Interactions over time between cereal leaf beetle (Coleoptera: Chrysomelidae) and larval parasitoid Tetrastichus julis (Hymenpotera: Eulophidae) in Utah

This article is the copyright property of the Entomological Society of America and may not be used for any commercial or other private purpose without specific written permission of the Entomological Society of America. Please note the copyright policy at http://www.entsoc.org/pubs/publish/copyright/index.htm. This item has been posted with the permission of the Entomological Society of America per correspondence with Alan Kahan, Director of Communications, Entomological Society of America, August 26, 2009.The phenology of parasitism of the cereal leaf beetle, Oulema melanopus (L.) Coleoptera: Chrysomelidae) by Tetrastichus julis (Walker) (Hymenoptera: Eulophidae) was studied in small grain fields from 2000 to 2005 in northern Utah, after release and redistribution of the partially bivoltine larval parasitoid during the 1990s. Host larvae first occurred in May, with peak infestation typically occurring in early to mid-June. Parasitism by overwintering females of T. julis was highest among earliest developing beetle larvae. Thereafter, rates of parasitism fell to low levels (5-10% orless) by the latter half of June, when heat accumulation had reached 280-350 degree-days (based on a minimum threshold of 8.9 degrees C). With the emergence of second generation parasitoids, rates of parasitism rose to levels approaching 100% among the relatively few late-developing larvae of O. melanopus. Clear and consistent differences over the years were not observed among different crops of small grains (barley, wheat, or oats) either in the phenology and intensity of beetle infestation, or in the rate of parasitism of beetle larvae. The rate of parasitism was especially high in 2005, and an increase in the minimum level of parasitism (observed each year at mid-season) was apparent over the course of the study. These results indicate that the parasitoid has become well established and seems to be continuing to increase in its impact on O. melanopus in northern Utah, despite a relatively hostile environment of crop management, wherein most fields are plowed and disked annually.Department of Biology, Utah State University; Cooperative Extension Service, Utah State University; Cache County Cooperative Extension Service, Logan UtahJournal of economic entomology, volume 99, no.6, 2006, pp. 1967-1973