Observations on growth, morphogenesis and programmed obsolescence of scent glands in the milkweed bug, Oncopeltus fasciatus (Heteroptera)

Abstract

Observations have been made on growth, morphogenesis, and programmed obsolescence in the scent glands of the milkweed bug Oncopeltus fasciatus. The dorsal scent glands of larvae cease to function in the adults. The results of treatments with allatotoxin (precocene-II) and a juvenoid suggest that the attainment of obsolescence is instar dependent and not dependent on hormonal changes at metamorphosis. Development of the adult metathoracic scent gland has been traced back to day 1 in larval instar IV. A cuticular intima forms around day 3 in instar V by which time all cell division has ceased and moulting to the adult commenced. Tubuligenesis and ventral closure of the future median reservoir occur early in the instar-V larva. Growth is continuous and the estimated cell-doubling time 19 h. In precocious adults, ventral closure fails to occur. As a result, the intima of the median reservoir evaginates to reveal the secreting faces of the accessory glands. The findings on development are discussed in relation to evolutionary speculation on the generation of the diversity of metathoracic scent structures to be seen in the Heteroptera.