Mechanical limitations on feeding by meadow spittlebugs Philaenus spumarius (Homoptera: Cercopidae) on wild and cultivated host plants

Abstract. 1. Field observations on the distribution of Philaenus spumarius (L.) on pearly everlasting (Anaphalis margaritacea) and alfalfa (Medicago sativa) showed that the range of feeding sites exploited increased with instar. Development of trichomes, depth of xylem elements, and tissue hardness were measured as possible factors determining the suitability of sites on food plants. 2. Spittlebugs caged outside their normal feeding sites experienced difficulty feeding. Experimental removal of trichomes showed that trichomes prevented younger instars from feeding on the stem. The depth of the xylem elements and tissue hardness were not significant barriers to feeding near the stem apex. 3. By caging fourth and fifth instar nymphs at increasing distances below the terminal bud on A.margaritacea stems, we showed feeding ability declined with distance below the apex, and feeding was more restricted in fourth compared to fifth instars. A similar decline was demonstrated in experiments with fifth instars on M.sativa. 4. On A.margaritacea, this restriction was associated with increasing tissue hardness of the stem with distance from the apex and the presence of trichomes in regions with hard tissues. On M.sativa the associated barriers were a combination of tissue hardness and reduction in the availability of xylem vessels in the penetrable region of the stem. Although the tissues impeding stylet penetration differed in the two hosts, the critical factor in both species was the increase in the amount of lignification of those tissues at increasing distances from the terminal bud.