Operation and Defensive Role of "Gin Traps" in a Coccinellid Pupa (Cycloneda Sanguinea)

The term gin traps, as applied to insects, was introduced by Hinton (1946) to denote certain intersegmental pinching devices commonly found in pupae of Coleoptera and Lepidoptera. Gin traps are essentially mouth-like elaborations of the intersegmental regions of the pupal abdomen. Typically they consist of localized, more or less pronounced intersegmental clefts, flanked by heavily sclerotized margins fashioned as jaws. Ordinarily, in the resting pupa, these jaws are held agape. But when the pupa is disturbed and thereby prompted to flex or rotate its abdomen, the jaws open and close in what is in effect a biting action (Hinton 1946). Gin traps occur singly or multiply in pupae, and may be medial or lateral in position. Hinton (1946, 1951, 1955) noted their presence in 10 families of Coleoptera and 3 families of Lepidoptera. The jaws of gin traps are variously serrate, and on occasion even elaborately dentate (Hinton 1946). Data on the defensive effectiveness of gin traps are scant. Hinton (1946) presents evidence that the devices can deter predaceous mites, but he did not test whether they protect also against such ubiquitous enemies as ants. We here describe the gin trap mechanism of a coccinellid pupa, and provide evidence of its defensive role vis 2 vis ants. Hinton (1955) reports the presence of dorsal gin traps in "many" coccinellid pupae, but does not describe the structures in these beetles. Our observations were done on pupae of a single species of Coccinellidae, Cycloneda sanguinea, a beetle found throughout the