Learn about the insect pests that damage pulse crops and its control.
1. Gram Pod Borer, Helicoverpa Armigera (Hubner) (Lepidoptera: Noctuidae):
The gram pod borer or the gram caterpillar is cosmopolitan and is widely distributed in India. It is a serious pest of chickpea, pigeonpea, pea, mungbean, urdbean, lentil, soybean and cowpea. The insect has also been found damaging cotton, sorghum, okra, maize, tomato, berseem and sunflower. In the United States of America, it is a well- known pest of corn (corn earworm) and cotton (cotton bollworm).
The moth is stoutly built and is yellowish brown. There is a dark speck and a dark area near the outer margin of each fore wing. The fore wings are marked with greyish wavy lines and black spots of varying size on the upper side and a black kidney shaped mark and a round spot on the underside. The hind wings are whitish and lighter in colour with a broad blackish band along the outer margin. The caterpillars cause damage and, when full-grown, are 3.5 cm in length, being greenish with dark broken grey lines along the sides of the body.
Life-Cycle:
The females lay eggs singly on tender parts of the plants. A single female may lay as many as 741 eggs in 4 days. The eggs are shining greenish yellow and are round. They hatch in 2-4 days in April to October and 6 days in February and the young larvae feed on the foliage for some time and later bore into the pods and feed on the developing grains, with their bodies hanging outside. They move from pod to pod and are full-fed in 13-19 days and measure 35 mm in the last instar.
The full-grown larvae come out of the pod and pupate in the soil. The pupa is dark brown and has a sharp spine at the posterior end. In the active season, the pupal period lasts 8-15 days, but in winter the duration is prolonged, particularly in northern India. There may be as many as 8 generations in a year. The caterpillars feed on their fellows if suitable vegetation is not available.
Campoletis chlorideae Uchida (Ichneumonidae) is a larval parasitoid of major importance. In vegetative phase, during the peak of its activity, it may parasitize 50-60 per cent of H. armigera larvae, whereas during podding phase, 30-40 per cent parasitization has been recorded.
Damage:
Although they prefer food plants like gram and red gram, the larvae are polyphagous. They feed on the foliage, when young and on the seed in later stages, and thus reduce yield. A single larva may destroy 30-40 pods before it reaches maturity.
Control:
(i) Timely sowing, i.e., upto mid-October or growing early maturing cultivars which complete podding by first week of March in northern region helps in escaping peak activity period of H. armigera.
(ii) Use of Helicoverpa-tolerant varieties like JG 315 and JG 74 for central zone and ICCV 7 for southern zone is recommended,
(iii) Mixed intercropping with non-preferred host plants like barley, wheat, mustard and linseed should be preferred over sole crop,
(iv) Apply nuclear polyhedrosis virus (NPV) @ 250-500 larval equivalents/ha. Spraying should be carried out in the evening hours,
(v) Spray the crop at the appearance of the larvae at pod initiation with 500 ml of indoxacarb 14.5 SC or 250 ml of fenvalerate 20EC or 400 ml of deltamethrin 2.8EC or 200 ml of cypermethrin 25EC or 2 kg of acephate 75SP or 150 ml of spinosad 4.5 SC in 200-250 litres of water per ha and or dust 25 kg of malathion 5% per ha at the time of pod formation. Repeat treatment after two weeks if necessary.
2. Plume Moth, Exelastis Atomosa (Walsingham) (Lepidoptera: Pterophoridae):
This insect is a specific pest of pigeonpea in many parts of India, particularly in Andhra Pradesh, Assam, Madhya Pradesh, Punjab, Tamil Nadu, Maharashtra and Karnataka. Outside India, it has also been recorded in Nepal and New Guinea.
The caterpillars cause damage by boring into and cutting through the pods while eating the grains. The full-grown caterpillar is greenish brown and measures 1.25 cm in length and has short hairs on the body.
Life-Cycle:
The female moths lay 17-19 eggs singly on tender parts of the plants. The eggs hatch in 2-5 days and the young larvae feed on the pods and become full-grown in 10-25 days. Pupation takes place outside the pod on its surface or in the entrance hole itself. The pupal period extends from 3 to 12 days. The life-cycle is completed in 17-42 days. The pest remains active throughout the year, provided suitable host plants are available, although its incidence remains greater in the monsoon season.
Damage:
The larvae first scrape the surface of the pods and finally make holes into them and feed on the seeds, reducing crop yield.
