Redgram

Insect Management

Introduction

• Pigeonpea provides very attractive and nutritious food, not only for humans but also for many animals.
• The seeds, and other parts of the plant, are fed upon by many insects, with over 200 species having been recorded in India alone.
• Some of these insects cause sufficient crop losses to be regarded as major pests, but the majority are seldom abundant enough to cause much damage, or are of sporadic or localized importance, and as such may be regarded as minor pests.
• Hundreds of other species of insects and other animals are found on pigeonpea plants and many of these are beneficial, for they feed upon the pests, either as predators or parasitoids.
• It is extremely important that farmers should become familiar with the insects and other animals that inhabit pigeonpea crops and not simply rush in to treat the plants with pesticides as soon as they see a few insects.
• Insects are found chewing or sucking pigeonpea plants from seedling to harvest, and no part of the plant is immune to attack.
• Plants that are heavily attacked before the flowering stage which can lose a large proportion of their leaf area and will apear to be very badly damaged.
• Pigeonpea has been described as a very forgiving plant, for it can recover from the many setbacks that it may encounter.
• Most pigeonpea genotypes produce an over abundance of buds and flowers, and most of these will be shed, so the loss of a large proportion to insect attacks may not result in measurable yield loss.
• Even the total loss of the flowers may not greatly reduce yield, for the plants can grow on to produce a compensatory flush, that will have a large yield potential, provided the pest attacks abate, and the soil fertility, moisture, and climate remain favourable.
• Pod damage or loss can greatly reduce crop yield, for the
• pigeonpea's potential to compensate for pod damage is limited ,thus, the pod-damaging insects are the most important pests on this crop.

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Aphids

Aphis craccivora Koch in pigeonpea and chickpea, Aphis fabae Scopoli in pigeonpea

Myzus persicae (Sulzer) in pigeonpea, Macrosiphum spp in pigeon pea

Acrythosiphon pisum (Harris) in chickpea

Order: Homoptera

Family: Aphididae

Distribution

• Several species of aphids have been reported in pigeonpea and chickpea, among which A. craccivora is the most prevalent.
• This species is widely distributed and has a broad host range.

History

• A. craccivora is common in a number of leguminous crops.
• The adults are black and shiny, up to 2 mm long and some are winged.
• The nymphs are similar to the adults but smaller.
• This species can reproduce without mating in Asia creating one generation in a week under optimum conditions.
• Individual adults can produce about 100 nymphs over a lifep of up to 30 days.

Symptoms

1. A. craccivora in Pigeon pea
2. Ladybird beetles attacking aphids

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2

• Aphids colonize the young shoots, flowers, and pods of both crops.
• Young leaves of seedlings become twisted under heavy infestation.
• Seedlings may wilt, particularly under moisture-stressed conditions.
• However, a more notable issue in chickpea is stunt disease, caused by the bean leaf-roll virus transmitted by these aphids.
• Stunt disease limits plant growth, rendering leaflets small, and reddish brown (yellow in kabuli-types).
• Scraping the lower part of the stem reveals brown phloem, a characteristic of the disease.

Control

• The winged adults that land on chickpea may be deterred and fly off, or be killed by the acid exudates on leaves and pods.
• Chickpea genotypes with little or no exudates maintain the largest colonies.
• Aphids are seldom key economic pests for either pigeonpea or chickpea crops.
• Natural enemies and abiotic factors generally keep aphid populations in check. Both general predators, such as and specific parasitoids, such as the Aphytis spp inflict heavy mortality on aphid colonies.
• Among abiotic factors, rain and wind can dramatically reduce aphid infestations.

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Blister Beetles

Mylabris pustulata Thunberg Mylabris thunbergii Billberg Mylabris spp

Distribution

• Blister beetles are widespread in pigeonpea in Asia.
• In addition to pigeonpea, these insects feed on the floral parts of several other plants.

History

• Mylabris pustulata adults measure about 25 mm in length and have red and black alternating bands on the elytra.
• Other species may vary in size but all are brightly colored.
• 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 complete biology of these species is not documented.

Symptoms

Mylabris pustulata adult

Adult beetles feed on flowers and tender pods, and may have a significant impact on yields, especially of short-duration genotypes.

Control

Hand picking of blister beetles

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. Chemical control may fail because the beetles are large and robust, and highly mobile. Manual picking and destruction of adult blister beetles is often the only practical control measure.

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Blue Butterflies

Lampides boeticus,

Catochrysops strabo

Order : Lepidoptera

Family : Lycaenidae

Distribution

• Both of these species are widely distributed in Asia. Larvae feed on pigeonpea, and on several other cultivated and wild legumes.

