Defensive Gin-Trap Closure Response of Tenebrionid Beetle,Zophobas atratus, Pupae

Abstract

Pupae of the beetle Zophobas atratus Fab. (Coleoptera: Tenebrionidae) have jaws called gin traps on the lateral margin of their jointed abdominal segments. When a weak tactile stimulation was applied to the intersegmental region between the two jaws of a gin trap in a resting pupa, the pupa rapidly closed and reopened single or multiple gin traps adjacent to the stimulated trap for 100200 ms. In response to a strong stimulation, a small or large rotation of the abdominal segments occurred after the rapid closure of the traps. Analyses of trajectory patterns of the last abdominal segment during the rotations revealed that the rotational responses were graded and highly variable with respect to the amplitudes of their horizontal and vertical components. The high variability of these rotational responses is in contrast with the low variability (or constancy) of abdominal rotations induced by the tactile stimulation of cephalic and thoracic appendages. Since the closed state of the gin traps lasts only for a fraction of a second, the response may mainly function to deliver a “painful” stimulus to an attacker rather than to cause serious damage.

A Third Type of Defensive Behavior in the Tenebrionid BeetleZophobas atratusPupae

“…Z. atratus pupae exhibit two types of reflex abdominal movements after mechanical stimulation of CS on the cuticle of the appendages and abdomen (Ichikawa et al 2012a, b). The abdominal segments have many CS and HS.…”

“…Trajectory patterns of the rotation were usually not simple circular or elliptical in shape, and they were characterized by an abrupt change in direction or a reversal of rotational direction halfway through the rotation (Figure 2). Ichikawa et al (2012b) found that similar complex patterns of abdominal rotations were often induced by bilateral stimulations of appendages, while a unilateral stimulation of an appendage induced a clockwise or anticlockwise rotation of a simple elliptical shape. To account for this result, they proposed that the central nervous system might have two pattern generation systems, and the complex rotation patterns induced by the bilateral stimulations may be due to an interaction or interference between the two systems (Ichikawa et al 2012b).…”

“…Ichikawa et al (2012b) found that similar complex patterns of abdominal rotations were often induced by bilateral stimulations of appendages, while a unilateral stimulation of an appendage induced a clockwise or anticlockwise rotation of a simple elliptical shape. To account for this result, they proposed that the central nervous system might have two pattern generation systems, and the complex rotation patterns induced by the bilateral stimulations may be due to an interaction or interference between the two systems (Ichikawa et al 2012b). Furthermore, each of the two putative systems for generating patterns seemed to consist of multiple pattern generators distributed in several abdominal ganglia of the abdominal segments (numbered A2–A6) having four bundles of intersegmental muscles (Ichikawa et al 2012a).…”

“…Others have observed mechanosensory mechanisms and trajectory patterns of abdominal movements in the pupae of a largesized tenebrionid beetle, Zophobas atratus Fabricius (Coleoptera: Tenebrionidae) (Ichikawa et al 2012a, b; Kurauchi et al 2011). Both types of abdominal movements result from stimulation of campaniform sensilla (CS) (strain sensors) in the pupal cuticle, although many sensory hairs (touch sensors) are on the surface of almost all parts of the body (Kurauchi et al 2011).…”

“…Both types of abdominal movements result from stimulation of campaniform sensilla (CS) (strain sensors) in the pupal cuticle, although many sensory hairs (touch sensors) are on the surface of almost all parts of the body (Kurauchi et al 2011). The rotation of the abdomen occurs in an all-or-none fashion, and all abdominal segments appear to be involved in this response (Ichikawa et al 2012b). In contrast, the closing of the gin-trap is graded, and different numbers of abdominal segments appear to bend the abdomen laterally or move the abdomen circularly (Ichikawa et al 2012a).…”