Thyroxine is a thyroid hormone which targets all tissues and stimulates metabolic rate, growth and development in human. Insects have endocrine glands and neuroendocrine cells. Neuroendocrine cells secrete “brain hormone”, a neurohormone, in response to changes in environmental factors. Brain hormone is stored in corpora cardiaca and when released, stimulates prothoracic glands to produce molting hormone. Ecdyson is a molting hormone, produced by prothoracic endocrine glands of insects and is responsible for growth and molting. Pheromones are the chemicals secreted by many insects and other animals which serve to alter the physiology or behaviour of other individuals of same species. The female silk moth releases bombykol, from her abdominal gland. The scent of bombykol activates the receptors under feathery antennae of male silk moth and attracts him to the female. Thus, the correct answer is option D.