Feeding on Normally Rejected Plants by Maxillectomized Larvae of the Tobacco Hornworm, Protoparce sexta (Lepidoptera, Sphingidae)1

Abstract

The larvae of P. sexta normally feed only on Solanaceae. Amputation of the maxillae led to continuous feeding on dandelion (Taraxacum officinale), a normally rejected plant, when no other food was available. Amputation of the antennae and the labial palpi did not have a similar effect. The chemoreceptors of the maxilla are confined to the third segment of the palpus and to the headpiece, a protuberance of the first segment. Removal of both of these groups of chemoreceptors led to as much feeding on dandelion as did removal of the entire maxilla. Amputation of the headpieces alone had an intermediate effect while amputation of the third segments alone had no effect. Maxillectomized larvae retained a reduced ability to distinguish between the leaves of dandelion and tomato, the normal host. They became adapted to dandelion and usually chose it over tomato in preference tests. They also fed more extensively on bland media such as an agar and cellulose powder gel than did intact larvae, suggesting that the maxillae spontaneously inhibit feeding. Maxillectomized fourth-instar larvae fed and grew well on some Plantaginaceae, Compositae, and members of families closely allied to the Solanaceae. Some of these plants were occasionally accepted by intact larvae. Other plants were either completely rejected or eaten in small quantities.