Beneficial insects support agriculture, protect environments

Harnessing bees to increase soybean yields

Ever since pollen-bearing flowers evolved, roughly 140 million years ago, beneficial insects have carried pollen between plants, enabling them to produce more and helping their descendants thrive. Offspring of cross-pollinated plants are stronger and healthier than self-pollinated plants, for the same reasons you shouldn’t marry your cousin: inbreeding limits genetic diversity, which decreases productivity and makes species more susceptible to disease and pests.  

Margaret Frank, assistant professor in the School of Integrative Plant Science, Plant Biology Section, is working to develop soybeans that can benefit from cross-breeding, with the help of cutting-edge scientific tools and bumble bees. Soybeans are a massive and growing component of the U.S. food supply – they are the second most planted crop after corn and the USDA expects that land planted to soybean will increase almost 20% in the next decade. 

Soybeans self-pollinate via tiny flowers that stay closed until after pollination, making natural cross-breeding nearly impossible. With help from Ph.D. candidate Nicole Szeluga, Frank’s lab is developing strategies to force soybean to cross-pollinate, with potentially significant payoffs for commercial production: other studies that painstakingly cross-bred soybean by hand increased yields by 10-20%. 

“If you could get that boost of hybrid vigor, that could have huge benefits in terms of increasing soybean outputs,” Frank said. “That would enable us to grow more food with less land and fewer resources.”

“Yield is always a top priority, but hybridization also gives us the chance to exchange genes for many different traits,” Szeluga said. “Such as increasing oil or protein content in plants, or improving disease, pest or drought resistance.”

Thus far, Frank, Szeluga and their colleagues have successfully adapted a system that temporarily sterilizes the male pollen in soybean flowers, preventing self-pollination, and then re-invigorates male fertility through a separate plant, achieving cross-pollinated seeds. A similar system was discovered in 1990 and used to create hybrid canola plants, which now produce roughly 11% more than non-hybrid canola. 

Next steps for this research include developing soybean flowers that are more attractive to pollinators, and exploring a variety of crossings to see which produce the best hybrid vigor, Frank said. 

“There are very few trials on cross-bred soybean, because this wasn’t thought to be a viable route,” she said. “So there’s a lot of work to be done, but the potential benefit is enormous.”

Recruiting beetles to control water chestnut

Water chestnuts have become the scourge of Northeastern waterways. The invasive plants form impenetrable mats of vegetation that block swimmers and boaters and prevent sunlight and oxygen from reaching aquatic plants and animals. Public and private agencies have spent untold millions of dollars trying to control water chestnut using herbicides and mechanical removal of plants, but without natural predators, plant populations roar right back. 

Bernd Blossey, professor of natural resources and the environment, believes a tiny leaf beetle, Galerucella birmanica, may succeed where humans have failed. For 20 years Blossey, who is also principal investigator of the New York Invasive Species Research Institute, has been working on biological strategies to control water chestnut and is just beginning the lengthy process to seek federal approval to release G. birmanica in the U.S. In its native China, the brownish-gold beetle eats the plants with such gusto, its common name is simply ‘water chestnut beetle.’

To test whether G. birmanica could be safely released to control the plants without harming other beneficial species, Blossey has conducted field-based research in China and carefully quarantined lab-based research in Ithaca. He’s found that the beetles feed almost exclusively on water chestnuts. 

“G. birmanica is very, very specific in feeding on water chestnut, and in fact cannot survive without water chestnut,” Blossey said. “It will occasionally nibble upon a plant that’s native to both China and here – water shield –  but water shield is also so abundant that it’s being treated with herbicide.” 

Blossey has been successful in such efforts before: in the 1990s, he led the team that released insects as a biological control for purple loosestrife, a European native that had spread through North American wetlands. Four non-native insects – two weevils and two other Galerucella family beetles – have reduced loosestrife populations “from a nuisance to a roadside attraction,” he said.

Because there is so much public attention on truly harmful invasive species, the public can sometimes adopt the belief that any introduced species must therefore be bad, Blossey said. But in reality, of all species moved outside their natural habitats, only 10 percent can even survive in the wild, and only one percent become invasive, he said.

“We need to focus less on whether a species is native or invasive and focus more on whether we want to manage that species – wherever it may have evolved – because it has an effect on something we care about: agriculture, human health, biodiversity,” Blossey said. “Native species can become harmful if they become too dominant in an ecosystem – like white-tailed deer are in much of the Northeast  – and non-native species can be very beneficial, as I believe G. birmanica would be in controlling water chestnut.”

Replacing pesticides with beneficial bugs

Every Wednesday afternoon, about 500 Cryptolaemus montrouzieri beetles are released into the Liberty Hyde Bailey Conservatory on Ithaca’s campus. The conservatory growers’ job is to maintain and protect Cornell’s internationally recognized plant collection, and C. montrouzieri – better known as the mealybug destroyer – helps them do that. 

As the name suggests, mealybug destroyers are avid pest controllers, whose voracious appetite for mealybugs is channeled to protect vineyards, orchards and greenhouses worldwide. Mealybugs suck the sap from a host of plants, stealing nutrients, stunting growth and eventually killing plants. Adult destroyers eat some mealybugs directly, but what really gets them is the larva: the beetles lay their eggs in patches of mealybug eggs, and when the destroyers hatch, the larva eat the young mealybugs. 

The Cornell AES professional greenhouse staff have been using biocontrols – the term for actively encouraging one living thing to control another, problematic living thing – for at least 20 years. They do also use pesticides to combat other harmful species, but the biocontrols let them minimize these chemicals. The conservatory is used by students, staff and faculty, and is open to the public. If visitors see insects in the conservatory, they may well be seeing a piece of the integrated pest management approach used to maintain a balanced and healthy environment.

Scientists began intentionally introducing beneficial insects to control pest species in the 1930s, but with the invention of DDT and other pesticides in the 1940s, commercial and scientific interest in biocontrols dropped off. It wasn’t until 30 years later, when some bugs began to develop resistance to pesticides, that inquiry into natural controls reemerged. 

Over the past 20 years, commercial use of biocontrols has become far more common, said Elizabeth Lamb, coordinator for ornamental plants, greenhouses and nurseries for the New York State Integrated Pest Management Program. When she began doing this work 18 years ago, only about 10% of growers used any kind of biocontrol. Now, she estimates, more than half do, with some growers using biocontrols near-exclusively. Almost all of the Cornell AES greenhouse complexes on campus and on Long Island use some biocontrols, where their use doesn't interfere with research, she said. Beetles, nematodes and wasps are among the species being commercially bred and sold to control pests.

“There’s a little faith involved in using these bugs because you release them and you may never see them again,” Lamb said. “But if you give them a chance to work, they can do wonders for your greenhouse.”

The growing interest in beneficial insects has been driven by several factors, Lamb said, including consumer preferences for less pesticide use and decreasing effectiveness of pesticides as bugs develop resistance to them. She expects such interest to continue growing, especially in New York state, where legislation signed in December 2023 will gradually phase out use of neonicotinoid pesticides. Neonicotinoids are believed to harm honeybees and other pollinator species.

“People can sometimes be insect-averse, but beneficial insects are really very important for our food supply,” Lamb said. “In field situations, the biocontrol is going on for free and helping limit pest damage.  In greenhouse production, it’s important for us to study how to replicate that benefit, and it’s important for us to tell growers and consumers why we’re doing it. These bugs are one more tool in our toolbox.  They’ve been doing this kind of work for us for centuries, we just need to help them do it.”

Krisy Gashler is a freelance writer for the Cornell University Agricultural Experiment Station.