Diversity of native bee visitors of cucurbit crops (Cucurbitaceae) in Yucatan, Mexico

Native bees in Yucatan, Mexico are treatened by agricultural land uses that limit their food resources, alter their reproductive habitats and increase their mortality. Various species may disappear before their importance for regional agricultural productivity and ecosystem maintenance is known. In order to assess their assemblage as visitors of cucurbit crops, we sampled more than 2000 bee specimens on fourteen fields of pumpkin, cucumber, melon and watermelon from five localities between 1995 and 1997; sample units consisted of all bees collected by net sweeping in a given field during 25-30 accumulated hours on separate days. The fourteen samples comprised bees of six families, 29 genera and 58 species. Composition per sample ranged between 10 and 27 species and abundance between 28 and 444 individuals. Seven species (six genera) of Apidae, Anthophoridae and Halictidae comprised around 80% of all the individuals collected. Yet, diversity measures indicated intermediate to high evenness in most sampled bee assemblages, i.e. despite the frequent abundance of some species of Augochlora, Partamona, Ceratina, Trigona or Peponapis, other bee visitors were also relatively important, particularly in small samples. Individual samples of pumpkin bee visitors had significantly different evenness among themselves and to other cucurbit crops. The percent similarity and number of shared species among the fourteen samples were both usually low; lumping data per crop and locality showed, however, higher evenness and more common species than individual samples. Results are discussed in terms of future research priorities: natural history of tropical native bees and strategies to monitor bee community changes for conservation purposes.