History

• Lampides boeticus adults are slender, bluish-gray with a wingp of 30 mm. Pale blue eggs are laid singly on buds.
• Larvae are about 12mm long, green, oval, flat and slug-like.
• In contrast to other lepidopterans on pigeonpea these caterpillars are relatively sedentary. Pupation occurs in the soil or in plant debris.
• Five weeks are required to complete one generation in field conditions.

Symptoms

Lampides boeticus adult

Lampides boeticus egg

Lampides boeticus larva

• The larvae chew leaves, buds, flowers, and pods.

Control

• Although these butterflies are common and lay many eggs on pigeonpea plants, relatively few larvae are found on the crop, probably because natural enemies reduce their numbers.
• Specific control for these insects is rarely required but the general management recommendation for H. armigera may be used here.

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Cow Bugs

Otinotus oneratus

W. Oxyrachis tarandus F.

Order : Homoptera

Family : Membracidae

Distribution

• These two species are widely distributed across South Asia. and feed on other legumes besides pigeonpea.

History

• The dark brown to black adults measure approximately 7 mm in length, and have horn-like projections on the thorax.
• Eggs are laid in clusters of 15-20 on stems.
• Cow bugs excrete honeydew, a sugary substance that attracts ants.
• The ants may protect the bugs from natural enemies. which would otherwise keep cow bug populations in check.
• To complete a cycle about a month is required under optimum conditions.

Symptoms

Cow bug adults and nymphs attended by ants

Nymphs and adults feed on tender shoots. These bugs are normally sporadic in occurrence and consequently of minor economic importance. However, their high visibility makes farmers over-react to infestations. Heavy infestations during early growth of the crop can result in stunting and reduced plant vigor. However, it is unlikely that cow bug damage adversely affects mature plants.

Control

• Because cow bug attacks are sporadic and do not generally cause any economic damage, no specific management strategies are suggested.

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Jassids

Empoasca kerri Pruthi

Order: Homoptera

Family: Cicadellidae

Distribution

• In most areas where pigeonpea is grown, jassids are found feeding on this crop.
• They are not easy to identify, frequently requiring the assistance of specialists.
• In India, Empoasca kerri is the species most commonly reported

History

• These small green insects 2.5 mm long, suck sap from both the upper and lower surface of the leaflets.
• The adult (Fig. 6) fly when disturbed.
• The nymphs and adults have similar shape and color, but the nymphs do not have wings and run sideways when disturbed. Eggs are laid along veins on the underside of leaflets.
• One generation requires 2 weeks under optimum conditions.

Symptoms

Empoasca kerri ault

Jassid-damaged leaves

• Leaflets damaged by jassids are cup-shaped and have yellow edges and tips.
• Seedlings that have sustained considerable feeding by jassids may be stunted and have red-brown leaflets followed by defoliation.

Control

• Jassids are usually a minor pest of pigeonpea.
• They can become a serious threat if the seedling stage is heavily infested.
• Under these conditions, application of any contact or systemic insecticide is adequate restraint.

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Jewel beetle

Sphenoptera indica

Order: Coleoptera

Family : Buprestidae

Distribution

• The destruction caused by this insect though sporadic, is widespread in Asia. It is associated with several legumes including pigeonpea.

History

• Adults are dark, shiny beetles about 10mm long and 3 mm wide.
• Eggs are laid singly on stems, at the soil surface. On hatching, grubs bore into the stem.
• A fully grown larva is 25 mm long with a conspicuous, globular head. Pupation occurs in the tunnel in the root or stem.
• A generation takes about 6-8 weeks.

Symptoms

Sphenoptera indica damage to stem

Different life stages of Sphenoptera indica

• Larvae tunnel in the stem above and below ground.
• A prominent gall may form around the stem at ground level, and may be mistaken for similar galls associated with other insects, including weevil larvae.
• Wilting and death may occur when young plants are attacked, but older plants may survive with little reduction in yields.

Control

• Because of the infrequent occurrence of this pest and its delayed infestation, it is difficult to recommend appropriate control strategies.
• Manual destruction of infested plant stems may help in reducing its population.

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Legume (or Cowpea) Pod borer

Maruca vitrata

Order: Lepidoptera

Family: Pyralidae

Distribution

• Maruca vitrata attacks several leguminous crops throughout Asia.

History

• Adults have distinctive white bands on brown forewings with a whngp of 20 mm.
• Eggs are laid in small clusters of 10 to 15 on leaves, buds, and flowers.
• A full-grown larva measures 15mm in length, with a pale body lined by rows of conspicuous black spots on its dorsal surface.
• The spots may be absent or obscure at the prepupal stage.
• Pupation takes place in the web or on the soil surface in a silk cocoon.
• Under optimum conditions. a complete life cycle takes 3 weeks. M. vitrata becomes a menace in early-season pigeonpea especially in areas with high relative humidity.

