Biology and Management of Key Insect Pests of Pulse Crops Essay Example

chapattis and cooked rice in the form of dhal. They can also be used as flour, for instance, chickpea flour which is referred to as 'besan'. These seeds, when sprouted, are commonly incorporated in different salads not just within India but also internationally. The sprouting process enhances levels of vitamins, minerals and protein while reducing both calories and carbs contents significantly. A vast expanse of land all across India is utilised for growing pulses.

In the past, it was commonly believed that pulses generally produced low yields. However, the tireless efforts of our scientists along with the emergence of newer technologies have resulted in pulses that have a higher production potential. Despite this improvement, several factors seriously hinder the production of pulses, such as insect pests and diseases, insufficient rainfall, and others. Such low yield perceptions may persist as pulses have traditionally been cultivated in marginal conditions and arid regions, making farmers heavily dependent on rainfall.

Various pulse crops are grown in different parts of India all year round, each boasting its distinct cultivation benefits, consumption requirements, and post-harvest processes. These encompass Chickpea or Bengal Gram also referred to as Gram (Cicer airetinem), Pigeonpea or Tur (Cajanus cajan), Black Gram or Urad (Vigna mungo), Green gram or Moong (Vigna radiate), Lentil or Masur (Lense culimaris), among others. The total annual production amounts to roughly 13 million tonnes, with pulses from the Kharif season contributing around 40%.

Gram, which constitutes almost 40% of the total yield, predominates India's domestic pulse production. Tur, a key Kharif season pulse crop, contributes roughly 17%. Urad, Moong, and Masur collectively account for an additional 28% towards the

overall pulse yield. Both Urad and Moong are grown in both Kharif and Rabi seasons with their primary yields coming from Kharif crops. These pulses predominantly thrive under rainfed conditions in Central, Western and Peninsular India's expansive arid and semi-arid regions.

Regions cultivating pulses are significantly influenced by the agro-climatic conditions, which are highly susceptible to variations in monsoon rainfall both geographically and temporally. This results in considerable fluctuations in production and subsequently local availability. The peak pulse production was noted at 14.91 million tonnes during 2003-04 (comprising of 6.17 million tonnes of Kharif pulses and 8.74 million tonnes of Rabi pulses), equalling the record set in 1998-99. This output surpassed the top yield recorded during the fifties by a margin of 14%, but it only marked an increase of merely 5% from ten years earlier.

Despite maintaining the farming area for pulses approximately between 20 and 23 million hectares for the past forty years, advancements in farming technology and their implementation have had virtually no noticeable effect on the productivity achieved in 2003-04. This productivity was mainly due to favourable climatic circumstances rather than technological influence. A significant reason for the low yield is the damage caused by a variety of insect pests on pulse crops, which act as defoliators, pod borers, flower feeders, seed feeders, or as carriers of numerous viral diseases. Roughly 150 insects feeding on diverse pulses in India have been registered (Srivastava, 1964).

Nonetheless, a few of these pose major challenges to the farming of several pulse crops. These injurious insects need to be controlled promptly to protect the yield and boost productivity. In order to manage

these pests effectively, comprehending their biology is of utmost importance. To keep the insect pests below economical threshold levels, it's necessary to undertake an in-depth study of the environmental necessities and their succession in each pulse crop. The introduction of high-yielding varieties coupled with imprudent deployment of insecticides has so altered the pest ecosystem of various pulse crops that erstwhile minor pests have evolved into primary threats.

Reports of fresh insect pests infesting various crops have emerged, necessitating a constant reassessment of the crop pest interactions for a distinct agro-climatic context to prioritize and develop appropriate pest control strategies. The situation exacerbates further with alterations in the cropping system where the practice of multiple cropping increases the existence of alternate host plants for these pests. Conversely, this change has modified the pest matrix and their pattern of succession in pulse crops.

