1. Institute of Biometeorology, National Research Council (CNR), Via Gobetti 101, 40129 Bologna, Italy;
2. (Author for correspondence:tel +39 0516399009; fax +39 0516399024;)
3. Department of Biology, San Diego State University, San Diego, California 92182, USA;
4. Institute of Biometeorology, National Research Council (CNR), Via Caproni 8, 50145 Firenze, Italy