Vol. 97, No. 1, January & February, 1986 11 HOST RELATIONSHIPS OF DIABROTICA CRISTATA (COLEOPTERA: CHRYSOMELIDAE) 1 Niamoye Yaro2,3, James L. Krysan^/* AJ3STRACT: Observations were made on host relationships of a natural population of Diabrotica cristata in pure stands of perennial grasses in eastern South Dakota. The larval host was determined by placing traps to capture adults which might emerge from soil under three species of grass, Bromus inermis Leyss (smooth brome grass), Panicum virgatum L. (switchgrass) and Andropogon gerardi Vitman (big bluestem). Beetles were captured only in traps over big bluestem. Sticky traps were deployed among plants of all three species; significantly more D. cristata were captured in plots of big bluestem than in plots of the other two plant species. Sampling the soil for eggs revealed no clear pattern of distribution of eggs among the three grasses, but did establish that D. cristata overwinters in the egg stage. Diabrotica cristata (Harris) is a rather inconspicuous occupant of relict prairie ecosystems east of the Rocky mountains in northern Mexico, the United States, and Canada (Douglas, 1929; Hendrickson, 1929; Smith, 1 966). It is a member of the virgifera species group along with three pests of corn, D. barberi Smith and Lawrence (the northern corn rootworm), D. virgifera virgifera LeConte (the western corn rootworm), and D. virgifera zeae Krysan and Smith (the Mexican corn rootworm). Larvae of Diabrotica are known to feed on the roots of plants, and the larvae of the above pest species are known to be oligophagous in that they feed only on the roots of certain grasses (Branson and Krysan, 1981). It has been inferred that D. cristata feeds on the roots of perennial grasses in the larval stage because of the host range of the relatives and the fact that adult D. cristata are collected in association with native perennial grasses (Smith, 1966; Krysan and Branson, 1981). Furthermore, adult D. cristata have been produced in the laboratory from larvae reared on the roots of corn (Branson and Krysan, 1981). Additionally, the adults of the two other species of the virgifera group which occur in the United States, D. lemniscata LeConte and D. longicornis (Say), are also collected in ecosystems characterized by perennial grasses (Krysan, 1982). Grasses may be the primary larval host for this species group. Our attempts to identify larval hosts of D. cristata have been foiled by a 'Received May 13, 1985. Accepted September 28, 1985. 2 Northern Grain Insects Research Laboratory, USDA-ARS, RR 3. Brookings, SD 57006. 3 Present address: C.N.R.F., B.P. 30, Bamako (Mali) West Africa. "^Present address: USDA-ARS, Yakima Agricultural Research Laboratory, 3706 W. Nob Hill Blvd., Yakima, WA 98902. ENT. NEWS 97( 1 ): 11-16. January & February, 1 986
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