Agroforestry: an ecofriendly land-use system for insect management

Agroforestry: an ecofriendly land-use system for insect management Chitra Shanker and K.R. Solanki Chitra Shanker is an agricultural entomologist with...
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Agroforestry: an ecofriendly land-use system for insect management Chitra Shanker and K.R. Solanki Chitra Shanker is an agricultural entomologist with the National Research Centre for Agroforestry, Pahuj Dam, Jhansi 284003, India. E-mail: [email protected]. K.R. Solanki is Director of the National Research Centre for Agroforestry.

Chitra Shanker is a scientist currently in the employ of the Indian Council of Agricultural Research and is working on pest problems in agroforestry. She graduated from the Tamil Nadu Agricultural University, Coimbatore. Her interest lies in integrated pest management (IPM), biological control and biopesticides of botanical origin. She has worked on the IPM of cotton pests, citrus black fly and citrus psylla. K.R. Solanki graduated from the University of Udaipur and the Indian Agricultural Research Institute, and was a fellow at the Oxford Forestry Institute. He has served as head of the Perennial Cropping Systems Division, Central Arid Zone Research Institute, and is now the Director of the National Research Centre for Agroforestry and Project Coordinator of the All India Coordinated Agroforestry Research Project. His experience covers arid zone forestry, project planning, appraisal, evaluation and training for agroforestry research and development, and the conservation, management and regeneration of natural resources. He has contributed to the development of many crop varieties, elite tree populations, technologies pertinent to agroforestry and to agribiodiversity through the collection of the germplasm of many tree species. He has had over 200 publications in books and journals. He was also the recipient of the ICAR team award.

Agroforestry is an ecofriendly land-use system that is favourable for the management of insect pests and beneficial insects. The biodiversity found under agroforestry is a close mimic of the natural ecosystem and is amenable to integrated pest management principles, especially biopesticides and biological control. These techniques in turn provide an ecofriendly basis for econ omic ventures such as apiculture, sericulture and lac culture. The profitability of these practices under agroforestry is discussed in this paper.

Agroforestry is a traditional land-use practice, but intensification of agriculture has led to a shift from polycultural systems towards spatial and temporal monoculture. Destruction of forests and the practice of monoculture in vast tracts of land has led to the decline of biodiversity. Selection of crop varieties for high yielding qualities has brought about a uniformity in genetic material with a concurrent increase in pest problems. This was well demonstrated on the cotton crop that was ravaged by pests such as Heliothis armigera and Bemisia tabaci1 with the introduction of high yielding varieties and vast areas being brought under cotton.2 Now the emphasis has shifted to sustainable pest management and herbage management. In the past decade, agroforestry has gained importance as an ecofriendly management practice, especially for smallholder farmers. It addresses the problems of soil erosion and declining soil fertility, contributes fodder and fuel wood, while simultaneously providing multiple outputs such as animal, crop and tree products. In this paper we discuss the amenability of the agroforestry system as a low-cost technology for integrated pest management, which also provides scope for profitable

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practices such as sericulture, apiculture and lac cultivation (Figure 1). Agroforestry is the science of designing and developing integrated self-sustainable land-management systems, which involves the introduction or retention of woody components such as trees, shrubs, bamboos, canes and palms along with agricultural crops including pasture /animals, simultaneously or sequentially on the same unit of land. At the same time, it meets both the ecological and socioeconomic needs of the local people.3 It can be broadly classified on the basis of the components 4 into: (i)

agrisilvicultural, or the growing of annual crops with multipurpose tree / shrub species 5 and fruit trees; (ii) silvopastoral, or the growing of trees with cultivated or natural pasture and animals; (iii) agrosilvopastoral or the growing of annual crops, pasture, trees and livestock; and (iv) others, including agroforestry and pisciculture, apiculture, sericulture and lac culture.

Pest status in agroforestry Diversified ecosystems are reported to have a lesser pest build-up than is

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Agroforestry: an ecofriendly land-use system for insect management

•

•

Figure 1. Agroforestry system and land management.

found in monoculture. The insect fauna occurring on a crop or tree, for example, will be the same whether cultivated in monoculture or polyculture. But the intensity varies for several reasons. Monocultural fields are easily detected and colonized by pests, while plant diversity results in fewer potential hosts for an individual pest and lesser colonization of the crop overall. The plant–insect interactions in an agroforestry system may be classified as primary interactions if the tree and crop species share pests or their natural enemies, and secondary interactions if one plant species influences the survival and growth of pests and their natural enemies on another. Cutworms, white grubs, termites, grasshoppers and crickets have been reported to feed on a number of tree and crop species.

