Back without much demand: Here comes the annual demonstration of the Japanese beetle, the embodiment of beauty and beast in one. The four to six week period of intense activity of the shimmering, copper-colored adult Popillia japonica has begun.
These bugs seem to be specifically suitable for your roses, raspberries, crab apples, or grapes, but these are just a few of the over 300 species of plants they feed on in North America.
The expert advice may sound contradicting itself: stop capturing them. (Farewell, beetle bags, despite the marketing promises.) And maybe hold back on watering the lawn in the July heat, because female beetles are looking for a moist place to lay eggs.
Yes, these are steps to make peace with this lingering invasive pest that scientists have been trying to suppress since shortly after it was identified in New Jersey in 1916.
Almost a century later, a 2015 U.S.D.A. The Japanese Beetle Management Homeowner's Guide puts the cost of inspection in the United States – including the removal and replacement of damaged lawn – at $ 460 million a year. Half of this damage is not caused by the adults, but by the larvae during the larval phase of the beetles.
Nevertheless, this is a troublemaker in both phases of life – and his wide-ranging diet does not harm his chances either.
Based on decades of tracking the seemingly unstoppable march of the beetles westward in North America, Daniel A. Potter, professor in the Department of Entomology at the University of Kentucky, described the arc: “The first few decades in a new area, the insect goes insane and builds up to a high level before the population begins to stabilize. Then it turns from a plague to a plague. "
For those of us in the harassment phase, here are some suggestions. But first, some background on the strategies behind the ongoing Japanese beetle invasion.
These bugs really do get around
Although the adult Japanese beetle has a life expectancy of only 30 to 45 days, it is "a highly mobile insect," said Dr. Potter, and that's one of his strategic advantages.
The ability to flee in this short, winged life allows the beetles to infest areas several kilometers away. And human movements have made long-distance travel possible: the Beetle hitchhikes and initiates control measures that include the regulation of some airports, with strict inspection of the aircraft. The larvae can be transported in the soil around the plant roots, and quarantines are currently in place to move nursery stocks from 28 eastern states and the District of Columbia to nine western states.
From their northeastern start, the beetles have managed to establish populations across the Midwest and are making strides in Nebraska and neighboring states and even into Colorado, said Dr. Potter, who described it as "not new to the Great Plains, but on the move."
A worrying detail: the beetles eat milkweed flowers (Asclepias), bite into their nectaries and empty them. The plants then fail to seed – another potential threat to the shrinking milkweed populations, which in turn threatens the monarch butterfly.
And the beetles march on. The Sacramento area is now trying to eradicate them before they establish themselves, as are places in the Pacific Northwest, including Portland, Oregon, and British Columbia.
Europe is also under pressure. This latest fight will be particularly challenging, said Dr. Potter, as is the case in the United States for organic grape or blackberry growers. Europe doesn't have a chemical lawn care industry like us, and chemical pesticides are often the first choice here to control maggot infestation. Overall, the European restrictions on synthetic insecticides are much stricter.
"It's a big deal – imagine what it would do in French vineyards," said Dr. Potter. "You can't squirt your way out of this problem."
They also like orgies
Ninety percent of insect species are specialists and focus their diet on no more than two or three plant families, said Dr. Potter. Not this one.
The Japanese Beetle is not just a generalist, but “an extreme one,” he said. “Even gypsy moths don't feed on as many plants as the Japanese beetle. It's probably the champion insect in North America – remarkable for a non-native. "
A Japanese beetle's gut contains very powerful enzymes that allow it to tolerate a wide variety of chemicals in plants, and those enzymes are revved up by an extra step – a starter, you might say: the beetles take a test bite that their stomach enzymes increased.
And they prefer not to dine alone. You will rarely see a single beetle feeding on a plant. Instead, they aggregate.
Dr. Potter's research from the 1990s showed what attracts additional beetles once feeding begins: They are attracted to the volatile compounds released by damaged foliage, he said, "like sharks to a trail of blood."
Tissue between the leaf veins is chewed out and the foliage is skeletonized. Flowers are just as attractive targets as overripe fruits such as blackberries – "a sugary beetle energy drink," said Dr. Potter.
It's also about sex, which he described as "many orgies of beetles on the plants". Between meals, the females fly away and dig into the ground several inches to lay five or six eggs at a time. After a day or more, they return to feeding and mating, a process they will repeat perhaps a dozen times in their lifetime.
In her short adulthood, a female can lay 40 to 60 eggs. These eggs quickly become inch-long larvae that live underground until they pupate the following spring and emerge as adults in summer.
So what's wrong with bug traps?
With two scented baits – one intensely floral and one synthetic pheromone to attract males – beetle bags do a great job. But they work too well in most settings, attracting far more bugs than they catch, from neighboring yards and beyond.
"We usually see more damage when traps are used," said Dr. Potter, a finding that came from research as early as the 1980s.
However, traps are effective tools for monitoring and monitoring in places where the beetles are not yet established – for example at airports and in rearing areas in northern Italy, Germany and Switzerland.
A non-toxic approach that works in the garden is a proven U.S.D.A. Recommendation: drown them.
In the cool of the morning, go out and pound the lazy bugs into a container of soapy water.
"Our research shows that they can't really fly below 70 degrees Fahrenheit," said Dr. Potter, results revealed by such heroic tactics as graduate students tickling the beetles with a long camel hairbrush at 3 a.m.
Shaking beetles off plants in the morning and evening will reduce food intake, which will decrease the volatile odors produced and in turn limit the ongoing attacks.
While this strategy isn't practical on sassafras or linden trees (or certain other favorite beetles), or in a vineyard, it can minimize damage to some valuable plants.
Can You Fight Grubs Without Chemicals?
Gardeners looking for non-chemical treatments for maggot-damaged lawns may have tried milky spore powder, a biological control agent that contains a living bacterium. However, modern university research has made no use of treating individual lawns.
Nematodes – tiny roundworms, especially the recommended species, Heterorhabditis bacteriophora – are another biological tool and more potent. These living organisms must be ordered in the mail (from companies like Arbico Organics) and sprayed on a lawn in a water solution. Application rates can be difficult to calibrate, and nematodes are very sensitive to heat and sunlight and require application in the early morning or near dusk. In addition, the lawn must be watered before and after application.
But here's some disappointing news: There's little evidence that controlling the maggot population will reduce damage to your roses or raspberries – or vice versa. Adult beetles can fly from afar in search of preferred food or lawns that are sufficiently moist to lay eggs (around 11 percent soil moisture is required for the eggs to survive and hatch).
Gardeners can make the lawn more resilient to the effects of root chewing by the maggots by increasing the cutting height of the mower. "It helps the lawn grow deeper roots so the lawn can tolerate more maggots before you see damage," said Dr. Potter.
For the cool season, fertilize the grasses in the fall, not the spring, for a more resilient lawn in the northeast.
And again: don't water too much in July. Let the lawn or something nearby rest; In dry summers, beetles avoid laying eggs on non-irrigated lawns. "If you're the only lawn on the block that's being watered, the beetles will fly to your property and lay eggs," said Dr. Potter.
There can be four to six times as many eggs in irrigated lawns, he said, explaining why drought causes great damage to irrigated golf course lawn if it is not treated with insecticides.
Beyond that, what makes a boom or bust year of the population? There's no evidence that a cold winter kills the beetles – and in general, there's not much concrete evidence of why their numbers fluctuate overall.
"Even after 40 years of studying Japanese beetles, I can't predict a bad or a good year," said Dr. Potter. "There are still too many things about them that we don't understand."
Margaret Roach is the creator of the website and podcast A Way to Garden and the book of the same name.
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