Review Article
Insect Pest Infestation, an Obstacle in Quality Mulberry Leaves Production
Residential Coaching Academy (RCA), Babasaheb Bhimrao Ambedkar University, Raebareli Road, Vidyavihar, 226 025, Lucknow, India
LiveDNA: 91.2817
Sericulture is the cultivation of silkworms to produce a natural fiber, silk. There are several species of silkworms, Bombyx mori are most widely domesticated and intensively used for silk production. Silk is most elegant textile with unparalleled grandeur, natural sheen, light weight, soft touch and high durability and known as the “Queen of Textiles” the world over. It is having an integral traditional and cultural importance, with its remunerative nature of production providing an opportunity for millions owing to high employment and income to the small land-holdings, marginalized and weaker sections of the rural farmers with low capital incentive. Increase in productivity will enhances profitability to these silkworm growers. Increased production of raw silk, to large extent, depends on timely supply of quality mulberry leaves to silkworms. Profitability of the sericulture industry is directly correlated with production of high quality mulberry leaves.
Mulberry is an extremely versatile plant, having multifaceted applications, the most important being the sole feed for the monophagous silkworm, Bombyx mori. Silkworms feed on mulberry leaves during their entire larval period and utilize the leaf contents, especially proteins, for the biosynthesis of silk. According to Miyashita1 several factors which contribute for successful cocoon crop are mulberry leaf (38.20%), climate (37.00%), silkworm rearing techniques (9.30%) and race (4.20%). It is therefore clear that mulberry leaf plays a dominant role in cocoon production as a source of nutrition to the silkworm. The production of nutritively rich mulberry leaf is influenced by numerous factors such as variety, agronomic practices, biotic and abiotic components2. The availability of nutrients and water in the soil, certain environmental factors as well as pests and diseases affect the normal functions of mulberry plants. This in turn affects their growth, yield (20%) and leaf quality3. In spite of adopting all standardized agronomic practices, sometimes the nutritive values are degraded due to diverse biotic stresses such as diseases (pathogens) and pest (insect and non-insect) damage due to its fast growing, perennial, lush green with advantageous nutritional character.
Though frequent leaf picking and pruning of the shoots are done, some of the insect pests a take high toll by finding enough time and place on the mulberry for their feeding and breeding habits. The average incidence and loss in mulberry leaf yield caused by these pests is estimated to be 34.24% and 4500 kg ha1/year, respectively4. So far, over 300 insect and non-insect species of pests are known to infest mulberry in different parts of the world to varying intensities during different stages of crop growth and seasons5-8. Santhi and Kumar9 explained taxonomic diversity of the insect communities in the mulberry ecosystem. They found that 60.86% belongs to order Hemiptera of total insects and also 22.05% are Hymenopteran, 8.65% are Coleopteran and the rest are belongs to Isoptera, Lepidoptera, Thysanoptera, Orthoptera and Dictyoptera. These insect pests are broadly classified into leaf eaters, leaf rollers, sap-suckers and stem borers belonging to different orders10. Among these pests few are sap suckers and defoliators. Sucking pests of mulberry is classified as major and minor based on the incidence of pest. Major sucking pests includes mealy bug, thrips and spiraling whitefly and minor includes the jassids, scale insects and non insect pest is mite. Govindaiah et al.11 reported the incidence of mealy bug (19.21%), thrips (17.18%), whitefly (12.62%), jassids (9.08%) and scale insects (8.24%) on mulberry. Most of the sap sucking insects, such as adult leaf hoppers, aphids and thrips cause direct tissue destruction. These insects use a specialized mouth part, the stylet, to locate, penetrate and drain sap from the phloem sieve elements of the plants vascular tissue. Heavy infestation caused by them leads to shortages of photosynthesis and thus severely reduce the growth potential of the plant.
