5The three universally appreciated insects are the honey-bee, the lac insect, and the silkworm. Honey extraction from wild hives is definitely a case of exploitation, but modern bee-keeping provides an illustrious example of science enabling man to enter into a just and ethically sound partnership at least with one species of honey-bee.
The relationship with the lac insect also need not be necessarily abhorrent, but that with the mulberry silkworm particularly is a simple case of a bio-industry in which, as in many other cases, an animal species is reared and cultured only to be ultimately killed and utilized.
There are 3 species of honey-bee in India, viz., the large rock-bee (Apis dorsata), the little bee (Apis florea), and the medium-sized Indian honey-bee (Apis cerana indica). All gather nectar and pollen from numerous species of flowering plants and in this process bring about pollination of the flowers. Man has been consciously interested since time immemorial in the nectar collected by these insects and later on appreciated the yeoman service they do as pollinators.
Therefore, scientifically minded people and later on professional scientists have tried to study and befriend these insects and enter into a mutually beneficial partnership with them; but so far they have succeeded in doing so only with the medium-sized honey-bee, Apis indica, the European counterpart of which is Apis mellifera. The rock-bee is too ferocious to deal with in a friendly way. It builds large open single combs measuring up to 1.5 or even 2 metres from side to side and 60 to 120 cm in depth.
These combs are suspended from rocks, ceilings of tall buildings, and branches of tall trees. It is the combs of this species with which most people are familiar. There are records of fatal attacks by rock bees on man and animals, and even armies are said to have been repulsed by swarms of these bees.
The little bee builds very small combs which are suspended from bushes, trees, roof corners, etc. People have not considered it worthwhile to devote much attention to this species. The medium-sized bee is reasonably docile in its habits and, therefore, this species has been carefully studied.
Before these studies, the honey collectors used to deal with these bees also as mercilessly as they do even today with the rock-bee, i.e., they used to practically overpower the bees with smoke, etc. particularly during night, and cut away the combs for collecting honey, this caused much wanton destruction of the bees, their young ones, and their combs.
Modern Partnership between Man and Medium-Sized Honey-Bee:
This partnership is the basis of the modern industry of apiculture, and its scientific principles are based on the following information about the habits and life economy of the medium-sized honey-bee. The Indian species is found all over the country. Unlike the other 2 Indian species, it Guilds several parallel combs generally in the hollow of tree trunks, hollows in rocks, and other common closed and covered places.
The bee colony is a highly sophisticated social community with rigorous laws, particularly about the division of labour between groups or castes of individuals. The division of labour is so perfect that it has its imprint even on the structural peculiarities of different castes.
There are 3 main castes:
(i) The queen, which is usually a single individual in a colony,
(ii) The drones, generally not more than a few hundred, and at times none, and
(iii) The workers, numbering 20,000 to 30,000.
The queen is the only fully developed female; it is the mother of the colony, readily distinguishable from the other members. From the workers it differs in being bigger in size and having an elongated shining black abdomen, which is striped and triangular in shape in the workers; because of the proportionately longer abdomen, the wings of the queen appear shorter than those of the worker. The queen does nothing but reproduce; during the period of highest activity it may lay as many as 1500 eggs a day.
The drone is male; its sole function is to fertilize the queen; it dies after mating. It has a black and rectangular abdomen with a blunt free end without a sting. It has large eyes, which meet over the head. Drones are reared and tolerated only during the breeding season in spring and autumn when new queens are there to be fertilized. When not required, before monsoon and during winter, they are driven out of the hive to starve and die; hence at certain times there may be no drone in the colony.
The worker-bee is an imperfectly developed female, unable to reproduce but possessing all the maternal instincts. It is smaller in size than the queen and the drone. The workers do all the work of the colony, build combs, gather nectar and pollen and certain other substances used in the hive, and care for the brood. They keep the hive clean, and regulate its temperature by fanning their wings. From nectar they make honey. To perform these duties satisfactorily, the workers are provided with the necessary structural adaptations.
Each worker-bee performs different types of work in its life-time, and its body becomes equipped for various duties in succession as it advances in age, i.e., it passes through a series of professions, changing its activity as it grows older. Since new broods of bees constantly arise, at any time there are bees engaged in different tasks of running the hive.