Symptoms

Maruca vitrata adult

Maruca vitrata Larva

• Larvae feed from inside a wbbed mass of leaves, buds, and pods. This behaviour makes Maruca a foliage feeder and pod borer.

Control

• This is a leading pest of pigeonpea and other grain legumes in many areas of Asia.
• Indeterminate pigeonpea genotypes suffer less damage than the determinate-type.
• This difference in susceptibility among genotypes may be used to develop cultivars resistant to this insect.
• Relatively few natural enemies, and no egg parasitoids, havew been reported to attack M. vitrata.
• Chemical control is complicated by the fact that larvae live in well-protected webs.
• Systemic pesticides may accomplish more restraint than contact insecticides.

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Lepidopteran defoliators

Amsacta albistriga Walker and A. morri Butler

Spilosoma (Diacrisia) obliqua (Walker) (Lepidoptera: Arctiidae )

Euproctis subnotata(scintillans) walker

Order: Lepidoptera

Family : Lymantridae

Distribution

• Larvae of a number of widely distributed, polyphagous Lepidopterans feed on pigeonpea leaves.
• Three of the most dominant are listed above. The damage caused by them is similar and distinct.

History

• The Amsacta spp has one generation per year in India while S. obliqua and E. subnotata have multiple generations in a year each with a generation time of 30-40 days.
• Larvae of Amsacta spp. and S. obliqua are up to 50 mm long with reddish-brown hairs.
• In contrast, those of E. subnotata are smaller, up to 25 mm long, darker, and less hairy.
• They are easily identified by the prominent, dense tuft of hair on the back of the head.
• The larval period for these three species is about a month and they pupate in the soil.

Symptoms

Amsacta albistriga adult and larva

Spilosoma obliqua adult and larva

Euproctis subnotata adult and larva

• Amsacta albistriga and spilosoma obliqua are the two most common of several species of "hairy caterpillars" that attack pigeonpea during the vegetative phase.
• Euproctis. subnotata, the so-called 'tussock caterpillars', also attack pigeonpea.

Control

• These species rarely cause serious economic damage, however there are occasional reports of severe defoliation, particularly by the Amsacta spp.

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Lima bean pod borer

Etiella zinckenella

Order :Lepidoptera

Family Pyralidae

Distribution

• This species is widely distributed on several legumes in Asia.

History

• Adults are small, brown moths with a wingp of about 20 mm.
• Eggs are laid in clusters of 2-12 on fully mature pods.
• The young larvae are green, but become pinkish- red as they get older.
• Larvae feed inside the pod, reaching a maximum length of 15 mm.
• Pupation takes place in the soil. One generation requires 4 weeks under favorable conditions.

Symptoms

Etiella zinckenella adult

Etiella zinckenella larvae

• Larvae are generally found infesting maturing and dried pods.
• Lima bean pod borer populations build up by the end of the pigeon pea season, when the temperature is high.
• The presence of dry, light-colored frass granules, and webbing in the pod is an indication of Etiella infestation.

Control

• In India, E. zinckenella is not ranked a noteworthy offender of pigeonpea, deserving any explicit course of action.

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Leaf webber

Grapholita (Cydia) critica

Order : Lepidoptera

Family: Tortricidae

Distribution

• Grapholita critica Eucosma = cydia critica is commonly found in pigeonpea throughout South Asia.

History

• G. critica is an inconspicuous, brown moth with a wingp of 10-15 mm.
• Eggs are normally laid in clusters of about ten, on buds and young leaves.
• The cream-yellow larva reaches a length of about 10mm before pupating within the webbed plant material.
• It takes 3-4 weeks for a full life cycle under optimum conditions.

Symptoms

Grapholita critica larva in webbed leaves

Bud damaged by Grapholita critica larva

Grapholita critica moth

• Larvae produce silk and use it to hold leaflets together.
• They feed from inside a web of leaflets, flowers, and pods.
• When infestation includes the terminal bud, further growth of that shoot may be severely impaired.
• Infestations may begin as early as the seedling stage and continue through to the flowering and podding stages.
• Though primarily a foliage feeder, G. critica may also attack reproductive structures, especially when infestation occurs late in the development of the crop.
• In such cases, the leaf webber also behaves as a pod borer.

Control

• The leaf webber damage is very conspicuous, causing farmers anxiety about possible yield losses.
• Although leaf-webber infestation being highly visible may induce the use of chemical pesticides, its impact on yield is usually negligible.
• In fact, plants may produce side branches to compensate for the loss of terminal buds.
• A large number of parasites and predators are also associated with this pest.
• Inappropriate use of chemical pesticides may have a negative impact on the natural enemies that attack major pigeonpea pest and little effect on well-protected, leaf webber larvae housed in the webbed leaves.

