Lac Insect any of the species of Metatachardia,
Laccifer, Tachordiella, Austrotacharidia, Afrotachardina, and Tachardina
of the superfamly Coccoidea, order Homoptera that are noted for resinous
exudation from the bodies of females. Members of two of the families viz.
Lacciferidae and Tachardinidae appear to be more concerned with lac secretion.
These insects have a global distribution excepting Europe.
Of the many species of lac insect, Laccifer lacca, (=Tachardia
lacca) is the commercially cultured lac insect. It is mainly
cultured in India and Bangladesh on the host plant, Zizyphus
mauritiana and Z. jujuba. The insect starts its life
as a larva or nymph which is about 0.6 mm long and 0.25 mm wide
across the thorax. The young settles down on a suitable place
of the host plant gregariously. On the average some 150 of such
larvae may be present per square inch of the twig.
They have the typical piercing and sucking mouthparts
as in all other Homoptera. A day or two after settlement, the larvae start
secreting lac all around the body excepting the rostrum, the brachial
plates and tip of the 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 duration of each
larval inster depends on environmental factors, such as, temperature,
humidity, host plant etc. The male larvae produce elongated lac cells
while the females produce oval.
After the first moult, the male as well as the female
larvae lose their legs, antennae and eyes. After the 3rd moult, the larvae
pass on to the so-called pupal stage. During this stage the mouthparts
become atrophied in male insects and they stop feeding. The male lac insect
may be winged or wingless and they copulate with the females while they
are still in encased condition.
During development, the female larvae lose their appendages after the first moult. 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. Besides lac's use as sealing wax, it is widely used in varnishes.
Lac culture Very little is known from literature about the time when man first started culturing lac insects. From Atharva Veda it appears that knowledge about the lac insects, their biology, nature of secretion, and the uses of the secretions of the insect was known to man from the prehistoric time. In Sanskrit literature the tree, Butea monosperma has been referred to as the Laksataru, which is known to be the most common lac host.
In the Medieval period lac was probably introduced in Europe by the Spaniards from India to be used as a dye and also in the fabrication of Arabian medical preparations. India is still being regarded as the principal lac producing country of the world. Burma appears to have been involved in lac trading since sixteenth century. Lac culture in China probably dates back to 4000 years. With the development of silk industry there, the Chinese were also engaged in lac culture. They used lac for dyeing the silk. Lac was also used in dyeing leather goods. In Thailand lac cultivation is of recent introduction and it dates back to the fifties of the 20th century. Thailand generally has an export market to Calcutta where shellac is extracted from sticklac.
In Bangladesh lac culture dates back to the same period as in India. In the Nawabganj district lac culture is one of the regular occupations of many local people. However, only the sticklac is produced. In Talaimari areas of Rajshahi city there are more than 100 cottage industries where shellac is extracted from the sticklac produced in Nawabganj.
Plants such as, Zizyphus mauritiana, Z. jujuba, Butea monosperma, Schleichera oleosa, Acacia arabica, A catechu, Cajanus cajan, Ficus benghalensis, F. cunia, and F. religiosa commonly horbour the lac insect Laccifer (=Tachardia) lacca. In Bangladesh lac culture is restricted to Z. jujuba although some sticklac is occasionally collected from the wild from other host plants. The finest quality of shellac is obtained from kusum tree, S. oleosa.
Lac culture involves two important steps: (i) inoculation, and (ii) cropping. Inoculation can be carried out through self-infection or artificial infection. In any case the brood lac is necessary. Artificial inoculation is most suitable immediately after crop cutting. In doing so, the brood lac (10 to 30 cm long) are to be tied in bundles of 2 or 3 sticks and in turn they should be tied up to the branches of the host tree. Care should be taken while tieing the bundles so that they have contacts with the branches. The brood lac bundles should be kept on the host tree for 2-3 weeks. If kept longer, ie even after the complete emergence of the lac larvae, there is the danger of a large number of enemy insects emerging from the empty brood lac sticks. Lac crops should be reaped only when mature.
There are four seasons of lac cultivation and according to the Bengali calendar, they have been named as Kartiki, Aghrani, Baisakhi, and Jesthi. The crop period, from inoculation to harvesting, for Kartiki, ranges from July to November, for Aghrani, from July to February, Baisakhi, from November to July, and Jesthi, from February to July. In Nawabganj areas lac is cultivated only once a year, ie Jesthi. In December, after harvesting the plum fruits, Z. jujuba trees are pruned. In January young shoots come up. The brood sticks are tied adjacent to the growing tender branches in the way described earlier. Within a week or two the larvae settle down. Through out the period (February-June) the lac insects secrete a resinous crust on them. In July they are harvested. The branches of Z. jujuba trees are cut into smaller pieces (2 to 4 feet) and tied in bundles. The encrusted lac is then scrapped off the stick and processed in order to get the crude lac.
In the late sixties a Lac Culture Centre was established
in Nawabganj which is now almost non-functional. Obviously the lac cultivation
is also reduced to its lowest ebb. Most of the locally available lac is
of Indian origin. Generally the crude lac is imported, and those locally
produced, are extracted in Rajshahi. [Md Mahtab Ali]