Soil-dwelling insect-pests can seriously reduce plant establishment, populations and subsequent yield potential. These insects can be damaging because they feed on the roots and stems of plants. Often soil borne pests, especially cutworms are common in uncultivated fields infested with grass and weeds and abandoned fields after growing the previous season. The important soil dwelling insects which damage agricultural crops are white grub, termite, wire worms, mole cricket, earwigs, black scarab beetles, cutworms, fire ant etc.
1. White Grub (Holotrichia Consanguinea, Order Coleoptera, Family- Scarabaeidae):
i. Description:
Whitegrub, Holotrichia consanguinea is the most serious scarab pest in India. This is a polyphagous pest in nature and prefers light sandy soils. This species predominantly found in Rajasthan, Gujarat, M.P., U.P., Haryana, Punjab and Bihar. Rajasthan and Gujarat have a long history of whitegrub. H. consanguinea infestation occurs in most of the kharif crops. The damage in different crops ranges from 20 to 100 per cent. This pest most preferably feeds on groundnut and bajara.
ii. Nature of Damage:
The beetles of H. consanguinea emerge from soil during dusk after good pre-monsoon or monsoon rain in mid-May or late June. The beetles are polyphagous, and may feed on the foliage of a wide variety of host trees and bushes found in the nearby places. However, they have some preference for certain hosts like Jujube or ber, Khejri (Prosopis cineraria), Neem (Azadirachta indica), Clusterbean (Cyamopsis tetragonoloba), Jambolana (Syzygium cumini) and Drumstick (Moringa oleifera).
The grubs make chamber by compressing the surrounding soil particles and then eats the rootlets exposed into the chamber; thereafter it little bit moves vertically into the foots to eat more of the same root. Then the grubs move horizontally making chambers and feeding on the exposed roots. The grubs continue active feeding from July to mid-October.
iii. Life Cycle:
The biology, of H. consanguinea has been worked out in Gujarat State (Desai and Patel, 1965) and Patel et al. (1967), and in Rajasthan. All the grubs pupate by the beginning of November. Before pupation the grubs enter deep into the soil to the depth of 40 to 70 cm or more in search of suitable moisture zone.
The average pupal length and width is 27.3 mm and 14.2 mm, respectively. The freshly emerged beetle is white in colour but with the lapse of time it becomes dull brown with light brown abdomen and dark brown legs. The beetles remain in the soil in inactive state up to middle of May at a depth of about one metre. The average duration of one life cycle is 122 days and there is only one generation in a year.
iv. Management:
i. The cultural management of white grub through deep summer ploughing exposes the grubs which are fed by birds and adult of grub can be killed by light trap.
ii. Annihilation of white grub beetles on host trees by application of insecticides and pheromone loading of selected host trees.
iii. Among the microbial control agents, entomopathogenic fungi, Metarhizium anisopliae and Beauvaria bassiana were more effective, when placed at soil depth of 10-15 cm. Nematodes, Setainernema glaseri and Heterorhabditis sp. were found to be pathogenic to several whitegrub species including H. consanguinea.
iv. Seed furrow application of Phorate 10G @ 20 kg ha -1 or Quinalphos 5G @ 30 kg-1/ha or Imidacloprid 17.8 SL ml-1/kg seed.
v. In groundnut, seed treatment with Clothinaidin 50 WG (Dantotus) @ 2g kg -1 seed or Imidacloprid 17.8 SL @ ml -1/kg seed.
vi. In standing crop, chlopyriphos 20 EC or quinalphos 25 EC @ 41-1/ha applied with irrigation water after 3 weeks of first shower of monsoon.
2. Termite (Order- Isoptera, Family- Termitidae):
i. Description:
Termite attacking on annual and perennial crops, especially in the semi-arid and sub-humid tropics cause significant yield losses. In general, damage by termites is greater in rain-fed than irrigated crops, droughts than periods of regular rainfall, in lowland rather than highland areas, and in plants under stress (lack of moisture, disease or physical damage) than in healthy and vigorous plants.
Termites causing greater losses in agriculture belong to the following families and genera: Hodotermitidae (Anacanthotermes and Hodotermes), Kalotermitidae, Rhinotermitidae (Copotermes, Heterotermes, and Psammotermes), and Termitidae (Amitermes, Ancistrotermes, Cornitermes, Macrotermes, Microcerotermes, Microtermes, Odontotermes, Procornitermes, and Syntermes as reported by Krishna et. al. (2013).
ii. Nature of Damage:
Many species of termites build large mounds often containing many thousands of individuals. Termites construct shallow subterranean foraging galleries radiating from the nest for distance of upto 50 m. They feed on roots and underground portions of stem causing wilting and withering of the affected plants. Patchy gaps are formed due to the death of seedlings resulting in poor and uneven plant stand.
