Predispersal Seed Predation of a Native Thistle,Cirsium canescens1

Abstract

Predispersal seed predation of the native Platte thistle, Cirsium canescens Nutt. (Compositae), by Paracantha culta (Wiedemann), Orellia occidentalis (Snow) (both Diptera: Tephritidae), and Homoeosoma stypticellum Grote (Lepidoptera: Pyralidae), was quantified and compared with other causes of seed mortality at three Nebraska sites. Damage to capitulae ranged from 16 to 25%; however, biotic agents damaged only 1 to 7% of the developing capitulae. Although non-biotic agents damaged 18 to 31% of the developing seeds, the three insect species damaged at least 21 to 54% of the seeds. The predominant insect species varied between sites. Only 9 to 24% of the total number of developing seeds per plant matured. Seed predation of the Platte thistle is expected to reduce its colonization of new habitats and its subsequent population growth.