Land use supplementation on the colony vigor of a tropical stingless bee

Background/Question/Methods

Native stingless bees (Meliponini tribe) play an important role as pollinators of tropical plants and crops. A growing number of studies have investigated the effect of landscape composition on tropical bee community assemblages and their associated pollination services. Nevertheless, there are scant data on the effects of landscape composition on stingless bee colony vigor and survival, and consequently bee abundance. In highly altered tropical mountains, with low proportion of native habitat remaining, mass recruiting stingless bee colonies might survive in small forest fragments by utilizing foraging resources provided by non-forested land uses (landscape supplementation hypothesis sensu Dunning et al. 1992).
To test this hypothesis, we conducted a quasi-experiment in a mountainous region of southern Costa Rica; an area dominated by forest, coffee and pastureland. We placed two colonies (pseudo-replicates) of the stingless bee Tetragonisca angustula at the center of 18 sites, which varied in land use composition (from 100% forest to >70% coffee). We measured brood comb & food pot weights and numbers, and bee foraging activity every 10 to 20 days, from February to July in 2011 and 2012. Concurrently, we assessed flowering plants availability via vegetation transects and palynological analysis of pollen pots and corbicular bee loads. 

Results/Conclusions

Palynological analyses confirmed that when abundant, coffee pollen constitutes an important resource for T. angustula colonies. However, selectivity for coffee pollen is inconclusive, due to the presence of corbicular loads from different floral sources during coffee blooming. At sites with low forest cover remaining, both food pot weights and bee activity increased during coffee flowering (dry period), indicative of a seasonal supplementation effect. However, flowering plant scarcity in the coffee-dominated landscapes (>70%), when coffee is not in bloom, resulted in sharp declines in food stores, having a detrimental effect on colony vigor and survival. Hives located within forested sites also experienced large weight increases due to flowering trees, during the dry period. Food pots at sites dominated by pastureland had small weight increases during the dry period and colonies used reserves as the wet season progressed. Visitation to coffee flowers by other stingless bee species indicates that the benefits from coffee pollen might be widespread in these agricultural landscapes. Consequences of landscape management on stingless bee colony vigor are discussed in light of these findings.