Leafcutter bees in Brazil as pollinators
Isabel Alves dos Santos
The genus Megachile contains 161 described species in Brazil (Silveira et al. 2002) and is abundant in almost every ecosystem in the country, as much in natural environments as in cultivated fields. Results from bee surveys performed in Brazil show that these bees are not narrow specialists, but have a preference for Asteraceae and Fabaceae flowers, which they are able to open the keel and remove the pollen (a difficult feat for other bees, such as Apis mellifera, to perform).
Megachile often appears to be yellow because of its dense fur. The females carry pollen on the ventral surface of the metasoma. Most species are solitary and nest in pre-existing cavities (hollow stems, beetle burrows in wood, etc.). In many species of Megachile, the females have specialised mandible edges for cutting pieces of leaves, which they use in constructing the brood cells in the nest. Cell walls and partitions are made of materials brought into the nest from the outside and include pieces of leaves, petals, chewed leaf material, resin or mud.
In the Northern Hemisphere, different species of Megachilids, mainly of the genus Megachile and Osmia, are bred for pollination purposes. Megachile rotundata, for example, is a valuable pollinator of alfalfa (used primarily for seed production) in northwestern North America and has also been found to be an effective pollinator of cranberry and blueberry (Vaccinium). Osmia spp. play an important role in the production of different Brassica, strawberries, blueberries, almonds and others. The biology of Osmia is well known and large-scale breeding is possible, since they readily adapt to artificial nests (man made holes).
Almost every study done in Brazil about the use of trap nests by solitary bees and wasps registered Megachile species using the traps to build their nests. This indicates that there is a good chance of improving or increasing the presence of Megachile bees in a crop field, offering traps (like wooden trap nests), which would allow the females to construct their nest. The lack of native pollinators in agricultural fields is mostly due to the absence of nesting possibilities.
In Brazil, knowledge of the benefits of Megachilids in crop pollination is non-existent. However, there are many important crops, such as soy, beans, alfalfa (Fabaceae) or sunflower, as well as many medicinal Asteraceae, that could have better yields with these bees as pollinators.
The potential of native Brazilian Megachile for use in crop pollination is high and should be evaluated. In several Brazilian regions, the appropriate species of Megachile for pollinating a given crop must be determined and their biology studied (seasonality, life cycle, parasites and phenology).
Silveira F. A; Melo G. A R. & Almeida E A B. 2002. Abelhas Brasileiras, Sistemática e Identificação. 1. Ed. Ministério do Meio Ambiente. 253p.