Effect of Jointworms on the Growth and Reproduction of Four Native Range Grasses of Idaho

Abstract

A study of jointworm larvae (Tetramesa Walk.) feeding in 4 native range grasses of Idaho was conducted to determine effects on their hosts. These insects were responsible for a decrease in the length of reproductive culms of red threeawn (Aristida longiseta Steud.), bottlebrush squirreltail (Sitanion hystrix (Nutt.) J.G. Smith), sand dropseed (Sporobolus cryptandrus (Torr.) A. Gray), and needleandthread (Stipa comata Trin. and Rupr.) Jointworms caused a decrease in the number of spikelets produced per inflorescence in bottlebush squirreltail and needleandthread, and a decrease in the inflorescence length of sand dropseed. They caused a decrease in seed weight, percentage germination, and germination rate of all 4 grasses. By adversely affecting native grasses, these insects contribute significantly to the degradation of valuable rangelands, and their control may be desirable.