New Insight on Pollinators May Aid Strawberry Production

May 22, 2002

TROY, Ohio - A steady rainfall soaks strawberry fields in this town just outside of Dayton, but the weather doesn't deter Ohio State University entomologists from trekking through standing water and mud to record the growth progression of strawberry blooms - food for many insects whose pollination transforms the flowers into fruit.

"The blooms have to be open wide enough for the insects to get in and pollinate," said Ohio State research assistant Diane Hartzler, pointing to blooms that were either partially or fully open. "If the blooms don't get pollinated, the result is irregular fruit, or no fruit at all." Though no pollinators were to be seen on this wet day, such observations are giving university researchers a better handle as to how insects, namely native feral or wild bees, affect strawberry fruit set, development and yield.

"People used to think that honey bees were the main pollinators of strawberry plants. They pollinate brambles like raspberries and blackberries," said Roger Williams, Ohio State leader of small fruit entomology with the Ohio Agricultural Research and Development Center in Wooster, Ohio. "Though other insects like ants and beetles help pollinate strawberries, we have found that the primary pollinators are native bees." Williams said the startling conclusion came after three years of identifying bee species that were visiting strawberry fields in Wooster and Moreland, Ohio. The researchers recorded 19 different species, all of which were native except the honey bee. Bee species included carpenter bees, leaf cutting bees, orchid bees, bumble bees, digger bees, cuckoo bees and small, metallic bees of the family Halictidae.

"We didn't know what to expect as not much literature exists that describes strawberry pollinators," said Williams.

Williams and his associates have expanded their research to other areas of the state in the hopes of compiling a comprehensive guide of bee pollinators. The goal of their work is to more clearly define which species pollinate strawberry plants, how field placement affects pollination and ultimately establish a new market of beekeeping in Ohio.

"More and more growers want to get their crop off earlier in the season. If we can identify which bee species pollinate fields in certain areas, then we may be able to create a new opportunity for beekeepers to provide those species to the grower," said Williams.

The honey bee, European in origin, clearly dominates the beekeeping industry in Ohio. Over 5,000 apiaries, or places where colonies are kept, exist in every county in the state. Honey bees are essential to Ohio's vegetable production, as the insects account for 80 percent of all crop pollination.

Though honey bees do pollinate strawberry plants, Williams said it's clear that native bees are the main pollinators, a discovery that could give both strawberry production and beekeeping a boost.

"One reason why we want to look into identifying and possibly marketing native bees is because of the recent problems honey bees have with mites and diseases," said Williams. "Also if the strawberry plant doesn't get pollinated, it affects fruit size, fruit quality and overall market value." Williams said that where strawberry fields are located in the landscape might also have an impact on how often the plants are pollinated. In their studies, the researchers found that strawberry fields located near native habitats, like woods, swamps, ponds and prairies, had higher berry development and less deformed berries, than those strawberry fields found in and around residential areas.

Author(s): 
Candace Pollock
Source(s): 
Roger Williams