3. Spotted Pod Borer, Maruca Testulalis (Geyer) (Lepidoptera: Pyralidae):
This pest is wide spread in tropical and sub-tropical regions of the world. It is an important pest of cowpea, lablab, green gram, black gram, red gram, soybean, etc. The moth has a white cross band on the dark brown forewings and a dark border on the white hind wings. The larva is green with a brown head, short dark hairs and black warts on the body.
Life-Cycle:
The eggs are laid singly in the flowers or buds or on the pods of the host plants. After hatching, the young caterpillar enters the bud, flower or the pod. It feeds on the seeds within pods. The entrance hole is plugged with excreta. It pupates within debris or near surface of the ground. The moths shelter among lower leaves.
Damage:
The larvae web together the flowers and feed on them and also bore into pods and feed on the seeds resulting in appreciable loss in yield of seeds.
4. Field Bean Pod Borer, Adisura Atkinsoni Moore (Lepidoptera: Noctuidae):
This is a cold weather pest of lablab and red gram having a wide distribution in India. The adult is a pale yellowish-brown moth, with V-shaped specks on fore wings and pale brown markings on hind wings. The full-grown larva is brownish-green and about 2.5 cm in length.
Life-Cycle:
The eggs are laid in the setting flowers and very young pods. A female may lay as many as 290-950 eggs. The eggs hatch in 2-3 days and the larvae bore into the pods and feed on the seeds. The larval stage lasts 14-15 days and pupates in the soil. The pupal period is 8-16 days. During February to November, it hibernates in the pupal stage.
Damage:
The larvae feed on flower buds and bore into the pods feeding on the developing seeds and cause considerable loss.
5. Lentil Pod Borer, Etiella Zinckenella Treitschke (Lepidoptera: Phycitidae):
It is a serious pest of lentils (Lens esculentus Moench.) and green peas (Pisum sativum L.) in northern India and is also found on a variety of other pulses in various parts of the country, Myanmar and Sri Lanka. The tiny greenish caterpillars enter the pods and eat away the young grains. The full- grown larvae are rosy, with a purplish tinge. The moths are grey with a wing expanse of 25 mm. The fore wings have dark marginal lines and are interspersed with ochreous scales.
Life-Cycle:
The moths emerge in February and March, and are nocturnal. The eggs are laid both singly and in clusters on various parts of the plant, including the pods. Under laboratory conditions, the eggs hatch in 5 days at 25°C, although in nature they may take up to 33 days, depending upon the climatic conditions.
The newly emerged larvae feed on floral parts and subsequently, they bore into the pods to feed on the seeds. The larval stage is completed in 10-27 days. Pupation takes place in the soil at a depth of 2-4 cm and the pupal development is completed in 10-15 days. The pest breeds throughout the year and passes through 5 generations.
Damage:
The larvae consume floral parts, newly formed pods and seeds inside the developing pods. The reduction in yield may be up to 5 per cent.
Control:
At flower initiation, spray the crop with 2.25 kg of carbaryl 50WP in 200- 250 litres of water per ha and repeat the treatment after three weeks, if necessary. Carbaryl should be used if the husk is to be fed to the cattle.
6. Pea Blue Butterfly, Lampides Boeticus (Linnaeus) and Catochrysops Strabo (Fabricius) (Lepidoptera: Lycaenidae):
Both the species of pea blue butterfly are found in Europe, Africa, Australia, and South and Southeast Asia. The adult of L. boeticus is a strong flyer with a jurky and rapid flight, and measures 24-34 mm in wing expanse. The male is dull purple with two black tornal spots on each hindroing. The female is brown with wing bases pale shining blue. Faint marginal spots and two tormal spots can be found on each hindwing of the female. The larva is pale green with a roughened skin and measures 14-15 mm when full-grown.
Life-Cycle:
The eggs are laid singly on young shoots, flower buds or leaves of the host plant. The egg is disc like (0.5 mm dia) with a depressed micropyle. The eggs hatch in 4-7 days. The newly hatched larva makes its way to a flower bud and spends much of its time protected by the petals. It stays within the flower bud and feeds on the flower parts.
The larva passes through four instars and the total larval duration is 9-27 days. Pupation takes place after one day of pre-pupal stage. The mature larva pupates on the leaves, twigs or on pods and the pupal period is completed in 7-19 days. The pupae can be found amongst the dry flowers and developing seed pods. The adults last for 2-6 days and the entire life-cycle is completed in 20-55 days.
Damage:
The larvae feed on flowers, buds, seeds and pods of red gram, cowpea, pea and dew bean and do considerable damage. The holes are seen in the damaged pods.