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Leaf-damaging weevils

Myllocerus undecimpustulatus , Phyllobius spp

Order : Coleoptera

Family : Curculionidae

Distribution

• Myllocerus spp and Phyllobius spp are widespread in Asia in pigeonpea and several other host plants.
  1. The adult M. undecimpustulatus is 5 mm long with 11 black dots on its ash-grey body, and hence commonly called "ash weevil".
  2. Grubs are white, legless, and stout-bodied.
  3. The biology of these species is not fully known.

History Symptoms

Leaves damaged by Myllocerus spp

Myllocerus undecimpustulatus adult

• Grubs live in the soil, where they feed manly on roots. Pupation also occurs in the soil. Thogh common, the damage caused by adults and grubs is not significant enough to merit separate control measures.

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Mites

Eriophyid mite : Aceria cajani

Order: Acarina

Family : Eriophyidae

Red spider mite: Schizotetranychus cajani , Tetranychus spp

Order : Acarina

Family: Tetranychidae

Distribution

• These mites are widespread and common in pigeon pea throughout South Asia.
• Both eriophyid and spider mites are generally found on the lower leaf surface.
• The eriophyid mite, A. cajani, is the vector of the pigeon pea sterility mosaic disease, the most serious viral disease of this crop.

History

• The eriophyid mite is about 0.2 mm long and difficult to see without magnification (10 x or more).
• They are light-colored, long and spindle-shaped, and deposit their eggs on young foliage.
• In contrast, spider mites are larger at 0.5 mm, oval-shaped, and dark-colored.
• Both groups of mites can complete a generation in less than two weeks under optimum conditions.
• Dispersal is either a direct plant-to-plant or wind-aided.

Symptoms

1. Pigeonpea leaves damaged by red spider mites

2. Schizotetranychus cajani (red spider mite)

3. Aceria cajani (eriophyid mite: close-up

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• Plants infected with sterility mosaic disease develop light green, chlorotic foliage.
• Leaves have a mosaic pattern, and early infection results in reproductively sterile plants.
• Spider mites cause yellow or white spots on the upper surface of the infested leaflets.
• Heavy infestation results in bronzing of the leaves, followed by defoliation.

Control

• In general, mite attack by itself does not pose an economic problem in Asia.
• However, the transmission of sterility mosaic disease by mites can cause significant yield reductions.
• The selective use of resistant cultivars is the most effective solution.
• Rain can also substantially reduce mite populations.
• Attack by red spider mites may become severe in pigeonpea plants grown in greenhouses as the intensive chemical apraying eradicates diseases that red spider mites would otherwise succumb to.
• A number of generalist predatiors such as spiders and coccinellids that feed on mits keep their population under control.
• Several Tetranychus spp have developed high levels of resistance to one or more pesticides, hence caution is advised in their use as a preventive step against further mite outbreaks.

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Plume Moth

Exelastis atomosa

Order : Lepidoptera
Family : Pterophoridae

Distribution

• This species is widely distributed on several legumes in Asia.
• It is common in pigeonpea and is a major post in several areas of India.

Symptoms

Exelastis atomosa adult

E. atomosa larva (green) and puma (brown)

• Larvae feed on buds, flowers and pods, resulting in reduced yields.

History

• Adult plume moths measure 10mm in length, and have fringerd wings that are held perpendicular to the body at rest.
• Eggs are laid singly on buds and pods.
• The full-grown larva is about 15mm long, green, and has a spindle-shaped body covered with short spines.
• Pupation occurs in the foliage and the pupa is similar in looks to the larva, except that it is brown.
• An egg to egg cycle can be accomplished in about 4 weeks.
• Plume moth caterpillars are more rampant during the postrainy season than during the rainy season.

Control

• Exelastis atomosa can be quelled by the same insecticides, excluding HNPV, employed to suppress outbreaks of H. armigera.

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Pod borers

Scientific Names Helicoverpa (Heliothis) armigera, Helicoverpa assulta, Heliothis viriplaca, Heliothis peltigera

Order : Lepidoptera

Family : Noctuidae

Distribution

• Helicoverpa armigera is commonly found throughout the tropics and subtropics in Asia, and has an assortment of host plants.
• It is the single most important constraint to pigeon pea and chickpea production throughout much of South Asia.
• In addition to its wide distribution and host range, high levels of insecticide resistance make this species one of the most difficult pests to manage.
• In West Asia, H. viriplaca and H. peltigera are also found in chickpea, while Ho assulta is occasionally reported in chickpea in India.

