Who’s Knocking?

Mike Ingles

October of last year, I was introduced to the brown marmorated stinkbug. It wasn’t a pleasant meeting. I found one in a downstairs bathroom, and deciding it didn’t belong in the house, I quickly crushed the Hemiptera between thumb and forefinger. A mistake I intend to never make again. The stinkbug comes by its name honestly. The odor is overwhelming.

Pictured: Tawny crazy ants are eating machines that swarm over territories in dense numbers with quick erratic movements, making them appear they are acting crazy. They’re fast displacing the red imported fire ant as the Southern United States’ No. 1 ant problem.

After a few hand-washes, pouring rubbing alcohol over my putrid hands and finishing with some lanolin, I was once again passable in polite company.

Both the brown and green stinkbugs feed on orchard crops, vegetables, grapes, other small fruits, row crops, ornamentals and nursery crops. Native to China and Asia, but like many invasive species threatening the homeland, they arrived in the United States quite by accident in luggage or shipping-containers and are making themselves at home. In the last several years spreading from Pennsylvania to the heartland and into my downstairs bathroom.

The stinkbug is a good example of how globalization has had some unwanted consequences. With only a few natural predators in America, such as parasitic wasps, the breeding numbers of the stinkbugs are simply too much for biological control agents (BCAs) to slow their growth. The best IPM seems to be assuring a good number of parasitic wasps are in the greenhouse, gardens and orchards, as studies at the University of Virginia reported only about 30% of stinkbugs were destroyed by pesticide use.

Crape myrtle bark scale
The crape myrtle trees are under continued stress this year from another invasive species, the crape myrtle bark scale (CMBS), which also arrived from Asia a few years ago, but has migrated from Texas to as far north as Tennessee.

Dr. Mike Merchant, professor and extension urban entomologist, Texas A&M AgriLife Extension Service says, “Heavy infestations of scale appear white, with scales covering the branches, limbs and tree bark. Perhaps the most notable feature of CMBS infestation is the black coating on the lower branches and trunks of infested trees. The black resulted from growth of a black sooty mold fungus, which feeds on honeydew deposits. The coating reduces the attractiveness of the trees.”

Female scales lay pink eggs, deposited under the scale covers. As the nymphs mature, they secrete a white thread that becomes matted over time into a thick, whitish/grayish protective covering over their bodies.

Because few natural BCAs have been found, with the exception of the twice-stabbed ladybug (ladybird beetle), Mike suggests spraying trees with water, which will dislodge some of the scale from its host.

“This ladybug beetle appears to be quite effective once it discovers CMBS colonies, but it is often too late to prevent sooty mold deposits,” he said.

Unfortunately, the twice-stabbed ladybug is not widely available for sale.

A plague of insects?
Hardly a month goes by without the discovery of some new invasive species, either making its way here or expanding its territory. February’s edition of “Entomology Today” reported a new aphid pest in the Albuquerque area that was first found in California eight years ago. It can be problematic when growers do not have an up-to-date understanding of how much territory an invasive species can cover in a season or a year or 10 years and how quickly populations might grow.

My new little friend, the marmorated stinkbug, for instance, has only been in central Ohio for the last few years, but was first discovered in Allentown, Pennsylvania in 1998—more than 15 years ago, so their migration seemed to be slow at first. But already the brown stinkbugs have been discovered as far west as Utah. Because the insects prefer warm-weather climates in which they can reproduce several times a year, it was assumed that northern states had little to fear from the infestation. But because they also can hibernate, they’ve adjusted, although they might not reproduce as fast in cold weather states.

It’s not all bad news. Of the one million insect species, only about 5% are considered pests, according to Texas A&M University. And the United States is working to better control invasive species arriving here through their heightened awareness and training of customs agents.

In December 2013, the U.S. Customs and Border Protection (CBP) intercepted an ant from Italy while inspecting a shipment of ceramic tiles in Baltimore. Now the U.S. Department of Agriculture has confirmed that the same CBP office recently made a first-in-the-nation pest discovery when they intercepted a moth, Nemapogon gersimovi. Progress.

