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First published online March 2, 2007
Journal of Experimental Biology 210, 993-1005 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.001990
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Clicking caterpillars: acoustic aposematism in Antheraea polyphemus and other Bombycoidea

Sarah G. Brown1, George H. Boettner2 and Jayne E. Yack1,*

1 Department of Biology, Carleton University, Ottawa, Ontario, K1S 5B6, Canada
2 Plant Soil and Insect Sciences, University of Massachusetts, Amherst, MA 01003, USA


Figure 1
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  		Fig. 1. A fifth instar Antheraea polyphemus larva. Scale bar, 0.5 cm.

 

Figure 2
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  		Fig. 2. Sound-producing structures of Antheraea polyphemus larvae. (A) Close-up of the head region. (B) Scanning electron micrograph of the mouthparts. The left and right mandibles (arrows) lie below the labrum. (C,D) Scanning electron micrographs of the left and right mandibles, respectively. Scale bars, 250 µm.

 

Figure 3
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  		Fig. 3. Oscillograms of Antheraea polyphemus sounds recorded from fifth instar larvae. (A) Sounds recorded from an individual feeding on Quercus rubra leaves at 10 cm. (B) A click train, showing the typical click pattern of a larva after being pinched with forceps at 10 cm. (C) Three clicks from the train in B (denoted by black circles) with an expanded time scale showing the multiple components of clicks. The most typical pattern, a double-component click, is shown on the left. (D) Click spectra from five different individuals. The bandwidth varies, but in all clicks most energy is between 8 and 18 kHz.

 

Figure 4
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  		Fig. 4. (A) Oscillograms of late instar Antheraea polyphemus sounds obtained during one-, two- and five-pinch trials. Arrows indicate the times when each larva was attacked. (B) Number of clicks in 60 s produced by late instar larvae following the first attack in one- (20.6±35.5), two- (25.1±22.5) and five-pinch (54.3±46.1) trials (means ± s.d.). The total amount of signaling is positively correlated with the number of attacks (*P<0.001).

 

Figure 5
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  		Fig. 5. (A) A representative oscillogram of sounds produced by a fifth instar Antheraea polyphemus larva when pinched five consecutive times with forceps. The larva first regurgitated (R) after the second pinch was administered. (B) Defensive regurgitation in a fifth instar larva in response to a simulated predator attack. (C) The percentage of regurgitating late instar larvae in one-, two- and five-pinch trials. (D) The number of pinches required to elicit regurgitation in late instar larvae. Larvae most commonly regurgitated after the second pinch.

 

Figure 6
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  		Fig. 6. (A) The escalation in behavioural responses of late instar Antheraea polyphemus larvae to increasing levels of disturbance. C–R–, neither clicking nor regurgitation; C+R–, clicking only; C–R+, regurgitation only; C+R+, clicking and regurgitation. C+R+ increased between one-, two- and five-pinch trials, whereas C+R– decreased between one-, two- and five-pinch trials. (B) The temporal relationship between clicking and regurgitation. In almost all five-pinch trials, the acoustic signaling occurred before regurgitation. *Significant difference (P<0.001).

 

Figure 7
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  		Fig. 7. The amount of time taken for ants to carry untreated mealworm segments, segments covered with distilled water, and segments covered in regurgitant, into one of their foraging holes. Note that two trials in which mealworms were coated in regurgitant were not included for analysis, because the mealworms were never accepted by ants. Values are means ± s.d. *Significant difference (P<0.001).

 

Figure 8
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  		Fig. 8. Mean consumption (± s.d.) of mouse chow coated in distilled water (control diet) versus mouse chow coated in regurgitant (experimental diet). (N=10). *Significant difference (P<0.005).

 

Figure 9
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  		Fig. 9. Fifth instar (A) Actias luna and (B) Manduca sexta larvae. Scale bars, 1 cm. (C,D) Oscillograms of sounds produced by A. luna and M. sexta, respectively, showing the typical click patterns of larvae after being pinched with forceps. (E,F) Clicks from the trains in C and D, respectively, with an expanded time scale showing that clicks generally have two components.

 




© The Company of Biologists Ltd 2007