Abstract
Differentiated management of alfalfa fields : a positive impact on butterfly populations (Lepidotera : Rhopalocera) The impact of differentiated management of alfalfa fields on butterfly populations (Rhopalocera) was investigated in 2009 and 2010 on 18 sites in Champagne-Ardennes and 6 in Haute-Normandie (France), in comparison with both conventionally managed alfalfa and cereal crops. The STERF method (Suivi Temporel des Rhopalocères de France), the national French program for butterfly populations follow up, was used. Alfalfa itself (classical management) and moreover a flowered strip maintaining (7 m-wide band alternating non-swath in each cut) are significantly favourable to richness (31 species on the 43 observed, compared with 15 in and on the edge of cereal fields) and the abundance of butterflies (53 ± 6 butterflies per 10 minutes of counting in the non-mown strip, against 15 ± 2 on the edge of mowed alfalfa crops and 6 ± 1 on the edge of cereal fields). The most abundant species were Vanessa cardui (amazing position linked to the exceptional migration of 2009, with a particular concentration on alfalfa), Pieris rapae, Polyommatus icarus, Colias croceus, Pieris brassicae, Aglais io and Pieris napi. The more the species were common, the more they seemed to be favoured by these alfalfa blooms. Bloom alfalfa condition is an essential parameter, especially in the second half of the season, when wildflowers are less numerous. There is an additional interest of the flowering bands of alfalfa for species such as P. icarus (sedentary) and C. croceus (migratory), whose caterpillars can feed with alfalfa.
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