Population density ofDiabrotica virgifera virgiferaLeConte beetles in Serbian first year and continuous maize fields

A 5-year field survey examined western corn rootworm (WCR) (Diabrotica virgifera virgifera LeConte) beetle density in Serbia from 2002 to 2006. First-, second-, third-, fourth- and fifth-year maize fields were sampled; they represented 64.61%, 21.66%, 9.45%, 3.53% and 0.75% of all sampled fields respectively. Results showed that the mean WCR beetle population density from 794 maize fields differed depending on cropping history. Minimum mean WCR/trap/day was 0.0 in the first-year maize fields in 2002 and 2006. Maximum mean WCR/trap/day was registered in the fourth-year and the fifth-year maize fields (27.8 and 21.2 respectively). Mean population density of WCR adults increased with the number of years of continuous maize from 1.17, 4.61, 6.41, 10.30 up to 13.53 WCR/trap/day for first-fifth-year maize fields respectively. Mean WCR/trap/day ± SE exceeded the economic population threshold of >6 WCR/trap/day in third-year continuous maize fields. Out of 794 maize fields, 697 (87.78%) registered a mean population density below the 6 beetles/trap/day, a finding that predicts a risk of economic damage to a subsequent maize planting. These data are representative of the Serbian situation from 2002 to 2006; they indicate that WCR are well dispersed across commercial maize fields in Serbia. These results provide new insight into the current low WCR population densities in maize fields managed by crop rotation, a finding that can help in creating long-term management strategy.