Mechanistic aspects of host plant preference in butterflies

University dissertation from Stockholm University

Abstract: Searching and locating resources is essential for survival. In herbivorous insects search behavior is conducted on several scales, requiring input and integration of information from different sensory modalities. Even though it is known that vision, olfaction and contact-chemoreception are employed to detect, navigate towards and evaluate resources their exact contribution is poorly known. To shed light on the importance of the different sensory modalities, one has to start with separating the stimuli of different quality from each other and to inspect them under controlled conditions. Olfactory cues are blends of volatile compounds emitted by plants that are used by many Lepidoptera and other insects to navigate towards targets. Despite this knowledge, butterflies are generally considered to rely mainly on visual cues. Following several indications that butterflies also use olfactory cues in search for targets, this thesis investigated the olfactory capabilities of two nymphalid butterfly species with different degrees of host plant specializations. In Paper I optical imaging studies on the primary olfactory center, the antennal lobe, revealed a well developed olfactory system. The two species responded similarly to the tested odorants, but the specialist butterfly Aglais urticae seemed to respond more discriminatively towards its host plant Urtica dioica than the generalist species Polygonia c-album. In Paper II we used a behavioral assay to verify the assumption that the two butterfly species can use olfactory cues to navigate towards odor targets. The two tested species differed in their responses in both studies with respect to their ecology. Inferior discrimination abilities of the generalist species are discussed in the light of possible neural processing constraints.

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