History

• Adult H. armigera have a wingp of about 40 mm with dull brown forewings.
• A single female can lay up to 2000 small white eggs usually singly.
• In pigeonpea eggs are laid on flower buds and young pods while in Chickpea' eggs are usually deposited on foliage.
• Full-grown larvae are 30 to 40 mm long and may have various body color and banding patterns.
• Pupation occurs in the soil or in plant debris. One generation takes 4 weeks under favorable conditions.

Symptoms

Male (down) and female (above) pod borer adults

H. armigera eggs on pigeonpea flower buds

H. armigera damaging pigeonpea leaves and pods

• The Helicoverpa spp destroys buds, flowers, and pods on both crops.
• If flowers and pods are not available, larvae will feed upon foliage.
• Foliar damage is more common in chickpea than in pigeon pea.
• Larvae prefer to feed on the protein-rich seeds within the pods.

Control

• H. armigera is one of the key pests of pigeon pea and chickpea and must be the focus of any pest management program.
• A full discussion of integrated pest management is provided in the last section.
• Individual pest management measures for their eradication are listed below and further information is provided under the "Additional Reading" section at the end of this booklet.

Cultivar adoption

• A number of pigeon pea and chickpea genotypes with resistance and/or tolerance to H. armigera have been developed.
• These genotypes, though effective, have not been adopted at large.
• The reasons include lack of seed, susceptibility to diseases, low yield quantity and/or quality, and less-preferred agronomic traits.

Natural enemies

Birds feeding on caterpillars

There reportedly exist a large number of natural enemies of H. armigera, though many are less effective in pigeon pea and chickpea than in other crops. Some success in restriction has been demonstrated by manipulating natural enemy populations, including vertebrate predators such as birds.

Crop management

• Cultural practices, including intercropping, time of sowing, spacing, water/nutrition management, and crop rotation may be effective in certain locations.
• It is difficult, to suggest general strategies irrespective of region.
• Insecticides are the most commonly used restraint for this pest in pigeonpea and chickpea.
• Several insecticides, individually or in combination, have been successful in checking the pod borer.

Organic pesticides

Podborer affected by NPV

Manual shaking of pigeonpea to dislodge Helicoverpa larvae

• A fatal viral disease of H. armigera attributed to the nuclear polyhedrosis virus (HNPV), is currently being produced as a means of control.
• High quality HNPV properly produced and applied has yielded good results.
• Another alternative to synthetic pesticides is the use of naturally occurring plant derivatives.
• These include extracts of neem seed kernel, tephrosia, tobacco, pongamia, chili/garlic, and others.
• Plant protection operations should be initiated in pigeon pea when one notices.
• 1 small larva or 3 eggs per plant in short-duration.
• 3 small larvae or 5 eggs per plant in medium-duration. 5 small larvae or 10 eggs per plant in long-duration.
• For chickpea, plant protection operations should not begin until the flowering stage as plants generally compensate for any damage that occurs earlier.
• The recommended action threshold for Helicoverpa in chickpea is 2 small larvae per plant.
• Female moths can be deterred from ovipositing by the spraying of 5% neem kernel suspension.
• Applying HNPV at a rate of 500 larval equivalents (LE) per ha in pigeonpea, and 250 LE in chickpea at egg hatch is potent.
• This application can be repeated at 15-20 days intervals.
• To minimize UV effects on the virus, spray in the evening and mix 1 ml of a mild detergent for every liter of spray fluid.
• In cases of heavy infestation, physical shaking of pigeonpea plants to dislodge larvae is favored.
• Bird perches placed just above the crop canopy will also help to reduce the numbers of this pest.
• Considering the frequent misuse of pesticides, and their secondary effects such as resistance, resurgence, and creation of secondary pests, synthetic insecticides should be used only as a last resort.

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Pod-sucking bugs

Clavigralla gibbosa

Spinola, Clavigralla scutellaris, Anoplocnemis spp , Riptortus spp

Order Hemiptera

Family Coreidae
Nezara viridula

Distribution

• Several species and genera of pod-sucking bugs attack pigeon pea and other legumes in Asia.
• For pigeonpea, the most dangerous genera is the Clavigralla. Nezara viridula, the green stink bug, is found on many legumes and other hosts throughout the tropics and subtropics.

