by Bruce Wenning
It is important for ecological landscaping professionals to know the differences between various insect pests and non-pests. Most can recognize common insects such as bees, wasps, butterflies, dragonflies, ants, scale insects, aphids, and perhaps a few others. Everyone knows what spiders look like and understand that spiders are beneficial garden arthropods. Correctly identifying beetles can be more difficult.
Most people in our industry can recognize beetles, at least most of the time; however, there are a few insects in the orders Hemiptera (the true bugs with piercing and sucking mouthparts) and Homoptera (aphids, scales, whiteflies, cicadas, psyllids, and hoppers) that, in some respects, mimic some beetles. Some hemipterans that mimic or are confused with beetles are the black bug, Corimelaena pulicaria, (Figure 1); the fourlined plant bug, Poecilocapsus lineatus, (Figure 2); and even the very common boxelder bug, Leptocoris trivittatus, to name a few.
Likewise, some homopterans that mimic beetles and confuse some novices are cicadas (Cicadidae) in the nymph stage, some scale species because of their hardened exterior, and leafhoppers, particularly the redbanded leafhopper, Graphocephala coccinea (Figure 3).
Some confusion can be resolved by checking a pocket field guide to the insects. This is a helpful addition to your tree and garden insect management toolbox. I personally recommend the Petersen Field Guide to the Insects (#19) as a quick source to insect identification.
Weevils Are Beetles Too!
Did you know that all true beetles including the weevils (snout beetles) are in the insect order Coleoptera? Insects in this order undergo complete metamorphosis, which means that they have four stages in their life cycle: egg, larva, pupa, adult. One distinguishing morphological feature of beetles is their wings. The forewings (elytra) are hardened, thick and function as protective covers for the hind wings which are membranous. Hind wings are used for flying, though a few beetles do not fly. One familiar example of a beetle that cannot fly is the black vine weevil Otiorhynchus sulcatus (Figure 4), a European native that makes the characteristic feeding notches on the edges of rhododendron leaves while feeding at night.
Beetle Abundance and Diversity
The beetles are an enormous taxonomic group within the Class Insecta. The order Coleoptera is the largest of all the insect orders, and almost all animal species on earth are beetles. Beetles comprise approximately 40% of all insect species (Borror, Triplehorn and Johnson, 1989). Have you ever studied or read about the life cycles of different beetles? Soil-dwelling beetles have different life cycle strategies than tree borers and both of these are far different from aquatic beetles of stream and pond.
And just like all other insects, the beetles are an evolutionary success because of their diversity in size, shape, behavior, feeding habits, and life cycle stages making them ideal for exploiting suitable substrates and changing environmental conditions.
What strongly piques our interest as green industry professionals is the insect group or individuals that are threatening enough to cause aesthetic and/or economic damage to plants. In other words, the ones that are classified as plant pests or potential plant pests needing control. This is what we are currently experiencing with the recent infestations of the exotic invasive Asian Longhorn Beetle (Figure 5) and the Emerald Ash Borer (Figure 6).
I. The Tree Pests Called Bark Beetles and Wood Borers
On average, the native bark beetle (Scolytidae) and the phloem wood borer (Buprestidae and Cerambycidae) families cause more economic damage to non-urban forest trees in the United States than all other plant feeding insects combined(Coulson and Witter, 1984). In commercial forest management, it is specifically the scolytid or bark beetle species that cause the greatest economic damage to economically important tree species in the U.S. They exhibit their own host tree dynamics; some kill living trees and others infest weakened and dead trees (Coulson and Witter, 1984).
The native buprestid and cerambycid larvae of concern to arborists feed primarily on the phloem or inner bark of their hosts and rarely are they the direct cause of tree death. Most of the time they are attracted to trees already weakened by other factors such as low temperature injury, prolonged drought or flooding, prolonged unseasonably warm temperatures, root disease, and/or other problems. Incidentally, it is when growing larvae feed on the highly nutritious green colored inner bark (phloem) that they also chew into the xylem, creating the characteristic wood surface galleries commonly seen under the bark of dead trees. For more information about these wood attacking beetle families check the following websites:
(1) www.barkbeetles.org shows various species of bark beetles (Scolytidae) and their galleries. The Scolytidae comprise over 500 North American species, and the family is divided into two groups that feed on trees: the wood boring ambrosia beetles and the bark beetles that feed on the inner bark (phloem) of many trees (Coulson and Witter, 1984).