Mahadeva12 made an elaborative attempt to understand the nutritive (biochemical components, micro and macro elements and photosynthetic pigments) status of the mulberry leaves under six major pests attack. It also tested suitability of pest infested mulberry leaves to silkworm. This review provides overviews major pests and their sway on post pest infestational changes in quality and quantity of mulberry. The type of feeding damage by different pest species triggered variations in foliage quality in mulberry, which leads to systemic stimulation of enzymatic activities followed by nutritional quality and biochemical alteration in leaf. Pest infestation not only reduces the quantity of mulberry foliage it also adversely alter the biochemical constituents13,14. Feeding pest infested leaves to silkworm are known to affect the commercial characters of cocoon15-17. The importance of quality of mulberry leaves on the healthy growth and development of silkworms and silk production has been stressed by many workers18-20. Hence, some of the important pests of mulberry foliage viz., Leaf sap-suckers (Jassids, Mealy bugs, Thrips and Spiralling whitefly), leaf roller and leaf eaters (Wingless grass hopper) are briefly described below:
Jassids: Jassid, Empoasca flavescenes F. (Homoptera: Cicadellidae) commonly called leaf hoppers is the major sucking pest of mulberry21. The incidence of jassids on M5 mulberry variety was found to be maximum during February (20.36%) and September (21.80%) months in Kanakapura, Bangalore rural district22. Both adult and nymphs of little greenish hoppers sucks the sap on the underside of the leaf, at the time of sap sucking from the veins and causing characteristic non-contagious symptoms known as “hopper burn”. Initially symptoms appear as triangular brown spots at the tip of the leaf. Similar triangles appear at the end of veins and the entire margin may roll upward and turn down at one time, as though scorched by fire or drought23. Gradually, the affected leaves become brick red or brown, crinkled and curled and ultimately the plant shows stunted growth. The characteristic symptom is a result of dynamic interaction of complex insect feeding stimuli and plant responses triggered by a unique type of stylet movement24. Pale yellow colored and elongated eggs are laid by female jassids on lower surface of the leaves and it hatches within 4-9 days. The wingless nymphs are pale yellow in colour and resembles adult. The nymph feeds on the same leaf and its growth is slow. It moults 4 times before to become mature adult. The adult jassids are pale green with a tapering posterior end and measures about 2-4 mm. The adult and nymphs moves sideways. The adult jumps to reach other leaves or plants. Pupation carried out on the leaf itself.
It is well known truth that the yield and quality of mulberry is varied due to pests and pathogens. Study about nutritive evaluation under Jassids infestation in mulberry is very scanty. However, Mahadeva and Shree25 have noticed changes in the biochemical parameters (free amino acids, total soluble proteins, reducing sugars, soluble sugars and phenol) and photosynthetic pigments (total chlorophyll, chlorophyll-a, chlorophyll-b, chlorophyll-a/b ratio and carotenoids) in Jassids infested leaves of indigenous popular mulberry varieties (M5, MR2, S36 and V1). There was a reduction in the free amino acid content of all the varieties due to Jassids infestation except V1 variety, which showed increase. The total soluble proteins were more in all the cultivars. The reducing sugars were decreased in M5 and V1, but it was increased in MR2 and S36. The soluble sugars, phenols and photosynthetic pigments were reduced in all the varieties, except the chlorophyll ratio in M5 which showed increase. Similar variation of biochemical and photosynthetic pigments were also observed in Mysore local and S54 varieties due to hopper burn26. Mahadeva27 made an attempt to know the influence of jassids infestation on the six macro (nitrogen, phosphorus, potassium, calcium, magnesium and sulphur) and seven micro nutrients (zinc, iron, manganese, copper, boron, molybdenum and chloride) level in mulberry foliage. They found wide variation in macro and micro-nutrients due to Jassids infestation.