Modern insecticides and their improved promotion have resulted in the imprudent usage of these substances, causing significant disruptions in crop yield. The destruction of natural adversaries by artificial insecticides and the persistent selection pressure exerted by insecticides have resulted in the pests developing resistance and experiencing resurgence, a situation that has now become a common topic of discussion. The goal of my paper is to enlighten you about the pests' most susceptible stages, allowing you to target them effectively and efficiently. Crucial insect pests impacting pulses

The notorious Gram Pod Borer, scientifically known as Helicoverpa armigera (Hubner), from the Noctuidae family and Lepidoptera genus, is a significant threat to a wide range of crops. For instance, it risks pigeonpea, a crucial legume crop in tropical and subtropical regions that accounts

for 5% of worldwide legume production (as mentioned by Hillocks et al., 2000). Not only does this pest wreak havoc to pigeonpea but also causes considerable damage to other crops such as chickpea, field pea, and field beans. The Gram Pod Borer has expanded globally but primarily impacts tropical and subtropical areas where it attacks main agricultural produce like cotton, maize, sunflower, soybean, sorghum,chickpea,pigeonpea,and groundnuts.

Women deposit eggs on the blooming and bearing parts of these crops. The capacity of egg-producing women to discover and exploit a variety of hosts belonging to multiple families is a key factor that advances the pestilence status of this moth (Fitt, 1989). The adult moths bear a yellowish to orange hue on their forewings in females and a greenish-gray shade in males, highlighted by a marginally darker transversal band situated in the distal third. A somewhat distinct, smoky, kidney-shaped marking can also be seen. The rear wings are light gray, marked by a wider, darker edge band, and a tiny brown mark near their base.

Typically, the wingspan of mature moths varies between 35 and 40 mm. The female moth is capable of laying hundreds of eggs on all parts of a plant including its flowers and fruits. These eggs, which range in color from white to brown, have an approximate diameter of 0.5 mm. If the temperature conditions are optimal around 27-28°C, these eggs can hatch within less than three days. Before reaching their full size approximately ranging from 30 to 40 mm, caterpillars experience four stages of growth (instars). Depending on what they consume, caterpillars' body colors may differ; they could be green, yellow, pink

or red-brown to nearly black but generally maintain a light brown head.

A multitude of faint, delicate, undulating, fragmented streaks extend down the body, joined by a noticeable broad stripe of cream colour on either side. Often, one can observe a single prominent dark strip traversing the central part of the back. The body sports thin, dark strips across its upper aspect, which are highlighted by paler bands on either side. Two distinct light-hued and wavy bands, where the darker spiracles are prominent, are a notable feature. The surface of the body is scattered with numerous tiny spines that can be clearly seen with a hand-held magnifying lens — a unique attribute of this caterpillar species. Dark, elevated spots frequently found at the base of fine bristles on the back are also common. The head of this caterpillar is encapsulated in a brown hue.

The background color can vary from different shades of green or yellow to a deep black-brown. It's crucial to note that the caterpillar displays assertive behaviors, showing characteristics akin to a predator and even engaging in cannibalism. These larvae undergo metamorphosis within silk-coated underground chambers. In moderately temperate regions, they overwinter as pupae buried deep into the soil during winter months. The pupa measures roughly 14-20 mm long and boasts a light brown hue with traces of green that become more pronounced as the moth grows inside it. Two elongated (1.2-1.3 mm), straight spines adorn the upper part of the pupa. The complete life cycle rarely extends beyond one month's time span. They inflict considerable harm by attacking reproductive structures such as flower buds and pods.

The larvae,

upon emerging, initially feed on soft leaflets, budding blossoms, and young pods. As they grow, they begin to consume the seeds developing inside the pods. When eating larger pods, half of the larval body remains outside as it eats the growing seed. The Bean Pod Moth is a sporadic pest known scientifically as Maruca testulalis (Geyer), belonging to both Pyralidae and Lepidoptera families. This moth predominantly causes damage to all legume crops but shows a particular liking towards Phaseolus spp. plants. The adult moth possesses brown upper wings marked with three white spots; meanwhile, its lower wing displays a greyish-white colour with end brown markings and has a wingspan that varies from 16-27 mm.

The host plant's flowers, buds, or pods are where the eggs are individually laid. Upon hatching, the caterpillars feast on fresh leaves, budding flowers and seeds growing within the pods. Every section of the caterpillar's body is white, with dark spots creating dorsal longitudinal rows. The fully-grown caterpillar reaches about 16 mm in length. Pupation occurs within a silken cocoon in the pod, although occasionally it can happen in the soil. The Redgram pod fly, known scientifically as Melanagromyza obtusa Malloch (Agromyzidae: Diptera), or Pigeonpea pod fly as it's commonly referred to as (Melanagromyza obtusa), is known to have induced substantial damage in India.

