EFFECT OF MANURE AND CORN HYBRID ON SURVIVAL OF WESTERN CORN-ROOTWORM(COLEOPTERA, CHRYSOMELIDAE)

The interactions between manure and hybrid tolerance and their subsequ ent effects on the survival of the western corn rootworm, Diabrotica v irgifera virgifera LeConte, and other soil arthropods were investigate d in 1992 and 1993. To evaluate alternative management strategies for the western corn rootworm, treatment combinations included 2 corn hybr ids ('Pioneer hybrid 3733' and 'Cornell 281'), 4 manure rates (0, 45, 90 and 135 metric ton/ha) and 3 western corn rootworm egg densities (1 992: 0, 500, 700 eggs per 30.5-cm row; 1993: 0, 400, 800 eggs per 30.5 -cm row). Pioneer hybrid 3733 has been rated superior to Cornell 281 i n resistance to stalk and root lodging. Plots of Pioneer hybrid 3733 c ontained fewer western corn rootworm larvae on 6 July 1992, but the nu mber of larvae and adults did not differ between hybrids on any other date. Although western corn rootworm larval counts did not differ by m anure rate in either year, adult emergence was reduced an average of 4 5% in manured plots compared with nonmanured plots in 1992. Wet soil c onditions probably contributed to the reduced larval counts and adult emergence found in all plots in 1992 compared with 1993 and could have interacted with manure to increase mortality in treated plots. Adult emergence increased with egg density, but the ratio of emergence to eg g density decreased as egg density increased. Numbers of mesostigmatid mites significantly increased in manured plots during both years. No evidence of enhanced predation was reflected in larval counts. Althoug h previous studies have reported increased western corn rootworm survi val in tolerant corn hybrids with large root systems, manure applicati ons and the subsequent increase in root mass did not lead to increased western corn rootworm populations.