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Leaf toughness changes the effectiveness of larval aggregation in the butterfly Byasa alcinous bradanus (Lepidoptera: Papilionidae)

Authors

  • Nami KAWASAKI,

    Corresponding author
    1. Department of Biology, International Christian University, Osawa, Mitaka, and
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    • Present address: Laboratory of Biodiversity Science, School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657 Japan.

  • Tadashi MIYASHITA,

    1. Laboratory of Biodiversity Science, School of Agricultural and Life Sciences, University of Tokyo, Yayoi, Bunkyo, Tokyo, Japan
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  • Yoshiomi KATO

    1. Department of Biology, International Christian University, Osawa, Mitaka, and
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Nami Kawasaki, Department of Biology, International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585, Japan. Email: kawasaki@es.a.u-tokyo.ac.jp

Abstract

Two subspecies of the papilionid butterfly Byasa alcinous, B. a. bradanus and B. a. alcinous, have varying degrees of larval aggregation. Early instar larvae of ssp. bradanus always occur in aggregations. To determine the functions of larval aggregation in this subspecies, we examined the effects of leaf toughness on larval performance when caterpillars were reared alone and in aggregations. Newly hatched larvae were reared either individually or in groups of 10 and were fed either tough or tender leaves of Aristolochia debilis. When fed tough leaves, more gregarious larvae survived the first instar. This difference between solitary and aggregated larvae did not occur when caterpillars were fed soft leaves. The effects of aggregation on larval weight and duration were not significant between leaf-toughness treatments. Larval aggregation of B. a. bradanus improves larval survivorship in early instars that use host plants with tough leaves.

Ancillary