Honey bees aren’t the only insects that pollinate crops, but we often overlook or lump together all other, non-bee pollinators – flies, beetles, moths, butterflies, wasps, ants, birds, and bats, just to name a few. According to new findings published in the Proceedings of the National Academy of Sciences this week, non-bee pollinators play a major role in global crop production, and they’re not as affected by environmental changes as bees.
A lot of pollinator-dependent crops are increasingly grown for our food, fiber, and fuel. And while the honey bee (Apis mellifera) is versatile and ubiquitous, relying on a single pollinator species is a risky strategy. Poor nutrition, parasites, and diseases threaten the health of honey bee colonies managed around the world. Yet, we haven’t really explored the potential of other pollinators for contributing to crop production, even though they seem to be more robust to changes in land use.
To fill in the gaps, a large international team led by Romina Rader from the University of New England in Armidale, Australia, analyzed 39 studies that measured how much and how well honey bees, other bees, or non-bee insects pollinate 17 different crops spanning five continents. The other bee species studied include bumble bees, sweat bees, plasterer bees, mining bees, and leafcutter bees; the non-bees include flies, butterflies and moths, beetles, ants, and wasps.
Non-bee insects were less effective pollinators than bees per flower visit, but they made more visits to flowers than bees. So overall, they offered similar total pollination services: Honey bees make up 39 percent, non-bees make up 38 percent, and other bees accounted for 23 percent.
There are many reasons why non-bees might make up more visits compared to bees other than honey bees. First of all, there are heaps of different types of non-bee insects, Rader explains to IFLScience, and when you can combine all of these, it adds up to quite a bit. Second, because of the diversity of non-bees as a group, they tend to have broader activity patterns and diverse life histories to perform across a range of environmental conditions, habitats, and times.
Some of the studies examined a measure of pollination success called fruit set or seed set. That’s when young fruits and seeds start to grow rapidly after the flower ovary is fertilized. Fruit set isn’t correlated with honey bee visitation, but it increased with non-bee insects – suggesting how non-bee insects provide a unique benefit that’s not provided by bees. If non-bee pollinators supplement (rather than substitute for) bee visitation, both are required for optimal pollination services.
Furthermore, while bees rely on habitats that support their host plants and nesting sites, non-bee insects are less affected by the loss of their natural habitats. That likely makes their services more robust to anthropogenic land use changes – which is thought to be one of the main drivers of bee declines.
Hoverfly and a watermelon plant in North America. Rachael Winfree
Image in text: Wasp with a passion fruit flower in Colombia. Catalina Gutiérrez-Chacón/University of Freiburg