Just after emergence as adult, and for a period of about 2 weeks thereafter, the worker’s principal task is to act as a nurse. It brings honey and pollen from the storage cells to feed the queen, the drones, and the larvae. As it grows older, it becomes able to produce wax from glands on the underside of its abdomen and begins to work on the construction of the combs. In addition, it performs the job of house cleaning, and of standing guard at the entrance of the hive against any intruders.
About 3 weeks after emergence it begins to attend to all outdoor duties and collects and brings into the hive nectar, pollen, water and propolis (bee-glue). When on outdoor duty, the workers divide into searchers and gatherers. The former fly around and bring back news of available food and communicate it to the latter by performing a dance indicating the exact distance and direction of the source. The gatherers then rush to the indicated spot and bring back loads of pollen and nectar. The variety of the dance forms the language of the bees. The worker-bee labours hard for the colony till it gets exhausted and dies.
The queen lays a small white egg, slightly curved on one side, at the bottom of a cell. In appearance and size the eggs of different castes are alike, but they may be either fertilized or unfertilized; for the queen is capable of laying both the types. The unfertilized egg produces a male (drone); the fertilized egg produces a female, which may become either a worker or a queen depending on the food available during the larval stage. The eggs are, however, laid in separate cells provided for rearing different castes.
The egg hatches in 3 days and a tiny larva emerges. Remaining in the cell, the larva feeds voraciously on the food supplied by nurse-bees. When fully fed, the larva spins a cocoon in the cell which is then closed with a waxen cap; inside which the larva transforms into a pupa, In the case of larvae which are to give rise to workers, the larval period lasts for 4 to 5 days. After 11 to 12 days of pupal period the worker-bee emerges, cutting open the cocoon and the wax cap of the cell. The total period of development in the worker-bee is about 18 to 20 days; it varies in the other two castes.
The young larvae are fed a special food called ‘royal jelly’, a secretion of special glands located in the head region of the nurse-bee; it is supplied to young larvae of the 3 castes up to the third day of their development. Thereafter the composition of food given to the larvae destined to become queens, workers and drones differs. It has been established that differentiation into worker or queen depends on the quality and quantity of food fed to the larva.
Partial starvation from about the third day onwards results in the production of worker. The larva destined to form the queen has constant access to abundant food and is reared in large cells specially made for the purpose at certain times of the year along the lower margin of the comb.
When a new queen emerges in a hive she may be killed by the old queen or may herself kill the old queen. Frequently, however, the old queen leaves the hive and takes with her a large number of workers to found a new colony. The division of a colony in this manner is called ‘swarming’. The new queen mates with a drone in the air. After some period it starts laying eggs, and routine activity in the colony starts all over again. A queen may live for 2 or 3 years.
The comb is made of wax secreted from a set of 8 glands, 4 on each side of the underside of the worker’s abdomen. It comprises numerous hexagonal chambers or cells built on the sides of a central midrib. The midribs of adjacent combs are at a distance of 3.2 to 3.5 cm depending on the variety of the honey-bee.
The cells are utilized for rearing the young and as store-rooms for pollen and honey. The cells meant for rearing individuals of different castes are different those for the workers being the smallest, those for the queen the largest, and those for the drones intermediate in size.
Both worker and drone cells can be used for storing honey and pollen. The arrangement of cells in the colony is quite orderly. The brood area consisting of cells in which the workers are being reared is generally in the lower part of the comb. In the top and the sides of the brood area is a band of cells stuffed with pollen, and above this is the band of cells containing honey. The comb in the middle of the hive contains the largest brood area and on the sides the brood area becomes progressively small. Thus, the brood space of the colony is a kind of sphere in the lower part of the hive.
A good working knowledge of the honey-bee was acquired by man right in the beginning of human history. Even neolithic man is said to have been acquainted with its value. Early Egyptians practised commercial bee-keeping, even migratory bee-keeping. The Greek also practised this art. So did the Romans. Aristotle wrote on bee-keeping. In India there is mention of the use of honey right from the Vedic period.
To primitive man the honey, the pollen, the brood, and even the young bees meant food. It was only during the last 100 years that bee-keeping became sophisticated and civil, after Langstroth invented his beehive with moveable frames.