The workers of the termite may invariably be found in soil or at the base of freshly damaged or wilting seedlings. At the early stage when plant is attacked the roots are completely or partially eaten, which directly kills the plant or indirectly lowers the yield through decreased translocation of water and nutrients. Such plants dry up without producing any grains and can be easily pulled out. Termites damage all the food material which contains cellulose.
iii. Life Cycle:
They are social insects and lives in colonies known as termitaria. The pest remains active throughout the year. The propagation of colony takes place generally during the rainy season when atmospheric conditions are favourable; the colonizing forms are leaving their parent colony. The members of the swarm comprise individuals of both sexes. Both the male and female participate in the early operation of forming a nest.
The queen termite (egg laying machine) is the most important termite in the life cycle. The queen is responsible for laying eggs and hence starting the entire cycle. The king is responsible for mating with the queen for her life. Both king and queen can live up to 25 years. The egg stage of the termite life cycle lasts for about 30 days and within 180 days the larvae develop to form soldiers or workers. After the king and queen, workers are arguably the most important parts of a colony.
They are responsible for foraging, food storage, feeding the queen and defence (in certain species, although soldiers are the main ones responsible for the colony defence). They are mainly the ones which damage the crops and other wood material by digesting the cellulose. The lifespan of a worker termite is 1 to 2 years. Both worker and soldier caste are sterile and the reproduction caste (king, queen and nymphs; supplemental reproductive) when produced mature in 12-24 months.
iv. Management:
i. Deep ploughing or hand tillage exposes termites to desiccation and to predators, thus reducing their number in the soils.
ii. Mounds are physically destroyed, flooded or burnt with straw to suffocate and kill the colony.
iii. Crop rotation may be useful in reducing the buildup of termites since intensive monoculture for long periods makes plants more susceptible to termite attack.
iv. Seed treatment with entomopathogenic fungus, Metarhizium anisopliae or Beauveria bassiana, provide promising results.
v. Before sowing treat the seed with Regent 5% SC (fipronil) @ 6 ml or Dursban/Ruban/ Durmet 20 EC (chlorpyriphos) @ 4 ml-1/ lit.
vi. In standing crop, apply chlorpyriphos @ 1 to 1.5 litre ha -1 with irrigation water.
vii. Swabbing with Neem oil 5% once on the base and upto 2 m height of the infested tree trunk for effective control.
Seed treatment is the most effective and economical method of termite control as compared to broadcasting of treated soil or fertigation.
3. Cutworms, Agrotis sp. (Order- Lepidoptera, Family- Noctuidae):
i. Description:
Cutworms are the caterpillars of various moths in the family Noctuidae. The insect belonging to genus Agrotis are subterranean in habit. The pest remains active throughout the year but minor pest during August to October and is major limiting factor in certain regions. This pest is distributed in India, Burma, Sri Lanka, China, Indonesia, Australia, America, Europe and North Africa. It has been reported from Kashmir, Tarai area of Uttar Pradesh and Bihar.
The moths pollinate flowers, and do not do any direct harm to garden crops. This pest feed on various plants such as maize, okra, tomato, chillies, egg-plant, cabbage, potatoes, corn, peas, beans, celery, carrots, lettuce, and many other common garden crops. Different cutworm species prefer different host plants.
ii. Life Cycle:
The pest is active from October to April. The female lays about 199 to 344 creamy white, dome shaped eggs in clusters of about 30 each either on under surface of the leaves of the food plants or in the soil. The eggs hatch in 2 days in summer to 8-13 days in winter.
The larval period is 30-34 days in February- April and full grown larva makes earthen chamber in the soil for pupation. The pupal period is 10 days and 30 days in summer and winter, respectively. The total life cycle is completed in 48-77 days. Three generations are found in a year.
iii. Nature of Damage:
The caterpillar, which hides during day time in cracks and crevices in the soil, become active at dusk, feed on leaves and also cut growing seedlings and tender shoots of the young plants. Initial damage is done by feeding on leaves by the younger larvae, while the older larval in stars of 4th, 5th, and 6th kill the plants by cutting it just above the soil surface.
iv. Management:
a. Remove weeds and plant residue to help reduce egg-laying sites and seedling weeds that nourish small cutworms.
b. Use light trap for mass trapping of cutworm moths from 3rd week of March to last week of July.
c. Deep summer ploughing of fields before planting which helps expose and kill over wintering larvae which also helps to discourage egg laying sites and avoid green manuring to reduce egg laying.
d. Pick the larvae from the base of the plants, where they take shelter under the clods during daytime.
e. Flooding of field could control the pest effectively.
f. Placing of aluminum foil or card board collars around the transplants as physical barrier which prevent cutworm larvae from feeding on garden plants.
g. Give prophylactic treatment of phorate 10G or carbofuran3G @ 15 kg ha-1. Carbaryl 5% @ 25 kg ha-1 was found superior and gave good control of cutworms under artificial infestation conditions in tobacco field at Anand, Gujarat (Patel, 2002).
