Corn rootworm survey in North Dakota and a comparison of two sticky traps

Northern, Diabrotica barberi Smith & Lawrence, and western, D. virgifera virgifera LeConte, corn rootworms are major economic pests of corn, Zea mays L., in the United States. This research was conducted to determine the geographic distribution, abundance, and species composition of Diabrotica species in North Dakota, and to compare effectiveness of unbaited green Scentry (TM) Multigard and unbaited yellow Pherocon(R) AM/NB sticky traps for monitoring. Fifty-one corn fields were monitored using traps from July through October of the 2013, 2014, and 2015 growing seasons for rootworm beetle activity. The overall species composition was 61% D. barberi and 39% D. v. virgifera. Both species were frequently captured, and the highest densities (i.e. >10 beetles per trap per week) were found in southeastern North Dakota. Low densities (i.e. <0.1 beetles per trap per week) of D. barberi were found in areas further north, but no D. v. virgifera were captured in those fields. The two different coloured sticky traps were not significantly different across 38 sites for D. barberi and across 21 sites for D. v. virgifera. However, green Scentry (TM) Multigard traps captured more D. barberi beetles than yellow Pherocon(R) AM/NB traps at 68% of the 38 fields. In contrast, the yellow Pherocon(R) AM/NB traps captured more D. v. virgifera beetles at 57% of the 21 fields. Findings also indicated that, although D. barberi was the predominant species in surveyed fields, populations rarely reached the economic threshold. Our study observed that economic populations of corn rootworms were infrequent among the field sites trapped in North Dakota. As a result, producers should scout fields regularly for corn rootworm populations levels to make sound pest management decisions. This knowledge can enable producers to effectively protect their crop when control is economically justified, and the information can also provide input cost savings when populations do not warrant control efforts.