Significance of opposing abdominal tergal spines on the pupae of the bagworm Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae).

The posterior row of abdominal tergal spines on pupae of psychid moths are anteriorly directed, whereas when pres ent in other lepidopteran families both anterior and posterior rows of tergal spines are posteriorly directed. Spines of the posterior row are slender hooklike processes that arise at a 60? angle from a colliculate surface and bend forward to form a 35? angle. They are initially used by both sexes to stablize the pupae within cocoons. In the male of Thyridopteryx ephemeraeformis (Haworth), the spines are present on segments II-VI and strongly developed on segments HI, IV and V. Spines on these 3 segments are used to suspend the partially emerged pupa at the opening of the bottom of the bag prior to adult emergence. Similar spines on the female pupa have a shorter taper length than on the male pupa. There are ca. 2lk times more spines on segment II of the female than on males. Females use these spines primarily for attachment to the cocoon and for support of mating and ovipositional activity in the pupal case within the bag. The anterior row of spines posteriorly directed on the male is strongly developed and used to facilitate movement of the pupa out of the cocoon prior to adult emergence. In females, the anterior row is weakly developed and non-functional. Male and female cocoon differences and functions are described. Paired dorsal rows of spines are common to pupae of Lepidoptera that project from the site of pupation on the host plant before eclosi?n as in Tortricidae and Sesiidae. Psychid pupae are unique in that the posterior row of paired dorsal spines is reversed and directed anteriorly. The spines are developed into hooklike processes in both sexes. The taxonomic importance and function of structures on bagworm pupae have received limited study. Consequently some taxonomists have failed to recognize the uniqueness of the arrangement of these spines. There have also been occasional inconsistent uses of the terms spines and seta. MacGillvray (1923), Comstock (1924)