Foodplant selection and induction of feeding preference among host and non‐host plants in larvae of the tobacco hornworm Manduca sexta

Ten host plant (Solanaceae) and twelve non-host plant species were tested as foodplants for first instar larvae of the tobacco hornworm, Manduca sexta. Only nine host and three non-host plant species elicited feeding and supported growth up to fifth instar. The range of acceptability suggested that plants be divided into hosts, acceptable non-hosts, and unacceptable non-hosts. Using the two-choice feeding preference test we found that the initial preference for hosts was preserved when larvae were reared on hosts, but was less strong or absent for larvae reared on acceptable non-hosts. Thus oligophagy in the tobacco hornworm is not induced, but must be inherited. Newly-hatched first instar larvae and fifth instar larvae showed a preference hierarchy among both hosts and non-hosts. Fifth instar larvae reared separately on two different host species showed slightly different preference hierarchies among hosts. The preference for the rearing plant was increased and also two other host species changed positions in hierarchies. Feeding preferences of larvae reared on hosts or acceptable non-hosts were determined using plant combinations of host vs. host, host vs. acceptable non-host, and acceptable non-host vs. acceptable non-host. Induction of feeding preference was found in all three of these categories. This shows that induction of feeding preference in the tobacco hornworm is not restricted to host plant species. The degree to which feeding preferences were induced ranged from very strong to undetectable and dependend on the plant species paired. The strength of induction in the tobacco hornworm was found to correlate inversely with taxonomic relatedness of the plant species paired. Analysis of induction data from the literature revealed a similar correlation for other lepidopteran species. RESUME Selection des plantes consommees et induction d'un choix alimentaire entre plantes hotes ou non chez les chenilles de Manduca sexta Vingt-deux especes de plantes, dont 10 plantes-hotes (Solanees), ont ete testes comme plantes alimentaires pour des chenilles de ler stade de Manduca sexta. Sur cet ensemble, seulement 12 plantes (dont 9 plantes hotes) induisaient la prise de nourriture et permettaient la croissance jusqu'au 5eme stade. La diversite des resultats suggere que les plantes pouvaient ětre classees en hotes, non-hotes acceptables et non-hotes refuses. En utilisant le test du choix alimentaire preferentiel entre deux rondelles de feuilles, les chenilles neonates de ler stade ont prefere nettement les plantes-hotes aux autres. Cette preference initiale pour les plantes-hotes etait preservee quand les cheniles etaient elevees sur plantes-hotes, mais devenait moins nette ou disparaissait pour des chenilles elevees sur d'autres plantes acceptees. Ainsi l'oligophagie ches M. sexta n'est pas induite, mais doit ětre heritee. Les chenilles neonates, aussi bien que celles de 5eme stade, presentent des preferences hierarchisees parmi les plantes hotes ou non. La seule frontiere nette observee etait entre especes de plantes acceptables ou non. Les hierarchies preferentielles des chenilles du 5eme stade differaient legerement lorsqu'elles avaient ete elevees sur deux plantes-hotes differentes. La difference essentielle etait l'observation d'une preference accrue pour l'espece ayant servi a l'elevage, mais deux autres plantes-hotes changaient aussi de position hierarchique. La cause de ces changements de preference a ete approfondie, les chenilles etant elevees sur des feuilles de chaque espece acceptable (hote ou non), Leurs preferences alimentaires ont ete definies en utilisant des combinaisons diverses (hote × hote, hote × non-hote acceptable, non-hote acceptable × non-hote acceptable). L'induction de la preference alimentaires a ete obtenue dans ces trois associations. Ceci montre que l'induction des choix alimentaires chez M. sexta n'est pas limitee aux plantes-hotes. Le degre d'induction de la preference alimentaire variait de tres fort a indecelable; il dependait de l'association examinee. La source de la variabilite de cette induction a ete examinee en fonction de la relation entre la force de l'induction et les rapports taxonomiques des plantes associees. La relation obervee etait inversee pour M. sexta L'examen des donnees de la litterature ont revele une relation du měme type pour les autres especes de Lepidopteres.