Phenology of Inachis io larvae and maize pollen deposition on nettles in Northern Italy field margins


Abstract: As part of the LIFE+ MAN-GMP-ITA project concerning validation of risk management tools for GM plants in protected areas, two years of field trials were carried out in a maize-cropped area within the SCI-SPA Biotopes and environmental restoration areas of Bentivoglio, San Pietro in Casale, Malalbergo e Baricella in Northern Italy.A first array of experiments was aimed to quantify the drift of maize pollen in the receiving environment. By means of Petri dishes covered with gelatin we confirmed the findings that most maize pollen falls very close to the crop edge. Collections by leaf-print technique were carried out on nettles (Urtica dioica) wild growing in maize field margins to evaluate the actual amount of pollen deposited and retained by nettle leaves. Three samplings were performed in the same fields at 80% maize flowering, at 100% maize flowering and at the end of anthesis. Nettles were at a mean distance of 6.2 m from maize and the maximum mean pollen density (2.1 grains cm-2) was observed in the first sample.Moreover, we checked the phenology of the second brood of peacock butterfly (Inachis io) in nettles growing in margins of maize field. Larval colonies were detected both in 2011 and 2012 and a complete temporal overlap with maize flowering was observed. The distribution of larvae was clumped with most nettles having no caterpillars and few plants being highly infested.

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