Abstract
Insect resources are vast and diverse due to their enormous diversity. The exploitation and utilization of insect resources is broadly classified into four different categories. The first category is the insects of industrial resources. This level includes the utilization of silk worm, honeybee, lac insect, dye insect, and aesthetic insect. The second category is the utilization of insects for edible and therapeutic purposes. Insects are high in protein and many are rich sources of vitamins and minerals. The third category is the use of insects in forensic investigation. By analyzing the stages of succession of insects at first, rough estimation of the postmortem intervals can be done. The fourth category is the insects of ecological importance. Many insect species act as potential predators and parasites of destructive pests of insect order Lepidoptera, Diptera, and Orthoptera. Insects are also used as bioindicator to assess the cumulative effects of environmental stressors such as pollutants. Despites these fascinating benefits, insect resources are often neglected in India due to lack of proper documentation, less expertise, and advance enterprises in these fields. Hence, the paper reviews the different fascinating facets of insect resources in order to explore and utilize it in a sustainable way with reference to Indian region.
1. Background of Insect Resources
Insects are one of the most successful groups of animal. They constitute about three-fourths of the total organisms present on earth [1]. Out of the 5.57–9.8 million estimated animals in the world, 4–8 million species are known to be insects [2, 3]. Approximately, 0.1 million species of insects occur in India [4]. However, a precise check listing of the insect fauna of India has not yet been done so far. Therefore, possibility of recording several new species in near future is very high. Insects are unique not only in diversity but also in number of individuals in each species. There are 200 million insects for every human, 40 million insects for every acre of land. In the Amazon, insect biomasses overweight all vertebrates at 4 : 1 ratio [5]. Depending upon the vast diversity, the resources from insects are also vast and diverse. With their multiple utilities, insects have been providing constant services to the mankind as other resources.
On the basis of their utility, insect resource is broadly classified into four different categories. The first category is the insects of industrial resources. This level includes the utilization of silk worm, honeybee, lac insect, dye insect and aesthetic insect. The second category is the utilization of insects for edible and therapeutic purposes. Some important edible insects are grasshoppers, crickets, termites, ants, grubs, moths, caterpillars, and pupae. Insects are also an important natural source of food for many kinds of animals. The muscoid (Diptera) larvae and pupae from poultry manure or other organic wastes are used as a high protein source for broiler production. Usage of insects in traditional medicine was recorded since time immemorial. The therapeutic application of honeybee venom (bee venom therapy) has been used in traditional medicine to treat diseases like arthritis, rheumatism, back pain, cancerous tumors, and skin diseases. The third category is the use of insects in forensic investigation. By analyzing the stages of succession of insects at first, rough estimation of the postmortem intervals can be done. The fourth category is the insects of ecological importance. Many insect species act as potential predators and parasites of destructive pests of insect order Lepidoptera (Butterflies and Moths), Diptera (Flies) and Orthoptera (Grasshoppers). As a biomass recycler, house fly larvae are used to recycle organic wastes to produce protein and fat. Insects are also used as bioindicator to assess the cumulative effects of environmental stressors such as pollutants.
People worldwide have been enjoying insect resources in diverse fields. The modern trends in the development of the utilization and industrialization of insect resources, including traditionally cultured industrial insects and newly developed industrialized species has been reviewed by Zhang et al. [6]. But in India, due to lack of proper documentation, less expertise and advance enterprises in these fields, their values do not get due recognition, as compare to insect resources utilization in different corners of the world. Though, India is having a rich diversity of insect [4], only known insect resources products like silk, honey, and lac are well utilized and developed, neglecting many other prospective fields. Considering these important facts, this paper is reviewed with an aim to explore and utilize the different fascinating facets of insect resources in a sustainable way with reference to Indian region.
