THE EFFECT OF HOST PLANT PHENOLOGY ON REPRODUCTION OF THE MILKWEED BUG, ONCOPELTUS-FASCIATUS, IN TROPICAL FLORIDA

A field study of the relationship between host plant phenology and the reproductive pattern of the large milkweed bug, O. fasciatus, was conducted in southern Florida. Since O. fasciatus need seeds of either milkweed or Nerium oleander plants to reproduce, reproduction takes place on only those host plants that are producing seed pods. Two of 4 major host plants, Asclepias incarnata and Sarcostemma clausa fruit seasonally, producing pods in early autumn and early winter, respectively. The 3rd milkweed host, A. curassarica, produces almost no pods midsummer and few pods midwinter. N. oleander (Apocynaceae) produces some pods all year but is only used by O. fasciatus in the summer when milkweeds are not producing pods. Reproduction of O. fasciatus has been observed year round, but relatively few females reproduce in midwinter coinciding with decreased pod production and low temperatures. This pattern is consistent with the hypothesis that a photoperiodic cue of short day lengths under conditions of cool temperatures may cause adult females to enter diapause and delay reproduction in the field. A comparison of plant phenologies and rainfall between 1976, a very dry year, and 1977, a year with normal rainfall, showed that extreme dryness disrupted the seasonal fruiting of the milkweeds and consequently the reproduction of O. fasciatus.