The Insect Fauna associated with Great Basin wildrye (Elymus cinereus Scribn & Merr) in southern Idaho

Youtie, Berta

Study of relationship between Great Basin wildrye and its associated insect fauna, with special reference to wheat stem sawfly. Study areas located at CRMO (Craters of the Moon National Monument) and Idaho National Engineering Laboratory. Geographic location: Regional, including CRMO (Craters of the Moon National Monument), Idaho National Engineering Laboratory site. Herbivorous and parasitic insect guilds associated with Great Basin wildrye (Elymus cinereus Scribn. & Merr) were investigated at the Idaho National Engineering Laboratory and Craters of the Moon National Monument during 1982 and 1983. Life-stage, abundance, plant part utilized and study site were recorded for each insect species collected. Forty-six species of phytophagous insects were observed feeding on various anatomical regions of the bunchgrass. Eight parasitoid species were reared from insect hosts in the plant culms and identified. The relatively high diversity of phytophages on basin wildrye was likely due to its tall, caespitose growth form, its abundance within its habitat, its broad geographic range, and the large number of related species of grasses in the region. The majority of the species that constitute the wildrye herbivore guilds were oligophagous (restricted to grasses). Many of the species identified are known to feed on grain crops as well as other native and introduced grasses. The wheat stem sawfly (Cephus cinctus Nort., Hymenoptera: Cephidae), a pest species associated with wheat, feeds internally in basin wildrye culms. The life history of this insect on wildrye and its impact on seed production of the bunchgrass were examined. From 62 to 88% of wildrye plants were infested with the sawfly. Adults sawflies emerged from wildrye culms at the time the inflorescences emerged from the grass sheaths. Larvae developed within culms, consumed vascular tissues and may have impaired transport of water and carbohydrates through the culm. Seed weight and number of caryopses developing within wildrye florets were significantly reduced in culms containing sawfly larvae (p O.OS).