Later, it became practicable to keep boxes over the hives in which surplus honey was stored by the bees. This led to the construction of the beehive in 2 storeys, so that honey could be stored by bees in the upper storey (super) and brood-rearing could be carried on in the lower storey (brood chamber).
This further made it possible to remove the movable combs containing honey in the super without disturbing the brood chamber. The question of killing the brood or the bees for extracting honey became a thing of the past. A further improvement was to extract the honey in a special extractor without destroying the comb, which could be put back in the hive to be filled with honey again. This meant a lot of saving of labour for the worker-bee, which could devote the energy thus saved to collection of nectar and pollen. It has been estimated that making 1 kg of comb is equivalent to production of 6 to 10 kg of honey.
All this improvement and sophistication has been possible by carefully studying the habits and requirements of bee. These studies have now made it possible even to understand the language of the bees. It is established that the honey-bee has its own language, which is not articulate but akin to the language of scouts. This is actually called the dance language of the honey-bees. The patterns of dance have definite meaning which can be decoded now by man.
The Lac Insect:
Many of us do not connect a stick of sealing wax, a gramophone record, or French polish (and other varnishes of the non-synthetic kind) with insects. Yet, all these in reality come from an insect known popularly as the lac insect and technically as Laccifer lacca.
Where and how this insect lives and produces lac makes a fascinating story. While lac cultivation is an industry, being increasingly run on highly commercialized scale, the basic limit of it is the lac insect; hence the entomologist is directly interested in lac cultivation.
Lac is produced by the insect as a brown resinous encrustation. The reddish encrustations one sees on such trees as kusum (Schleichera oleosa), palas (Butea monosperma), and ber (Zizyphus mauritiana), and occasionally on Ficus spp., are actually the secretions of the lac insects. The first 3 plant species are the most favoured hosts of the lac insect, although it is also found on a variety of other plant species.
The female insect lays eggs inside the lac cell with which it is covered, and the eggs hatch immediately after laying. Each female produces about 300 minute, soft-bodied, crimson larvae. Larval emergence in large numbers takes place at certain times of the year. Immediately after emergence the larva crawls over the host plant and rests only when it finds a suitable place on a shoot. It pierces the plant tissue with its needle-like mouthparts and sucks up the juice of the plant.
Once settled, the larva does not move about and goes on depositing resin around itself except about the mouthparts, breathing pore, and anus. The larvae grow and moult 3 times before becoming sexually mature males and females. Female larvae have larger and thicker cells than male larvae. Both kinds lose their legs, antennae and eyes after the first moult, but the males eventually regain these organs after they turn into pupae. The duration of the development varies with the prevailing climatic conditions.
The adult males are of 2 types, winged and wingless. They move about in search of females, which remain fixed to their original sites. The males live for a short period (62-92 hours) during which they mate and fertilize the females. From this time onwards lac is secreted by the female at a faster rate, and the size of the insect as well as that of the enveloping lac cell increases rapidly to several times the size of the male lac cell; therefore the female is the chief source of lac.
This state of activity lasts for a varying period according to climatic conditions. As the time for egg laying approaches, the body of the female contracts on one side, gradually vacating space inside the cell in which eggs are laid.
The foregoing account of the life-history of the lac insect constitutes the scientific basis of the lac industry. As the lac insects settle in close proximity on the branches of the host tree, their profuse encrustations make a sort of continuous sheet; and when the young larvae of the next generation have crawled out to new and younger shoots the old encrustation, which is practically lifeless, is scraped off and processed.
However, in systematic large-scale lac cultivation the young larvae are helped by human agency to reach twigs of plants specially made suitable for fresh infestation. Host trees are pruned so that they may throw out new shoots at the proper time. Then the twigs of the old host plant are cut a few days before larvae of the next generation are expected to emerge, and these twigs (carrying seed lac) are hung on fresh plants processed as above for the young ones to come out and infest fresh shoots.
