Phagostimulant and deterrent fractions in P. bombycina (host) and L. grandifolia (non host): detection by chemosensory organs of A.assama Westwood

Food selection in phytophagous insects is largely affected by plant chemicals detected by their peripheral sense organs. There is longstanding debate as to how animals identify and discriminate taste stimuli. The golden yellow muga silk producing insect Antheraea assama , thrives primarily on Persea bombycina and Litsea polyantha . Such insects with restricted diet breadth are ideal for understanding the mechanism of detection of taste stimuli by insects. The present study was undertaken to evaluate phagostimulatory and deterrent fractions in the host ( Persea bombycina ) and acceptable non-host (Litsea grandifolia) of A. assama and determine the chemosensory basis of selection of food through food choice test. Different fractions from leaves were prepared by fractionating ethanol extract into neutral, acid, basic, alkaloid , polar and nonpolar lipid phases by using different solvents .Larvae having different chemosensory organs remaining after microsurgery were subjected to food choice test. Choice was given individually between food disc of plant fraction and water . Differences in food choices were expressed in a choice index (-100 to 100) based on time required for consumption of fifty percent of food disc. A two tailed Mann-Whitney test was used for determination of significance of difference in food choices. The study showed that polar lipid and neutral fraction of P. bombycina had phagostimulants which could be identified by maxillary palp , galea and labrum-epipharynx . Information mediated by sensilla styloconica of galea was necessary to detect feeding deterrent fractions of nonhost . Certain fractions of the nonhost were acceptable to larvae having only gustatory sensilla. Temporal coding through gustatory sensilla might help in plant chemical discrimination by silkworm larvae