Positive interactions

• The tree may act as a physical or

•

chemical barrier for pests. Maize attacked by Macrodactylis sp. was reduced in a maize / apple agroforestry system. 6 The intercrop system attracts more predators and parasites than monoculture. In China, it was found that intercropping rice with pond cypress trees increased spider abundance in rice fields and reduced the population of brown plant hoppers. 7

Negative interactions

• The presence of woody compo92

nents alters the microclimate (including temperature, relative humidity, interception of solar radiation, etc) in the system. This directly influences the pest intensity, especially that of sucking pests. • The trees provide shelter and alternative food sources throughout the year. In Jhansi, India, Acacia tortilis trees grown as a border planting suffered increased damage from blister beetles on the accompanying pulse crop because of synchronization of flowering and the beetles feeding on both tree and crop.8

•

•

Integrated pest management A properly designed agroforestry system with the right choice of components can create conditions that deter pests and favour natural enemies. • Cultural control / management practices: Choice of the tree / crop components helps to maintain pest balance. They should not belong to the same botanical taxa if crossinfestation is to be avoided. Design and configuration of the field also plays a role in regulating pests. Leucaena planted as a hedge with maize, cassava and upland rice had less psyllid damage. 9 • Resistant varieties: Cultivating resistant varieties with an inherent resistance to pests and diseases in an agroforestry system helps to reduce the pest load. But tree

breeding for pest resistance is not a common area for research. Mechanical control: Trees act as shelter for adult pests. Mechanical collection of the pests will considerably reduce the load and the cost of insecticide. The mechanical collection of white grub adults from host trees (Prosopis specigera) at the time of emergence after monsoon showers was found to be cheap and more effective in a pearl millet cropping system than soil application of insecticide. 10 Physical control: Different types of traps have been used by entomologists and pest managers for the monitoring and mass trapping of adult pests in different ecosystems. Yellow sticky traps are efficient in trapping weak flying adults of sucking pests, such as aphids and white flies. Calopepla leayana, a defoliating beetle of Gmelina arborea is highly attracted to white light and can be mass trapped using light traps. Semiochemicals / pheromones: These insect behaviour-modifying chemicals have been identified, isolated and commercially produced for many forest insects and crop pests. Pheromone traps can help monitor and trap pests, especially those such as Heliothis armigera, which infest both trees and crops. Semiochemicals also play an important role in attracting predators and parasitoids of pests. 11 Biological control: Natural enemies are most successful in stable forest ecosystems, where they can keep more than 90% of populations of arthropod herbivores below outbreak levels. 12 Agroforestry is considered as a stable ecosystem which closely resembles the natural ecosystem and can be used to augment and conserve natural enemies of pests. The parasitization of the gram pod borer, Heliothis armigera by a hymenopteran parasitoid, Campolitis chloridea was higher when grown with bamboo (Dendrocalamus strictus).13

Botanical pesticides in agroforestry Plant-based pesticides could be of great advantage in agroforestry systems. They would not only help Outlook on AGRICULTURE Vol 29, No 2

Agroforestry: an ecofriendly land-use system for insect management

Table 1.

Agroforestry trees with insecticidal properties.

Tree species

Family

Plant part with reported insecticidal activity

Active ingredient

Azadirachta indica

Meliaceae

seeds and leaves

Annona squamosa

Annonacea

Madhuca indica Melia azadirach Hardwikia binata Pongamia glabra

Sapotacea Meliacea Leguminosae Leguminosae

stems, leaves and semi-ripe fruits seeds fruits and seeds heart wood stem and seeds

Azadirachtin, nimbidin, salannin, etc Annonine

Figure 2. The neem tree grown under agroforestry.

the poor and marginal farmers economically, but would also be ecofriendly, safe and sustainable. Such pesticides may be available from tree / plant components included in the agroforesrtry system. A number of trees that are commonly found on the farm, or deliberately grown under agroforestry, possess insecticidal properties in their various parts, namely leaf, bark, seeds, roots, etc (Table 1). A notable tree in this category is the neem tree, Azadirachta indica (Figure 2). The insecticidal properties of this tree have been known to farmers since ancient times. About 50–60 kg of seeds can be harvested every year from each tree, even in droughtprone areas.14 The seed and seed oil are available in plenty and possess bitter principles that are contact toxins, anti-feedants and oviposition deterrents. A total of 231 species of insects belonging to the orders Coleoptera, Diptera, Heteroptera, Homoptera, Lepidoptera and Outlook on AGRICULTURE Vol 29, No 2

– Melia cin Mopanol, epicatechin Karanjin

Orthoptera and three species of mites, 17 species of nematodes and 15 fungi have been reported to be sensitive, 15 and more are being added every day.