The insect is prevalent throughout India. It deposits its eggs on developing pods as it lays them. It's documented that a single fly can lay up to 80 eggs, which incubate over a span of 2-3 days. Once the maggot hatches, it burrows into the pod and feeds on the maturing seed. Generally, one seed

is enough for its growth. The larval stage lasts approximately a week. After creating a tiny hole in the pod and sealing it with a slim membranous structure, the larva transforms into a pupa within the pod. This pupation phase can range from 7 to 15 days (Shanower, et al., 1998). Following this, adults come forth through the exit hole that the larva initially made.

Another species identified as M. chalcosoma appears to only inhabit Asia. This species, along with another, are exclusive feeders on pigeonpea and its related species in the subtribe Cajaninae (Minja, 1997). A collective known as the redgram plume moth complex is formed of three species - Marasmarch liophanes, Exelastis atmosa and Sphenarches anisodactylus (Pterophoridae: Lepidoptera). These are tiny and fragile moths that are found throughout India. Females lay their green oval eggs one at a time on pigeonpea buds and pods. A single female has the capacity to lay as many as 55-60 eggs.

Females typically possess a remarkable inclination to lay eggs on the young, tender pods. The eggs normally hatch within the span of 2-4 days. The moment they hatch, the larvae penetrate into the maturing pods, feasting on the soft seeds. The fully mature larvae are about 14mm long, colored in shades of green or brown, are spindle-shaped, and garnished with short spines and larger hair. The larval phase usually lasts around two weeks. The pupae, having a close resemblance to larvae, are often spotted clinging onto the pod surface or on the pedicel. The duration of the pupal stage ranges from 3-5 days. The matured insects showcase brown wings that resemble plumes.

During

the bloom phase of plants, one can typically observe plume moths, but they may also appear in the stage before flowering. Certain polyphagous defoliators known for their detrimental effects on pigeonpea crops in India have been documented. These insects' larvae consume the leaves, flowers and unripe pods of these plants. Noteworthy defoliators encompass species from Amsacta spp., Spilarctia obliqua (Walker) (Arctidae: Lepidoptera), Chrysodeixis orichalcea (Fab.) (Noctuidae: Lepidoptera), and Euproctis spp. (Lymantridae: Lepidoptera).

Insects, when they surge in massive quantities, can significantly damage crops by intense defoliation. Nonetheless, with proper and timely management, these creatures can be controlled, thereby avoiding economic downfall. Notable among the leaf webbers that cause substantial crop harm are Grapholita critica Meyr. and Leguminivora ptychora (Meyr.) (Tortricidae: Lepidoptera). The G. critica moth, which is small and brown-colored, lays its eggs on leaf buds and fresh leaves. Its larva, characterized by a creamy-yellow color, binds the leaves and ingests the remaining chlorophyll within its web.

The mature larvae measure approximately 10 mm and go through metamorphosis inside the web, which usually encompasses the terminal buds, impacting the growth of that particular branch. The damage to the crop tends to be more severe if the infestation begins during the seedling stage, and typically persists all through the crop season. Flower buds may also be infested in the later stages of crop growth. The Termites, specifically Microtermis spp. and Odontotermis spp. (Termitidae: Isoptera), consume dry and dead flora and play a crucial role in nature by converting dead plant matter into organic material.

Wood used in construction is unfortunately irresistible to termites, which can cause significant damage to both residential and

commercial properties. Subterranean termites inhabit the soil and cohabitate in colonies. They transit through mud tubes to connect to food sources above the ground. A mature termite colony consists of three categories: a) reproductives (king and queen), b) soldiers, and c) laborers. The complete growth of a colony can take about 4 to 5 years and might consist of 60,000 to 200,000 laborers. When winged males and females from a pre-existing colony burst into flight or swarm, new colonies are established.

Renowned for their dark brown to nearly black hue, this species features two pairs of wings that exceed the size of their bodies and are of equal length. These winged creatures are known to form swarms during the spring and fall seasons, usually after periods of rainfall. Once these flights conclude, the males and females return to earth and begin discarding their wings. Without wings, they start looking for moist soil and wood sources. The selected duo then hollows out a space close to a wood source in the soil, enters it, and seals off the entrance. Mating occurs inside this enclosed area followed by egg-laying from the queen. A queen has a lifespan up to 25 years with an extraordinary capacity to lay over 60,000 eggs throughout her life.