History

• Clavigralla bugs are brown-gray with C. scutellaris being more robust that C. gibbosa.
• In the field, C. gibbosa and C. scuttelaris are often mistaken for each other.
• The eggs of the two Clavigralla species however, are easily separated; those of C. scutellaris being smooth and shiny, and not roughly sculptured like the C. gibbosa's. C. gibbosa generally lays clusters of 10-12 eggs compared to the 18-20 of C. scutellaris's.
• Nezara viridula is 15 mm long, normally green, but may also have some yellow coloration.
• The adults of the Anoplocnemis spp vary in color from dark brown to black 30 mm, long and are the largest of these bugs.
• The Riptorlus spp are 18 mm long, brown in color, and more slender than the other species.
• All of the pod-sucking bugs lay their eggs in clusters on leaves and pods.
• Most of these species require 4 to 5 weeks to complete one generation.
• Since adults live for more than 3 months, all the stages of its life cycle can be simultaneously observed in the field.

Symptoms

Pigeonpea seed damaged by pod sucking bugs

C. scutellaris and C. gibbosa eggs

Nezara viridula adult and eggs

Anoplocnemis spp adult

Clavigralla gibbosa and C. scutellaris adults

Riptortus adult

• The adults and nymphs of all of these bugs use their piercing mouthparts to penetrate the pod wall and suck the liquid from developing seeds.
• Damaged seeds become shriveled, and develop dark patches. The injury being similar to that of drought stress, and the impact of these pests has been underestimated in the past.
• Seeds spoiled by pod- sucking bugs neither germinate nor acceptable as human food.

Control

• Because pod-sucking bugs are highly mobile, insecticides may be inadequate in repressing the extent of their spread, especially in small fields.
• Natural enemies, in particular various species of egg parasitoids can cause high levels of bug mortality by the end of the season.

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Pod Fly

Melanagromyza obtusa

Order : Diptera

Family : Agromyzidae

Distribution

• Melanagromyza obtusa is a widespread and major pest of pigeonpea in Asia.
• It has a narrow host range and only feeds on pigeonpea and closely related species.

History

• The small, black fly is about 5 mm in length.
• Eggs are laid in the wall of an immature pod.
• The white maggots feed on the developing seed and reach a length of 3 mm before pupating.
• The brown puparium is formed between the remnant of the seed and the pod wall.
• One generation requires 3 to 4 weeks under field conditions.

Symptoms

Melangromyza obtusa adult

M. obtusa larva, and puparia, in a damaged pod

• Podfly infested pods do not show external evidence of damage until the fully grown larvae chew holes in the pod walls.
• This hole provides an emergence "window" through which the adults exit the pod.
• Podfly-damaged seeds will not germinate and are unfit for human consumption.

Control

• No specific control strategy has been universally implemented for podfly management.
• However, use of systemic insecticides can lessen the extent of podfly damage.
• Work on developing podfly-resistant pigeonpea genotypes is in progress and may provide the ultimate solution to this problem.

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Pod Wasp

Tanaostigmodes cajaninae

Order : Hymenoptera

Family : Tanaostigmatidae

Distribution

• Pod wasp is a minor but widely encountered pest of pigeonpea in India.
• Its incidence outside of India is not known.

History

• Adults are small, only 2 mm long, and shiny-black in color.
• Females lay small, oval eggs on or in flowers, and tender pods.
• The grubs feed on developing seeds reaching a length of 2 mm.
• The wasp pupates in the same locule where it fed.
• In 3 weeks one generation of pod wasp can be completed.

Symptoms

Damaged pods

T. cajaninae adult

T. cajaninae larva

• Eggs are laid very early in pod development, per-haps even in the newly fertilized ovary of the flower.
• Feeding by the grubs produces malformed, atrophied pods that do not grow at all.
• Locules or individual seed compartments that escape invasion may develop into normal seeds, while locules containing pod wasp remain undeveloped giving an abnormal appearance to the pod.
• Pod wasp exit holes are smaller than those of podfly.

Control

• This species is probably a secondary pest resulting from the increasing use of pesticides on pigeonpea which have destroyed its natural enemies.
• In India, pod wasp populations do not cause appreciable harm to warrant any control.

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Scale Insects

Ceroplastodes cajani, Icerya purchasi

Order: Homoptera

Family : Coccidae

Distribution

• Though a number of scale insects have been reported to feed on pigeonpea, the two listed above are the most common species in Asia.

History

• These insects are not major pests of the annual pigeonpea; perennial pigeonpea is more frequently attacked, as their populations need a number of seasons to build up.
• One generation can be completed in as little as 2-3 weeks.
• Young nymphs are mobile and can be dispersed by wind.
• Adult females do not disperse and are usually found in colonies.
• Ants are attracted to the honeydew excretions of scale insects thus protecting the scale insect colony from natural enemies.

Symptoms

Colony of scale insects

Scale insects feed on the fluids in stems and occasionally, on leaves.

Control

• Scale insects seldom reach population levels requiring control.
• There are several parasites and predators that keep scale insects in check.
• The abstinence of pesticides will allow these natural enemies to breed and multiply, keeping scale insect levels down.