(2) Many metallic wood boring beetles (Buprestidae) are depicted online.
(3) bugguide.net/node/view/171 shows various roundheaded borers (Cerambycidae).
II. Native Buprestidae and Cerambycidae Encountered in Arboriculture
There has been renewed interest in wood-boring insects in recent years primarily due to the onslaught of tree attack by the Asian longhorn beetle (Cerambycidae), Anoplophora glabripennis an exotic invasive insect from Asia that can attack healthy trees! Cerambycids are called roundheaded phloem borers because the newly emerging adult beetles exit from round emergence holes they create by chewing as they emerge to the outside of their host tree, whereas the buprestids chew and emerge from oval or D-shaped emergence holes. Adult cerambycids are called longhorn beetles by some and roundheaded borers by others. Both common names are accepted. Likewise, buprestid beetles are called metallic wood borers by some and flatheaded borers by others. Both families contain many genera and species that infest deciduous and coniferous hosts nationwide (Coulson and Witter, 1984).
Many arborists have pruned or felled weakened and dead trees riddled with certain buprestid larval damage without giving much attention to the insect borer involved. After all, the buprestid larval galleries were most likely not the direct cause of tree death.
The majority of buprestid larvae bore into trees and shrubs and feed on the phloem and the surface of the outer sapwood (xylem) of trunks, stems, branches, and roots. Some infest wooden building materials (Johnson and Lyon, 1991).
A brief introduction to common native buprestid and cerambycid insects will clarify how common they are in the urban landscape. The following descriptions may help the arborist to identify insect activity as one of the multiple causes contributing to host tree death. Check for adult emergence holes and larval feeding galleries and match these characteristics to the tree species in question.
(Johnson and Lyon, 1991; Cranshaw, 2004)
The bronze birch borer, Agrilus anxius (Figure 7) is a native to North America and a pest of paper birch Betula papyrifera, yellow birch B. alleghaniensis, European weeping birch B. pendula, black birch B. lenta, and gray birch B. populifolia. It has been observed that the bronze birch borer, attacks black, yellow, and paper birches in various stages of decline. Dirr (1998) reports that river birch B. nigra is resistant to the bronze birch borer. Although this pest can attack healthy birches, it does so with little success, because the healthy trees respond immediately by forming callous tissue. First instar larvae find it very difficult to bore the callous tissue and eventually succumb to the successful callous formation of the tree (Coulson and Witter, 1984). Keep in mind, however, that this host reaction does not prevent damage to our native ash trees (Fraxinus spp.) when they are attacked by the exotic invasive emerald ash borer.
Healthy ash trees that are attacked by the emerald ash borer (Buprestidae: Agrilus planipennis) probably produce various kinds of host defense chemicals that slow down larval feeding and development, but it appears not to stop it. McCullough, Schneeberger, and Katovich (2010) state that healthy ash trees have a resistance affect on developing young larvae of emerald ash borer because the standard life cycle of one year (egg, larva, pupa, adult) takes two years to complete in healthy ash trees, but only one year in stressed trees.
As the healthy ash trees weaken over time from larval feeding, the insect’s life cycle reverts to the standard one-year time frame because the feeding larvae have less host resistance as the tree declines in vigor. This type of feeding behavior illustrates just how effective some exotic invasive insects are at adapting to their new host plants in an ecosystem that is foreign or non-native to them. A strategy not available to our native bronze birch borer.
- The flatheaded apple tree borer Chrysobothris femorata (Figure 8) is a native pest and attacks willow Salix spp., rose Rosa spp., cotoneaster Cotoneaster spp., sycamore Platanus occidentalis, tuliptree Liriodendron tulipifera, oak Quercus spp., hickory Carya spp., and maple Acer spp.
- The twolined chestnut borer A. bilineatus (Figure 9) is a pest of American chestnut Castanea dentata and oaks.
