Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2000
Publication Date: 12/1/2000
Citation: DOWD, P.F. DUSKY SAP BEETLES (COLEOPTERA: NITIDULIDAE) AND OTHER KERNEL DAMAGING INSECTS IN BT AND NON-BT SWEET CORN IN ILLINOIS. JOURNAL OF ECONOMIC ENTOMOLOGY. 2000. v. 93(6). p. 1714-1720. Interpretive Summary: Sweet corn ear pests cause millions of dollars of economic losses each year. Bt sweet corn may potentially control caterpillar pests but not other pests such as sap beetles. It may be necessary to monitor these sap beetles to ensure that insecticides used for their control are not applied unnecessarily. A 2-year comparison of commercial Bt and nonBt sweet corn hybrids indicated highly effective control of caterpillar pests, but sap beetles remained pest problems. A sap beetle trap/attractant combination was as effective as plant scouting in detecting sap beetle populations, but collecting trap data was much quicker than collecting scout data. These trap/attractant combinations should be important tools for sap beetle management in sweet corn. Use of these trap/attractant combinations should also be of value in managing sap beetles in field corn, where they serve as carriers of fungi that produce economically important mycotoxins.
Technical Abstract: Dusky sap beetles were typically present at about equal frequency on Bt and nonBt sweet corn hybrids from onset of silking through milk stage harvest. Sap beetle numbers determined by scouting were often proportional to numbers of beetles captured in baited traps, increasing and decreasing at about the same time. However, values determined with traps were typically less variable than when scouted, and time of sampling was typically 4x more rapid for each trap than for each 10 plant scout sample when measured in 1999. The occurrence and damage by Helicoverpa zea (Boddie) and other caterpillars was reduced by at least 80% in each year for the Bt compared to the nonBt hybrid. The incidence of adults and larvae of the dusky sap beetle, Carpophilus lugubris Murray, on milk-stage ears was not significantly different between the Bt and nonBt hybrids in 1998. However, the incidence of sap beetle adults was higher and larvae lower for the Bt vs. nonBt in 1999. The incidence of ears with >5 kernels damaged by sap beetles was higher for the Bt vs. nonBt hybrid in 1998. In 1999, incidence of ears with >5 kernels damaged by sap beetles was essentially equivalent for the Bt vs. nonBt ears, as was distribution of predators (primarily Orius spp.). Ears with husks flush with the ear tip or with ear tips exposed had significantly higher sap beetle damage for both hybrids, and the Bt hybrids had significantly higher incidence of exposed ear tips in both years.