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Soil beetles

Gonocephalum spp, False wireworms

Order : Coleoptera

Family : Tenebrionidae

Distribution

• Several species of false wireworms are widespread in Asia.
• These insects attack a number of cereal and legume crops in addition to pigeonpea and chickpea.

History

• The adult insect is a dull black in color, about 10 mm long and 5 mm wide beetle.
• In recent years, sporadic but severe seedling mortality in chickpea in southern India has been reported.
• Details of the biology of these species is not available

Symptoms

Gonocephalum spp

Adults feed on seedlings at ground level, killing the plants, and reducing crop stand. Plants that survive will often fill in the open spaces to compensate for low levels of damage.

Control

• Because little is known of these insects, it is not possible to prescribe specific management strategies.
• Close monitoring of their populations is recommended, especially in areas that typically suffer above-average levels of seedling mortality.
• Increased seeding rates to compensate for seedling mortality may minimize crop losses.

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Thrips

Megalurothrips usitatus

Order: Thysanoptera

Family : Thripidae

Distribution

• Several genera and species of thrips attack pigeonpea flowers in Asia.
• The most common species is Megalurothrips usitatus

History

• Adults are black and about 1mm long. Both adults and nymphs feed on flowers.
• Minute eggs are laid in flowers and flower bud tissues.
• When flowers begin to senesce the thrips move to new flowers.
• A generation takes about 3 weeks.

Symptoms

Megalurothrips usitatus

A large number of (up to 50) thrips may be present in each pigeonpea flower. This species also occurs in the flowers of a number of annual and perennial crops. Heavy thrip infestations may result in flower drop.

Control

• Populations of thrips can become quite large, though there is no evidence that thrips cause losses in yield.
• Pigeonpea plants produce more flowers than the plant can sustain, so many are lost naturally.
• No specific control measures are needed for the management of thrips.

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Natural And Biological Pest Control

• Very many factors can adversely affect pest populations.
• High, or low temperatures may slow down or stop their feeding and reproduction.
• Rainfall may wash some insects from the plants and drown them.
• Strong winds may dislodge some pests from the plants, and prevent immigrating adults from landing on the crop.
• These abiotic factors combine with naturally occurring predators, parasitoids, and pathogens to constitute "natural pest control".
• Action to enhance the reduction of pest populations by biological agents is generally referred to as biological control.
• This may be through actions that enhance the build up or effectiveness of the natural enemies, or through "classical biological control" where natural enemies are imported (sometimes from other continents) to supplement the local natural control elements.
• It was observed 19 species of insects, and many species of spiders and birds preying on the eggs and larvae of Helicoverpa.
• Feeding tests in the laboratory have shown that spiders such as Clubiona sp can consume 59.3 eggs or 3.2 small Helicoverpa larvae per day (ICRISAT, 1982).
• Most of the life stages of the podfly are protected from predators, but many of the adults have been observed trapped in spiders' webs.
• It has been suggested that posts should be erected in fields to provide nesting sites for mud wasps such as Delta spp that carry off many large Helicoverpa larvae to feed their young.
• It is also possible to' rear large numbers of predators such as Chrysopa in the laboratory, but such measures are unlikely to be economic Perhaps the greatest potential for biological control in pigeonpea lies in the use of the nuclear polyhedrosis virus (NPV) as a biological insecticide for the control of Helicoverpa.
• Another pathogen that has obvious potential as a biological pesticide is Bacillus thuringiensis (BT) Berliner, and various formulations are commercially available.

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Pesticide Application

• The pesticide chemicals must be spread evenly over the target areas of the crop (usually the upper foliage, flowers, and pods) in order to control the pests.
• Most application is in the form of sprays, using water as the carrier, through manually operated pumps.
• Large quantities of water, up to 1000 L/ha are often recommended to ensure adequate coverage.
• More powerful, and costly, motorized mist blowers can give good plant coverage using much less water 200 L/ha-l.
• Such spraying requires considerable quantities of clean water, which is seldom readily available close to the farmer's field. Such problems encourage the use of dusts, in which the insecticide is mixed with an inert, finely divided carrier such as kaolin. Cheap and efficient crop-dusting machinery is seldom available, so farmers resort to shaking the dust onto the plants through muslin bags, or even throwing handfuls of dust in the air in the hope that the wind will spread it evenly over: the crop. Much of the dust falls to the soil, and heavy rain will wash many formulations from the plants. An apparently attractive alternative means of application, particularly where water is scarce, is provided by battery driven, spinning-disc sprayers which generate many small droplets and can give adequate crop coverage with less than 15 L ha-l. This ultra-low volume spraying is commonly referred to as controlled droplet application(CDA), for the size of the droplets can be controlled within a fairly narrow range by varying the disc speed and the flow rate of the liquid (Mathews, 1979). Care must be taken to ensure that the droplet size is small enough to give adequate crop coverage, but not so small that the droplets drift without landing on the crop. For this type of spraying oils are better carriers than water, since small water droplets may evaporate before they reach the plants.
• Usually, there will be little or no profit in applying insecticides to this crop before the flower buds appear, or before the companion crop is harvested. The height of most traditional pigeonpea crops at the flower bud stage is well over 1m and may exceed 2m. The target for insecticide coverage will be the flowers and pods, most of which will be at, or above, the shoulder Jevel of the farmer.