Sericulture and agroforestry Sericulture-based agroforestry systems have a great potential for bringing higher returns to farmers. The silk industry can open up new vistas of employment and social elevation amongst the poorer sections of the society. There are three types of silkworm, namely mulberry, tasar and muga in India. Mulberry (Morus alba)-based agroforestry systems have been found to be highly successful in the north-eastern regions of India. 16 Three sericulturebased agroforestry systems (Figure 3) were compared and found to be economically viable and preferred by farmers. In Karnataka, India, growing mulberry intercropped with soy beans or green gram gave the best economic returns. 17 A cost-benefit analysis has demonstrated that tasar silk culture could be a paying proposition and significantly bolster the rural economy. 18 Many agroforestry tree species are hosts (Table 2) of the

Figure 3. Sericulture-b ased agroforestry systems for the north-eastern region of India. Source: S.K. Dhyani, D.S. Chauhan, D. Kumar, K.V. Kushwaha and S.T. Lepcha, ‘Sericulture-based agroforestry system for hilly areas of north-east India’, Agroforestry Systems, Vol 34, No 3, 1996, pp 247–258.

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Table 2.

Agroforestry trees that are hosts for silkworms.

Tree

Common name

Family

Silkworm species

Other uses

Anogeissus latifolia Lagerstoemia parviflora Madhuca latifolia

Dhau Sidi Mahua

Combretaceae Lythraceae Sapotaceae

Tasar Tasar Tasar

Morus alba Terminalia arjuna T. tomentosa T. bellerica Shorea robusta

Mulberry Arjun Asan Baheda Sal

Moraceae Common silkworm Combretaceae Combretaceae Tasar Combretaceae Dipteroca rpaceae

Fodder, fuel wood, timber for tools and tannins Versatile timber, fuel wood, leaf fodder, dye Small timber, fuel wood , liquor from flowers and berries eaten raw, seed oil for soap industry Fodder, fuel wood, timber for sports goods

tasar (Antheraea paphia, A. mylitta) and muga silkworm (A. assami) and can provide additional income to farmers. Tasar cultivation in India is a traditional cottage industry. The challenge is to utilize the natural resources and manpower of the tasar industry through scientific conservation. Agroforestry can play a major role here. If less productive cultivated land were brought under agroforestry plantation of the host plants of the tasar silkworm and intercropped with pulses, vegetables etc, it would provide employment and income to the farmer all year round. Arjun trees (Terminalia arjuna) grown at a spacing of 1.2 × 1.2 m and intercropped with vegetables bring in approximately US$440 per annum. 19 But the success of such endeavours rests on the support system provided by the government and non-government agencies for educating the farmer and creating market outlets for the produce.

Table 3.

Fodder, fuel wood, tannins, dye, oxalic acid Tasar

Fodder, fuel, resin

Bee forage properties of some important multipurpose tree species.

Family

Tree species

Common name

Anacardiacea

Buchanania lanzan Mangifera indica Terminalia arjuna Terminalia chebula T. bellerica Emblica officinalis Acacia auriculiformis A. catechu Butea monosperma Dalbergia sissoo Tamarindus indicus Albizia sp. Cassia sp. Pongamia pinnata Azadirachta indica Melia azadirach Toona cialiata Syzygium cumini Psidium gujava Moringa oleifera Grewelia robusta Zizyphus mauritiana Citrus reticulata Aegle marmelos Sapindus emarginatus Madhuca latifolia Grewia asiatica

Chironji Mango Arjun Hirad Baheda Amla – Khair Dhak Shisham Tamarind Siris – Karanj N eem Baccain Toon Jamun Guava Sohjan Silver oak Ber Orange Bael Soap nut Mahua Phalsa

Combretacea

Euphoriacea Leguminosae

Meliacea

Myrtacea Moringacea Proteacea Rhamnacea Rutaceae Sapindacea Sapotaceae Tiliacea

Nectar source

Pollen source

+ + + + + + + + + + + + + + + + + + + + + + + + + + +

– – + + + + + + + – + + + + + + + – + + – + – + – + +

Apiculture and agroforestry The honey-bee is one of the most beneficial insects to man. Honey is a wholesome food and also possesses innumerable medicinal properties. The most serious problem for Indian bee-keeping has been the decrease in nectar-producing plants and the toxicity of chemicals used on crop plants. Agroforestry would give an impetus to bee-keeping by providing shade and bee pasturage. Honeybees have a double role to play in a crop ecosystem. They can provide economic products such as honey, royal jelly and bees wax while they help in pollination and seed-settin g on crops and trees. A number of multipurpose tree species recommended in agroforestry are good

