這是啥唧唧聲? 天蠶蛾幼蟲的超聲波與聲響警訊

What’s the buzz? Ultrasonic and sonic warning signals in caterpillars of the great peacock moth (Saturnia pyri)

Veronica L. Bura & Alan J. Fleming & Jayne E. Yack

幼蟲在面對許多天敵的情形下發展出不同的禦敵策略。多數的研究著眼於以視覺導引捕食者的策略，如偽裝、背腹顏色對比的隱蔽色與警戒色。然而，防禦性的聲音雖然已被報導了超過一百年，卻仍鮮少受到研究。作者在常見的歐洲大孔雀眼天蠶蛾(European Great Peacock moth, Saturnia pyri) 幼蟲上發現一新型態的聲音產生—唧唧聲(chirping)。 這種唧唧聲是由大顎的”齒”進行快速而連續的敲擊所發出 ，頻率主要集中在聲波 (3.7 kHz)與超聲波(55.1 kHz) 之間。一系列的敲擊聲可由模擬捕食者的攻擊而引發，表皮的刺毛會同時或在敲擊聲後分泌防禦性化學物質，支持作者認為此行為是聲音的警戒行為之假說。作者認為這些幼蟲針對擁有不同主要感覺方式的天敵們(鳥、蝙蝠與無脊椎動物)發展出多重的警告訊號: 視覺、化學與聲音。

Abstract
Caterpillars have many natural enemies and, therefore, have evolved a diversity of antipredator strategies. Most research focuses on those strategies (crypsis, countershading, and warning coloration) targeting visually guided predators. In contrast, defensive sounds, although documented for more than a century, have been poorly studied. We report on a novel form of sound production— chirping—in caterpillars of the common European Great Peacock moth (Saturnia pyri). Chirps are broadband, with dominant peaks ranging between the sonic (3.7 kHz) and ultrasonic (55.1 kHz) and are generated by a rapid succession of mandibular “tooth strikes.” Chirp trains are induced by simulated predator attacks and precede or accompany the secretion of a defensive chemical from integumental bristles, supporting our hypothesis that these sounds function in acoustic aposematism. We propose that these caterpillars generate multimodal warning signals (visual, chemical, and acoustic) to target the dominant sensory modalities of different predators, including birds, bats, and invertebrates.