(Johnson and Lyon, 1991; Cranshaw, 2004)
The locust borer Megacyllene robiniae (Figure 10) prefers young black locust Robinia pseudo – acacia trees over mature ones. Adults emerge from host in late summer and early fall. Black locust is not native to New England, but is planted as an ornamental.
- The painted hickory borer M. caryae (Figure 11) is known to attack hickory Carya spp., butternut Juglans cinerea, oak, black walnut J. nigra, hackberry Celtis spp., black locust, honey locust Gleditsia triacanthos, mulberry Morus spp., and ash Fraxinus spp.
The locust borer and painted hickory borer adults look very similar with their black and yellow markings and are frequently confused with one another by novice collectors.
III. Emerald Ash Borer mistaken identity: quick and colorful doesn’t make it a borer!
Adult buprestid beetles are very attractive due to their brightly colored metallic or iridescent green, blue, copper-bronze, or black body parts. Their most notable feature is metallic colored elytra or wing covers. Adults range from 3mm to 100mm in length (Borror et al, 1989).
Many buprestid adults can move swiftly, running over branches, tree trunks and other objects or flying off quickly as a defense response to oncoming predators, including humans that are trying to catch them.
Before we get into the emerald ash borer, let’s get some common identification mistakes out of the way. Most are mostly committed by novices. There is a green metallic colored tiger beetle, Cicindela sexguttata (Cicindelidae) that also exhibits quick movements scurrying about over the ground and can be confused for the emerald ash borer by novices. Both of these beetles spend time basking themselves in sunny exposures, which may also confuse some people. Unlike buprestid beetles, however, the cicindelids or tiger beetles are very quick-moving ground predators and do not colonize woody plants to feed and mate. If you can catch a tiger beetle, consider yourself a lucky, stealthy, and dedicated naturalist! Most tiger beetle adults range in length from 10 to 20 mm and are in the genus Cicindela (Figure 12) (Borror et al, 1989).
Some ground beetles (Carabidae) in the genus Calosoma are brightly colored with an iridescent hue, a characteristic that also may confuse novices (Figure 13). They are commonly seen around trees and shrubs preying on caterpillars. One in particular, C. sycophanta, is from Europe and was introduced to control the gypsy moth outbreaks decades ago (Borror et al, 1989). It is an iridescent green color with a blue pronotum and at one time was known as the “gypsy moth killer. Study pictures of the adult emerald ash borer and remember that it can fit on the surface of a penny.
Confusing a tiger beetle or a ground beetle with an emerald ash borer should not discourage anyone. Most people working in the green industry have limited instruction in entomology and get to know about insects by learning about pests of plants. Many garden designers also have limited knowledge about insects. Although you can’t know everything, do know when to find someone who can help you. That is what being a professional is all about. If you are unsure of an insect and/or plant damage caused by an insect or a disease, get it diagnosed by a knowledgeable colleague, arborist, or your local extension service.
IV. Our Newest Threat: The Emerald Ash Borer (Coleoptera:Buprestidae)
The newest beetle threat in New England, causing great economic and ecological damage specific to ash trees, is the emerald ash borer, Agrilus planipennis. The emerald ash borer is an exotic invasive insect originally from Asia and is in the family, Buprestidae. As previously mentioned, the buprestids are commonly referred to as metallic wood-borers or flatheaded phloem borers.
Many native adult buprestids are attracted to dead, weakened, or recently stressed trees. Some infest cut branches and logs piled on the ground (slash) after logging operations (Coulson and Witter, 1984). Most host trees that are colonized are in a stressed condition. Although tree and shrub hosts with good vigor are not immune to attack, most native buprestids prefer low vigor or stressed specimens. To repeat, when the emerald ash borer attacks healthy ash trees it undergoes a two-year life cycle instead of its typical one-year life cycle. Thus a tree might still look reasonably healthy the first year of an infestation, but undiagnosed the infestation will most likely kill a tree the second year.
The Emerald Ash Borer (EAB): General Description and Hosts
Adults: The adult insect can fit on the surface of a penny (Figure 14). Body width is narrow, and body length ranges between 7.5 to 13.5 mm; males are smaller than females (McCullough, et al, 2010). For comparison, a penny is 20 mm in diameter.
