Contrary effects of leaf position and identity on oviposition and larval feeding patterns of the diamondback moth

Abstract

Abstract The influence of leaf position and leaf identity on oviposition and neonate feeding site establishment by the diamondback moth, P lutella xylostella ( L .) ( L epidoptera: P lutellidae), were investigated in laboratory experiments. Leaves were excised from cabbage [ B rassica oleracea L . capitata , cv. S ugarloaf ( B rassicaceae)] and the plants reconfigured on artificial stems made from oasis floral foam. Excised leaves were arranged in their normal (natural) order, in reverse order, or in random order. Relative leaf position, but not leaf identity, significantly influenced the choice of oviposition site; when exposed to female moths, leaves in the lowest three positions always received most eggs. To eliminate the effect of leaf position, oviposition experiments were conducted on excised leaves held at uniform height in individual blocks of oasis foam that had been randomly allocated to a position in a circle at the base of an oviposition cage. Moths laid significantly more eggs on younger leaves, but egg density per unit area did not vary among leaves, supporting the finding that leaf identity did not affect moth oviposition. In experiments that investigated the establishment of neonate feeding sites in reconfigured plants, feeding sites were always concentrated on the youngest two leaves of plants, regardless of their position in normal‐, reverse‐, and random‐order plant configurations. This indicates that leaf identity rather than leaf position determines the site of neonate feeding site establishment. The contrary effects of leaf identity and leaf position on oviposition and neonate feeding site establishment in the same species suggests that different life stages utilize different plant cues (perhaps both physical and chemical) in life stage‐specific ways.