(Dr. Girish Chandra)
Members of two families of Hemiptera, namely, Lacciferidae and Tachardinidae secrete lac over their bodies for protection. Lac Insect belongs Laccifer of superfamily Coccoidea of order Hemiptera. In all 22 species have been recorded under the genus Laccifer in Indian subcontinent.
Plants such as, Zizyphus mauritiana, Z. jujuba, Butea monosperma, Schleichera oleosa, Acacia arabica, A catechu, Cajanus cajan, Ficus benghalensis, F. cunia, and F. religiosa are common hosts of the lac insect Laccifer (=Tachardia) lacca.
Laccifer lacca, (=Tachardia lacca) is the commercially cultured lac insect. It is mainly cultured in India and Bangladesh on the host plants such as ber, Zizyphus mauritiana, palas, Butea monosperma and kusum, Schleichera oleosa.
Female insect is viviparous, producing about 1000 nymphs, deep red in colour with black eyes. The larvae settle down on a suitable place of the host plant gregariously. A day or two after settlement, the larvae start secreting lac all around the body except on the rostrum, spiracles and on the tip of abdomen. Thus it gets encased in a cell of lac which gradually increases in size along with the increase in size of the insect. The insect moults twice before reaching maturity. The male larvae produce elongated lac cells while the females produce oval cells
After the first moult larvae lose their legs, antennae and eyes and become bag-like. After the 3rd moult, the larvae pass on to a pseudo-pupal stage. Males emerge and copulate with the females and die. The female larvae never regain appendages and continue to remain under the lac cell, become adults and reproduce. As the lac insects remain close together, lac secretion from adjacent cells coalesces with each other and forms a continuous encrustation on the tree branch.
Lac culture involves two important steps: (i) inoculation, and (ii) cropping. Inoculation can be carried out through artificial infection of tender branches by brood lac stick obtained form mature lac trees immediately after harvesting. In this process, the brood lac sticks are tied in bundles of 2 or 3 sticks on the branches of the host tree, allowing maximum contact with the branches.
There are four seasons of lac cultivation and according to the Hindi calendar, they have been named as Kartiki, Aghani, Baisakhi, and Jethwi. The crop period, from inoculation to harvesting, for Kartiki, ranges from July to November, for Aghani, from July to February, Baisakhi, from November to July, and Jethwi, from February to July.
When young shoots come up on branches, the brood sticks are tied adjacent to the growing tender branches in a way so that maximum contact between shoots takes place. Within a week or two the larvae emerge and settle down on tender shoots.
PROCESSING OF LAC
Lac encrustations are removed from the twigs of host plants by scraping. The raw lac thus obtained is known as scraped lac or stick lac. Stick lac is crushed into small grains, sieved, washed with mild alkaline water and dried. This semi-refined product, called seed lac or grain lac or Chowrie, which is further refined by a system of hot melting, filtration and stretching into thin sheets which are subsequently broken into brittle flakes called shellac. Alternatively the purified lac resin can be in the form of circular discs called button lac. If a solvent process is used to purify the raw lac, de-waxed, decolorized lac can be obtained as the end product. The normally amber coloured resin can also be bleached with sodium hypochlorite to obtain bleached lac, which is white in colour. Bleached lac has specialised demand for coating medicinal tablets, confectioneries etc.
USES OF LAC
The various applications of lac can be summarized as follows:
Lac resin is used in food processing industry; cosmetics and toiletries industry; varnish and printing industry; coating of fruits and vegetables; electrical industry; leather industry; adhesive industry; pharmaceutical industry; perfumery industry; miscellaneous applications.
Lac dye (erythrolaccin) has been used in India as a skin cosmetic and dye for wool and silk. In China it is a traditional dye for leather goods. The use of lac for dye has been supplanted by synthetic dyes. It is used in medicine to protect liver and to fight obesity.
Lac is used in food, confectionery and beverages industry and textile industry.
Lac wax is used in polishes for shoe, floor, car polishes etc. It is used in electric insulations, lamination of papers, hat proofing and coating of pictures and fossils.
Lac is used for manufacture of tailors chalks, crayons, bottle sealers, lipsticks, enamels, printing inks, gramophone records and in fireworks.
NATURAL ENEMIES OF LAC
Two moth predators cause a lot of damage to lac.
- Eublemma amabilis. The larva is dirty white in colour and tunnels through the lac encrustation and feeds on larvae and adults. It pupates within the tunnel and adults after emerging lay their eggs near the lac encrustation.
- Holcocera pulverea. The damage by the brownish larva is similar to the above species. Pupa is slightly bigger and yellowish-brown.
The following insects are parasitic on lac insect.
Paraecthrodryinus clavicornis; Erencyrtus dewitzi; Tachardiaephagus tachardiae; Eupelmus tachardiae; Tetrasticus purpurens.