ミヤマシジミ幼虫・蛹とその随伴アリの体表炭化水素 Cuticular hydrocarbons of larva and pupa of Reverdin's blue, Lycaeides argyrognomon (Lycaenidae) and its tending ants

ミヤマシジミの幼虫や蛹は数種のアリと任意的な共生関係を築いており,山梨県ではクロヤマアリ,クロオオアリ,エゾアカヤマアリ,アミメアリなどが随伴アリとして観察されている.我々はミヤマシジミとアリとの共生関係を制御する要因を明らかにすることを目的とし,3齢・4齢幼虫や蛹の体表炭化水素(CHC)の化学組成について,上記随伴アリの組成と共に調べた.幼虫は,齢や随伴アリの種類に関わらず一定のCHCプロフィールを示した.その主成分はC27,C29を主成分とする直鎖アルカンであり,副成分は分枝アルカンであった.蛹も幼虫と同じCHCを持っていた.一方,4種の随伴アリは識別可能で種特異的なCHCプロフィールを示した.クロオオアリとクロヤマアリのCHCはC27,C29の直鎖アルカンとアルケンを主成分にしており,エゾアカヤマアリとアミメアリのCHCはC25,C27,C29,C31の直鎖アルカンであった.以上の結果からミヤマシジミは,数種のゴマシジミ族が利用することで知られるCHCの化学擬態とは異なる機構を用いて働きアリの攻撃を回避すると考えられる.

The immature of Reverdin's blue butterfly, Lycaeides argyrognomon (Lycaenidae), exhibits facultative symbiosis with several ant species; Camponotus japonicus, Formica japonica, F. yessensis, Pristomyrmex punctatus, and two other species are its tending ants observed in Yamanashi Pref. In our attempt to clarify key factors regulating the symbiotic association between this myrmecophilous butterfly and ants, we examined the chemical compositions of cuticular hydrocarbons (CHCs) of third- and fouth-instar larvae and pupae of the butterfly, together with those of the above ant species. Larvae, irrespective of their instars and attendant ant species, showed a consistent CHC profile, in which n-alkanes, especially C27 and C29, were predominant, with methyl-branched alkanes being minor components. Pupae also possessed almost the same set of CHCs as did larvae. In contrast, the four ant species exhibited distinct and species-specific CHC profiles. The CHCs of C. japonicus and F. japonica consisted mainly of n-alkanes and alkenes of C27 and C29, while those of F. yessensis and P. punctatus contained n-alkanes of C25, C27, C29, and C31. The results strongly suggest that the protection of L. argyrognomon from aggression by ant workers is not due to concealment by chemical camouflage based on CHCs, as is known in some Maculinea butterflies.