ASSOCIATION OF POLYPHAGY IN LEAFHOPPERS (AUCHENORRHYNCHA, HEMIPTERA) WITH UNPREDICTABLE ENVIRONMENTS

The relationship between host plant predictability and food niche widt h was tested using monocotyledonous plants (Juncales, Cyperales, Poale s) and leafhoppers (Auchenorrhyncha, Hemiptera). Plants with unpredict able dynamics were represented by species in initial phases of seconda ry succession on drained pond bottoms and predictable plants were stud ied in such permanent habitats as alpine meadows. wetlands, peat bogs. and forest understories. The average host plant range of leafhoppers was wider in ephemeral than in permanent habitats. The majority of tro phic interactions between leafhopper and host plant found in ephemeral habitats involved polyphagous leafhoppers. whereas the opposite patte rn, with specialised leathoppers prevalent, prevailed in permanent hab itats. The difference between the average host plant range width of le afhoppers in permanent and in ephemeral habitats results from a higher number of polyphagous leafhoppers per plant in the ephemeral habitats ; average number of specialists per plant was approximately the same i n permanent and ephemeral habitats. Extremely polyphagous leafhoppers feeding on all three orders of plants were collected exclusively from host plants of ephemeral habitats. These species. classified as ''dist urbance specialists''. have high host plant searching efficiency and m ake great demands on host plant quality. An expansion of their host ra nge to permanent plants is restricted by the low nutrient suitability and, possibly, the better anti-herbivore defences of permanent plant s pecies.