The eggs, characterized by their pale yellow coloration, typically require 50 to 60 days of incubation. The fully grown workers have a soft and wingless body with no ability to see; they display a creamy white hue. During the early phases of their development, these workers consume pre-digested food provided by the colony's king and queen. Once they gain the capacity to

digest wood, they take up the responsibility of feeding the entire colony. They do all the laborious tasks which include searching for food, attending to other caste members particularly immature ones, unearthing dried plant matter as well as activities related to tunnel construction. After maturing within a year's duration, their lifespan usually lasts from three up to five years. Soldiers termites share similarities with worker termites in terms of being sightless and wingless and having soft bodies colored in creamy white.

Characterized by their lengthy, brownish heads fortified with a set of jaws, soldier ants are unable to feed themselves and rely on worker ants for sustenance. Despite being fewer in number compared to the worker ants within the colony, they play a vital role in safeguarding the colony from enemies. These soldiers attain maturity within an annual cycle and have a lifespan that can extend up to five years. Shifting our focus to Mylabris pustulata Thunberg (Meloidae: Coleoptera), also known as blister beetles, these insects primarily inhabit India and largely pose threats to flowers. Although not typically categorized as pests, under specific conditions they could inflict significant damage to crops.

Large beetles making up the adult population measure between 25 and 35mm in length and boast a flamboyant pattern of either red or yellow combined with black. Despite showing a somewhat lethargic disposition, these beetles are actually capable fliers. When touched, they secrete a bitter yellow fluid filled with cantharidin, which is responsible for skin blisters and hence their name 'blister beetle'. Their reproduction involves laying eggs en masse in soil, from which highly mobile triangulin larvae emerge. These larvae devour the

egg masses of grasshoppers and other Orthopteran species. As they mature, the larvae often become less active and their bodies enlarge while their legs shrink. These mature larvae then undergo pupation in the soil.

Various types of cutworms, such as the early-season armyworm, Agrotis ipsilon (Hufnagel) (Noctuidae: Lepidoptera), are typically observed in dry pulse fields at the beginning of the season. However, they seldom cause substantial harm. The probability of encountering severe cutworm problems is low in northern India due to the early cultivation of pigeonpea crops. Armyworm moths show a particular preference for freshly tilled soil because it provides an optimal environment for egg-laying during fall, thus posing a potential risk to chickpea fields more so than others. The impact caused by armyworms on pulses can be recognized through plants that have been sliced off at ground level or noticeable leaf feeding on young sprouts.

Armyworms will ascend the plant and consume the leaves. The destruction they cause is most severe in the seedling stage, as they feed at or beneath the soil surface, capable of severing and killing whole plants. A threatening compound referred to as the Leafhopper complex, consisting of Empoasca fabae (Harris) and Empoasca kerri (Pruthi) (Cicadellidae: Hemiptera), may greatly harm dryland pulses. This event is not consistent but owing to the potential extensive damage from this insect, it's essential to familiarize oneself with it. Furthermore, Jassids have been detected pervasively infesting pigeonpea throughout India.

It's challenging to identify these insects at the species level in their natural environment due to their tiny size and bright green shade. Their primary food source is the sap they extract from

leaf bases. The females usually deposit their eggs within the veins on the undersides of leaves. The life span of these bugs, which involves five harmful nymph stages, lasts about two weeks, during which they cause damage to their host plants at every phase. These leafhoppers inject a poisonous substance into plants while feeding, leading to detrimental effects like leaf discoloration and stunted growth. This damage becomes evident when leaf edges and tips begin to yellow before ultimately turning brown and withering away.

Often, plants display a reddish-brown color in their leaves and might occasionally shed them when under severe attack, leading to hindered growth. Recovering from such damaging effects is usually slow-paced, potentially causing the plants to stay small throughout the season. Aceria cajani Channabasavanna (Eriophydae: Acarina), also known as Eriyophid mite, is a prevalent mite species in India notorious for transmitting sterility mosaic disease - the most destructive disease of pigeonpea crops in India. These microscopic bugs are 0.2mm in length with a pink hue and an elongated body shape, typically observed feeding on the undersides of leaflets. They deposit milky white eggs at locations where plant growth occurs.

