Functional Morphology of Gustatory Organs in Caterpillars

The sense of taste plays a pivotal role in the behavior of insects. Caterpillars depend largely on taste cues from plants to detect and locate food sources. Taste stimuli can be either simple or complex as multimolecular mixtures. The insect faces the task of deciphering the nature of these tastants and must then make appropriate feeding choices. Typically, caterpillar larvae possess four types of bilateral gustatory sensilla on their mouthparts. The lateral and medial styloconic sensilla are thought to be the primary organs involved in feeding. These sensilla are in continuous contact with plant sap during feeding and can detect different phytochemicals present in the plant. The gustatory sensory input is encoded as patterns of nerve impulses by gustatory receptor cells housed in these sensilla. Therefore, these gustatory receptor cells form the first layer of a decision-making process that ultimately determines whether food is accepted or rejected by the insect. Caterpillars, such as gypsy moth larvae (Lymantria dispar) (L.) (Lepidoptera: Lymantriidae) are major forest pests in most of the United States. These larvae are highly polyphagous feeders and defoliate a variety of tree species, including forest, shade, fruit, and ornamentals. This chapter discusses morphological, feeding behavioral, and electrophysiological aspects of gustatory sensilla with respect to gypsy moth caterpillars.