Learn about how to control polyphagous pests!
1. White Ants:
Termites (Isoptera- Termitidae):
These are commonly called white-ants, the name being used because though not related to ants, they live in colonies and in many of their ways resembles the ants. Their colour varies from whitish pale to brown. Termites form the most important insect pest as they cause very great damage. The termites are polyphagous. Their food is principally composed of cellulose which they obtain from living or dead vegetation, books and other articles of wood, fabric etc.
Maize, jowar, bajra, pulses, paddy, wheat, sugarcane, potato, tea, coffee, coconut, jute, sunnhemp, fruit trees, forest trees are badly damaged by termites. They cause considerable damage to the dry and dead wood, furniture made out of the dry wood, books and almost all articles containing cellulose.
Life History:
The termites have two main forms viz. reproductive and sterile. The colony consists of one male or king, one female or queen and a variable but generally large number of workers and soldiers. The queen is a giant and has no other work than of continuously laying millions of yellowish or cream coloured kidney shaped small eggs. They are deposited in particular cells for hatching.
The nymphs resemble miniature adults. The nymphs undergo several moults producing workers and soldiers. Periodically they produce winged forms or primary reproductive, which swarm out and repeat the cycle. With the first few showers of rain there particularly appear a few winged male and female forms. They leave the termitarium when mature, fly about, copulate, shed their wings become kings and queens, burrow in soil and establish new colonies.
Workers:
These are small white insects most commonly seen doing damage. They can be easily recognized by their vertically carried head and small broad jaws. These are injurious form and constitute 80-90% of the whole population.
Soldiers:
These are a little larger than workers and carry long pointed jaws placed horizontally in front of the head. They are about 2 to 3% of the population.
Winged Adults:
They are bigger than the soldiers and possess four equally long wings, which when folded lie flat on the back and are readily cast off after nuptial flights.
King:
This is still bigger wingless male and is the partner to form the colony. It lives in the nest and repeatedly copulates. There is generally only one king in a colony.
Queen:
This is the biggest wingless member of the colony about 10 cm. in length and is the cofounder of the colony. The head and thorax are small when compared with the abdomen. Thousands of eggs are laid per day for several years.
Supplementary Reproductive:
These special females whose duty is to reproduce in emergency if the queen happens to die. These are fed on special food to activate their reproductive organs.
Control:
The affected parts in the trees should be sprayed with paris green or sanitary fluid or osfoetoid solution banding the trees by coal tar, renewed half yearly.
Protection of wooden structures can best be obtained by taking care that no wood comes in contact with the ground and that light and dryness are ensured as much as possible. Timbers thoroughly treated with coal tar, creosote are repellant to the insects.
When termites are already in the wood, all infested parts will generally need to be removed and the nest should be located if possible and destroyed by using kerosene or by fumigation. Treatment of the soil near a building with a mixture of trichlorobenzene one part, fuel 11 or creosote two parts aids for a few years in keeping termites away.
Termites penetrate through lime mortar but not cement provided there are no cracks. A plinth 8-15 cm. thick of cement before erecting walls will bring about desired safety. The floor of the house may be treated with arsenic solution.
Soil treatment for eradication or as a protective barrier must be thoroughly applied. Around the foundation, the normal procedure is to trench the soil and flood or rod-inject the formulation into the soil. The rate for shallow foundation is 9 litres per lineal 1.5 m. or deep foundation 10 litres per lineal 1.5 m.
All wood that have contact with the soil should be termite proof by pressure impregnation with coal tar, creosote etc. When building, no bits of waste wood such as grade stakes and concrete forms should be left buried in the soil near the structure. Stumps and waste wood should be removed from the premises.
Soil treatment with the dust of endosulfan 4% @ 25-30% kg/ha be done uniformly after the last ploughing and before sowing the seeds.
2. Desert Locust:
Schistocerca Gregaria Forskall (Orthoptera- Acrididae):
It is a polyphagous pest and virtually all crops are at risk so far as locusts are concerned but there is some preference of cereals. The leaves and soft shoots are eaten from margin inwards leaving irregularly shaped feeding marks. Swarm damage usually results in complete defoliation of crops.
The life history of a locust consists of egg stage, hopper stage and the adult stage. The eggs are laid in a hole made by thrusting the ovipositor 10-15 cm. deep in sand embedded in a frothy mass which hardens to form a tubular egg pod. Each egg looks like a grain of rice which is yellowish in colour and 7 to 8 mm. in length. Each egg pod contains 70-150 eggs and each female can lay 4-5 pods of eggs. Egg development takes 2-4 weeks according to temperature.
The first larva is rather vermiform and it has to wriggle up through the egg pod to the sand surface. On reaching the surface it moults and becomes a hopper over a period of 3-10 weeks depending on the temperature. The hoppers develop through 5 instars before they become adult. The hopper exist in two distinct phases, solitary and gregarious with difference in colour and behaviour.
The adults are large; male 40-50 mm. and female 50-60 mm. pale yellow or brownish. The elytra are greenish yellow, translucent with many brown spots. There is a characteristic peg like process between the bases of the forelegs and the under surface of the thorax is not smooth. There are several generations per year.