Mealy bugs: Mealy bug is widespread in tropical regions and polyphagous and sap sucking pest. Two species of mealy bug infest the mulberry i.e., Pink mealy bug (Maconellicoccus hirsutus Green) and Papaya mealy bug (Paracoccus marginatus). The pink mealy bugs is one of the major pests of mulberry, causing severe damage and recurring loss in leaf yield of about 3000-6000 kg ha1/year28. Mealy bugs is a native to Southern Asia and have spread to other parts of the world like Africa and more recently to North America and Caribbean islands29. In India, the occurrence of this pest was reported in Murshidabad district of West Bengal30. The pest occurs in both irrigated and rain fed gardens causing a characteristic disease “tukra”. The pest is found to inhabit the folds and knots of the crumpling31.
Immature and mature mealy bugs are found in clusters on the stalks under overlapping leaf sheath, below the node and spread up and down to the other internodes and buds32. Sriharan et al.33 concluded that mulberry shows a tukra symptom/disease after the 15 days of inoculation of healthy plants with adult mealy bugs. The morphological changes in the tukra affected plant include arrest of linear growth of the stem, followed by petiole thickening and shorten inter nodal distance leading to characteristic bunchy top. Mealy bugs feed on plant by sucking a cell sap by piercing stylets. This sap feeding weakens the plant by depriving essential nutrients which, may lead to slow plant growth, yellowing, deformation of leaf lamina followed by early leaf drop32. Babu et al.34 found structural and morphological alterations in tukra affected mulberry leaves and stem. They observed a highly crumbled, uneven thickened, rough surface and thick covering with epidermal appendages in the infested leaves. Mealy infested shoot shown irregular outline, multiseriate epidermis, a parenchymatous cortex and less number of vessel groups. The stem had larger diameter due to hypertrophy and hyperplasia of parenchyma cells. This penetrative mechanical feeding damages the plant by draining its sap and may possibly transmit bacterial and fungal infections. In addition, mealy-bug play a vital role in virus transmission and the growth of black sooty-mold fungus due to large amount of honeydew secreted by the insect35 and also these honey dew also attracts an ants. Damage is not often significant at low pest levels; however, heavy infestations can kill a plant. The availability of information about the qualitative and quantitative value of mulberry leaves during mealy bug’s infestation is not a short-fall36. There is a wide variation in biochemical, photosynthetic pigments, macro and micro nutrients due to mealy bugs infestation in the leaves of various mulberry varieties as listed in Table 1.
Table 1: | Variation in nutritive content in mealy bugs infested mulberry leaves |
The suitability of tukra affected mulberry leaves on silkworm economic characters are well documented by various groups. The results were positive as well as negative impact on silkworm. Dhahirabeevi48 tried mealy bug infested foliage mixed with healthy and fed to silkworms and observed retarded silkworm growth and reduced cocoon weight. Kumar et al.28 noticed a highly significant decline in the economic characters like effective rate of rearing, larval weight, cocoon weight, shell weight and shell ratio when silkworms fed with tukra affected leaves. Kumar et al.16 reported that feeding silkworm with tukra affected leaf caused significant decline in economic characters of silkworm rearing like larval weight, cocoon weight, shell weight, silk ratio and effective rate of rearing. Singh et al.49 had notified marginal increase in the larval weight and reduction in total larval span (polyvoltine, MY1) in silkworms fed with tukra affected mulberry leaves from hatching till spinning (treated group) and chawki rearing upto 3rd instar with tukra infested leaves and latter states with healthy mulberry leaves treated control). But, they also observed that no significant variation in other quantitative characters viz., fecundity, hatching (%), effective rate of rearing (g), cocoon weight, shell weight, shell ratio (%), filament length and denier.
