"Tergal gland" is a generalized term describing a great variety of functionally similar glandular structures that have evolved on the backs of males (Roth, 1969). Male tergal glands occur in almost all cockroach families, but are rare in Polyphagidae and Blaberidae. Within the latter, the glands are restricted to the Epilamprinae and Oxy-haloinae. The most complex and morphologically varied glands occur in male Blattellidae, but at least 73 blattellid genera have species that lack these specializations (Roth, 1969,1971a; Brossut and Roth, 1977).
Males display their tergal glands to potential mates during the wing-raising (or in wingless species, "back-arching") phase of courtship. The female responds by approaching the male, climbing on his dorsum, and feeding on the gland secretion. The glands thus serve to maneuver the female into the proper pre-copulatory position and arrest her movement so that the male has an opportunity to clasp her genitalia (Roth, 1969; Brossut and Roth, 1977). The extraordinary morphological complexity of the glands in some taxa, however, suggests that they may serve additional roles in courtship and mating.
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