4. Mole Cricket, Gryllotalpa Orientalis and G. Africana (Order- Orthoptera, Family- Gryllotalpidae):
i. Description:
Mole cricket prefers light soils (sandy soils, heavier soils that are made friable by cultivation and mud) which are easier for them to dig into.
ii. Nature of Damage:
Seedlings are cut at the base leading to, poor seedling growth, seedling death, missing plants, root damages. G. africana feed on roots and near ground plant parts of tobacco, but the main harm to tobacco is through physical damage to seedbeds by creating the burrows just under the surface, which uproot the germinating seedlings.
iii. Life Cycle:
The eggs are deposited in a hole constructed by the adult female. Neonate nymph has a white and bluish prothorax and legs. With age, it turns gray to black with white markings. The adult mole cricket is brownish and very plump. It measures 25-40 mm long. The enlarged front legs, which are modified for digging, have strong teeth-like structures.
iv. Management:
a. Cultural control includes maintaining standing water, which can help to remove the eggs from the soil.
b. Construction of a raised nursery should be avoided to reduce feeding damage on seedlings.
c. Conserve natural predators like sphecid wasp, carabid beetle and nematodes.
d. Poisoned baits made by mixing moistened rice bran and insecticide that can be placed along rice bunds can kill night-foraging mole crickets in rice crop.
e. Drenching of chlorpyriphos 0.04% effective to control the pest.
5. Earwigs Forficula Auricularia (Order- Dermaptera, Family- Dermapteridae):
i. Description:
Earwigs feed most actively at night and seek out dark, cool, moist places to hide during the day. Common hiding places are under loose clods of soil, boards, or dense growth of vines or weeds or even within fruit damaged by other pests such as snails, birds, or cutworms. The adult earwig is readily identified by a pair of prominent defence appendages that resemble forceps at the tail end of its body.
ii. Nature of Damage:
Earwigs may attack soft fruit such as apricots, strawberries, raspberries, or blackberries but do not harm hard fruit such as apples. On corn, earwigs feed on silks and prevent pollination, causing poor kernel development. Earwigs may also seriously damage flowers including zinnias, marigolds, and dahlias. This insect causes damage in night and can be seen in flashlight.
iii. Life Cycle:
Female earwigs dig cells in the ground in the fall and winter where they lay masses, of 30 or more eggs. Eggs hatch into small, light brown nymphs and remain in the cell protected and fed by their mother until their first molt. Generally there is one generation a year, but females produce two broods.
iv. Management:
The following insecticides can be used as baits, liquids, sprays, granules, or dusts- carbaryl, acephate, cyfluthrin, fenvalerate, and propoxur.
6. Black Scarab Beetles (Order- Coleoptera, Family- Scarabaeidae):
i. Description:
Most scarab beetles are robust, convex insects with brown or black coloring. Whatever the colouration, size, or shape, scarabs beetles have a key common feature, lamellate antennae that can be closed tightly. Scarab beetle larvae (grub) are c-shaped and usually live in the ground, feeding on roots.
ii. Nature of Damage:
In many species, the larvae feed on plant roots, though some feed directly on dung or carrion. The scarabs found in black soils have a two year larval stage. The eggs would have been laid in the pasture in spring/summer and the small larvae developed while feed on the roots of the pasture grasses. The larvae are large (up to 30 mm), and feed voraciously. When the pasture was removed and the winter cereal planted, the scarab larvae start feeding on the emerging cereal plants.
iii. Life Cycle:
Scarabs complete metamorphosis with four stages of development – egg, larva, pupa, and adult. Scarab beetles generally lay their eggs in the ground, in dung, or in other decomposing materials including carrion.
iv. Management:
a. The rapid removal of plantings following harvest and pre-plant fumigation destroy beetle larvae and pupae in the soil.
b. Soil solarisation may be effective for beetles in the Central Valley.
c. The use of sudan grass as a cover crop may serve to increase the population levels in the field.
d. Parasitic nematodes like Setainernema, Heterorhabditis that target immature insects in the soil are available commercially.