In contrastingly, there were adverse effect on economic traits of mulberry silkworm (Bombyx mori L.) fed with papaya mealy bug affected mulberry leaves is reported by Sakthivel et al.50. Ahamed et al.51 noticed a lesser consumption of tukra affected leaves in bivoltine silkworm. They also noticed a shortened larval duration and significantly increased conversion rate, conversion efficiencies, water absorption efficiency, water content in the body and water retention efficiency, larval biomass, cocoon, pupal and shell weights in silkworm fed with mealy bugs infested leaves. Ramesha et al.52 found contrasting influence on quantitative traits of silkworm after feeding them with tukra infested mulberry leaves. They found that decreased larval duration and increased economic characters like larval weight, pupation rate, cocoon weight, shell weight and reeling parameters in the tukra affected leaves ingested polyvoltine silkworm. Zaman et al.53 found that matured larval weight was increased significantly when fed on tukra affected mulberry leaves and single cocoon weight, single shell weight and length of filament did not significantly. Nagaraja and Somasundaram54 have reported enhanced cocoon yield in the silkworm, B. mori which fed with tukra affected chawki mulberry leaves. Singh et al.49 had notified marginal increase in the larval weight and reduction in total larval span (polyvoltine, MY1) in silkworms fed with tukra affected mulberry leaves from hatching till spinning (treated group) and chawki rearing upto IIIrd instar with tukra infested leaves and latter states with healthy mulberry leaves treated control). But, they also observed that no significant variation in other quantitative characters viz., fecundity, hatching (%), effective rate of rearing (g), cocoon weight, shell weight, shell ratio (%), filament length and denier.
Table 2: | Variation in nutritive content in thrips infested mulberry leaves |
The impact of feeding mealy bugs infested leaves on silkworm also studied by various researchers16,18,28,55,51. More or less all of them observed decline economic characters of silk. It is positively correlated with the variation in nutritive nature of the mealy bugs infested mulberry leaves and adverse effect on growth and development of silkworm ultimately it leads to poor quality and quantity of silk production.
Thrips: The thrips-Pseudodendrothrips mori Niwa, (Thysanoptera: Tripiidae) are tiny, slender insects and adults are unique by virtue of their fringed wings while immature thrips do not. With their sword-like mouthparts, adult and immature thrips feed by slicing or rasping open epidermal cells on the ventral surfaces of leaves. They then suck the contents out of the ruptured cells which lead to rows of empty and dead cells, later it forms numerous tiny dots of silver streaks. The usual transpiration process of leaves is quickened through these wounds especially during summer seasons56. If leaves are still growing when attacked by thrips, the damaged surface cells stop growing and undamaged cells continue to develop around them. This causes deformed leaves (http://landscapeipm.tamu.edu/ipm-for-ornamentals/ diagnosing-insect-and-mite-damage-ornamentals/). The highest number of thrips per leaf may even exceed 1000. Finally the leaves are dwindled and dried just like a piece of craft paper, being unfit to be used as feed to silkworms57.
Devaiah and Kotikal58 reported the incidence of thrips on mulberry in Karnataka. Bhattacharya et al.59 reported thrips on mulberry in West Bengal. Shery 60 reported a presence of new thrips species, Pseudodendrothrips bhatti Kudo in Karnataka in addition to earlier reported species, Pseudodendrothrips mori (Niwa)61. The damage by thrips causes loss of moisture from mulberry leaves besides causing appreciable reduction in nutritive value of leaves by inducing biochemical changes in leaves62. It also causes loss in leaf area and leaf weight resulting in yield reduction to the tune of 20-40%. Feeding damage by thrips causes 8.0-10% loss of moisture content, about 10% reduction in protein content and 5-10% reduction in total sugar content in popular Indian mulberry varieties63. Studies by the various research groups are listed under Table 2.
It was opined that decrease in protein content in infested leaves may be partly due to utilization by thrips at a faster rate for its multiplication. Hydrolysis of protein by proteolytic enzyme secreted by the pest itself may be the other cause of lowering the protein level67. Decrease in protein content in infested leaves may be partly due to utilization by thrips at a faster rate for its multiplication. Hydrolysis of protein by proteolytic enzymes secreted by the pest itself may be the other cause of lowering the protein. Decrease in chlorophyll and carotenoid contents in infested leaves may have been due to loss in chlorophyll synthetase activity in response to thrips infestation65. The content of photosynthetic pigments varied depending upon the pest, intensity of pest-infestation, extent of damage and mulberry varieties. The reduction in the photosynthetic pigment(s) and/or laminar area caused due to feeding nature of insect pests will result in decreased photosynthetic efficiency and thereby the productivity. Sengupta et al.67 observed a significant difference in the photosynthetic rate of nitrate reductase and proteins between the healthy and thrips-infested leaf as well as in different positions of the diseased leaves.
