I was so busy studying last night I completely forgot to post what I had already written....
While acoustic communication in adult Lepidoptera (moths and butterflies) has been extensively studied, investigations into larval stages (caterpillars) of some members of this insect order that communicate with audible signals have been limited. This study, in part published by UMass Entomology post-doc Jeff Boettner, describes the mechanism and context in which this behavior occurs in a silkworm common to this area, Antheraea polyphemus. The authors hypothesized that the cryptically colored caterpillars of this species are using sounds aposematically, as a warning to potential predators.
Following this hypothesis, the authors predicted that sound production would occur when associated with a predator, that increasing amount of attack from predators would be accompanied by an increase in sound production and that the natural predators of these caterpillars could detect and induct meaning from this mechanical production of sound. Their study also included an investigation into how these sounds are produced by the caterpillars and its relation to the regurgitation behavior that follows that is also used as a defense mechanism, as well as surveying related species for similar auditory abilities.
Using forceps to mimic the bite of a predacious insect, and chicks as representative avian predators, the researchers stimulated the caterpillars to believe they were being attacked so that they could record data about the prevalence of the clicking behavior as well as measurements about the duration and quantity of clicks. They also used scanning electron microscopy to document the mandibular structure that they use to produce the clicking sound that is audible to even human ears.
Results indicated that the clicking behavior functioned to warn potential predators that further defenses could be employed, namely the regurgitation of distasteful substances, and thus clicking was acting as a reinforcing signal of aposematicism or unpalatability. In the survey of an additional 12 Bombycoidea larvae from 3 families it was found that there were a few other examples of this behavior spread throughout this superfamily, but all caterpillars who used an acoustic signal would also resort to regurgitating distasteful materials when an attack would persist.
Overall I found this article to be of particular interest because normally when we think of aposematicism we think of brightly orange, black or white coloration that warns predators of the potential toxicity. These lepidopterans are combining both cryptic and aposematic strategies by not being colored in conspicuous manner, but instead can use an aposematic signal only when an attack is imminent.
Brown, SG, GH Boettner, and JE Yack. 2007. Clicking caterpillars: acoustic aposematism in Antheraea polyphemus and other Bomycoidea. The Journal of Experimental Biology 210: 993-1005.
Posted by: Anna Morkeski (1)
It's always interesting to hear what studies are going on around UMass.
ReplyDeleteDo the catepillars make any other noises? Does the clicking noise mean anything else besides a warning to predators?
-Tricia Carlson
I'm curious about how affective the clicking noise is in protecting the catipillars when a predator is nearby. Is this something that was studied at all? Also, how did this clicking noise come about? Why did the catipillars start making this noise, and is it only ever used for this purpose?
ReplyDeletePosted by Sarah Benjamin
Excellent article. Is the clicking sound always effective? Are there any predators (despite their poison) who can still manage to prey on these caterpillars? What is it that makes the clicking sound and what other signals, if any, does this clicking sound produce? Mating? Recognition? Great article.
ReplyDelete-Carlos Varela
Great write-up! I'm wondering if the clicking is a learned behavior or something already hard-wired. Is there any ontogeny related to the clicking behaviors? As in, when the caterpillars are younger, do they click for food or do they just innately know that when a predator is near that they need to click?
ReplyDeletePosted by Bethany Rappleyea
Very interesting, I have seen these caterpillars and have some samples of adult male moths of the polyphemus and these are some very large caterpillars! Did the article talk at all about Lunar moth caterpillars also doing this "clicking behaior" because, it is my understanding that these these two species are closely related and both are native to this area. If they do preform this behavior then it would help both, if not several of these species make predators acknowledge the acoustic signal as a warning.
ReplyDeleteposted by Jeremy Ross
Because these species produce this clicking sound with the mandibulate mouthparts they have as caterpillars, they cannot produce sound as adults when they have siphoning mouthparts. The caterpillars do not function to mate and may have little need to recognize each other so I would assume that they probably only function as a defense mechanism. The acoustic signals are also likely to only be heard by birds because they have ears unlike most insects. Some insects do communicate using vibrational signals sent through substrates such as plants or the ground. There are also other caterpillars that use such signals (ie vibrational or stridulatory) to communicate with other species of insects that will help protect them (ants that at least think they will get a honeydew reward).
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