Larvae: Larvae, after hatching from eggs laid in bark, pass through four growth stages called instars before they pupate. Larvae are white to cream colored with an enlarged thorax region of a light brown color. The enlarged, dorso-ventrally flattened head and thorax gives the family its common name, flatheaded borers. The body is also dorso-ventrally flattened and not round in cross section like the cerambycid, round headed borers.
The larvae have 10 segments with serrated edges. Since the larvae lack functional back legs, the serrated edges help the larvae produce a feeding-gallery motion (Figure 15). The mouthparts are chewing, and the last abdominal segment has a brownish colored pair of appendages called a pincer. (Lawrence, 1991; Wang, Yang, Gould, Zang, and Lui, 2010). Larval lengths vary depending on instar stage. Full grown larvae range from 13 to 22 mm in length and 3 to 4 mm in width (Wang, et al, 2010).
Life Cycle: The larval or immature stage is the longest living stage of the beetle. Its feeding behavior, consuming mostly phloem tissue, results in eventual death of the host tree. The following description of the EAB life cycle is based on information provided in McCullough et al (2010) and Wang et al (2010).
The EAB’s life cycle takes one year to complete on stressed hosts. The EAB, like all beetles, has complete metamorphosis: egg, larva (four instars), pupa and adult.
From May to early June adults emerge from the pupal chamber, located under tree bark. Both male and female adults live approximately 21 days. Adults begin leaf feeding more regularly between mid-June to mid-August. This is dependent upon time of emergence, host tree size and condition, location and local climatic conditions. Males and females mate and egg fertilization occurs. After mating, females resume feeding on ash leaves and have been noticed to feed longer than males. This instinct driven extra feeding duration can range between 7 and 14 days and helps ensure that the female’s fertilized eggs reach embryonic maturation for greater hatching viability. If fertilized eggs are not viable during egg laying (deposition), first instar larvae hatch will be low. Consequently, a female’s extra feeding time, compared to the male, is very important and necessary for eggs to be viable and to hatch successfully.
Females generally lay between 30 and 60 eggs at a time and close observations have revealed that they can lay close to 200 eggs in total and possibly more during their short adult life stage. Some, but not all females, have the capacity to mate more than once.
Eggs are deposited by females in the bark cracks, folds, and crevices of host trees and hatch in 7 to 10 days. The first instar (growth stage) larvae chew their way out of the egg and down into the phloem. As the larvae feed and grow through their instars, their feeding galleries get wider and slightly deeper, etching into the xylem creating the characteristic serpentine shaped gallery one sees in the sapwood under the bark.
Pertinent Information about Host Trees
Ash trees [Oleaceae: Fraxinus spp.] and white fringetree [Oleaceae: Chionanthus virginicus] are hosts of the EAB. There are 16 species of ash that are native to the United States (Wright, 1957), though white ash F. americana, green ash F. pennsylvanica, black ash F. nigra. and blue ash F. quadrangulata are the major representatives in natural areas as well as in suburban and rural landscapes.
Distribution ranges and shade tolerance ratings of economically important ash species
White, black and green ash grow in the Midwest, the Southeast, and northeastern portions of the U.S., and all of their individual ranges overlap to some extent. Green and white ash naturally range more southerly in the U.S. giving the EAB a huge potential for expansion into the southern states.
White ash attains the greatest size as compared to the other two ashes, but it’s not the most widespread. This species thrives on moist, well drained soils and can tolerate periodic flooding. Droughty soils and permanently flooded soils are limiting to germination, growth, and establishment (Wright, 1959).
Black ash grows in poorly drained soils in bogs and woodlands and is common along stream banks and areas of periodic flooding (Wright, 1957).
The natural range of blue ash covers Ohio and the upper Mississippi River Valleys (Harlow and Harrar, 1969).
Green ash and blue ash have a shade tolerance rating of intermediate or mid-tolerant. In other words, they can tolerate partial shade (not full shade). White ash and Black ash are shade intolerant (i.e. cannot tolerate full shade). Once these ash trees are overtaken by shade-casting associates, they become more stressed and more prone to EAB attack.