Table 3: | Variation in nutritive content in spiraling whitefly infested mulberry leaves |
Etebari and Bizhannia72 observed that there was a significant decrease in total cocoon production, cocoon weight, pupal weight and shell weight due to feeding of thrips infested leaves. Geetha et al.73 studied the rearing performance and cocoon production by feeding silkworm with thrips infested mulberry leaves. They observed that significant decrease in larval weight, ERR, total cocoon production, cocoon weight, pupal weight, shell weight, silk filament length and silk filament weight, due to feeding of thrips infested leaves. However, shell ratio, denior and renditta were not significant.
Spiralling whitefly: Aleurodicus dispersus Russell, belongs to the order: Homoptera, family: Aleyrodidae, sub family: Aleurodicinae is a highly polyphagous pest and a native of Caribbean region. It is more commonly known worldwide as ‘spiralling whitefly’ because it lays eggs in a typical spiral pattern. It was noticed in Hawai in 1987 on Terminalia catappa, a non-mulberry food plant74. Geetha et al.75 reported it on mulberry. David and Ragupathy76 reported eight species of spiralling whiteflies from mulberry, Morus alba in India, among them Aleurodicus dispersus take a heavy toll in the southern part of the country. Every 1% of leaf damage by spiralling whitefly would reduce the cocoon yield by 2.08 kg77. Both nymphs and adults remain in colonies under the surface of leaves and suck the sap which results in chlorosis, falling of leaf and reduction of plant growth. The copious white, waxy, flocculants, material secreted by all the stages of pest is readily spread by wind, causing nuisance78. The honey dew excreted by these insects will fall on the upper surface of the lower leaves which becomes a medium for developing sooty mold fungus, Capnodium sp. It, in turn, reduces the photosynthetic area by blocking the leaf79. Further, the honey substances and the white waxy flocculent material are fed by insects like bees, wasps, ants which would give protection to white flies80.
The adults look like a very small moth and have a body length of about 2 mm, total length from vortex to wing tip is greater than 2 mm and the wing span is 3.5-4 mm. The wings of the adults are plain white or occasionally have pale or dark spots on the forewings. The eyes are dark reddish brown and the forewings with two characteristic dark spots males have a very short simple adeagus and often have extremely long claspers81. Eggs are smooth surfaced, elliptical and yellow to tan in colour, 0.3 mm long and are laid singly at right angles to the leaf veins and associated with irregularly spiraling deposits of white flocculent wax. Egg have a characteristic short subterminal stalk or pedicel which is inserted during oviposition into the host plants usually on the lower surface of a leaf 82 mainly into leaf stomata in order to facilitate the egg to meet its moisture requirements83,84. The first stage of the larva is mobile but the later immature stages are sedentary and have an oval disc shaped soft body that is light green in colour. The final immature stage is the pupa and is about 1 mm in length. The sedentary larvae have characteristic waxy tufts and the final larval stage (pupa) has glass like rods of wax along the sides of the body85. The impact of spiralling whitefly infestation on mulberry are emphasised by various groups, it has been mentioned in Table 3.
