AgKnowledge: Number 71: Researchers Seek Balance Between Alfalfa Seed Yields and Healthy Bees

Researchers Seek Balance Between Alfalfa Seed Yields and Healthy Bees

very June and July, the Treasure Valley’s alfalfa seed growers bet their yields on the pollinating power of their alfalfa leafcutter bees. Simultaneously, seed-stripping lygus bugs—the state’s No. 1 alfalfa seed pest—begin their annual population explosions, eventually reaching up to four generations.
Kill the lygus bugs, and you’ll likely kill some of the bees. Don’t kill the lygus bugs, and you won’t get a crop. With the profit-eating lygus bug apparently developing resistance to a popular prebloom spray,

Karen Strickler, back on left, assistant Janet Lewis, seated, and technical aide Crystal Booth, back right, examine X-ray cells of a grower’s bees for signs of disease or parasites.

it has become even more critical to find ways to check lygus damage without checkmating bees.
     At the University of Idaho’s Parma Research and Extension Center, entomologists are evaluating new chemicals that would be friendlier to bees. They are also examining the lygus-reducing potential of biological control agents. In 1996 and 1997, they released tiny Braconid wasps they hope will successfully parasitize the pests.
     “We need to explore all these possibilities,” says Craig Baird, UI extension entomologist at Parma. “It’s finding the right combinations of things to make it work.”
     Combinations are the scientific focus of ecologists. While most studies of alfalfa seed production and bee mortality address individual factors, UI pollinator ecologist Karen Strickler is beginning to model the dynamic and complex system of interacting factors within alfalfa seed fields.
     According to Strickler, maximizing seed production while minimizing bee mortality will demand a precise understanding of the relationships among bloom times, bee numbers, bee release dates, temperature, humidity, soil moisture, carbohydrate reserves, and pests like lygus bugs and thrips.
     To manage alfalfa seed for bee survival, growers would put out fewer bees and keep their flowers blooming later into the season, says Strickler. But that would compromise seed yields, which benefit from early releases of generous numbers of bees.
     Those generous numbers of bees, on the other hand, produce high seed yields but pollinate flowers so rapidly that the alfalfa plants divert their energy toward maturing seed pods—starving out the bees. “We need lots and lots of bees, but the tradeoff is that a lot of them are going to die as the resources decline,” Strickler says.
     Each year, Idaho alfalfa seed growers spend about $150 an acre to manage their bees or to replace those they have lost. Through an industry-sponsored X-ray service she provides at Parma, Strickler helps growers monitor the health of their overwintering bees. The
     X rays tell Strickler how many bee-board cells are occupied by live larvae and how many other larvae have fallen victim to the bee-killing fungus chalkbrood, to predators, or to parasites.
     But the ecological secrets within alfalfa fields will take more than a diagnostic test to unlock. They will take patient and persistent ecological research.
     For more information, call (208) 885-6681.

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