Unfortunately, the tawny crazy ant (TCA) somehow got through the gates. These voracious eating machines swarm over territories in dense numbers with quick erratic movements, making them appear they are acting crazy. But these pests are fast displacing the red imported fire ant as the Southern United States number one ant problem and offer growers a distinct new problem.

Joe MacGown, research technician at the Mississippi Entomological Museum and Mississippi State, explains that TCAs are omnivorous, but appear to prefer sweet, sugary foods, such as the nectar produced by certain plants, wherein species of hemipterans (aphids, plant hoppers, scale insects, whiteflies, mealy bugs, etc.) reside.

“They protect the hemiptera, resulting in massive spikes in hemiptera populations,” says Joe. “And the large numbers of plant-sucking hemipterans can be devastating to plants. TCAs simply out-compete many native species, even the invasive ones, reducing biodiversity by preying on insects and small vertebrates, both on the ground and in trees.”

For growers, honeydew-producing hemipterans should be monitored and managed. Often, products containing the active ingredient imidacloprid or other systemic neonicotinoids are a good option for hemipterans. The drenching of container plants with a synthetic pyrethroid insecticide will also aid in removing the TCA before the containers are transported.

Whiteflies infecting popular flowers like poinsettias offer ideal sweet food sources for the TCA. And, because the whiteflies are somewhat resistant to pesticides, they’re difficult to eliminate entirely. A recent study at Texas A&M indicated that about 70% of whiteflies were killed when using pesticides, but because they breed so quickly the overall affect was negligible.

As growers know, Impatiens walleriana are the most popular bedding plant in the United States, ideal for containers, hanging baskets and beds. Impatiens downy mildew is a destructive foliar disease of Impatiens walleriana. While there have been sporadic reports of this disease in production greenhouses in the United States since 2004, widespread regional outbreaks of impatiens downy mildew were observed for the first time in North American landscapes in 2011. Growers are having some success with New Guinea impatiens (Impatiens hawkerii), which are highly tolerant to this downy mildew and have been successfully grown in greenhouses and landscape beds even under high disease pressure for downy mildew.

Keeping your enemies close
Entomologists track migration patterns and monitor populations of all invasive species, simultaneously looking for best practice, IPM strategies. But with such a diverse number of new species being introduced each year and many with no BCAs to help control infestations, pinpointing which insects, scales, mites, aphids or viruses that will become troublesome in any one city or state is problematic until growers report the problems.

Keeping up-to-date reference books on pests and invasive species is central to the understanding of what each grower might expect and the best practices in control. All growers are cognizant of aphids, fungus gnats, thrips, whiteflies, caterpillars, leafminers, mealybugs, mites, slugs and snails, as these pests tend to thrive in damp, warm, controlled areas; their harmful effects on plant life well-known. Too often pesticides and insecticides are quickly administered, often killing beneficial species of predators, pollinators and recyclers and, oftentimes, doing more overall harm than good.

In addition, as these well-known pests and new species evolve to adapt to life in the states, many develop resistance to certain insecticide agents. Clemson University reported in 1996, “There are over 1,000 insect/insecticide resistance combinations and at least 17 species of insects that are resistant to all major classes of insecticides.”

As part of an overall IPM strategy, many entomologists suggest spraying plants with a strong stream of water (including the underside of leafs) and, when possible, introducing BCAs—such as parasitic wasps, spider mites, ladybugs and green lacewings—into the growing areas.

But sometimes, natural remedies aren’t enough, and although sanctioned types of greenhouse pesticides are limited, they’re the best solution. Greenhouse operators need to maximize the effectiveness of insecticides and miticides, and these agents must be applied at the proper rate and when the pests are present. Measured coverage and sufficient pressure are needed to penetrate dense foliage and reach the target pests. This is especially important for sucking insects that infest the lower surfaces of leaves. GT

Mike Ingles lives in central Ohio where he writes about green initiatives, innovation and trends in the gardening industry. Story ideas are always welcomed at duckrun22@gmail.com.