Blueberry plants depend on insects for their pollination. The U.S. produces more than 700 million pounds of highbush blueberries per year, so blueberry pollination is important economically as well as ecologically. Because blueberry flowers are bell shaped, with their interior recessed in a tube of petals, effective release of pollen from the flowers depends on an insect behavior of rapidly vibrating wing muscles, called buzz pollination. Honey bees (Apis mellifera) do not perform buzz pollination, and thus are thought to be inefficient as blueberry pollinators. Despite this, all large blueberry farms of five or more acres rent honey bee hives, and the honey bees successfully aid in crop pollination.
To determine the mechanisms with which honey bees achieve successful blueberry pollination, George Hoffman, Ph.D., of Oregon State University and colleagues studied how pollen gets picked up by honey bees on blueberry flowers and how pollen is transferred back to blueberry flowers to achieve pollination. Their findings were published in a new report in November in Environmental Entomology.
In their study, Hoffman and colleagues collected honey bees from 11 Oregon blueberry farms and quantified the amount of pollen found on four main body parts: head, thorax and abdomen, upper legs, and tarsi. They also made 327 observations of honey bees foraging on blueberry flower clusters, noting how many times each bee probed the corolla of a flower, grabbed a stigma with the tip of a tarsus (a tarsal claw), brushed a stigma with a tarsus or leg, or probed deep enough into a flower with a tarsus to touch an anther of a flower.
It was observed that a lot of transfer of pollen happened when body parts holding pollen touched the stigmas of flowers during non-foraging behaviors, such as grooming and walking across clusters of flowers. Interestingly, pollen transfer often happened when a bee stabilized its body by grabbing the stigma with a leg, and they often resulted in touching the stigma in a flower adjacent to the flower from which nectar was being gathered.
Hoffman and colleagues discovered that although the access honey bees have to blueberry flowers are constrained by the bell shape of the corollas, when widening the frame of reference to look at the full range of honey bee behaviors, it is clear how adequate pollination can be achieved. This is a powerful finding for our understanding of highbush blueberry pollination dynamics and also for understanding the process of designing effective scientific tests.
Read more about this study at Entomology Today.