Ash breeding systems
White, green and black ash trees are dioecious (male and female flowers are on separate trees) and therefore, are wind-pollinated (Symonds, 1958).
Blue ash has a monoecious condition, producing male and female reproductive flower parts in the same flower (i.e. perfect flowers) on the same tree (Symonds,1958) and is insect pollinated! The presence of pollinators raises a caution flag to applicators who want to 1) protect pollinators, 2) rely on systemic and cover spray insecticides, 3) encounter an EAB infestation on blue ash, and 4) must make a pollinator friendly control decision. Don’t use insecticides on blue ash during its flowering time!
Ash trees flower in May and are known to hybridize among themselves, making species identification occasionally difficult (Symonds,1958).
Blue ash grows naturally in the mid-western and some southern states, but it is used in eastern Massachusetts (and elsewhere) as an ornamental. Be prepared to properly identify your ash trees before you consider the proper chemical insecticide, because you may encounter that lone ornamental blue ash tree that a client wants to save. I have encountered both blue ash and green ash trees planted as ornamentals in my travels in eastern Massachusetts and on the Mass Audubon site in Belmont, after 15 years working there. Some neighbors of the Belmont site also had both blue and green ash growing as ornamentals on their properties. Emerald ash borer researchers proclaim that blue ash is the least susceptible of all the ash species to EAB attack. Least susceptible does not mean immune.
A note of caution: Green ash and black ash are natural inhabitants of various wetland environments (Thunhorst, 1993) and one must consider the proper insecticide or non-insecticide controls to use near and in wetlands where these species are more prevalent.
Trunk injections are considered appropriate to use on ash trees growing on wet soils, whereas soil drenches are determined not legally appropriate (Herms, McCullough, Smitley, Clifford, and Cranshaw, 2014).
V. Host Damage Symptoms: What to look for on your ash trees
When an ash tree is first infested it is very difficult to see any tell-tale signs. Once the eggs hatch, the first instar larvae bore through the bark down into the green colored inner bark (phloem) where they remain for several months feeding and growing.
Woodpecker damage is the first most obvious sign of infestation. Woodpeckers search, peck, and ingest late instar larvae (McCullough et al, 2010). By the time you see the characteristic woodpecker damage called “blonding” (Figure 16), due to the lighter color of exposed sapwood, you may see D-shaped emergence holes a short time later.
Bark cracking or splitting occurs over larval galleries. The bark dries out and cracks enough to be visually noticeable, and if you remove the loose bark you can easily see the larval galleries.
Epicormic sprouting (figure 17) of new shoots from trunks and roots is an additional external sign of tree decline due to heavy larval feeding (Wang et al, 2010; McCullough et al, 2010).
Blonding, adult emergence holes, bark splitting, and epicormic sprouting are the visible external signs of EAB infestation (McCullough et al, 2010). The S-shaped larval feeding galleries etched into sapwood kill the tree. Eventually the feeding galleries frequently cross each other indicating a growing infestation. When this situation occurs, trees can die in two to three years (Wang et al, 2010).
When larval infestations are large, branch, leaf, and limb die-back occurs, and many trees can lose up to 50% of their canopies within a few years (McCullough et al, 2010).
VI. Emerald Ash Borer Chemical and Biological Control Options
There are a number of treatments available to combat emerald ash borer. Treatments are either internal, taken up into the tree through the soil or by injection, or external, applied to the outside surfaces of the tree.
Internal Tree Protection
Internal protection of ash trees involves the application of appropriate insecticides to the mineral soil surrounding the host tree or injection of insecticide into the trunk. Both methods give protection by being translocated up through the roots or trunk to the leaves. This kind of internal tree protection utilizing the tree’s vascular system kills the phloem-feeding EAB larvae. The applicator must read and follow all insecticide label instructions for proper timing, rates of application and environmental precautions (Herms et al, 2014).
Soil Applied Systemic Insecticides
These various soil formulations are applied as liquid drenches to the top of the soil, liquid injections into the root zone, or solid granular products applied to the soil surface (Herms et al, 2014).
