[1] Agroscope Liebefeld Posieux, Swiss Bee Res Ctr, Res Stn ALP, CH-3003 Bern, Switzerland
[2] Rhodes Univ, Dept Zool & Entomol, ZA-6140 Grahamstown, South Africa
[3] Agroscope Reckenholz Tanikon, Res Stn ART, CH-8046 Zurich, Switzerland
[4] INRA, UMR Abeilles & Environm INRA UAPV 406, F-84914 Avignon 9, France
[5] Univ Maryland, Dept Entomol, College Pk, MD 20742 USA
[6] Univ Georgia, Dept Entomol, Athens, GA 30602 USA
[7] Smithsonian Trop Res Inst, Balboa, Ancon, Panama