Food discrimination and induction of preference for artificial diets in the tobacco hornworm, Manduca sexta

Abstract

ABSTRACT. Feeding discrimination of Manduca larvae reared on leaves and a variety of artificial media was tested against leaves, various media, solvent fractions of leaves and media, and media components, including pure chemicals. Field‐collected animals showed the same preferences as did animals cultured in the laboratory for many generations. Rearing larvae on a leaf species, an artificial diet, or homogenized leaves added to artificial diet induced a preference for that food in subsequent choice tests. Extracts of these foods using organic solvents (particularly hexane) elicited feeding choices resembling those evoked by the foods themselves: water extracts were effective as stimulants or deterrents, but responses to them differed considerably from responses to the foods. Animals raised on a defined artificial diet showed an increased preference (or decreased deterrence) for the lipid component (linolenic acid) of that diet in behavioural tests. Thus induction of preference was shown to be influenced by a specific nutrient compound. Fifteen artificial diets were tested; three were successful, including a completely defined medium. Various components of the diets were tested for feeding preferences, both as omissions from the main diet and as pure compounds. Some were stimulatory, most were neutral or slightly deterrent; a few were strongly deterrent. With the exception of linolenic acid, preferences for pure compounds were not significantly correlated with the food on which the animals were reared. The data suggest that food discrimination depends on the perception of a complex chemical message comprised of both polar and non‐polar compounds, with the latter being of somewhat greater importance. The results are consistent with the explanation of the induction of feeding preferences being due to a reduced responsiveness to deterrents, to an increased preference for feeding stimulants or to both.