Defensive Sound Production in the Tobacco Hornworm, Manduca sexta (Bombycoidea: Sphingidae)
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The tobacco hornworm (Manduca sexta) is a model organism extensively studied for many aspects of its biology, including its anti-predator strategies. We report on a novel component of this caterpillar’s defence repertoire: sound production. Late instar caterpillars produce discrete clicking sounds in response to disturbance. Click trains range in duration from 0.3–20.0 s (mean 3.3 ± 4.8 s) and contain 2–41 clicks (mean 7.1 ± 9.5). Sounds are broadband with a dominant frequency of 29.8 ± 4.9 kHz. We investigated the mechanism of sound production by selectively ablating three identified sets of ridges on the mandibles, and determined that ridges on the inner face strike the outer and incisor ridges on the opposing mandible to produce multi-component clicks. We tested the hypothesis that clicks function in defence using simulated attacks with blunt forceps. In single attack trials 77% of larvae produced sound and this increased to 100% in sequential attacks. Clicks preceded or accompanied regurgitation in 93% of multiple attack trials, indicating that sound production may function in acoustic aposematism. Sound production is also accompanied by other behaviours including directed thrashing, head curling, and biting, suggesting that sounds may also function as a general warning of unprofitability.
KeywordsSound production caterpillar acoustic communication defence Manduca sexta
We thank Ed Bruggink for providing the host plants and two anonymous reviewers for helpful comments. The Natural Sciences and Engineering Research Council of Canada (CGS M to V.L.B.; Discovery Grant to J.E.Y.), the Canadian Foundation for Innovation (J.E.Y.), and the Ontario Innovation Trust (J.E.Y.) provided funding.
- Bowers MD (1993) Aposematic caterpillars: Life-styles of the warningly colored and unpalatable. In: Stamp NE, Casey TM (eds) Caterpillars: ecological and evolutionary constraints on foraging. Routledge, Chapman and Hall, Inc, New York, pp 331–371Google Scholar
- Broughton WB (1963) Method in bio-acoustic terminology. In: Busnel RG (ed) Acoustic Behaviour of Animals. Elsevier, New York, pp 3–24Google Scholar
- Dooling RJ (1991) Hearing in birds. In: Webster D, Fay R, Popper A (eds) The evolutionary biology of hearing. Springer, New York, pp 545–560Google Scholar
- Lederhouse RC (1990) Avoiding the hunt: primary defenses of Lepidopteran caterpillars. In: Evans DL, Schmidt JO (eds) Insect defenses: adaptive mechanisms and strategies of prey and predators. State University of New York Press, New York, pp 175–190Google Scholar
- Pittaway AR (1993) Hawkmoths of the Western Palaearctic. Harley Books, EnglandGoogle Scholar
- Schwartzkopff J (1955) On the hearing of birds. Auk 72:340–347Google Scholar
- Stamp NE, Wilkens RT (1993) On the cryptic side of life: Being unapparent to enemies and the consequences for foraging and growth of caterpillars. In: Stamp NE, Casey TM (eds) Caterpillars: ecological and evolutionary constraints on foraging. Routledge, Chapman and Hall, Inc, New York, pp 283–330Google Scholar
- Thurston R, Prachuabmoh O (1971) Predation by birds on tobacco hornworm larvae infesting tobacco. J Econ Entomol 64:1548–1549Google Scholar
- Tuttle JP (2007) The Hawk Moths of North America. The Wedge Entomological Research Foundation, Washington DCGoogle Scholar