The hoppers may be attracted through the use of suitable baits as well as dusting, ground spraying and aerial spraying with carbaryl and methyl parathion. Against aerial swarms, malathion is widely used. Barrier spraying with persistent insecticides can be very successfully used against large swarms.
3. Red Hairy Caterpillar:
Amsacta species (Lepidoptera- Arctiidae):
It is a polyphagous insect which feeds on a variety of plants like jowar, bajra, maize etc. Among the whole group of hairy caterpillars, the “red hairy caterpillar” (Kutra/Katra) is most injurious to agriculture throughout India. The habits and nature of damage etc. of all the species of the genus Amsacta (e.g. A. moorei Butl., A. collaris Hamp. and A. albistriga Walk.) are so similar that separate descriptions are not called for.
The fully mature caterpillar measures about 4-6 cm. in length. The body of the caterpillar is covered with reddish brown or brownish orange hairs. The moths are robust having white wings with black spots. The outer margins of the fore wings, the anterior margin of thorax and the abdomen is scarlet red. There are black bands and dots on the abdomen.
The caterpillars of Amsacta are active from late June to September. The insect is normally univoltine and occasionally bivoltine; when there are two generations a year, the first generation is non-diapausing and the pupa of the second generation undergoes diapause.
The moths of the red-hairy caterpillars appear in large number after the first shower of monsoon. They lay light yellow, spherical eggs in large prominent clusters on the cultivated plants as well as on weeds. A single female may lay upto 1500 or more eggs. The larvae hatch out in about 3-5 days and begin to feed. They feed continuously, grow and migrate from one field to another field after almost completely browsing the area they visit.
The caterpillars undergo 6-7 moultings and complete their development in 4-6 weeks depending on the climatic conditions. The full grown caterpillars go down into the soil for pupation. In the soil they remain for about 8-10 months i.e. whole of the winter and summer and emerge as moths after the first few good showers of rain. The duration of pupal period largely depends on the arrival of monsoon. There is only one generation in a year.
The moths can be attracted by light traps. The clusters of eggs are quite large in size and that can be easily destroyed by hand picking. The young caterpillars of the Amsacta can be killed by dusting the cultivated crops with malathion 5% @ 30 kg/ha. For full grown caterpillars spraying endosulfan 35EC @1.5 litres in 1000 litres of water per hectare controls the pest.
4. Surface Grasshopper:
Chrotogonus Trachypterus Blanch. (Orthoptera- Acrididae):
The surface grasshopper is worldwide in distribution. The grasshoppers are polyphagous and besides cotton and wheat, they also feed on a number of other cultivated crops. Both the nymphs as well as the adults feed on leaves by cutting germinating plants of cotton, wheat etc. particularly in areas near by the waste lands.
Life History:
Chrotogonus remains active throughout the year but its activity is reduced during winter when only eggs and adults are found. A female may lay 36-434 eggs in 2-15 egg pods at a depth of 3-6 cm in the soil. Each egg pod consists of 16-46 eggs. In the summer, eggs hatch in 19-33 days where as in winter they hatch in about 5 months. The nymphs feed on grasses or other soft plants, moult 5-7 times and are full fed in 40-70 days.
The adults are stoutly built, about 20 mm. long and 8 mm. broad with a rough greyish appearance. There are two longitudinal rows of black dots on the underside of the body which is otherwise white. The body of the female is larger and flat than the males; the females live for about 3 months and the male almost half as long. There are two generations in a year.
The pest can be controlled by dusting the crops with malathion 5% or 12.5 Kg. 5% carbaryl (sevin) dust per hectare on first appearance of the grasshopper(s).
5. Bihar Hairy Caterpillar:
Diacrisia obliqua Walk. (Lepidoptera- Arctiidae):
The Bihar hairy caterpillar is a sporadic pest and is widely distributed throughout the country particularly in Bihar, M.P., U.P. and some other states. It is a polyphagous pest, specially of sesumum, moong, linseed, mustard some vegetables and a number of other vegetable crops. The damage is caused by the caterpillars.
The pest breeds from March-April, and July-November. It passes the hottest part of summer and the coldest winter in the pupal stage amidst plant debris. The female lays about 400-1150 light green spherical eggs in groups of 50-100 on the underside of the leaves. The eggs hatch in about 4-10 days and the larvae feed gregariously. They grow to maturity through 7 stages within 3-6 weeks. The full grown caterpillars measure about 40-45 mm. in length.
They are covered with long greyish hairs. The pupation take place in the plant debris or soil in a loose silken cocoon. The pupal stage lasts 1-2 weeks and the moth lives for about one week. The moth measures about 50 mm across the wings when spread. The head, thorax and under side of the abdomen is light yellow in colour. The antennae and eyes are black. The whole life cycle is completed in about 6-12 weeks and the pest passes through 3-4 generations in a year depending on the climatic conditions.
The pest can be controlled by spraying the endosulfan 35EC or sevin W.P. 50% @ 1 kg/ha in 1000 litres of water or quinalphos 25EC @ 750 ml/ha mixed in 1000 litres of water.