Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/12/2003
Publication Date: 4/1/2004
Citation: Spurgeon, D.W., Esquivel, J.F., Suh, C.P. 2004. Population patterns of Mexican corn rootworm (Coleoptera: Chrysomelidae) adults indicated by different sampling methods. Journal of Economic Entomology. 97(2):687-694. Interpretive Summary: Mexican corn rootworms in Texas corn are usually controlled by soil insecticides, but recent efforts to decrease the amount of pesticides in the environment have focused on control of adult beetles by toxic baits. Use of adult controls requires accurate monitoring of population levels. Seasonal population patterns have been less studied for the Mexican corn rootworm than for other rootworm species, and recent adoption of a new trap (the CRW trap) has further emphasized the need for additional information on trapping. Yellow sticky traps (AM trap) and CRW traps were evaluated at distances of 0, 2, 5, 10, 20, and 30 m into the field. Only the CRW trap consistently caught fewer beetles at the field edge (0 m) than at other distances, but captures by the AM trap and counts of beetles on plants also showed this general trend. Captures at other distances were usually similar to each other, thus, traps do not need to be placed far into the field. Both trap types indicated highest beetle numbers 2-3 weeks later than were indicated by counts of beetles on plants. Neither trap captured beetles very efficiently until after the corn was pollinated, and trapping efficiency increased with time thereafter. Our results should increase acceptance of the traps for monitoring rootworm beetle populations, and suggest that treatment thresholds may be improved by accounting for changes in trap efficiency during the growing season.
Technical Abstract: The Mexican corn rootworm, Diabrotica virgifera zeae Krysan and Smith, is a serious pest of corn in several areas of Texas. Recent demonstrations of areawide adult control suggest this tactic has promise for rootworm management, but additional information regarding treatment thresholds and sampling methodology is needed. In 2000 and 2001 we examined the influence of distance into the field on rootworm captures by CRW and Pherocon AM traps, the fidelity of trap captures to population estimates from visual counts of beetles on plants (whole plant samples), and the seasonal population patterns indicated by each sampling method. Only the CRW trap consistently indicated reduced trap captures at the field margin compared with other distances. However, trends for the AM trap and whole plant samples suggested sampling on the field margin should be avoided. Population estimates at other distances into the field (2-30 m) were usually statistically similar. Thus, monitoring does not require trap placement far into the field. Both trap types indicated population peaks after flowering in corn, while plant samples indicated peak populations during tasseling and flowering. Both the CRW trap and plant samples showed the proportion of female beetles increased as the season progressed, but the CRW trap underestimated the proportion of females until after flowering. Regressions relating captures by trap counts from plant samples indicated efficiency of both traps increased with increasing plant development. Our findings should increase acceptance of the CRW trap by producers and consultants, and provide a rationale for development of improved, plant growth stage-specific treatment thresholds.