There are several brand names of imidacloprid and dinotefuran compounds that licensed pesticide applicators and homeowners can use. These soil formulations are taken up by ash tree roots and translocated up into the tree leaves for complete EAB control.
Uptake through the soil is faster using dinotefuran products than imidacloprid products because dinotefuran is a more soluble compound and does not bind tightly to soil organic matter (Herms et al, 2014). Imidacloprid is less soluble (i.e. more stable), and therefore works more slowly than dinotefuran because it binds tightly to soil organic matter and soil surface organic debris (Herms et al, 2014). It is strongly advised that you rake away leaves, sticks, and other organic debris from the base of your ash trees in order to expose mineral soil before you apply either of these products.
Additionally, moist, well-drained soils offer the best conditions for maximum control using these products. Dry soil should be watered and allowed to drain before application. Soils that are high in silt and clay, subjected to periodic flooding, or showing signs of poor drainage will limit root uptake of these insecticides. Such conditions will also contribute to insecticide dilution and simultaneously pose a higher risk of environmental contamination to surface water flows and below ground water movements (Herms et al, 2014). Do not use soil applied products in consistently wet soil environments!
Avoid using soil drench products on poorly drained soils. Remember that green ash and black ash are tolerant of wet soils and are naturally found along stream banks and ponds (Harlow and Harrar, 1969).
Only licensed pesticide applicators can legally purchase and use soil drench and soil injection products of professional grade formulations. Homeowners who have had EAB confirmed (See Caution below.) may treat trees using soil drench and granular formulations of a lower rate that also work for EAB control; however, use of these products is restricted to only one application per year (Herms et al, 2014). Homeowner products do not require a pesticide license and the accompanying insurance to purchase and apply. Read and follow label directions.
Caution: Before any appropriate EAB specific insecticides are applied, homeowners first must have government EAB experts diagnose their infested ash trees. There is no charge for this service! Only after a professional diagnosis is made can the proper, site-appropriate EAB control measures be granted or suggested. The homeowner may be able to treat his or her ash trees with granular or soil drench products (not soil injection) or the situation presented may be more complex and require the involvement of a licensed pesticide applicator working for a professional arborist company.
Trunk Applied Systemic Insecticides
Trunk injections using imidacloprid, azadirachtin, and emamectin benzoate compounds are recommended for use after ash trees have leafed out, but before EAB eggs have hatched – between mid-May and mid-June (Herms et al, 2014). There are different insecticide formulations that can be injected into the sapwood (xylem) and taken up by the tree more quickly than formulations used exclusively for soil injection and soil drenching techniques.
Depending on local climatic conditions, soil drainage and tree size, most trunk injected products will translocate from the points of injection to the top of the tree within two to four weeks (Herms et al, 2014).
Insecticide spray for bark penetration
Dinotefuran has been formulated to be applied directly to the bark surface at lower trunk height. The insecticide penetrates the bark and enters the sapwood or vascular system and by way of transpirational pull, travels up into the tree tops to the leaves for control (Herms et al, 2014).
External Tree Protection
Insecticides applied to the outside of the tree (bark, branch, and leaf surfaces only) are called protective cover sprays. Protective cover sprays are not used as frequently as internal tree protection insecticides.
Cover sprays for adult control
In this situation, the insecticidal compounds used for EAB control are carbaryl, cyfluthrin, permethrin, and bifenthrin products. Complete spray coverage is required for best control against EAB adults and first instar larvae that have just hatched and have not yet begun to bore into the tree making them vulnerable to insecticide exposure. (Herms et al, 2014).
The most effective kill with this spray method is when adults are freely feeding on leaves, which occurs during a 21 day time frame. Herms, et al (2014) recommends two applications: the first when black locust approaches full bloom in your area and the second about one month later.
Natural biocontrol agents
Feeding and searching behavior by woodpeckers on ash hosts are the cause of “blonding” and are indicators of the presence of bark/sapwood insects on ash trees. They feed on EAB larvae as well as other insects. Woodpeckers destroy the bark exposing the lighter colored inner sapwood where the larvae live and feed. Blonding is the term used to describe the recently exposed sapwood revealed by woodpecker feeding activity.
