Good bug, bad bug
March/April 2017 California Bountiful magazine
Story by Shannon Springmeyer
Photos by Stephen Osman
and courtesy of Mark Hoddle and USDA Agricultural Research Service
The worldwide search for prized pest fighters
A lemon leaf is examined for pests and the beneficial bugs that eat them.
Mark Hoddle sees a hidden world that others often overlook.
"The most fascinating and really important stuff that's happening all around us is too small for 99 percent of people to see," he said.
Hoddle's expert eye is trained on the world of bugs, a dramatic landscape with predators and prey locked in a primal struggle for survival. Watching them in his garden was one of Hoddle's earliest enthrallments. As an entomologist and extension specialist in biological control for the University of California, Riverside, his childhood passion has become a life's work, using the insect food chain to protect gardens, farms, orchards, urban landscapes and forests from invasive insects.
Hoddle relies on the unsung heroes of the insect world: natural enemies of bugs we consider pests.
"Most people's reaction when they see an insect is they want to kill it," Hoddle said. "What they don't appreciate is that (people are) often killing things that are really helpful."
Entomologist Mark Hoddle of the University of California, Riverside, right, shows a Pakistani farmer beneficial insects collected from his orchard. Hoddle travels the world in search of the natural enemies of invasive pests.
Bugs to the rescue
Beneficial bugs come in many forms: winged and crawling beetles, tiny mites, carnivorous caterpillars and parasites that live on or in their hosts, even laying eggs inside their hosts' bodies. California is home to many native species of these beneficial, natural-born killers. But when invasive, non-native pests make their way to a new territory where there are few natural enemies that feed on them, their populations can explode, Hoddle said.
That's what happened in the 1880s, when a pest called cottony cushion scale arrived in California from Australia and began devastating citrus groves. No available control method proved successful, and growers grew desperate, Hoddle said.
"It's kind of mind-blowing to think that that one insect had the potential to derail California's citrus industry right at its inception," he said.
That's when the chief entomologist for the U.S. Department of Agriculture did something that had never been done: He sent a colleague to Australia to find the pest's natural enemy in the wild.
From left: A Tamarixia radiata wasp attacks an Asian citrus psyllid; psyllids can infect trees with a deadly plant virus, destroying entire groves; and a vedalia beetle eats cottony cushion scale.
The scientist returned with a few hundred small vedalia beetles that he'd collected and managed to keep alive during the weeks-long sea voyage. After the USDA liberated the beetles in California, the problem disappeared completely within nine months, Hoddle said.
"The citrus industry couldn't believe how spectacular this biological control program was," Hoddle said. "That beetle is still working in California today, and you don't have to spray your trees for cottony cushion scale."
It was the birth of a revolutionary new approach to pest management, and California remains a world leader in biological control. The approach is more essential than ever in an age of globalized trade and transit. The annual rate of the introduction of non-native insects into the state has accelerated by 50 percent since 1989, Hoddle said.
Hoddle spends much of his time studying invasive pests, combing the globe for their natural enemies, and rearing and studying the populations he's brought back. When a natural enemy with good potential for success is identified, tested and approved by officials for release, it often becomes the job of insectaries to figure out how to raise millions of them at a time.
Clockwise from left: Associates Insectary worker Ramiro Fraile places a tray of potatoes to sprout, beginning the process of raising beneficial mealybug destroyer beetles; Production Manager Victor Perez collects adult beetles from a light screen; and white, feathery beetle juveniles feast on mealybugs on sprouted potatoes.
Bug farming for farmers
Associates Insectary in Ventura County is the oldest commercial insectary in the nation, rearing several essential beneficial species for citrus and avocado growers. The insectary also sells to growers on the East Coast and in Canada, Mexico and Central America. Brett Chandler, president and general manager, emphasized beneficial insects alone can't solve all of a commercial grower's pest problems, but they are an important tool.
"The insects have a tremendous role," he said. "A significant portion of the pest control is performed by natural enemies in the field—both native and the extra, introduced ones that we add to the field. It is such an integral part of what we do that we don't even consider how we would function without them."
Raising 800 million head of tiny "livestock" each year is a job that never gets boring, Chandler said.
