| Changes in corn rootworm (Coleoptera: Chrysomelidae) behavior and biology, combined with greater regulatory scrutiny of pesticides, threaten the future of insecticides, crop rotation, and even transgenic, corn rootworm-resistant corn as single control tactics for these pests. Entomopathogenic nematodes offer a novel management alternative.; Field trials conducted in 1993 and 1994 tested Steinernema carpocapsae , All strain (Weiser), S. riobravis (Cabanillas, Poinar and Raulston) and Heterorhabditis bacteriophora, New Jersey strain (Poinar), against early third instar western corn rootworms (Diabrotica virgifera virgifera LeConte). Effective application rates were determined, using corn rootworm mortality (50% reduction in adult emergence) and corn root injury (root ratings below 3.0, the damage threshold): S. carpocapsae, 105 to 107 infective juvenile nematodes (Us) per 30.5 row-cm; S. riobravis, 10 5 to 106 1Js; H. bacteriophora, 104 to 106 IJs. Adult emergence was more rate-responsive than root injury. More aggressive host location by H. bacteriophora and higher susceptibility to host hemocytic encapsulation in S. carpocapsae may underlie performance differences.; Northern (D. barberi Smith and Lawrence) and western corn rootworm larvae were targeted in 1997 grain and silage corn trials that included factorial combinations of nematodes (H. bacteriophora [Hbl strain], S. carpocapsae [South Dakota isolate SD1]), treatment dates (Diabrotica spp. peak second, early third instar) and rates (3.3 × 104, 105 3 × 105 IJs per 30.5 row-cm). The grain site's mixed Diabrotica spp. population responded differently to treatment than the pure D. barberi population at the silage site. Second instar treatments reduced root injury more in the grain trial; lodging and yield responded better at third instar. Only third instar treatments affected the developmentally synchronous silage population. Heterorhabditis bacteriophora reduced root injury (105) and lodging (3 × 10 5, grain), and improved yield (3 × 105, silage; 9 × 105, grain). Diabrotica spp. emergence declined at 3.3 × 104 H. bacteriophora IJs (third instar) per 30.5 row-cm. Steinernema carpocapsae was less effective in grain corn (lodging, 3 × 105; adult emergence, 105 [second instar]) and ineffective in silage corn. Eight (grain) to 41% (silage) of D. barberi adults from S. carpocapsae treatments bore encapsulated nematodes. This resistance reduced S. carpocapsae efficacy. |