Problems Associated With Insecticide Use

• Toxicity Dangers
• Natural Enemy Destruction
• Resistance to Insecticides
• Host Plant Resistamce
• Differences in Susceptibility

Monitoring The Pests

• Several night-flying insects, including Helicoverpa are attracted to lights,and it is not difficult to construct a cheap trap that will catch them. Pheromone traps are available for several pest species, including Helicoverpa; a pheromone being a chemical scent that is exuded by a female insect to attract a mate.

Economic Threshold

• Pesticides should only be used when it is evident that the pest-caused damage that will be prevented will considerably exceed the cost of the treatment. Economic thresholds vary across areas and years, depending on the cost of the treatment (pesticide plus application), and the price for which the pigeonpea can be sold.
• Thresholds are normally expressed in average numbers of pests per plant. As a very rough generalisation, insecticide application may be economically justified when there are more than 15 Helicoverpa eggs or larvae on a well grown pigeonpea plant. It must be stressed that insecticide use is only likely to be profitable on well grown crops which have a good yield potential. Pesticides cannot conjure high yields from poorly grown crops.

When To Apply The Pesticide

• Timely application is essential. The appropriate pesticide should be applied on a "need basis" in response to pest counts. All too often the farmer sees his crop being devastated by the pests and then goes off to buy the insecticide, so losing both the crop and his money. Insecticides must be applied as soon as it is evident that a damaging attack is probable, but before the pests have caused much damage. For Helicoverpa, and other chewing pests, insecticides should be applied when their eggs are seen on the crop. It is relatively easy to see and count the white Helicoverpa eggs, but almost impossible to see or count the young larvae.

Choice Of Insecticides

• Pesticides must be effective, profitable, and safe. For most farmers the ideal insecticide would be a cheap chemical that kills all pests and persists on the plant, so that one application would protect the crop. No available pesticide is effective against all of the pests that attack pigeonpea, so the choice of insecticide must depend upon the pest that currently threatens the crop. Contact and stomach poisons tend to be most effective against the chewing pests, while systemic insecticides which penetrate and are carried around inside the plant are particularly effective against the sucking pests. Endosulfan and the synthetic pyrethroids (eg., cypermethrin, deltamethrin, and fenvalerate) are particularly popular for the control of the chewing insects (including Helicoverpa) while dimethoate and carbofuran are commonly used against the sucking insects and mites.

Calendar-Based Application

• The application of pesticides "according to the calendar" is widely practised on pigeonpea in areas where Helicoverpa is a major pest in worst years. When they have invested a great deal of labour and other resources in a crop, the additional cost of pesticides as an insurance against crop loss appears good value. Farmers must be encouraged to monitor their crops from the flower bud stage, and to be prepared to spray as soon as they see more than a few Helicoverpa eggs or larvae on the crop. Repeat the application at 1O-day intervals if there are still many pests on the crop.

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Integrated Pest Management (IPM)

• The recent indications that Helicoverpa in southern India is becoming resistant to insecticides further emphasise the folly of relying upon chemical pest control.
• There is little doubt that insecticides are needed to ensure a profitable increase in pigeonpea production.
• But, they must be used judiciously, in combination with other elements of pest management, otherwise we may soon be faced with pests that are impossible to control.
• Thus, the new genotypes produced by ICRISAT will either be at least as resistant, or tolerant as the cultivars that they are to replace, or will be high-yielding and/or high quality types that can be profitable when adequate protection is available.
• All the farmers in an area should sow simultaneously, so that the pests will be diluted across the crop, rather than building up on the early flowering fields and then migrating to the later ones.
• Insecticides should only be applied when needed; this will seldom be before the flowering stage, so the natural enemies will have an opportunity to build up.
• If any means of biological pest control are available, then these should be used to replace or reduce insecticide use.
• After harvest, the crop residues should be either removed and used as fuel, or ploughed in to the soil, to reduce the numbers of pests surviving from one season to the next.

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