Lac is secreted by which insect?

The correct answer is B, Bombyx mori, the mulberry silkworm, the only fully domesticated insect of the silk group and the source of most of the world's raw silk. Option A, Antheraea mylitta, is the tropical tasar silkworm, which lives in the open on Asan and Arjun trees. Option C, Samia ricini, is the eri silkworm, reared on castor leaves, whose broken fibre is spun rather than reeled. Option D, Kerria lacca, is not a silkworm at all but the lac insect, a scale insect whose female secretes the resin called lac. The way to keep the four apart is to attach each to its host plant: mulberry for Bombyx mori, Asan and Arjun for tasar, castor for eri and Som for muga. Note also that this insect has been bred by people for so long that the adult moth can barely fly and depends entirely on rearers, which is what makes it the one truly domesticated silk insect.

The correct answer is C, Assam. Muga silk comes from Antheraea assamensis, reared on Som and Soalu trees of the Brahmaputra valley, and Assam's muga carries a Geographical Indication tag. Option A is wrong as an answer to this question although Karnataka leads the country in mulberry silk, which is a different variety; students who remember only the words largest silk producer mark it wrongly. Option B is wrong because West Bengal is known for mulberry silk and for the research institute at Berhampore, not for muga. Option D is wrong because Jharkhand is famous for tasar silk and, above all, for lac. Remember the pairing: mulberry with Karnataka, muga with Assam, tasar with Jharkhand and Chhattisgarh. One more fact from this topic is often paired with the state: muga is reeled into a golden yarn that needs no dyeing, and its natural colour is the reason it is prized.

The correct answer is B, castor. The eri silkworm, Samia ricini, feeds on castor leaves, and its silk is called ahimsa silk because the moth is allowed to emerge before the cocoon is used, leaving a broken fibre that is spun like cotton instead of being reeled. Option A is wrong because mulberry is the food of Bombyx mori, and growing mulberry for it is called moriculture. Option C is wrong because Arjun, along with Asan, is the host of the tropical tasar silkworm. Option D is wrong because Som, with Soalu, is the host of the muga silkworm of Assam. The examiner's favourite trick here is to offer two tree names from the tasar and muga groups beside castor. Castor is Ricinus communis, grown widely in Assam and the North-East, which is why eri rearing is concentrated there alongside muga.

The correct answer is C, Apis dorsata, the rock bee, the largest of the Indian honey bees, which builds a single huge comb on cliffs and tall buildings and yields the most honey per colony, yet is fierce and cannot be kept in hives. Option A is wrong because Apis florea, the little bee, is the smallest and gives the least honey. Option B is wrong because Apis cerana indica, the Indian hive bee, is the species traditionally kept in Indian hives, so it is domesticated. Option D is wrong because Apis mellifera, the Italian or European bee, is the species most used in commercial apiaries for its gentleness and high yield in managed hives. Note the contrast the question rests on: highest yield in the wild against the best bee to manage.

The correct answer is B, unfertilised eggs. The queen can lay both fertilised and unfertilised eggs; the unfertilised ones develop into haploid males called drones, a form of parthenogenesis, while fertilised eggs give rise to diploid females. Option A is wrong because fertilised eggs become workers or queens, not drones. Option C is wrong because although a laying worker can sometimes produce drones in a queenless colony, that is an exception and not the normal origin of drones, so it cannot be stated for all cases. Option D is wrong because royal jelly fed throughout the larval period produces a queen, not a drone; caste among the females is decided by diet, while the drone's sex is decided by the egg being unfertilised. Drones do no work in the hive, gather no food and have no sting; after the nuptial flight they are driven out of the colony, so their number falls sharply in a lean season.