Temporal and developmental aspects of diet-induced food preferences in larvae of the tobacco hornworm, Manduca sexta
Gerrit de Boer
Department of Ecology and Evolutionary Biology, Entomology Program, University of Kansas, Haworth Hall, 1200 Sunnyside Avenue, Lawrence, KS 66045, USA Accepted: 23 September 2004
Key words: food choice, learning, caterpillar, tomato,cowpea, diet switching, Lepidoptera, Sphingidae, Lycopersicon esculentum, Vigna unguiculata
Diet-induced changes in food preferences in an oligophagous caterpillar were studied in order to characterize the conditions under which this induction occurs. The time course of acquisition and extinction of induced food preferences by larvae of the tobacco hornworm, Manduca sexta (Johan.)(Lepidoptera, Sphingidae), was examined by varying the food and duration of larval food experience. Larvae were given feeding experience with the host plant tomato, Lycopersicon esculentum (Mill.) (Solanaceae), or the acceptable non-host plant cowpea, Vigna unguiculata (Walp.) (Fabaceae), or switched from one to the other during different instars. Food preferences for V. unguiculata by the fourth orﬁfth instar larvae were measured individually in two-choice tests with discs of V. unguiculata and moist ﬁlter paper. The acquisition or extinction of an induced food preference for V. unguiculata was indicated by larvae preferring V. unguiculata to ﬁlter paper or the reverse, respectively. Results showed that: (1) the period required for the acquisition of induced preference for V. unguiculata canbe short (36 h), (2) food experience in either the third or fourth instar period is sufﬁcient, and (3) the most recent feeding experience appears to be important. In contrast, the period required for extinction of induced preference for V. unguiculata appeared to be longer (1–3 instars), and both the most recent feeding experience and total duration of larval experience with the inducing food seemto play a role. Experience is not restricted to a particular instar period to acquire or extinguish such an induced food preference. The induced food preference for V. unguiculata was not very rigid and could be reversed by having one instar of feeding experience on L. esculentum. The ﬁndings indicate that diet-induced food preferences in M. sexta contains elements of habituation and associativelearning, but do not support food imprinting and induction of oligophagy.
Plasticity in insect feeding behavior has been demonstrated in six orders of insects with herbivorous habits (Papaj & Prokopy, 1989; Szentesi & Jermy, 1990). A diet-induced food preference has been described as a change in food preference in favor of food that has been previously eaten exclusively for 24 ormore hours (Jermy et al., 1968). The induced preference is speciﬁc for the inducing plant species and is not merely a change in the insect’s general threshold of food acceptability. The degree and persistence of a diet-induced food preference varies with the insect
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species (Szentesi & Jermy, 1990) and plant species tested (de Boer & Hanson, 1984). Adiet-induced food preference may result in changes in the host-plant preference hierarchy such that plant species low in the hierarchy become fully, rather than marginally, acceptable (Dethier, 1988). Perhaps by enhancing attentiveness to certain host-speciﬁc stimuli and therefore allowing faster feeding decisions, a diet-induced food preference may keep the animal on its food (Bernays, 1999). This mayprevent larvae from having to switch foods and to metabolically adjust to new food sources (Szentesi & Jermy, 1990). The diet-induced food preference in phytophagous insects may be the result of one or a combination of several different physiological processes, such as habituation to
© 2004 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 113: 197– 204, 2004...