1. Natural biological control. Jennifer Forman Orth (2016) reported at the Emerald Ash Borer Preparedness Forum (EABPF) about a native ground nesting wasp, Cerceris fumipennis (Hymenoptera: Crabronidae), that kills EAB adults. Adults have a longitudinal yellow band around their abdomens. She has a citizen science bio-surveillance volunteer program underway that locates and identifies these wasps and their habitats. Forman-Orth encourages the detection and protection of these native bio-control agents and their habitats. To find out more about this program visit www.bit.ly/masswaspwatchers
Unfortunately, woodpeckers and wasps are not enough to effectively reduce EAB populations to below threshold levels. However, they have some effect and their activities and presence contributes to our understanding of animal behavior and associated ecological principles as they relate to ash tree pest control!
2. Classical biological control using parasitoids against the EAB. UMass/Amherst, entomology graduate student, Theresa Murphy (2016), gave a presentation at the EABPF about three small predatory wasps (Hymenoptera) from China that have been approved for use in EAB infested areas in the U.S. They are (1) Tetrastichus planipennis (Eulophidae), a tiny beneficial wasp that parasitizes EAB larvae; Spathius agrili (Braconidae), also attacks EAB larvae; and Oobius agrili (Encyrtidae), an EAB egg parasitoid (Figure 18).
Monitoring these beneficial wasps over the next few years and determining if they reduce EAB populations should reveal the effectiveness of predatory wasps in controlling EAB.
The newest braconid wasp, Spathius galinae, is from Russia and has been approved for EAB biological control. Murphy (2016) said that it will be released this year. Entomology researchers are working hard at finding and testing the effectiveness of insect and fungal organisms for EAB control. Wang et al (2010) report that a few more wasps and pathogenic fungi show promise for EAB biological control in China. Only time will tell.
VII. An Integrated Pest Management Approach for EAB Control
Integrated Pest Management (IPM) is a pest management philosophy that utilizes multiple pest control strategies to reduce and not necessarily eliminate pest populations. In IPM, pest control chemicals can be used in concert with other non-chemical control strategies as an integral part of pest population management. If possible, the chemical chosen for pest population reduction should be the least toxic to the environment. Currently, due to the severity of the EAB infestation in the U.S. and its continued threat to our native ash tree populations in Massachusetts and other New England states, insecticide efficacy is of the utmost importance. Unfortunately, there are no lone effective organic pest control methods for EAB infested trees.
Homeowner and Landscape Contractor IPM Pest Control Strategies
1. Cultural controls. Visually inspect your ash trees for signs of EAB infestation. This action is called monitoring in IPM. As you carry out the monitoring process you must be able to correctly identify your ash trees. Monitor EAB bark damage caused by woodpeckers using binoculars if necessary. Visually inspect for loose bark and woodpecker damage, “blonding,” and larval S-shaped or serpentine galleries under loose bark. Epicormic branching (i.e. short clumps of woody shoots) from trunks and roots are evident on EAB stressed trees. (figure 19) Adult emerald ash borers, when present can be seen on trunks, branches, and leaves.
Prevention is another cultural control. Keep your home ash trees healthy by watering them during droughty conditions and mulching the root zone three feet from the trunk to reduce weeds and prevent soil water loss, and especially to protect against weed-wacker damage. Do not plant or encourage the planting of any ash trees and the white fringetree, which has also been infested with EAB, until government and university pest management officials approve of such actions.
Do not transport felled ash tree firewood out of your immediate area if you can not afford to have it processed through a wood chipper.
Reporting EAB infestations to the proper government authorities is a cultural control and good citizen conservation. Herms et al (2014) states that EAB infested ash trees threaten trees located 10 to 15 miles away. Reporting the presence of EAB allows the authorities to treat nearby trees early. Mark Whitmore (2016) stated at the EABPF that most homeowners contact tree companies for EAB information rather than contacting government or university extension personnel. EABPF experts stressed that if you suspect EAB damage on your ash trees or trees in your neighborhood you should first call:
- The USDA EAB Toll Free Hot Line 1-866-322-4512
- UMass extension plant diagnostic lab in Amherst 1-413-545-3208
- In Massachusetts – Forest Health Program 1-617-626-1251
- In New York – Department of Environmental Conservation 1-866-640-0652
- In Rhode Island – Division of Forest Environment 1-401-222-2445
For more information about the Emerald Ash Borer, visit www.emeraldashborer.info.