Lac cultivation is practised in Bihar, Madhya Pradesh, Uttar Pradesh, West Bengal, Assam, Orissa and Maharashtra, the first 3 states producing the largest quantities of commercial lac. The major lac factories are located in Bihar, Madhya Pradesh and Calcutta. Lac exports earn about Rs.14 crore of foreign exchange, and hence the cultivation of lac has a direct impact on our trade balance. There is scope for considerable improvement in this bio-industry. Research on scientific lines can do much to make lac cultivation a profitable business.
Lac cultivation in India is of great antiquity, references to it being found in the Vedas. In the Mahabharata is recounted the story of the abortive attempt by the Kauravas to burn alive the Pandavas in a mansion built of lac as denoted by its name laksha griha. The Sanskrit word for a hundred thousand and for lac is the same, viz., laksha, possibly to indicate that lac is produced by large or countless numbers (of insects).
Silkworm is not given humane treatment, although it is reared on industrial scale and its product is used for a prosperous industry. The silkworm from which silk is obtained, the king of fabrics, is the caterpillar of the moth Bombyx mori. The moth is medium-sized, with a soft body and creamy white wings. In spite of the wings being present the moth has practically lost the power of flight because it has been completely domesticated for ages.
The knowledge of the production of silk from the silkworm is from time immemorial; it is on record that an Indian ruler sent silk fabric to an Iranian ruler more than 6000 years ago. Since then this insect has been reared in captivity.
Silk is secreted by the salivary glands of fully grown caterpillars, and this secretion on exposure to air at once hardens into a fine delicate thread. The caterpillar, which feeds exclusively on mulberry leaves (hence known as mulberry silkworm), spins out this fine thread to make a cocoon for its own protection in the pupal stage. Man has, however, found means to utilize this thread for his own purpose.
The female moth lays 300 to 400 whitish eggs. The caterpillars on hatching start feeding on fresh mulberry leaves and begin to grow. In 4 to 5 weeks they become fully mature and are yellowish white with a cylindrical elongated body about 5 cm long and having a small horn at the hind end. When ready to pupate, each caterpillar spins a yellowish-white cocoon inside which it pupates.
About 10 to 12 days thereafter the moth is ready to emerge. Just before emergence, the moth secretes a fluid that softens one end of the cocoon from where it squeezes out breaking the silken strands. The moths live for only 23 days and do not take any food. They mate and lay eggs; and thus the life-cycle is repeated.
Depending on the number of life cycles passed in a year, there are 2 main races of the silkworm, univoltine and multivoltine. In the univoltine silkworm there is only 1 life-cycle in a year, i.e., the eggs remain in diapause for 5 to 7 months. This race is reared in Italy, France, Japan, China, and India (mainly Kashmir). In the multivoltine silkworm, on the other hand, there are many life-cycles in a year, there being no diapause in the egg stage. The multivoltine silkworm found in India and commonly reared in Karnataka, West Bengal, Assam, and Tamil Nadu has 4 to 7 life-cycles in a year.
How Silk is Collected?
Each cocoon is composed of a single continuous thread, which may be 200 to 350 metres long in the case of multivoltine races. If the moths are allowed to emerge, this single unbroken thread would be dissolved and broken into tiny pieces and become useless. Therefore, about 10 days after the cocoon is made, the pupae are killed by dropping them into hot water, by steaming, by exposure to the heat of the sun, or by fumigation.
The cocoons are sorted according to colour and texture and soaked in warm water to soften. When the silk thread becomes loose, it is skillfully unwound. The threads from several cocoons are wound together to form reels of raw silk, which is then processed to bring out the lustre; finally it is spun. It has been estimated that about 25,000 cocoons (consume about a ton of mulberry leaves) give 1 lb of silk.
Some Other Silkworms:
Silk in nature is produced by caterpillars of several species of moths, but there are only a few from which it can be utilized commercially. The important ones in India besides the mulberry silkworm are the eri silkworm, the tusser silkworm, and the muga silkworm. Mulberry silkworm is the most important because of the superior quality of silk obtained from it and the ease with which it can be handled. Tusser and muga silkworms are found wild in nature.
Silk Industry in India:
It is an important industry in India producing large quantities of silk for our own use and for export to many countries in the form of silk fabrics. The total production in 1962 was 17.80 lakh kilograms, Silkworm-rearing thrives primarily as a cottage industry.