Narayanaswamy87 reported a deteriorated influence on economic parameters of silkworm (Cross Breed, PM X NB4D2) after feeding a spiralling whitefly infested mulberry leaves (M5 variety) to them. Mahadeva and Shree19 fed the silkworm with spiralling whitefly infested mulberry leaves and observed a negative impact on them in respect of silkworm growth and cocoon parameters. Qadri et al.90 found drastic reduction in economic parameters (Larval period, larval weight, ERR/No., ERR/., cocoon weight, shell weight, shell ratio, fecundity and hatchability) in silkworms fed with spiralling whitefly infested mulberry leavers leaves. They estimated to cocoon yield loss of 48.09% and monetary loose of 71.31% in the treated set. The economic parameters of the silkworm and the monetary loss was varies with the intensity of spiralling whitefly infestation, more pest attack more loss. Ahamed et al.91 conducted studies on the effect of feeding spiralling whitefly affected mulberry (variety: M5) leaves to the silkworm. They found that the larval duration was significantly prolonged by 6 days and significant decrease in the conversion of food into body substance, conversion rate, conversion efficiencies (K1 and K2), feeding rate, assimilation rate, dietary water intake and utilization parameters.
Table 4: | Variation in nutritive content in leaf roller infested mulberry leaves |
There was a significant reduction in the biomass, cocoon weight, shell weight, cocoon shell ratio, pupation rate, shell conversion efficiency and effective rate of rearing by number and weight in the multivoltine X bivoltine hybrid (PM X NB4D2) silkworms which were fed on spiralling whitefly infested mulberry leaves compared to healthy leaves during final instar.
Leaf roller: Leaf roller, Diaphania pulverulentalis (Lepidoptera: Pyralidae) has been noticed in Karnataka since 1995 and has spread to neighbouring states of Tamil Nadu andhra Pradesh and Kerala92. Rajadurai et al.93 noticed leaf roller infestation on mulberry and causing leaf loss. The reduction in leaf yield of 12.8% with an average incidence of 21.77% resulting in economic loss to sericulturists94. Being seasonal in nature, its infestation starts with onset of monsoon, remains up to February, but maximum infestation is observed from September to November. The pest completes several over lapping generation from June to December. The most active period was September to December with mean infestation ranged from 1-2 larvae to 5-6 larvae/leaf93. The female moth lays 150-200 eggs at the rate of 1-2 eggs per apical shoot of mulberry plant and they hatch into larvae after 4 days. The larvae have 5 stages (instars) and then pupate into the soil or in dry leaves. The total life cycle completes within 17-24 days95.
Diaphania pulverulentalis infests and defoliate apical shoot after webbing the tender leaves together and inhibit the growth of plants. Larvae mainly infests the apical portion of mulberry shoot and binds the tender leaves by secreting silky substance facilitating the larva to remain inside the rolled leaves. Occasionally, a single leaf is also rolled by the web and larvae stays inside the rolled leaf. Hence, it is commonly named as leaf roller/leaf webber96. The young larvae start feeding on the tender leaves and finally causing drying of shoots. Hence farmers face shortage of tender leaves to rear chawki (young age silkworms). Since the larvae feed on the tender leaves, the growth of the plant becomes stunted97. Kumari95 made a qualitative analysis of leaf roller infested and healthy mulberry leaves. They revealed the loss of protein percentage over control was 29.08, carbohydrates were 24.92, phenols 13.7 and chlorophyll was 13.6%. The nutritive content under leaf roller attack is noticed by few researchers (Table 4).
The early stages of leaf roller larvae inhabits apical succulent portion of the shoot and leads to its destruction, resulting in stunted growth thereby affecting considerable decline in leaf yield about 12.8% with an average incidence94 of 21.77%. The life cycle of D. pulverulentalis is comparatively shorter than that of other lepidopteron pests of mulberry and it ranges between 17-24 days. As a result, the pest completes 8-10 generations during the period of its occurrence in mulberry garden100.