Educating your neighbors, friends and clients about the dangers of the EAB to trees and to the native ecosystem is an enormously valuable cultural strategy. By communicating to others the dangers of this exotic invasive tree borer, you are raising awareness of the problem and encouraging other people or organizations to follow your example. Cooperation is the key to saving our native ash trees from further destruction.
2. Mechanical controls. This strategy is also referred to as physical controls in IPM circles. Mechanical control strategies are the most widely used control methods and are the most laborious in many IPM programs. For EAB control, the cutting down and processing felled trees through a wood chipper is highly encouraged to reduce the insect’s spreading potential. Wang et al (2010) reports that many more adult emerald ash borers emerge from dead ash trees than newly infested ones. Cutting down heavily infested ash trees, including dead and dying trees, and processing the wood through a wood chipper reduces available hosts for the next generation of borers. Mechanical control methods in combination with a sound, ongoing monitoring program are necessary to prevent any EAB populations from spreading to new areas and reaching unmanageable levels.
3. Biological controls. Biological control incorporates the implementation and long-term use of beneficial living agents (insects, mites, microbes, etc.) to control pest populations (Cloyd, Nixon, and Pataky, 2004). Biological control for exotic invasive insect pests is in its infancy. Government and university researchers are painstakingly investigating possible bio-control agents for insect pests every year in the U.S. More research and grant money is needed in this area of pest control.
You can encourage natural biological control of EAB by learning to properly identify the Cerceris wasp and then protect its habitat from foot and vehicle traffic. The wasp’s habitat includes sandy soils of roadways, paths, fields, and sunny exposed woodland areas. Again, visit the wasp web site to find out more about this native wasp and how you can help: www.bit.ly/masswaspwatchers.
4. Chemical controls. After you have had your ash trees properly identified and you have had government EAB experts (phone numbers listed above) properly diagnose your EAB problem with recommendations for control, then call a tree company for advice on treatments. Government EAB personnel should be the first responders!
Trunk injections, systemic bark sprays, and soil applied insecticide formulations of professional grade will protect pre-infested and slightly infested healthy ash trees (Herms et al, 2014). Homeowners can buy EAB soil drenches and a granular product and get excellent results, but these soil applied products act slower than professional grade trunk and soil injection products.
Also, chemical products vary in their effectiveness due to the type of product, method of application, timing of application, soil type and moisture conditions, application rate, local climatic conditions, ash tree abundance, and EAB population size.
At the EABPF, Dr. Phil Lewis (2016) presented his trunk injection case study conducted in 2008 with colleague Richard Turcotte andreported in the Journal of Biodiversity Management & Forestry. Their research showed that pressurized trunk injections of the commercial insecticide Tree-age(R) (4% emamectin benzoate) when applied only once gave a 99% control of EAB larvae in ash trees (Lewis and Turcotte, 2015). A very effective EAB insecticide.
If you have EAB infesting your ash trees, it may be necessary to use a foliar spray on leaves and branches and consider trunk or soil injections. It will be up to you to decide on the type of chemical control you will need based on the diagnosis you receive from government and university experts.
For more information about the emerald ash borer including control options and ecology visit the following websites which were given to me at the Emerald Ash Borer Preparedness Forum, presented by the Massachusetts Forest Pest Task Force, Tower Hill Botanic Garden, Boylston, Massachusetts. January 6, 2016.
USDA Forest Service: www.na.fs.fed.us/fhp/eab/
USDA Animal and Plant Health Inspection Service: www.aphis.usda.gov/plant_health/
About the author
Bruce Wenning has been an ELA Board member since 2003. He is the horticulturist at The Country Club, Chestnut Hill, Mass and has university degrees in plant pathology and entomology.
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