John F. Witkowski

Dispersal of Adult European Corn Borer (Lepidoptera: Crambidae) Within and Proximal to Irrigated and Non-irrigated Corn

Abstract The European corn borer, Ostrinia nubilalis (Hübner), causes economic damage to corn, Zea mays L., throughout the Corn Belt. Because this insect has become the primary target of Bacillus thuringiensis Berliner (Bt) transgenic corn, current efforts addressing the management of O. nubilalis resistance to Bt corn require information on adult European corn borer dispersal and factors affecting its dispersal. In 1998 we conducted mark-release-recapture, release-recapture, and caged-mating studies to directly measure and compare local dispersal patterns of O. nubilalis adults within and proximal to irrigated and non-irrigated cornfields. Releases of marked adults were made corresponding to the first and second flight of O. nubilalis in eastern Nebraska. Adult dispersal was significantly different between irrigated and non-irrigated cornfields. Released adults tended to remain in and near irrigated cornfields, but dispersed out of and away from non-irrigated cornfields. When released at the edge of the cornfield, neither male nor unmated female O. nubilalis displayed an initial tendency to move out of irrigated corn and into the mixed smooth bromegrass (Bromus inermis Leyss) and broadleaf-weed field edge. Mating efficiency in a late-season cornfield was not significantly different than in dense foxtail (Setaria spp.). Generally, we found that adult O. nubilalis dispersal may vary depending on variables such as action-site availability and agronomic practices and their interaction with O. nubilalis life history.

Oil-Soluble Dyes for Marking European Corn Borer (Lepidoptera: Crambidae)

The European corn borer, Ostrinia nubilalis (Hubner), is a pest of corn throughout the Corn Belt. It also is the target pest of the first commercially available transgenic corn hybrids. These transformed hybrids contain a modified gene from the bacterium Bacillus thuringiensis Berliner that expresses an insecticidal protein (Koziel et al. 1993, Bio!T echnol. 11 : 194-200). The widespread use of these hybrids has fueled the development of resistance management models and protocols.

Parasitism Rates in European Corn Borer (Lepidoptera: Crambidae) Larvae Collected from Six Maize Hybrids

The parasitoid complex and level of parasitism of European corn borer, Ostrinia nubilalis (Hubner), larvae in six maize, Zea mays L., hybrids was determined in Nebraska during 1995 and 1996. Three ...

IMPACT OF TILLAGE AND PLACEMENT METHODS ON TERBUFOS INSECTICIDE RUNOFF

On a national scale, the damage caused by corn rootworm (Diabrotica virgifera virgifera LeConte), can cause economic loss of up to

Effects of Manure, Hybrid Root Strength, and Reduced Rates of Insecticide on Corn Rootworm (Coleoptera: Chrysomelidae) Injury to Corn

650 million annually. To limit these losses, corn producers apply terbufos insecticide to approximately 11% of all corn acres at a time when there is a high probability of intense precipitation. When combined with low vegetative cover and disturbed soil surfaces, there is a high potential for terbufos transport into surface water bodies. Increased public concern for environmental contamination from the use of agricultural chemicals has prompted many crop growers to look for crop production practices that minimize the transport of insecticides by surface runoff. A field experiment was conducted at the Haskell Agricultural Laboratory in northeast Nebraska in the spring of 1989 to develop best management practices for applying corn rootworm insecticides. The objective of the study was to determine the influence of three tillage practices (DISK, NOTILL, and PLOW) and two insecticide placement methods (BAND and FURROW) on the transport of terbufos insecticide (Counter.) with runoff water resulting from high intensity simulated precipitation after chemical application. A randomized complete block design of four replications was utilized. Treatments were laid out in a split-plot fashion with tillage as the main plot and insecticide placement as the subplot. Corn was planted up-and-down hill in 0.76 m row spacings on a Nora silt loam (fine-silty, mixed, mesic Udic Haplustoll) with a field slope of 6 %. Water runoff was not significantly affected by either tillage practice or insecticide placement method (P < 0.05). Sediment losses from NOTILL plots were significantly less than from the DISK and PLOW treatments. Overall, terbufos transport was significantly affected by tillage practice with the NOTILL treatment resulting in less terbufos transport than the PLOW or DISK treatments. However, terbufos transport was not affected by placement method. Samples collected 10 and 20 min after runoff initiation indicated that sediment-adsorbed terbufos accounted for more than 90% of total terbufos transport. No significant differences in the sediment-adsorbed levels were noted due to tillage treatment or insecticide placement method (P < 0.05). Tillage and insecticide placement methods significantly affected the dissolved terbufos concentration, especially for samples collected 20 min after runoff initiation where the BAND placement was greater than the FURROW placement. Within tillage treatments, the PLOW treatment had greater dissolved terbufos concentration than the NOTILL treatment after 20 min of runoff.

Population Suppression of Western Corn Rootworm by Adult Control with ULV Malathion

ABSTRACT Field studies were conducted at the Haskell Agricultural Laboratory, University of Nebraska, Concord, NE during 1996, 1997, and 1999 to evaluate the effects of manure application, hybrid root strength, and reduced insecticide rates on corn rootworm (Diabrotica virgifera virgifera LeConte and D. barberi Smith and Lawrence) larval injury and corn (Zea mays L.) yield. Treatment combinations consisted of two corn hybrids, three manure rates (0, 67, and 135 MT/ha), and 4 in secticide rates (0, 2.8, 5.6, and 11.2 g (AI)/100 m-row terbufos, T-band). Overall, manure reduced root injury 7% to 11% and increased yield 1% to 8%. All insecticide rates reduced root injury, but did not affect yield. When manure was combined with insecticide applications, there was no significant increase in root injury protection over that provided by the insecticide. Hybrid root strength did not contribute to root or yield protection. Root injury was relatively low during all years of the study (control root ratings < 4). Manure application did not interfere with the terbofos application. More detailed studies are required to characterize the effects and joint effects of manure application, hybrid root strength, and reduced insecticide rates on rootworm feeding and plant response.