Leaf trait variation on Erythroxylum tortuosum (Erythroxylaceae) and its relationship with oviposition preference and stress by a host-specific leaf miner
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It has been suggested that plant physical and chemical traits vary considerably in space and time. Hence, leaf-mining insects may adjust their oviposition in response to leaf attributes representing high quality. Moreover, herbivorous insects can modify leaf morphology by acting as stressors, increasing, for example, fluctuating asymmetry (FA) levels. Here, we investigate oviposition preference in Agnippe sp.2, a leaf-mining moth of Erythroxylum tortuosum, in relation to differences in leaf nutritional quality (i.e. levels of water, nitrogen and tannin content), leaf area (i.e. quantity of resource hypothesis) and FA. We also verify whether temporal variation in plant nutritional quality emerges as an alternative hypothesis to explain oviposition distribution in time, and whether this leaf miner is a stress-causing agent, increasing FA during larval development. Mined leaves and leaves with and without eggs were periodically collected from plants located in a Cerrado fragment in Brazil. In the laboratory, leaf traits were assessed (using image analysis software) and quantified (biochemical analysis) according to the aims previously determined. Oviposition probability did not change in relation to variations in nitrogen, tannins and FA of leaves. However, leaf-miner females preferred to oviposit on leaves having large areas and low water contents. It was also verified that new leaves of E. tortuosum, which carried most leaf-miner eggs, presented significantly lower tannins and greater levels of nitrogen and water than old leaves. The oviposition choice exhibited by leaf miners was found to be non-random because they appear to use resource quantity and water content as cues as where to lay their eggs. The temporal variation of plant nutritional quality is likely to influence the time of leaf-miner oviposition; and leaf FA was not increased during larval feeding, suggesting that these herbivores do not cause variations in FA levels.