Spatial accuracy of a rapid defense behavior in caterpillars

Abstract

SUMMARYAimed movements require that an animal accurately locates the target and correctly reaches that location. One such behavior is the defensive strike seen in Manduca sexta larva. These caterpillars respond to noxious mechanical stimuli applied to their abdomen with a strike of the mandibles towards the location of the stimulus. The accuracy with which the first strike movement reaches the stimulus site depends on the location of the stimulus. Reponses to dorsal stimuli are less accurate than those to ventral stimuli and the mandibles generally land ventral to the stimulus site. Responses to stimuli applied to anterior abdominal segments are less accurate than responses to stimuli applied to more posterior segments and the mandibles generally land posterior to the stimulus site. A trade-off between duration of the strike and radial accuracy is only seen in the anterior stimulus location (body segment A4). The lower accuracy of the responses to anterior and dorsal stimuli can be explained by the morphology of the animal; to reach these areas the caterpillar needs to move its body into a tight curve. Nevertheless, the accuracy is not exact in locations that the animal has shown it can reach, which suggests that consistently aiming more ventral and posterior of the stimulation site might be a defense strategy. Supplementary material available online at

Central neural alterations predominate in an insect model of nociceptive sensitization

“…Manduca sexta has a very distinctive defensive strike response, that has been well described by Walters et al () and van Griethuijsen et al (). In brief, the head swings directly at the site of the noxious stimulus, with a rapid bending motion.…”

“…This is consistent with previous literature on the multidendritic complex in M. sexta (Grueber et al, ). It has previously been suggested that nociception and the initiation of the strike occur in this network of sensory cells originating on the body wall, whose axons extend to the ganglia through the dorsal nerve (Levine et al, ; Grueber and Truman, ; Grueber et al, ; van Griethuijsen et al, ; for a review, see van Griethuijsen and Trimmer, ). Drosophila also shows a homologous complex of neurons (Grueber et al, 2012), indicating that further examination of this system in conjunction with other model organisms—where genetic manipulation is possible but electrophysiological study is less amenable—may yield insight into nociceptive sensitization as a conserved process.…”

“…Given the simple in vivo assay available to quantify nociceptive responses in M. sexta (McMackin et al, ), the relative simplicity of M. sexta's nervous system, and its lasting viability in simple unoxygenated saline (Waldrop and Levine, ; van Griethuijsen et al, ; van Griethuijsen and Trimmer, ), we sought to develop an in vitro electrophysiological preparation to characterize nociception and nociceptive sensitization in this terrestrial invertebrate. To this end, we have shown that, in contrast to many other models in mammals and mollusks, nociceptive sensitization of the defensive strike response in M. sexta is associated primarily with central rather than peripheral neural hyperactivity.…”

Use of von Frey filaments to assess nociceptive sensitization in the hornworm, Manduca sexta

“…This behavior is observed as a midline bending of the animal to bring the head towards the noxious stimulus. The strike response occurs as a defense against noxious stimuli such as might occur during predation by birds or parasitic wasps (Walters et al ., 2001; van Griethuijsen et al, 2013). To measure this response, researchers originally applied a single von Frey filament (1.5 mN, exerting a pressure of 15 gmm −2 or approximately 1.5×10 5 Pa) to a sensitized animal, to measure changes in the frequency of defensive strikes, among other behaviors, after noxious stimulation.…”

“…The behavior being monitored was called a “defensive strike response” whereby an animal rapidly bent, bringing its head and mouth close to the site of insult as a defensive response (Walters et al ., 2001; van Griethuijsen et al ., 2013). Although other responses have been observed in M. sexta, such as thrashing (Walters et al, 2001) or proleg withdrawal (Wiel and Weeks, 1996), the strike response is optimum for behavioral testing due to its robust and objectively distinct nature.…”