Chemosensory tuning to a host recognition cue in the facultative specialist larvae of the mothManduca sexta

Abstract

SUMMARYLarvae of Manduca sexta are facultative specialists on plants in the family Solanaceae. Larvae reared on solanaceous foliage develop a strong preference for their host; otherwise, they remain polyphagous. The host-specific recognition cue in potato foliage for Manduca larvae is the steroidal glycoside, indioside D. Two pairs of galeal taste sensilla, the lateral and medial sensilla styloconica, are both necessary and sufficient for the feeding preferences of host-restricted larvae. We conducted electrophysiological tip recordings from sensilla of solanaceous or wheat germ diet-reared larvae. For each animal, recordings of the responses to indioside D, glucose, tomatine and KCl were compared. All responses included both phasic and tonic portions. The sensilla styloconica of solanaceous-reared larvae were tuned to indioside D, defined as maintaining a high sensitivity to indioside D, while showing lower sensitivity to other plant compounds. Half of the sensillar neurons of solanaceous-reared larvae were `tuned' to indioside D,whereas those of wheat germ diet-reared larvae were not. The different responses between the two types of animals were a result of changes of individual receptor cells' responses in the sensilla. Feeding on solanaceous foliage therefore appears to result in a modification of the physiological responses of individual taste receptor cells that causes them to be tuned to the host-recognition cue indioside D. We propose that this tuning is the basis for the host-restricted larvae's strong behavioral preferences for solanaceous foliage.

The plastic response of Manduca sexta to host and non-host plants

“…adult stages, although several studies have shown that larvae can also respond to volatile cues (del Campo, 2003;del Campo et al, 2001;Glendinning et al, 2009). This study provides the first insight into the molecular olfactory repertoire of Manduca larvae.…”

The parasitic wasp Cotesia congregata uses multiple mechanisms to control host (Manduca sexta) behaviour

“…Manduca sexta larvae were parasitized by allowing Cotesia congregata (Say 1836) females to oviposit into 3rd instar larvae. After parasitization, larvae were returned to their individual chambers (7 cm×10.5 cm height), fed ad libitum on a wheatgerm-based diet (Binghamton colony, del Campo and Miles, 2003; Dalhousie colony, pre-prepared diet from Recorp Inc., Georgetown, ON, Canada) and allowed to develop. The wasps emerge during the caterpillar's 5th and final larval instar (de Buron and .…”

“…For some studies, parasitized caterpillars were shipped to Dalhousie University. Colonies of both M. sexta (del Campo and Miles, 2003;Adamo et al, 2016) and C. congregata (Miles and Booker, 2000) were maintained as previously described.…”

The hungry caterpillar: an analysis of how carbohydrates stimulate feeding inManduca sexta

“…This is based on the observation that rearing M. sexta on their host plants (e.g. tomato, potato or tobacco leaves) induces a strong preference for leaf disks treated with host plant extracts (Hanson and Dethier, 1973;de Boer, 1993;del Campo et al, 2001;del Campo and Miles, 2003;Haribal et al, 2006). Another possibility is that taste-mediated responsiveness to carbohydrates increases following starvation or prolonged consumption of a carbohydrate-deficient diet.…”