engleski

Study of WCR adult movement and possible egg laying in fields bordering maize fields

Western corn rootworm (WCR) larval damage in maize following soybean was observed in Croatia in 2003. Damage was recorded along the edges and within soybean fields which bordered continuous maize fields in 2002. The only explanation was that WCR adults moved from the continuous maize to the neighbouring soybean fields to lay eggs. Larval feeding damage in the first-year maize the following year was recorded up to a distance of 50 m into the fields. Farmers’ fields in Croatia are commonly up to about 50 m wide and the above described situation could diminish crop rotation as a valuable tool for WCR management. As a results of this situation, research was carried out to determine how far WCR adults will go into neighbouring fields to lay eggs. The WCR adult population was monitored in a continuous maize field in 2003 by using Pherocon&reg ; AM (PAM) traps in the middle and on the borders of the maize field and up to 50 m distance from the edge of the continuous maize field into neighbouring fields to the south, east and west. Larval presence and root damage ratings (ISU1-6 scale) were recorded at different locations within the field in 2004. The field was 120 m wide and was divided into 3 sections in 2005. On two sides, maize was planted and in the middle section soybean was planted. The WCR adult population was monitored using PAM traps in the middle and on the borders of the maize fields and each 5 m within the soybean field to a maximum of 40 m. No significant differences in number of WCR adults on PAM traps located in the centre and on the edges of maize field were observed in 2003. The number of WCR adults on PAM traps located 50 m within neighbouring fields was significantly lower. Number of WCR larvae/plant was 3.5 in the centre and 2.25 and 2.75 on the west and east edges, respectively. The average root rating was 4.46 in the centre and 3.93 on the west edge. On the east edge of the field and at all observed distances eastward, lower root damage ratings were recorded (between 1.66 and 2.23). The average root damage ratings at 5, 10 and 15 m to the south were between 2.98 and 3.58. The average root damage rating to the south at 20 m was 2.4. At the distance of 50 m, no significant root damage was recorded in any direction. Maximum daily captures of WCR adults in 2005 in the centres of the maize fields and on the south edges of both maize fields did not significantly differ. At all other distances and on the north edge of the maize fields, maximum daily catches were significantly lower. Investigations will conclude after root ratings are taken in 2006. It appears that the so called “ edge effect” could happen within distances of 15-20 m of maize field borders and that the direction of the prevailing winds can impact this movement.

WCR; egg laying; movement

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