Department of Zoology, University of Oklahoma, Norman, OK 73019
Membracids are phytophagous parasites (1) that are closely associated with certain plant-hosts (2). Some species of treehoppers are ant-attended and considered to be presocial (3). Differences have been found between populations of treehoppers associated with specific hosts (4). Membracid species and their host plants were described for Oklahoma by C.J. Dennis (5).
Three species of treehoppers were collected in Cleveland Co., Oklahoma on June 9, 1983 on the broad-leafed gumweed (Grindelia squarrosa) and on sunflower (Helianthus spp.). Both the gumweed and the sunflower grow in overgrazed, dry prairie soils, in the same early successional plant association. We collected: Campylenchia latipes (Say), Stictocephala lutea (Walker), and Vanduzea triguttata (Burmeister) feeding on gumweed, a new host record for all three species in Oklahoma. Kopp (2,6) lists sunflower as a host-plant for C. latipes and S. lutea but V. triguttata has not previously been reported on sunflower.
Vanduzea triguttata was collected on sunflower and gumweed in Oklahoma City (Oklahoma Co.) during August, September and October of 1978. Both Cleveland and Oklahoma counties are new records for V. triguttata. Collections on sunflower were also made on August 26,1978 in Konawa, Seminole Co., Oklahoma and on July 3, 1979 in Houston, Texas.
Twenty host-plants of each species were inspected on June 9 and 15, 1983 in Cleveland Co., Oklahoma. Both gumweed and sunflower had three species of treehoppers and some ants, but no aggregations were observed. The adult treehoppers rested at the base of the leaf stem, while the nymphs of S. lutea were found on the stem base and on the underside of the leaf. We found C. latipes as fifth-instar nymphs and adult females. Only two S. lutea were collected, both fifth-instar nymphs, which emerged as a male and a female in two days (June 11). One male and two fifth-instar nymphs of V. triguttata were collected on June 9. On June 15 we observed 3 males and 2 females on gumweed and one female on sunflower. The populations of V. triguttata on a total of 40 plants were dispersed, few in number, and had no observed ant attendance.
In contrast we observed dense aggregations of V. triguttata attended by ants in September to November 1978 on gumweed (on 3 of 20 plants in close association examined in Oklahoma Co.) and sunflower (4 of 4 plants checked in Oklahoma Co.). These colonies were clustered on the upper one-third of the plant at the junction of leaf and stem, feeding on both structures. The age structure of these colonies consisted of all stages of nymphs and adults, very much like those of Vanduzea arquata (Say), which aggregates on locust (Robinia spp.) (1,6). Mating pairs of V. triguttata were observed until the first week of October at the Oklahoma Co. site (NW of Oklahoma City). As fall progressed colonies decreased by approximately 50%, with adults and fifth-instar nymphs predominating. In Seminole Co. sunflowers were examined on October 15, 1978 and proved to have adults and fifth-instar nymphs feeding alone or in small groups of 2 - 6. Vanduzea triguttata was also collected on October 28, 1978 on sunflowers at the O.U. Health Sciences Center in Oklahoma City. At this site adults and fifth-instar nymphs were clustered with ants in the leaf stem junctions on all regions of the plant. At the base of the plant we found underground ant galleries containing several females.
Variation in life history characteristics (7) such as aggregation may be a phenomenon associated with host plant or with ant attendance in Vanduzea triguttata. Wood (8) speculates that a critical number of nymphs may be necessary to produce enough honeydew to attract ants, which subsequently protect the nymphs and plant from predators. The differences
observed in aggregating tendencies in V. triguttata between early and late summer and fall may result from a combination of increase in population and attraction of ants.
1. P.W. Price. Evolutionary Biology of Parasites, Monographs in Population Biology 15, Princeton Univ. Press, Princeton, NJ, 1980.
2. D.D. Kopp and T.R. Yonke, J. Kansas Entomol. Soc. 46: 42 - 64 (1973).
3. C.D. Michener and M.H. Michener, American Social Insects, Van Nostrand, New York, NY, 1951.
4. T.K. Wood, Sociobiology 2: 257 - 272 (1977).
5. C.J. Dennis, Proc. Okla. Acad. Sci. 45: 50 - 64 (1964).
6. D.D. Kopp and T.R. Yonke, J. Kansas Entomol. Soc. 46: 233 - 276 (1973)
7. S.C. Stearns, Quart. Rev. Biol. 51: 3 - 47 (1976).
8. T.K. Wood, in: D. H. Janzen, Costa Rican Natural History, Univ. Chicago Press, 1983, pp. 773-774.