2. Insects of Industrial Resources
2.1. Sericulture and Allied Purposes
The natural fibre silk is the product of insects that belong exclusively to the order Lepidoptera. India is home to variety of silk secreting fauna which includes an amazing diversity of silkmoths. This has enabled India to achieve the unique identity of being producer of all the five commercially traded varieties of natural silks, namely, mulberry, tasar, oak tasar, eri, and muga [7] produced by silk moth species Bombyx mori, Antheraea mylitta, A. proylei (Figure 1), Samia cynthia ricini, and A. assama, respectively. As far as nonmulberry (tasar, oak tasar, eri, and muga) silk moth species are concerned, India alone recorded as many as 40 different species [8]. India also has native populations of wild silkmoths such as Theophila religiosa, B. mandrina, and Antheraea compta. The North-eastern region of India makes ideal home for a number of wild sericigenous insects and is centre of wild silk culture including muga, eri, oak tasar, and mulberry silk [9]. There are still many species in the forests of this region of India that are yet to be explored [7].
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Asia is the top producer of silk in the world contributing 95% of the total global output. Though there are over 40 countries on the world map of silk, bulk of it is produced in China and India, followed by Japan, Brazil, and Korea [10]. India, the world’s second largest producer of silk after China, is also the largest consumer of silk. In India, mulberry silk is produced mainly in the states of Karnataka, Andhra Pradesh, Tamil Nadu, Jammu & Kashmir, and West Bengal, while nonmulberry silks are produced in the state of Jharkhand, Chattisgarh, Orissa, and north-eastern region [7]. In the north eastern states of India, Assam contributes almost 90% of Muga silk and 65% of Eri silk production [11]. Meghalaya and Manipur also appear in the map of silk producing states of this region (Table 1).
Apart from silk, there are several other by products from sericulture which can be utilized as commercial input in many fields. The foliage of mulberry is used as a fodder for cattle [12]. Silkworm pupae were traditionally used as fertilizer, animal feed, food material, and medicine in some countries, such as China, Japan, Korea, India, and Thailand [13–15]. Human consumption of silkworm pupae has been practiced in China [16] and India by many tribal communities [10]. Recently, silkworm pupae have been put in the list of “Novel food resources managed as common food” by Ministry of Health PR China [15]. The waste liquor containing sericin, which is yielded through process of the degumming of silk fiber, is also regarded as another raw material for the production of sericin powder. Sericin powder is used in a variety of industries as a raw material in production of food, cosmetic, medicine, and so forth [17]. Thus sericulture not only provides silk for fashionable clothing, it also offers several useful by products to the human society [12].
2.2. Apiculture and Allied Purposes
Honey production has been proven as a promising profitable venture, which is a mean of low-cost or high-yield enterprise without requiring compulsory land ownership or capital investment. It has been used traditionally in various diet preparations, such as medicine, cosmetic, ointment, candle, and household bee-wax items [18]. The propolis of the bee hive is used in lip balms and tonics whereas royal jelly is used to strengthen the human body, for improving appetite, preventing ageing of skin, leukemia and for the treatment of other cancers. On an estimate, about 80% honey is used directly in medicines and 10% in Ayurvedic and pharmaceutical production. Honey bees during foraging for pollen and nectar from flowers of different plant species, enhance agricultural productivity to the tune of 30%–80% annually through cross-pollination [19]. Of the five honey bee species of the world, namely, Apis florea, A. cerana, A. dorsata, A. mellifera, and Trigona iridipennis, only two species, A. cerana and A. mellifera (Figure 2) are reared in India [20].
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There is a long history of honey hunting and traditional beekeeping by utilizing Asian wild honeybees. Asia has a suitable agro-climatic background for development of modern beekeeping. Currently, China captures 40% of the world market. The biggest importers of honey are Germany, Japan, and the United States. India produces about 70,000 tonnes of honey every year of which 25000–27000 tonnes is being exported to more than 42 countries. The major honey-producing states in India are Punjab, Haryana, Uttar Pradesh, Bihar, and West Bengal [21]. Study on honey and honeybee is a never ending venture in a vast country like India. The unexplored forests of the country especially those of north east may unfold the wealth of newer bee species in future. G. K. Ghosh and S. Ghosh [22] also cited the traditional importance and practices of apiculture in Manipur in their book, “Woman of Manipur.”
