PROC. ENTOMOL. SOC. WASH. 87(4), 1985, pp. 699-713 TRIGONOTYLUS CO£L£57//iL/C/M (HETEROPTERA: MIRIDAE), A PEST OF SMALL GRAINS: SEASONAL HISTORY, HOST PLANTS, DAMAGE, AND DESCRIPTIONS OF ADULT AND NYMPHAL STAGES A. G. Wheeler, Jr. and Thomas J. Henry (AGW) Bureau of Plant Industry, Pennsylvania Department of Agriculture, Harrisburg, Pennsylvania 17110; (TJH) Systematic Entomology Laboratory, IIBIII, Agricultural Research Service, USDA, % U.S. National Museum of Natural His-tory, NHB-168, Washington, D.C. 20560. Abstract. — Trigonotylus coetestialium (Kirkaldy), a holarctic plant bug (Mirinae: Stenodemini), is known as a pest of small grains in the Palearctic Region but has remained little studied in the Western Hemisphere. Presented are a summary of its seasonal history and host plants in Pennsylvania, its relative density in oat fields, the effects of different densities of adults on growth of oat seedlings under greenhouse conditions, and its potential for injuring cultivated grains. Even small numbers of adults (1-2 per 2 seedlings) significantly inhibited growth, and it is concluded that this multivoltine bug is potentially injurious to spring grains. The nymphal stages are described and illustrated; the adult is illustrated and diagnosed with emphasis on its separation from the related T. ruficornis (Geoffroy). Entomologists are becoming more aware of plant bugs as pests of grasses and small grains. Species of the mirid genera Irhisia Renter (McKendrick and Bleicher, 1980; Schwartz, 1984) and Lahops Burmeister (Todd and Kamm, 1974; Hewitt, 1980) decrease productivity of range grasses in western United States. Feeding occurs mainly on grass blades, causing chlorotic spots in areas of stylet penetration. Other grass-associated plant bugs feed more on culms (stems) or on maturing flower and seed heads. Their injury appears as silvery-white heads that, although mature, produce sterile flowers. Usually referred to as silvertop (or sometimes white ear), this condition results from the piercing of culms before pollination occurs. In North America the agents responsible for silvertop may differ among regions, but mirids often are important causal agents (Amot and Bergis, 1967; Peterson and Vea, 1971; Kamm, 1979; Gagne et al., 1984). Species implicated in producing silvertop belong mainly to the subfamily Mirinae, except for the phyline Amblytyhis nasutus (Kirschbaum). Most of the mirines are members of the tribe Stenodemini, e.g., the genera Leptopterna Fieber, Litoniiris Slater, Meg-aloceroea Fieber, and Stenodema Laporte. In Europe, the holarctic Leptopterna dolabrata (L.) is known to cause silvertop of grasses (Wagner and Ehrhardt, 1961). Species of the stenodemine genus Trigonotylus, often abundant in grasses and small grains, have received little attention in North America, though they have been studied in the Palearctic Region. In the USSR, Agafonova and Belizin (1964)
Trigonotylus coelestialium (Heteroptera: Miridae), a pest of small grains: seasonal history, host plants, damage, and descriptions of adult and nymphal stages
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