Abstract
Butterflies are believed to use mainly visual cues when searching for food and oviposition sites despite that their olfactory system is morphologically similar to their nocturnal relatives, the moths. The olfactory ability in butterflies has, however, not been thoroughly investigated. Therefore, we performed the first study of odour representation in the primary olfactory centre, the antennal lobes, of butterflies. Host plant range is highly variable within the butterfly family Nymphalidae, with extreme specialists and wide generalists found even among closely related species. Here we measured odour evoked Ca2+ activity in the antennal lobes of two nymphalid species with diverging host plant preferences, the specialist Aglais urticae and the generalist Polygonia c-album. The butterflies responded with stimulus-specific combinations of activated glomeruli to single plant-related compounds and to extracts of host and non-host plants. In general, responses were similar between the species. However, the specialist A. urticae responded more specifically to its preferred host plant, stinging nettle, than P. c-album. In addition, we found a species-specific difference both in correlation between responses to two common green leaf volatiles and the sensitivity to these compounds. Our results indicate that these butterflies have the ability to detect and to discriminate between different plant-related odorants.
Highlights
Larvae of phytophagous insects are dependent on the maternal choice of oviposition site for survival and growth
Antennal lobe morphology is similar in the two species First we performed an anatomical investigation of the antennal lobe (AL) in the two species
We showed that A. urticae responded more discriminatively than P. c-album to the common host plant U. dioica. In both species we found a correlation between structural similarity and the similarity of responses, whereas both correlation between hexan-1-ol and hexan-1-al and sensitivity to these compounds differed between the species
Summary
Larvae of phytophagous insects are dependent on the maternal choice of oviposition site for survival and growth. The final close-contact evaluation of an oviposition site may rely on olfactory, gustatory or mechanical signals or a combination of those [1]. Diurnal insects as butterflies are generally believed to rely mainly on vision, while e.g. moths use olfaction to find a suitable oviposition site [2]. Whereas the olfactory system is well studied in moths, their diurnal relatives have attracted less attention. A handful of studies have reported odorant evoked EAG responses from butterfly antennae [3,4,5]. Representation of odour information in the primary olfactory centre, the antennal lobe (AL) has not previously been investigated in butterflies
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