It's possible to observe various nymphs on fresh, folded leaflets. The process of infestation spreading from one plant to another is made easier by wind carrying infectious mites. Sterility mosaic virus results in the appearance of green mosaic patches on the leaflets. If plants contract this infection during their early vegetative stage, it may lead to total sterility. Spider mites commonly found on pulse crops such as beans include the two-spotted spider mite, strawberry spider mite, and Pacific spider mite. Schizotetranychus urticae

(Tetranychidae: Acarina) is recognized as the two-spotted spider mite.

Infestations often consist of varied species of spider mites. These adult mites are roughly 0.06 inches in size, possessing four pairs of legs, and their bodies can range from greenish to pink or cream with differing sizes of black spots. When the environment is warm, these spider mites move swiftly within their colony zone. They undergo four developmental periods: an oval, mildly clear egg; a larval stage with six legs; a nymphal phase with eight legs; and ultimately, the mature adult stage with eight legs. A dormant or idle phase is also seen following the larval and nymphal stages.

In the balmy period of midsummer, a spider mite can complete its life cycle in as short as 5 to 7 days compared to an entire month in chillier conditions. This pest is damaging to beans throughout its active stage by sucking juices from infected leaves and pods. Evidence of their invasion is usually evident on the top surface of impacted leaves which frequently turn grey due to webbing underneath. Spider mites are a significant risk to ordinary dry beans and may introduce problems for blackeyes. They become particularly troublesome near fields adjacent to roads and following treatments for lygus bugs. Moreover, various kinds of aphids also plague diverse pulse crops; notable ones encompass cowpea aphid (Aphis craccivora Koch), bean aphid (Aphis fabae Scopoli), pea aphid (Acyrthosiphon pisum(Harris)), and green peach aphid (Myzus persicae(Sulzer)).

The two species often sighted on beans are the cowpea aphid and the bean aphid. The cowpea aphid is not limited to beans and it's also prevalent on black-eye beans

(cowpeas). Characterized by its relatively small size, shiny black body and white or pale yellow legs and antennae with black tips, it's easily recognizable. The bean aphid, although only marginally larger than the cowpea aphid, has unique attributes like a dark olive green to black body, and legs of a lighter color. There's also the pea aphid which is common on peas. It's fairly larger than the other two, with a green body that shines slightly. A. raccivora, measuring about 1.6 mm in length, is another shiny black aphid; whereas A. pisum, comes in a gray-green color and is slightly longer at 2 mm.

Aphids, particularly asexual reproducing females with three wings, are transported by the wind, and they often land on chickpea plants. They either leave because of disappointment or perish as a result of the plant's acid secretions. Young aphids strongly resemble their adult counterparts and can mature in under two weeks. These pests harm plants in several ways including: (1) sapping nutrients from the plant which results in severe leaf curling and inhibited growth; (2) excreting honeydew that causes leaves to become sticky, shiny, and eventually turn black due to sooty mold fungi; and (3) serving as vectors for multiple plant diseases since many viruses utilize aphids for transmission.

Infestations typically manifest in localized areas where heavily infested leaves demonstrate a downward curl. A key example of this is the Thrips Megalurothrips usitatus (Bagnall) (Thripidae: Thysanoptera). These tiny insects, measuring about 0.04 inches long, are known for their two pairs of hair-fringed, narrow wings in their adult phase. Immature Thrips, on the other hand, have no wings and display colors

ranging from whitish to a yellowish hue. They are frequently located in buds, blossoms, or on the undersides of leaves. Throughout the warm seasons, adult Thrips continue to appear and can be found along with their immature counterparts in beans during early and blooming periods.

Typically, eggs are laid in plant tissues and they usually hatch within approximately 5 days during the summer. The growth phases of these immature forms often finish within a time span of 5 to 7 days. Young plants are frequently the most noticeable and worrying hosts. Their eating behaviors result in plants looking messy because they consume young leaves and buds. Signs of substantial infestation often involve leaf deformation, visible as brown-edged leaves that curl up. Nonetheless, these plants normally manage such situations by growing away from affected areas, demonstrating resilience similar to their response to severe wind damage.