Innate and acquired components of oligophagy in the herbivorous lepidopteran, M anduca sexta

Innate and acquired aspects of oligophagy were investigated in the tobacco hornworm, M anduca sexta L. ( L epidoptera: S phingidae), a species normally restricted to members of the family S olanaceae. Larvae were reared in the laboratory on solanaceous species tobacco ( N icotiana tabacum L.), strawberry groundcherry ( P hysalis pruinosa L.), and potato ( S olanum tuberosum L.), as well as the non‐solanaceous foods cowpea [ V igna sinensis (L.) ( F abaceae)], rapeseed [ B rassica napus L. ( B rassicaceae)], and artificial diet. Feeding assays were conducted using the above plants plus corkscrew vine [ V igna caracalla (L.) Verdc. ( F abaceae)], lettuce [ L actuca sativa L. ( A steraceae)], and moist glass‐fiber filter paper. Larval feeding was characterized using two camera‐monitored assays: (1) a quantitative no‐choice disc test that determines consumption over time, delays in initiation of feeding, and % of larvae rejecting the food, and (2) a novel no‐choice emigration test that measures how soon a larva abandons a whole plant. Experimental results from both assays revealed that larvae displayed high levels of acceptance of S olanaceae regardless of whether they had been reared on solanaceous or non‐solanaceous food. We conclude that solanaceous oligophagy in M . sexta is primarily innate and does not require (but may be strengthened by) previous feeding experience on S olanaceae. In contrast, larvae tested on non‐solanaceous plants or moist filter paper showed large variation in both acceptance of foods and emigration times that were strongly dependent on the food on which they had been reared (analogous to the ‘induction of preference’ of earlier literature). Two types of induction were identified: an increase in acceptability of a plant of (1) the same species as the one on which the larva was reared, or (2) a related species. These discoveries both challenge and expand our current understanding of oligophagy in the tobacco hornworm.