Wound-Induced Changes in the Acceptability of Tree-Foliage to Lepidoptera: Within-Leaf Effects

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Abstract
Leaves of alder, hawthorn and birch were artificially damaged with a single hole and offered to larvae of Spodoptera littoralis Boisd. (Noctuidae) at a range of intervals following damage. Grazing levels were compared between the damaged and undamaged sides of each leaf at two or three different spatial scales. Bioassays conducted in May revealed that within 1 d, acceptability of the damaged side of alder and birch leaves was significantly reduced compared with the undamaged side. (The most extreme reductions in acceptability were apparent in the immediate vicinity of the damage in both species). These effects persisted for at least seven days in birch and at least 14 d in alder. Within 6 h, grazing levels on the damaged side of hawthorn leaves were significantly lower than on the undamaged side. These effects also persisted for at least 14 d. Bioassays conducted in August revealed significant reductions in grazing on the damaged side of alder leaves 14 d afer damage and of hawthorn leaves after two days. Possible explanations for reduced acceptability surrounding a hole are discussed with particular reference to chemical defences. The ecological significance of these changes are discussed in relation to insect behavior and pattern of natural grazing.