2.3. Lac Culture
Lac is a resinous substance produced by an insect popularly known as lac insect. Lac insects, the crowning glory of India’s rich insect fauna (representing 21.8% diversity of the known lac insect species) are exploited for their products of commerce, namely, resin, dye, and wax. The total numbers of lac insect species reported from the world are 87 species under nine genera, of which 19 species belonging to two genera are found in India [23]. Concerning the economic viewpoint, India is the largest producer of lac in the world, accounting for about 50%–60% of the total world lac production. India produces about 20,000 metric tones of raw lac every year. The major lac producing states are Jharkhand (57%), Chhattisgarh (23%), and West Bengal (12%) while Orissa, Gujarat, Maharastra, Uttar Pradesh, Andra Pradesh, and Assam are minor producers. India fetches approximately Rs.120–130 crore of foreign exchange through export of lac every year. Lac resin being natural, biodegradable and nontoxic, finds applications in food, textiles, and pharmaceutical industries in addition to surface-coating, electrical, and other fields. It provides immense employment opportunities in the country [24]. Species belonging to genus Paratachardina produce a hard, horny substance, which is insoluble in alcohol. These are univoltine and are generally treated as parasites of economically important plant such as tea and sandal. Recently, Paratachardina spp. have been found to be potential biocontrol agents for managing weeds [25]. Of the 19 species of lac insects reported from India, Kerria lacca is mainly exploited for commercial production of lac. K. chinensis in the northeastern states and K. sharda in coastal regions of Orissa and West Bengal are also cultivated to a certain extent. Potential of other lac insect species reported from the country remains to be exploited [24] and also a persistent exploration of new species is required.
2.4. Natural Dye from Insect
The demand for natural dye is constantly increasing with an increase in awareness of the public on the ecological and environmental problems associated with synthetic dyes [26]. The effort of cultivating natural dye from insects has been suggested by Prasad [27] with a view to exploit it from India. The coccid, Dactylopius coccus (Hemiptera: Dactylopiidae) is the most important species due to its being used for the extraction of carmine acid, a natural red dye used in food, pharmaceutical, and cosmetic industries [28]. The coccid is an insect living on cladodes of prickly pears (Opuntia ficus indica). Dried females are a source of red dyes widely utilized in food, textile, and pharmaceutical industries [29]. D. opuntiae is another wild species found in Mexico and has a shorter lifespan and reproduction cycles with a larger number of generations per year [30]. All the cochineal species have a high content of proteins and minerals. The residuals from coloring extraction can be used to enrich food for avian species or to prepare fertilizers [31]. Cochineal is used to produce scarlet, orange, and other red tints. The production and exploitation method of the dye was also studied by many workers in this field [32, 33]. The insects are killed by immersion in hot water or by exposure to sunlight, steam, or the heat of an oven. Each method produces a different colour which results in the varied appearance of commercial cochineal. It takes about 155,000 insects to make one kilogram of cochineal [34]. Likewise, oak galls were gathered and used commercially as a source of tannic acid. It was a principal ingredient in wool dyes and black hair colourants used during the Greek empire as early as the 5th century BC. It is still used commercially in the leather industry for tanning and dying and in manufacturing of some inks. Tannic acid was obtained from the Aleppo gall found on oak trees (Quercus infectoria Olivier) in Asia and Persia. The trees produce gall tissues in response to the chemical substance secreted by the larvae of tiny wasps (Cynips gallae tinctoriae Olivier; Hymenoptera: Cynipidae) that infest the trees. 50%–75% of gall’s dry weight is composed of tannic acid [35]. The aspect of exploring as well as utilizing natural dye-producing insects is quite virgin in the India. North-eastern region being a main region of oak cultivated area, there is an absolute scope in this field and thus enthusiastic approach is required in near future.
2.5. Insect Trade for Aesthetic Purposes
The body colouration, beauty, and mode of life of the insects always attract us. Coloured wing and elytra of many coleopterans are used in jewellery, embroidery, pottery, and basket makings [27]. Among the insects of aesthetic value, butterfly attains maximum attention from museums and collectors for which it is established as one of valued items in market. For satiating the growing need of butterfly amongst the collectors, numerous butterfly farms have been developed in European countries [4]. In such butterfly farms like Brinckerhoffs, all the pupae are captives reared exclusively for sale as live insects, which yield $100,000,000 annually [36]. Such view also captures thousands of income generating aspects utilizing insect resources.
