Appendix B. Procedures for measuring Leptinotarsa decemlineata egg predation in commercial potato fields and their grassy field margins in Wisconsin in 2005 and 2006.
In 2005, entire potato leaves with egg masses were collected from no-insecticide plots at the University of Wisconsin’s Arlington Agricultural Research Station (Columbia Co.). A small tab of labeling tape was placed over the ends of each leaf; leaves with egg masses were then stapled to field vegetation through these tape-tabs. Egg masses were deployed in three transects extending perpendicularly from field edges along two sides of each field and the adjoining corner (Fig. B1). Along each transect, two egg masses were placed in the center of each field margin and one was placed in potatoes at 5 and 100 m from the potato-field margin interface. An additional three egg masses were distributed among transects in field margins and potato and covered with 23 × 46 cm sleeve cages of polyester no-see-um tent mesh (Quest Outfitters, Sarasota, Florida, USA). In potato, these three egg masses were haphazardly distributed between field edges and centers. Overall, 570 egg masses were deployed, of which 20 were destroyed or hatched before collection.
In 2006, protocols were modified to reduce experimental error. Eggs were collected from lab colonies maintained in outdoor field cages on the University of Wisconsin campus (Dane Co.). In addition to these, 170 egg masses were collected from no-insecticide field plots at Arlington, Wisconsin (Columbia Co.), USA. Egg masses were excised from leaves on 18 mm diameter leaf discs. One-month old potato plants (var. ‘Russet Burbank’) were then infested with one egg mass per plant before transport to the field. Leaf discs were attached to the underside of leaves using water-soluble white glue. To obtain uniform plants, 13 g pieces of tuber containing a single bud were removed using a 3 cm diameter melon baller. Seed pieces were planted in 4 cm diameter pots containing a mix of peat moss, perlite, and vermiculite. Before exposure in the field, plants and root balls were transferred from plastic pots to 470 mL plastic cups containing 240 mL of vermiculite saturated with water; this helped retain soil moisture. At each field site, potted plants infested with eggs were placed in four transects, two extending from the sides of potato fields and two from adjoining field corners. Along each transect, three plants were placed in the center of field margins and three more at 5 and 50 m into potatoes away from the margin. Pots were sunk into the ground and mesh cages placed over one plant at each distance to exclude predators. Overall, 792 egg masses were deployed, of which 53 were destroyed or hatched prior to collection.
FIG. B1. Colorado potato beetle (L. decemlineata)egg masses were deployed in three transects extending from two sides of each potato field and an adjoining corner in 2005, while in 2006 transects extended from two sides of a field and two adjoining corners. In 2005, transects consisted of two uncaged egg masses (open circles) placed in the field margin and one each placed in the edge and center (100 m from the edge) of the adjoining potato field. One egg mass was covered with a mesh cage (filled circles) and placed in the field margin at the start of each transect, with an additional caged egg mass haphazardly located in either the edge or center of the adjoining potato field. In 2006, one caged and two uncaged egg masses were placed at each position along transects. Finally, egg masses in the center of potato fields were only 50 m away from the edge of the field in 2006.