7. Red Gram Pod Fly, Melanagromyza Obtusa (Malloch) (Diptera: Agromyzidae):
This pest occurs wherever red gram (arhar) is grown in India but is most common in northern India. It is a small metallic-black fly, whose tiny maggots bore into the pods and feed on seeds.
Life-Cycle:
The adult female fly thrusts its minute eggs into the shell of a tender pod. They hatch in 2-4 days. The maggots feed under the epidermis for some time and then enter the seed. They are full-grown in 5-10 days. Pupation takes place inside the damaged pods and the pupal period lasts 4-13 days. The adults emerge by cutting holes. The life-cycle is completed in 11-27 days and several generations are produced in a year.
Damage:
The maggots eat away only a part of the seed and the partially damaged seed becomes subject to bacterial and fungal infections. The damaged grains do not germinate and become unfit for human consumption.
Control:
Spray 1.75 kg of carbaryl 50WP in 200-250 litres of water on dwarf varieties and 300 litres on tall varieties per ha at the time of 50 per cent flowering. Repeat the spray after 15 days.
8. Blister Beetle, Mylabris Pustulata (Thunberg) (Coleoptera: Meloidae):
Blister beetles are widespread in pigeonpea in several Asian countries. In addition to pigeonpea, these insects feed on floral parts of several other plants. M. pustulata adults measure about 25 mm in length and have red and black alternate bands on the elytra. Other species may vary in size but all are brightly coloured.
Life-Cycle:
Eggs are usually laid in the soil and the diet of the larvae consists of other soil insects, including major pests. Thus while the adults may cause considerable damage, the larvae are beneficial. The pest has been found to be active during August to October, particularly in southern India.
Damage:
Adult beetles feed voraciously on flowers and tender pods greatly affecting pod setting. This may have a significant impact on yield, particularly of short duration varieties. In locations where pigeonpea is a primary crop, the after effect of blister beetles is inconsequential because their numbers are diluted over a large area. Pigeonpea genotypes that flower early or crops cultivated on small holdings may suffer substantial injury inflicted by these insects.
Control:
(i) Manual picking and destruction of adult beetles is quite useful.
(ii) Spray 500 ml of indoxacarb 14.5SC or 2 litres of acephate 75SP or 500 ml of deltamethrin 2.8EC in 200-250 litres of water/ha.
9. Semilooper, Autographa Nigrisigna (Walker) (Lepidoptera: Noctuidale):
Several species of semiloopers have been reported to feed on chickpea, but A. nigrisigna is the most important causing economic loss to the crop in northern India. Adults have typically patterned forewings with a wingspan of 25 mm. The larvae are green and reach a length of 25 mm when full-grown.
Life-Cycle:
Greenish white, spherical and sculptured eggs are laid singly or in clusters of 2-15 eggs per mass on the lower surface of the leaves or on the tender parts of stem of the host plant. The incubation, larval and purpal periods last for 3-4, 9-27 and 6-8 days, respectively. The larvae moult five times before pupation. Pupation takes place in the silken cocoon hanging on the host plant Total life-cycle is reported to last for 28-39 days. Four generations have been recorded during November-March.
Damage:
The newly hatched larvae scratch the chlorophyll from the leaves of the host plant with the result that whole leaves become whitish and skeletonized. Grown up larvae feed on leaves, buds, flowers and pods. The larvae produce ragged, irregular damage to the pod walls and normally eat away the whole pod. In contrast, H. armigera larva makes a neat, round hole in the pod and feeds on seeds inside.
Control:
Spray 500 ml of dichlorvos 100 in 200-250 litres of water/ha.
10. Tur Pod Bug, Clavigralla Gibbosa Spinola (Hemiptera: Coreidae):
This insect is widely distributed in the Indian Sub-continent and adjoining countries including Myanmar. It feeds on pigeonpea, lab-lab, cowpea, chickpea, kidney bean, cluster bean, etc. In India, it has been recorded from Delhi, Orissa, Tamil Nadu, Uttar Pradesh, Maharashtra, Madhya Pradesh, Andhra Pradesh, Karnataka and Bihar. Both the nymphs and adults suck cell sap and are harmful to the crops.
The adult bugs are greenish brown in colour, having a spined pronotum and the femur, swollen at the apical end. The bugs are about 20 mm long. The young nymphs are reddish and show prominent lateral spines on the prothoracic and abdominal segments.
Life-Cycle:
The bugs appear on crops in October. They mate several times in end to end position and the copulation period varies from an hour to nearly 24 hours. After a lapse of about 11 days, which is the pre-oviposition period, the females lay eggs. The eggs are usually laid on pods and, less frequently, on leaves or the floral buds, in clusters of 5-25 each. A female, on an average, lays 60 eggs during an oviposition period of 15 days.