3. Edible and Therapeutic Insects
3.1. Insects for Human Consumption and Animal Feed
Over 1,500 species of edible insects have been recorded in 300 ethnic groups from 113 countries. Many species of insects have served as traditional foods among indigenous peoples and the insects have played an important role in the history of human nutrition [37]. The insects are high in protein and many are rich sources of vitamins and minerals. DeFoliart [38] provided a brief general overview of the nutritional quality of edible insects. In some ethnic groups, insects provide 5%–10% of animal protein input as well as fats, calories, vitamins, and minerals [39]. Edible insects have been reported to have more nutritional content than the other conventional foods (Table 2). Studies on nutrient analysis for various insects were conducted by many authors in different countries like Quin [40] in South Africa, Santos Oliveira et al. [41] in Angola, Malaisse and Parent [42] in Zaire, Gope and Prasad [43] in India, Sungpuag and Puwastien [44] in Thailand, and Ramos-Elorduy and Pino [45] in Maxico.
Some of the commonly eaten species of insects include grasshoppers, crickets, termites, ants, beetle larvae, moth caterpillars, and pupae. Insects generally have higher food conversion efficiency than other higher animals. For example, house cricket (Acheta domesticus) when reared at or more, and fed a diet of equal quality to the diet used to rear conventional livestock, they show a food conversion twice as efficient as pigs and boiler chicks, four times that of sheep, and six times higher than steer when losses in carcass trim and dressing percentage are counted [47]. Protein production from insects for human consumption would be more effective and consume fewer resources than vertebrate protein. This makes insect meat more ecological than vertebrate meat. The use of insects particularly locust and grasshopper (Figure 3(a)) as food have been a great significance not only from the nutritional value, but also controlling pests as many ethnic human societies believe. In Asia and Oceania increased consumption of grasshoppers and locusts has coined with decreased pesticides use [48]. Insects are not used as emergency food to ward off starvation but are included as planned part of the diet whenever and wherever available. Among them, many of these organisms are taken for their flavor, for example, Belostoma indica (Figure 3(b)). The long history of human use suggests that the insects do not pose any significant health problem [49]. Some of the renowned works on edible insects from different parts of India are those of Singh et al. [49, 50], Alemla and Singh [51], and Singh and Chakravorty [52] (Table 3). This trend toward reducing the bias against insects as food is promising, by promoting nutritional value to stable diets and maximizing ecological benefits with edible insects. Despites these awesome benefits, the modernization have led indigenous population around the world away from this traditional food source, without providing nutritional equivalent substitutes [53].
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Insects are also well known as an attractive and important natural source of food for many kinds of animals, including birds, lizards, snakes, amphibians, fish, insectivore, and other mammals [54–56]. The vast majority of studies in the west have dealt with the nutritional value of muscoid (Diptera) larvae or pupae used to recycle nutrients from poultry manure or other organic wastes as a high-protein source for broiler production [57]. According to Davis [58], there is no difference in taste of eggs from grub-fed hens and others, in fact, the former had better yolks. Cotton and George St. [59] also summarized the early use of the meal worm, Tenebrio molitor as animal feed.