Multiple types of pests may feed on mulberry at a time and resulting damage leads to variation in leaf quality. The plant responses depended on the type of insect feeding, as this is related to the quantity of plant damage and alteration in the physiological response occurs in host. The decrease in nutrient content may induce several changes in mulberry plant physiology, to make plants less palatable for insect pest and also affect their development. These changes may obstruct a nutritive availability to silkworm. The decrease in the crude protein contents may be attributed to the damage caused by the insect, thus altering the metabolic functions leading to either decline in protein synthesis or mobilization of proteins for repair of the damaged tissues in order to develop resistance to insect bite. It may be also due to utilization of nutritive sap for fast multiplication of insect. Hydrolysis of proteins by proteolytic enzymes secreted by the pest itself may be the other cause for lowering of proteins23. Increase in the protein content may be due to changes in the protein synthesis pattern to overcome the injury and develop resistance68. Abrupt decline in nutrient values may be due to heavy population build up of the pest and utilization of nutrients by them at a faster rate for its multiplication. In addition, the pests enzymes secreted during feeding may hydrolysis of proteins may be cause for reduced protein level66. Alteration in the reducing sugars may be due to reduction in leaf lamina and malformation of leaves in pest affected plants resulting in less productivity38. The increased levels of carbohydrates in infested rice plants suggested their role in plant defense mechanism by inducing the signaling pathways. The infestation causes physiological changes that reduce photosynthesis or alter the translocation of photosynthates, it may cause decrease in carbohydrate content101. An increase in phenolics is considered to be a common reaction to herbivorous insect pests102. The increased phenol content is correlated with its negative effects on the further advances of feeding by insect pest103, they cannot be effectively digested and assimilated by insects104. Felton et al.105 found that increased concentration in phenolic compounds is according to the extent of tissue damaged by feeding insects or due to pathogen infection. The accumulation of phenolics in the host may inactivate the enzyme which inhibits the further advance of the pathogenic organism by limiting its source of nutrients106. The most important phenolic compounds implicated in the defence mechanism of plants against pathogens are coumaric acid, phloretin, umberlliferons, caffeic acid, chlorogenic acid and ferulic acid107. When such substances are ingested by the phytophagous insects along with the food, they get access to the natural defence mechanism.
Pest attacks generally set in motion or accelerate a complicated series of metabolic disturbances in the host, rather than effecting a simple change in a unique process. Malformation of leaves due to pests will affect the photosynthesis by the crop in 3 ways: by lowering light interception, by reducing photosynthetic efficiency, or by altering normal distribution of assimilates within the plant. Ultimately results in the variation of net availability of plant productivity108. Thus, the content of photosynthetic pigments varied depending upon the intensity of pest-infestation, extent of damage and mulberry varieties. The altered chlorophyll content adversely affected the photosynthetic activity109, productivity which ultimately leads to reduce protein synthesis110. Consequently, the mulberry foliage suffers from nutritional inferiority.
The pest infestation also alters the presence of macro and micro nutrients in mulberry leaves27,46,111. The role of nutritive (macro and micro) elements in the potential growth and development of Silkworm and its economic characters were emphasized by various research groups112-117. Therefore, the pest infestation may also have impact on quality silk production due to variation of its availability to silkworm.
The pest infestation on mulberry not only reduces quantity, it also hinders the quality leaf production by causing a deficiency or physiological disorders and they become malformed, deformed, chlorotic and nutritionally inferior. The varied nutritive status of the mulberry leaves influences the growth and development of silkworms in turns leads to the poor commercial characters of silk production. Therefore, the pest is detrimental and causes economic losses to the farmers at multiple levels by hindering the potential mulberry leaf production and low quantity and quality silkworm cocoon output. Hence, farmers must be informed to protect mulberry foliage from the pest attack by following suitable eco-friendly Integrated Pest Management (IPM) practices.
This review emphasises the hindrance of pest infestation on the production of nutritionally rich mulberry leaves, which is a sole for food silkworm. The consolidated information helps to select host-pest interactions studies, in turn facilitates to analyse the varietal preference of particular pest and also to select a resistant varieties for breeding purposes. The study also helps to conclude that feeding silkworm larvae with pest attacked leaves will deprive the normal growth and development of them and results in poor quantity and quality silk, which ultimately leads to low income return to the farmers. The farmers may be advised to protect mulberry plants from the herbivorous insect pests attack by practicing suitable Integrated Pest Management (IPM) methods.