Within‐plant distribution of Rhopalosiphum padi on wheat seedlings is affected by induced responses

Abstract

Cereal aphids have distinct patterns of occupation of plants, both in spatial and temporal terms (Dean, 1974). The preferred feeding site of the bird cherry-oat aphid, Rhopalosiphum padi (L.), on cereal seedlings is the stem base and lower leaves (Dean, 1974; Leather & Lehti, 1982), and this holds for both field and laboratory observations (Wiktelius, 1987). Previous works discussing this pattern of within-plant distribution have considered factors such as nutritional value of the tissues (Leather & Dixon, 1981; Weibull, 1987; Wiktelius, 1987; Wiktelius et al., 1990) and avoidance of extreme temperatures in the field (Wiktelius, 1987). Plant quality for herbivorous insects can decrease after feeding, due to induced responses of the plant (reviewed in Karban & Baldwin, 1997). Effects of induced responses on the within-plant distribution of the herbivore have also been reported (Edwards et al., 1991 and references therein). This work presents results suggesting that induced responses of wheat (Triticum aestivum L.) seedlings to aphid feeding play a role in shaping the within-plant distribution of R. padi. In particular, it compares the constitutive as well as the induced quality for the aphid of the stem (preferred site) and the third leaf (non-preferred site) of a three-leaf seedling.