"In order to grow a beneficial insect, you have to grow something for it to eat," he explained. "You also have to grow something for that something to eat, a food for the food."
The result is a complex, highly synchronized operation in which different species of insects are raised through all life stages in 43 separate, climate-controlled rooms. The insects are sensitive to subtle changes in the environment, such as atmospheric pressure, and have a herd behavior that changes daily, Chandler said.
Link Leavens of Leavens Ranches in Ventura and Monterey counties is one of 150 member-growers who benefit from the program. For 25 years, the insectary's production of a parasite called Aphytis melinus has helped Leavens control red scale infestations and maintain the delicate ecological balance of his citrus grove.
"It's worked really, really well," he said.
Associates Insectary General Manager Brett Chandler and citrus and avocado grower Link Leavens survey Leavens' groves in Ventura County. Controlling pests is key to growing quality produce.
Waging war on a new pest
Now, Leavens has turned his attention to a challenging new foe, the invasive Asian citrus psyllid. The tiny insect can infect trees with a deadly bacterial disease called huanglongbing, or HLB. The plant disease has caused catastrophic citrus losses in Florida and Brazil in recent years. California growers fear their trees will be next.
Though psyllids have become common pests in commercial citrus groves, so far HLB has been found only in backyard citrus trees in urban areas of Southern California. To help contain the disease, growers and researchers are again turning to biological control.
Hoddle traveled for several years to Pakistan, where the Asian citrus psyllid is a native pest, searching for a suitable natural enemy. He returned with Tamarixia radiata, a tiny parasitic wasp that targets psyllids. A single female can kill hundreds of the pests in her lifetime. After testing and government approval, Tamarixia was introduced in affected areas in 2011. Psyllid populations have since dropped considerably in urban areas, in some instances by as much as 75 percent, Hoddle said.
"We've sort of set the battle lines," he said. "This is urban guerilla warfare."
For growers such as Leavens, Tamarixia offers an important line of defense and a ray of hope in a desperate fight. Leavens said he tries not to imagine a future where enjoying oranges becomes a thing of the past, but the threat to the industry is real.
"If you don't control those psyllid populations, HLB will be here," Leavens said. "We just know it's coming. We're kind of treading water."
Growers are spending $25 million through the California Citrus Pest and Disease Prevention Committee to combat HLB. Leavens, a board member, said they would like to multiply production of the wasp a hundredfold to keep urban psyllid populations at bay. And Associates Insectary has begun experimenting with raising Tamarixia as a possible tool to fight >psyllids in commercial groves.
In this case, biological control won't likely be the only solution, but it's an important start. Once again, a tiny insect may just prove one of California farmers' greatest allies.
Build a better yard with beneficial bugs
Every fruit tree, flowerbed and vegetable garden throughout California provides a natural home to beneficial insects that gobble plant-munching pests. Help them help you by following these tips from the experts.
Start with healthy plants.
"Everything is related," said Brett Chandler, general manager of Associates Insectary. "How you water, how you fertilize your plants impacts the ways that the pests attack them. Water and fertilize well, and the natural insects will help you out."
If you feed them, they will come.
Certain types of flowering plants can encourage beneficial insects to visit your garden and stay there longer, providing the nectar and pollen in their diets so they can focus on hunting the "meat." Choose plants of varying heights for both shady and sunny areas, and those with many small flowers such as aster, cosmos, alyssum, lavender and basil.
Think before you treat.
Experts say it's often possible to control lawn and garden pests with reduced use of insecticides. "The less insecticide you use, the less disruption you have, and the more you preserve the native beneficial insects," Chandler said.
Know your bugs.
"Often, people have misidentified the bug they're trying to control," said Mark Hoddle, biological control specialist at the University of California, Riverside. For example, many people want to kill spiders, which actually eat the pests. Visit the galleries to learn to recognize the good bugs from the bad.
Mind the ants.
Argentine ants often attack good bugs because the ants eat a sugary substance produced by psyllids, whiteflies, aphids, mealybugs and other pests, and don't want to lose that food source. Try ant bait stations, which deliver highly targeted control that won't harm a lot of beneficial insects. "Taking out the ants allows the natural enemies to do much more work in your gardens," Hoddle said.