3.2. Insects in Medicine and Research
In many parts of the country, different sections of the society have been using the medico-entomological drugs in their day to day life [27]. Costo neto [61] termed entomotherapy for use of insects for therapeutic purposes. Some of the popular authors who have given the account of use of insects and the various stages in therapeutic activities are Antonio [62], Fosaranti [63], Alexiades [64], Zimian et al. [65], Green [66], Namba et al. [67], Maya [68], and Padamanbhan and Sujana [69]. One of the most commonly used insects in medicinal purposes is the blow fly larvae. During World War II, military surgeons noticed that wounds which were left untreated for several days healed better than noninfested wounds, when infested with the blow fly larvae maggots. It was later discovered that the larvae secreted a chemical called allantoin which had a curative effect. The therapeutic application of honeybee products has been used in traditional medicine to treat various diseases like diarrhoea, tuberculosis, impotency, asthma, exophthalmic goiter, and mouth galls. The practice of using honeybee products for medicinal purposes is coined as Apitherapy. One of the major peptides in the bee venom, called melittin, is used to treat inflammation in sufferers of rheumatoid arthritis and multiple sclerosis. Melittin blocks the expression of inflammation genes, thus reducing swelling and pain [70]. The therapeutic application of honeybee venom (bee venom therapy) has been used as a traditional medicine to treat a variety of conditions, such as arthritis, rheumatism, back pain, cancerous tumors, and skin diseases [71]. The use of traditional knowledge could be extended further in modern medicine system by identifying the proactive biomolecules with pharmacological action [72–75]. Bee venom contains at least 18 active components, including enzymes, peptides, and biogenic amines, which have a wide variety of pharmaceutical properties (Table 4). Recently, it was reported that melittin inhibited the DNA-binding activity of NF-kB, a critical transcriptional factor regulating inflammatory gene expression, by inhibiting IkB phosphorylation [76]. Bee venom also has anticancer activity. Several cancer cells including renal, lung, liver, prostrate, bladder, and mammary cancer cells as well as leukemia cells can be targets of melittin [77–80]. Pharmaceutical companies are currently funding extensive research into the potential of venom as the next generation of cancer fighting drugs. Thus, bee can be cited as a spectacular example as medicinal insects. Likewise, there may be many such insects having similar or superior medicinal properties. Cantharidin is another medicine obtained from blister beetle (Figure 4), an insect belonging to order Coleoptera and family meloidae. Its medical use dates back to description in Hippocrates (ca. 460–377 BC) [81]. It was administered as a diuretic and to alleviate epilepsy, asthma, rabies, and sterility. The eggs of red ants are said to be used as a constituent of medicine for the control of malaria. Extract of cocoons of mulberry silkworm is believed to check profuse menstruation and chronic diarrhoea [26]. Pierisin, a protein from pupa of cabbage butterfly, Pieris rapae exhibit cytotoxic effects against human gasteris cancer. Extract of the body fluids of other cabbage butterflies, P. brassicae and P. napi also contains the same protein, pierisin [60]. Insect cell lines have been reported to be efficient expression hosts for the production of many glycoproteins, including monoclonal antibodies [82]. Tang et al. [83] proposed the idea that antimicrobial molecules from insects may serve as a potentially significant group of antibiotics. It was revealed from their experiment conducted on the Chinese traditional edible larvae of housefly, Musca domestica. Some of the insects used in Indian traditional medicine are highlighted in Table 5.
4. Forensic Entomology
Forensic entomology, the use of insects and other arthropods in forensic investigations, has gained a lot of importance during the past few decades [88]. Some of the recent literatures like, “The Manual of Forensic Entomology” by Smith [89], “The entomological review” by Catts and Goff [90] and the installation of the International homepage of Forensic Entomology [91] may be cited as examples. Mende [92] listed a number of animals which feed on corpses. This list includes flies, beetles, and other insects. By analyzing the stages of succession of insects a first rough estimation of the postmortem intervals can be made [89]. Depending on the biogeographical region and ecological habitat, different species of necrophagous insects are involved in the decay of a corpse. For example, examinations on insect-succession from Canada are not applicable in the conditions of Germany [88]. However, the primary purpose of forensic entomology in today’s context is the use of insects in determining elapsed time since death [93]. Forensic entomology, therefore, holds a vital position in the arena of forensic science. The unique role played by insects in this field is overwhelming, whose place is nonreplaceable by other organisms.