The eggs hatch in about 8 days and the newly-hatched nymphs move away from the egg shells within 10-15 minutes and gather together at a suitable feeding spot. They are gregarious in nature and are seen feeding in groups. The nymphs take about 17 days to complete development, after passing through five nymphal stages. The pest is active from the middle of October to the end of May and completes six overlapping generations during this period.
A minute insect, Hadronotus antestiae Dodd (Scelioni-dae), parasitizes the eggs of this pest. It has been observed in nature that upto 55 per cent of the eggs might be attacked and destroyed.
Damage:
Both the adults and the nymphs suck cell sap from the stem, leaves, flower-buds and pods. As a result of this damage, the pods show pale yellow patches and later on shrivel up. The grain inside remains small in size and the yield may be reduced significantly.
Control:
Spray 1.25 litres of monocrotophos 40EC or one litre of trichlorphon 50EC in 625 litres of water per ha. Two sprays during flowering and three during pod formation are quite effective.
11. Pod Bug, Riptortus Pedestris (Fabricius) (Hemiptera: Coreidae):
This is a pest of red gram, cowpea, lablab, soybean and other pulses, and is widely distributed. The adult is a dark-brown bug measuring 15 mm long.
Life-Cycle:
The adults mate 2-3 days after emergence and repeat it throughout life. Egg laying starts 12-14 days after emergence. A female lays, on an average, 115 eggs during on oppositional period of 30 days. Eggs are laid singly on pods at their base and hatch in 3-4 days. There are 5 nymphal instars in about 16 days. The adult lives for 45-47 days.
Damage:
The damage is caused by nymphs and adults by sucking juice from seeds piercing the pods in the process. The seeds within the pods become rough and rugged. Tender pods when attacked do not develop.
12. Green Potato Bug, Nezara Viridula (Linnaeus) Hemiptera: Pentatomidae):
The green slink bug is cosmopolitian and is believed to have originated in Ethiopia. It is now widely distributed in tropical and subtropical regions of Europe, Asia, Africa and the Americas. The adult is shield-shaped with an overall dull green colour (Fig. 14.4). The adult has three white spots on the pronotum and measures about 15 × 8 mm. Newly hatched nymphs are deep orange and later instars turn into shades of black, green with multicoloured spots.
It is highly polyphagous, feeding on plant species in more than 30 families. It causes considerable damage to various crops including cucurbits, crucifers, avocado, cocoa, pecan, sunflower, groundnut, okra, tomato, potato, rice, black gram, mungbean, ricebean, pigeonpea, cowpea and soybean. Stink bugs are well known for the obnoxious odour produced by the scent glands located on the metasternum.
Life-Cycle:
Eggs are laid in tightly packed, single layered rafts in the upper canopy of the herbaceous host plants, mostly under leaves or fruiting structures. The pre-oviposition, oviposition and postoviposition periods average 4.5, 13.0 and 7.6 days, respectively. Each female lays 165-290 eggs, with an average of 260. The eggs hatch in 6-7 days.
The first instar nymphs do not feed and form light clusters at their natal site. Second and third instar nymphs also cluster, perhaps for protection, but they disperse if disturbed. Fourth and fifth instar nymphs do not aggregate. In all, there are 5 nymphal instars, which average 12.3, 9.0, 4.3, 10.9 and 10.6 days, respectively.
The total nymphal period is 45.1 days and the total life-cycle from egg to adult emergence is completed in 53 days. The adult lifespan is 8.5 days for males and 25.1 days for females. The insect overwinters as an adult and hides in the bark of trees, leaf litter or other locations to protect from the weather. Adults leave their hibernation sites in spring, start feeding, mainly nocturnally, and soon mate and oviposit.
Damage:
Both adults and nymphs cause damage and may attack all parts of the plant including the stems and leaf veins, but the bugs feed mostly on fruiting structures and growing shoots. The piercing and sucking mouthparts puncture the plant tissues and form minute, hard, brownish or blackish spots. Feeding punctures also provide access to fungal and bacterial infections.
The bugs reduce seed yield, increase the proportion of seedless pods and decrease germinability of the seeds. Pods punctured during early endosperm formation are largely drained of their contents. Developing seeds from which the bugs have fed usually do not grow to full size, and are shrivelled and deformed.
Control:
(i) Same as in case of the pod bug.
(ii) Fourth and fifth instar nymphs and adults bask outside the plant canopy until about mid-day, so application of insecticides is most effective at that time.