wing expanse about 9.4 cm. The adult is a black and yellow, swallow tail butterfly. Its hindwings have a brick red oval patch near the anal margin and tail like extension behind known as swallow tail butterfly. The antenna are black and club shaped. Caterpillar is darkish-brown in colour with whitish stains, measure about 38 mm length and hump like.

Life cycle - Eggs are laid singly or in small group of 2-3 on the under surface of leaves and shoots; upto 180 eggs are laid by each female. They hatch out in 3-6 days shave five instars. When disturbed the caterpillar pushes out from top of its prothorax a bifid, purple structure called, the osmenterium which emits a distinct smell. The pupal period lasts about 2-3 months in Winter and emerge out as adult.

Nature of Damage - The caterpillars cause destruction of the citrus plants. They usually feed on tender leaves and terminal shoots. The severe attack by full grown caterpillar causes complete defoliation of citrus plants thus rendering them unfit for fruit bearing.

Control measures -

1)Handpicking of the caterpillar and pupae from plants in initial stages infestation and removing alterative host plants are mechanical control measures.

2)The pests can also be controlled by treating the plants with a short term contact insecticide such as 0.04% monocrotophos or phosphamidon.

6)Rice weevil (Sitophilus oryzae Linn) :- 

Host - S.oryzae prefer nice, they can be found feeding on wheat, maize and other grains. Identification marks - The adults are small weevil about 4 mm in length with reddish brown, dark brown or almost black in colour with cylindrical body and a long curved rostrum. Head bears long snout with chewing mouth parts located on its tip. The functional wings hidden beneath the dark brown elytra with four light reddish or yellowish spots and insect inable to fly. The life span of adult weevil is 4 to 5 months. They are always found inside the kernels.

Nature of damage - Generally, infestation starts in grains only during storage. The S.oryzae feeds on whole grains of rice, wheat, jowar, bajri, maize, etc. Both larva and adult harmful. The thin tunnel (hole) is formed by the grub from the surface towards inside of grain. Circular exit holes and stained spots on the surface of the grain kernel is the symptom of damage.

Life cycle - The female starts laying eggs 5 days after the emergence. The female bores a small, round hole in soft part of grain by means of mouth parts and there she lays a single egg and sealing it with a mucilaginous secretion. The eggs are translucent, white, oval, minute (0.7 x 0.3 mm in size). A female lays a total of 300-400 eggs during her life time.

The incubation period ranges from 4-7 days in summer to 6-9 days in winter. The grub (larva) batches out of the egg is legless (Apodous), translucent white with fleshy body and yellow-brown head. The pupa is curved or humpy in appearance and takes 3-6 days to emerge as an adult. The emerged weevil immediately starts breeding and gives rise to new generation for destruction of grain. several generations are possible during a normal storage season of grains. The adults live on an average for 2 to 5 months.

Control measures - To control the stored grain pest. Both the control methods are adapted i.e. the preventive and curative.

I)Preventive method -

1)After harvesting, dry the grains in sunlight sufficiently so that the moisture content is reduced to less than 8% moisture because most of the stored grain pests cannot multiply in grain at such percentage of moisture.

2)After drying in the sun, the grain is stored in a new sack to free the grain from infection.

3)Use of neem leaves, mercury, mixing of ash, powder of sweet flag rhizome, etc.

4)To make the insect free godown one or more of the following methods may be used.

a)Rat holes should be sealed with glass pieces mixed with cement or sand.

b)Fumigates the warehouse with EDBR.

c)Spray with insecticides like pyrethrum, malathion or BHC to avoid the chance of contamination.

d)All dirt, refuse material should be removed and destroyed and all the cracks, crevices, holes in walls, floors or ceiling of godown should be filled with cement.

II)Curative measures -

This measures becomes essential when the grains get infested with the stored grain pests.

i)Sieving and cleaning removes all the stages of pests.

ii)After above method the grains must be followed by sunning and fumigation with suitable fumigants. iii)The larvae and adults are killed by exposing them for 48 hours to the vapours of ethylene dichloride carbon tetrachloride mixture under gas proof covers.

7)Pulse Beetle (Callosobruchus chinensis Linn.) :-

Common Name - Gram dhora / Mung dhora.  Distribution - All over India and many other countries though not world wide. This is very important pest of various pulse crops in India, both in field crops and in store.

Host plants (main) - Gram, Peas, cowpeas, lentils, arhar.

Alternative - Chick pea, maize, soyabean, other pulses.

Identification marks - The adults are small, roundish chocolate or brown beetles, 4mm long. There are dark markings on the elytra and a which, raised spot on the middle of the body. When observed from above, the beetle presents a heart-shaped appearance, with two ivory coloured spots in the middle of the dorsal side of its body. The beetles has a conspicuously swollen abdomen. The grub is white, cylindrical, fleshy and wrinkled, found always inside the grain and it has brown head.

Life cycle - The mature female lays upto 90 eggs. Singly on the seeds or on the pods in the field. The incubation period is 4-6 days. The young larvae burrow into the grain and feed inside for 2-3 weeks, undergoing 4-5 moults. The full grown larva is about 1 cm long, white and curved in appearance. Pupation occurs within the grain or grain dust and takes about 7 days to complete.

Nature of Damage - The pest attacks leguminous pods in the field from where they are carried to storage godowns. The mung, gram, tur, lang, bean, masuri (lentil) and udid are generally infested when the grain is whole. The damaged grains are hollow inside bearing small holes and are unfit for human consumption.

Control measures -

i)Cultural control can be achieved by growing susceptible crops atleast a kilometre away from storage godowns which are the main source of infestation.

ii)Remaining measures are same as rice weevil.

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