5. Insects of Ecological Importance
5.1. Insects as Biological Control Agent
Biological control means the action of parasitoids, predators, and pathogens in maintaining other organism’s density at a lower average than would occur in their absence. In modern context, when we are becoming aware of the harmful effects of unilateral use of chemical insecticides in various agricultural field or ecosystem, the role of insect as biocontrol agent is immensely vital. The first dramatic example of deliberate biological control was the importation of vedalia ladybeetle, Rodolia cardinalis (Mulsant) in California, in 1888 to control the cottony-cushion scale insect, Icerya purchasi Maskell on citrus [94]. Many insects act as potential predators and parasites of destructive pests of insect-order Lepidoptera (Butterflies and Moths), Diptera (Flies), and Orthoptera (Grasshoppers) [27]. Predators are scattered in about 167 families of 14 orders of the class, Insecta [95]. Major groups of entomophagous parasites belong to the order Hymenoptera and family Tachinidae of the order Diptera. The well-known parasitoids acting as potential biocontrol agents are Ichneumonids, Chalcids, Proctotrupoids, and Evanoids. The Tachinid flies species of Sturmia and Tachinia parasitize the insect pests like paddy armyworm and fruit moth larvae [27]. Biological control effort against noxious weed, Parthenium hysterophorus L. through the utilization of insect species, Zygogramma bicolorata (Coleoptera: Chrysomelidae) has also been advocated by Gautam [96]. However, only few species are well established and employed in the field of biocontrol. Thus, further studies are required to explore successful insect species as biocontrol agents.
5.2. Insects in Biomass Recycling
Lindner [97] was the first to suggest the use of house fly larvae to recycle organic wastes, specifically human waste, to produce protein and fat as a useful byproduct. Although insect herbivory is common in terrestrial ecosystems, it has only recently been considered an important and persistent control on ecosystem processes and has not been included as a factor in most ecosystem models. Herbivore alteration of litter inputs may change litter decomposition rates and influence ecosystem nutrient cycling too [98].
5.3. Insects as Indicator of Water Pollution
Water quality researchers often sample insect populations to monitor changes in water bodies. The insects are monitored over time to assess the cumulative effects of environmental stressors such as pollutants. Environmental degradation resulting from pollution will likely decrease the density of insects found by eliminating those that are less tolerant to unfavourable conditions. Insects such as the mayfly, stonefly, and caddis fly larvae are sensitive or intolerant to changes in stream conditions brought about by pollutants [99]. Composition of species tells water conditions. Presence or absence of particular species like certain chironomid midge species is very specific in their environmental needs. For example, specific species will survive only in pH 2, high-acidic conditions, high-nitrogen water, and so forth. Insects are effective indicators because they have a short generation time [100]. Trace metal contaminants can affect both the distribution and the abundance of aquatic insects. Insects have a largely unexploited potential as biomonitors of metal contamination in nature [101, 102]. Lithocerus niloticum (Hemiptera: Belostomatidae) was reported to be an efficient biomonitor for heavy metal pollution in lakes [103].
6. Perspective
There is no doubt that insects are potentially a more efficient source of many fascinating facets for mankind and others vertebrates. There is a need to link the potential of this bioresources to economic prosperity. Owing to the above facts, there is a debating question about the biomass availability of the insect species. In this regard, Benjo et al. [104] stated that wild harvest of insect pests in established crop or horticultural systems may be more practical. Collecting such pests would not only protect plant but it could benefit the environment by reducing the need to use pesticide [105]. Establishment of mass breeding insectaries with modern artifact such as raising them in artificial diet or through biotechnological intervention could provide a hope for golden aspects for income generation too. For instance, farmers may earn as much as $1000 or more each year in New Guinea by harvesting emerging adult of wild butterflies for trading [36]. Some interesting challenges also include the integration of mass rearing of insects into small scale farming ventures such as development of organic waste recycling systems using insects [37, 106]. Insects have long been significant dietary factor and remedy for illnesses in different regions of the world. Scientific validation and updating of traditional wisdom in bioprospecting has assumed greater significance. There is a need for more and more analysis of insect biodiversity for the development of virgin resources and their industrialization particularly in India. It is a high time that researchers recognize the manifold utilities of insects and begin to build on it.
Acknowledgments
The authors are indebted to Dr. N. C. Talukdar for his constant inspirations and suggestions in the preparation of this paper. Thanks are also due to Dr. W. Gusheinzed for critically evaluating the paper for its improvement. Much of this work would not have been possible without the facilities of literatures from DBT’s e-library Consortia (Delcon) in the institute. The authors are thankful to Department of Biotechnology (DBT), New Delhi for providing financial support and working facilities in the Inset Bioresources Division, Institute of Bioresources and Sustainable Development (IBSD), Manipur, India. Further support was also provided to the first author by DBT, through the DBT Research Associateship grant in Biotechnology and Life Sciences program.