Ecological Archives E093-156-A2

Holly M. Martinson, William F. Fagan, and Robert F. Denno. 2012. Critical patch sizes for food-web modules. Ecology 93:1779–1786.

Appendix B. Analysis of diet composition of Tytthus alboornatus in laboratory mesocosms.

In contrast to all the other species interactions discussed here, the dietary composition of Tytthus alboornatus was unknown prior to this work. Previous investigations had established that members of the genus Tytthus feed on eggs of small herbivorous insects and tend to specialize on particular herbivore species (Döbel and Denno 1994, Fink and Denno 2002). Thus, to test whether T. alboornatus feeds on eggs of either of the two most common planthoppers in Spartina patens, we set up a laboratory mesocosm experiment. We purchased S. patens as 5 cm plugs (originally grown from seed) from Environmental Concern (St. Michaels, Maryland, USA) and grew these plants at the University of Maryland greenhouse for one month before use. Mesocosms were constructed with one plug of S. patens in a 9.5 cm wide pot, with a 30 cm high × 7.5 cm diameter cellulose butyrate cage topped with organdy mesh (as in Denno et al. 2000, Finke and Denno 2002). Tumidagena minuta, Delphacodes detecta, and T. alboornatus were collected in Tuckerton, NJ using a D-Vac suction device with a 0.093 m2 sampling nozzle (D-Vac Company, Ventura, California, USA) and transported back to Maryland separately in spare mesocosms. Twenty adult T. minuta or D. detecta were added to 14 S. patens mesocosms each and allowed to oviposit for eight days. Two female and two male were added to half the cages and allowed to feed for two weeks. The number of herbivore nymphs per mesocosm was then assessed, and t-tests were used to compare predator-free and predator-addition treatments for each of the two herbivore species.

Fewer nymphs of the most common S. patens herbivore, T. minuta, were produced in the laboratory mesocosms also containing the egg predator T. alboornatus than in predator-free mesocosms (Mean number of nymphs with predators present: 21.14 (± 4.92 SE); without predators: 40.71 (± 3.06); t = 3.38, df = 10.04, P = 0.007). In contrast, T. alboornatus had no significant effect on nymphal production for the second most common herbivore, D. detecta (t = 1.48, df = 11.34, P = 0.167). We thus focus on the egg predation interaction between T. alboornatus and T. minuta for the remainder of our analyses.

Literature Cited

Denno, R. F., M. Peterson, C. Gratton, J. Cheng, G. Langellotto, A. Huberty, and D. Finke. 2000. Feeding induced changes in plant quality mediate interspecific competition between sap-feeding herbivores. Ecology 81:1814–1827.

Döbel, H. G., and R. F. Denno. 1994. Predator-planthopper interactions. Pages 325–399 in R. F. Denno and T. J. Perfect, editors. Planthoppers: their ecology and management. Chapman & Hall, New York, New York, USA.

Finke, D. L., and R. F. Denno. 2002. Intraguild predation diminished in complex-structured vegetation: implications for prey suppression. Ecology 83:643–652.

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