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pollen and nectar sources (Table 3). The trees also provide shelter and nesting sites for honey-bees. Three species of honey-bee are economically important: the rock bee, Apis dorsata, the Indian honey-bee, Apis cerana indica, and the European bee, Apis mellifera. Of these three, Apis dorsata is the only one that cannot be domesticated. They prefer tall trees such as the semul (Ceiba pentandra) for nest-building. Tribespeople and honey sellers collect honey from these nests. The other two species can be domesticated and maintained in nest-boxes. These colonies provide pure honey, while the foraging bees increase pollination and seed-settin g

in the crop ecosystem. There are a number of other bee species that are major pollinators, though their honey production is low. Apis florea, or the lesser honey-bee, is one such example. This honey-bee is a very good pollinator of many crops. The trees associated with crops in agroforestry provide an optimum nesting site for this shade-loving honey-bee. This bee builds its nest on the lower branches of trees such as the babul (Acacia nilotica), ber bushes (Zizyphus sp.), citrus (Citrus reticulata), amla (Emblica officinalis) and kardai (Anogeissus sp.) — see Figure 4. This species cannot be economically utilized because of its

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Agroforestry: an ecofriendly land-use system for insect management

harvested and the percentage of fruit set can also be increased.

Lac cultivation in agroforestry

Figure 4. Apis florea nest on Emblica officinalis grown under agroforestry.

Figure 5. Mango in full bloom, grown under agroforestry.

frequent swarming. The honey production is also lower, but in a wooded system such as that of agroforestry they occur naturally and are the major pollinators in the system. Many crops grown under agroforestry, such as coffee, maize, mustard, sesamum, sunflower, lucerne, cruciferous vegetables, coriander and fennel are good sources of nectar and pollen. Bee-

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keeping associated with agroforestry has two-way benefits. It increases fruit and seed production in addition to economic production. In mango (Mangifera indica) the number of florets produced per panicle is 10,000, and in a good season the trees are completely covered by the blossoms (Figure 5). The flower-drop is around 27–30%. With the introduction of honey-bees, the nectar can be

Lac is a natural resin secreted by insects belonging to the genus Laccifera lacca syn Kerria lacca, which produces most of the commercial lac in India. Lac cultivation has been known in India from ancient times and is considered to be an important income-generating non-timber forest product for the rural people of India, particularly tribal communities. India held a virtual monopoly of the lac trade until 1950, accounting for nearly 85% of the world’s production of stick lac. Since 1950, Thailand has gained hold, and now supplies 25– 30% of the world requirement. The species cultivated in Thailand is L. chinensis. Two strains of lac insect are prevalent in India — the rangini and kusumi, depending on the host plants . The rangini strain is cultivated mainly on the Indian dhak (Butea monosperma) and ber (Ziziphus mauritiana). The kusumi crop is raised on the host plant, kusum (Schleichera oleosa). Large-scale cultivation of lac is not practised due to great fluctuations in price. Introducing this tree into agroforestry systems will help in agrodivers ification and in risk-spreading. Lac production per tree on Butea monosperma has a value equivalent to about US$5. In one hectare of cropland, 40–60 Butea trees can be maintained, eg on the field bunds of paddy fields. The trees reportedly have no apparent adverse effects on the adjoining rice crop in the Chattisgargh region of India. 20 Under agroforestry, trees maintained on the farm should be pruned regularly. This has a two-way benefit. It increases coppicing in the trees, which is beneficial for lac cultivation, while reducing the shading effect on crops. Successful lac production requires knowledge of the life-cycle of the insect as related to the sylvicultural management of host plants. Improved management of Butea monosperma for lac production can ensure higher and more sustainable yields, leading to enhanced income generation at both local and national levels, while continuing to complement other resource roles of

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the tree. The trees can be divided into coupes on which lac cultivation is alternated in order to maintain the vigour of the tree. 21 Other agroforestry trees that are hosts of the lac insect are Albizia lucida, Ficus lacor and Zyzyphus stylophora.

P.K.R. Nair, ‘Classification of agroforestry systems’, Agroforestry Systems, Vol 3, 1985, pp 97–128. 3

K.R. Solanki, ‘Agroforestry’, in G.B. Singh and B.R. Sharma, eds, 50 Years of Natural Resource Management Research, ICAR, New Delhi, 1998, pp 447–476. 4

A multipurpose tree/shrub is a single woody species with a variety of outputs in various combinations, such as wood/ timber, fuel, food, fodder, exudation, thatching material, fibres, medicinal and ornamental materials and services such as windbreaks, fire-breaks, shelter belts, mulches, live hedges, soil amenders, soil binders, environment ameliorators, etc.

Lymantridae) in low to moderate populations in Central California’, The Canadian Entomologist, Vol 109, 1977, pp 727–746. Chitra Shanker, ‘Pest problems in agroforestry’, Annual Report, National Research Centre for Agroforestry, India, 1997–1998. 13

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Conclusion Agroforestry is a sustainable, economically viable and ecofriendly agricultural practice. When this system is managed using sound ecological principles such as integrated pest management, it can help minimize the use of synthetic pesticides, thus reducing pollution and other associated problems of their use. The pesticide-free atmosphere becomes amenable to such economic ventures as silk, lac and honey production, thereb y increasing the economic returns for the farmer while safeguarding the environment for future generations. The need of the hour is to educate the farmer to adopt alternative agricultural practices and simultaneously create marketing outlets for the produce. This would set the cycle of development, as revenue flow would provide impetus for continued adoption.

Acknowledgments The authors acknowledge the technical assistance provided by Rajesh Srivastav in photography and illustrations. They are grateful to Dr K.S. Dadhwal for some useful suggestions and to A.K. Shanker for critically perusing the article.

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V.T. Sundaramurthy and K. Chitra, ‘Integrated pest management for cotton’, Indian Journal of Plant Protection, Vol 20, 1992, pp 1–17.

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M.A. Altieri, F.J. Trujillo and J. Farrell, ‘Plant–insect interactions and soil fertility relations in agroforestry systems: implications for the design of sustainable agroecosystems’, in H.L. Gholz, ed, Agroforestry: Realities, Possibilties and Potentials, Dordrecht, Martinus Nijhoff/ ICRAF, 1987. 6

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Chitra Shanker, K.R. Solanki and Rajendra Singh, ‘Blister beetle damage in agroforestry’, Agroforestry Newsletter, Vol 10, No 4, 1999. 8

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R.C. Saxena, ‘Insecticides from neem’, in J.T. Arnasen, B.J.R. Philogene and P. Morand, eds, Insecticides of Plant Origin, ACS symp ser 387, ACS, Washington, DC, 1989, pp 110–135; M. Jacobson, ‘The neem tree: natural resistance par excellence’, in M.B. Green and P.A. Hedin, eds, Natural Resistance of Plants to Pests: Roles of Alelochemicals, ACS sym, ser 286, ACS, Washington, DC, 1986, pp 110–135; R.C. Saxena,‘ Neem as a source of natural insecticides — an update’, in M.S. Chari and G. Ramprasad, eds, Botanical Pesticides in Integrated Pest Management, Indian Society of Tobacco Science, Rajamundry, India, 1993, pp 1–24. P. Vivekanandan, ‘New system: neem production in south India’, Agroforestry Today, Vol 10, No 1, 1998, pp 12–14. 15

S.K. Dhyani, D.S. Chauhan, D. Kumar, K.V. Kushwaha and S.T. Lepcha, ‘Sericulture-based agroforestry system for hilly areas of north-east India’, Agroforestry Systems, Vol 34, No 3, 1996, pp 247–258. 16

B.R.D. Yadav and T.D.N. Kumar, ‘Effect of row arrangement on yield and monetary benefits in mulberry (Morus alba) + soybean (Glycine max) and mulberry + green gram (Phaseolus radiatus) intercropping’, Indian Journal of Agricultural Sciences, 1998, Vol 68, No 3, pp 149–151. 17

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D.L. Dahlste, R.F. Luck, E.I.. Schlinger, J.M. Wenx and W.A. Copper, ‘Parasitoids and predators of the Douglas-fir tussock moth, Orgyia pseudotsugata (Lepidoptera:

R.K. Gupta, Multipurpose Trees for Agroforestry and Wasteland Utilisation, Oxford & IBH Publishing Co Pvt Ltd, New Delhi, 1993. 18

C.M. Misra and Ajay Prakash, ‘Growing arjun trees for Tassar silk’, Indian Farming, Vol 36, No 9, 1986, p 21. 19

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