The Case for Biological Controls Against the Emerald Ash Bore

By: Eric DeLeo, Brendan French, Ross Howard

 

University of Massachusetts Amherst

Spring 2014

The Emerald Ash Borer and Why its a Problem

Invasive species seem to be popping up everywhere in North America lately. From exotic plants choking out native vegetation in our forest, to zebra mussels clogging up pipes in our lakes and ponds. Invasive species of all types are on the rise and now it’s our job to try and prevent them from spreading, and possibly eradicate them from our native environments.

There is one invasive species in our region that has caused significant damage to our Ash tree species, Fraxinus Spp. The Emerald Ash Borer (EAB), Agrilus planipennis, is an invasive wood boring insect from Asia that infest and kill our native ash trees, let it be green, white, or black ash. EAB was first detected in Michigan in 2002. However it was suspected to arrived there in 1998 getting itself established in the environment for a few years before being noticed. Researchers believe EAB made its way to America via untreated ash wood like pallets used for stabilizing cargo in ships transporting heavy consumer goods from Asia. The ash wood pallets are usually treated with high heat or toxic fumes, but are suspected to have been mistreated in the case of EAB. Since 2002 EAB has established itself firmly in our forest, killing ash trees and has developed a range spanning from Canada to Georgia and from Colorado to New Hampshire. The pest is in nineteen different states and two Canadian provinces, and is now an international pest that seems to be making its mark with little sign of slowing down.

The Life Cycle and Damaging Signs of the Emerald Ash Borer

In the beginning of summer after adult EAB emerge from the bark of ash trees, female EAB lay their eggs in the furrows or grooves in the bark. Larvae hatch from these eggs in one to two weeks and begin to eat through the bark and bore a serpentine or S-shaped path called a gallery through the phloem and cambium of the tree. The phloem and cambium are located just under a tree’s bark, and are the tree’s “highway” for transporting water and nutrients absorbed from the roots throughout the rest of the tree. Boring through the phloem and cambium can sever the ties of the tree’s water and nutrient resource and eventually kill the tree. Larvae feed under the bark for several weeks, usually from late July or early August through October. Larvae typically pass through four stages, eventually reaching up to an inch and quarter in length. Most EAB larvae overwinter in a small chamber in the outer bark or in the outer inch of wood. Pupation occurs in spring and the new generation of adults will emerge in May or early June, to begin feeding on the tree’s vegetation and to start the cycle again.

[Emergence of adult EAB from the phloem depends on] its variable life cycle of one or two years. When larval densities of EAB are low within an Ash tree… Adult emergence may require two years. Adult emergence decreases when larval densities increase to higher levels. Apparent competition for the phloem resource causes an increase in the speed of development. (United States Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine Program. 2009.)

Depending on density, larvae could be in a tree for one or two years causing damage to the phloem and cambium, that eventually kills the tree by having too many or just enough larval galleries cutting its water and nutrient supply.

With EAB being able to reproduce in only one or two years, densities could rise rapidly from one tree to another depending on the initial size of the infestation. High density within a tree causes the insect to spread to other trees that are less densely populated so competition is decreased but the infestation is increased. EAB is known to be able to fly up to a half mile away from whatever tree they emerged from. However, most infestations are caused by humans transporting infested ash wood into uninfested areas. Regulations and quarantines are now in place on shipments of ash wood products such as nursery trees, logs, firewood with bark on them, wood chips, or any other means of conveyance an inspector can determine as a risk of spreading EAB. (Dudley, Conlee 2014) The major problem is the transportation of ash firewood into uninfested areas. It is now illegal to transport firewood outside of a quarantine zone, but individuals who are not familiar with the laws do so without knowing. Mostly people who go camping occasionally try and find cheap firewood but don’t consider if it is infested with bugs or not. Campgrounds have done a good job by prohibiting firewood from outside the camp to be used or even brought into the campground. Signs, bumper stickers, and hand-out pamphlets have also helped spread the word to not transport firewood.

You can find detection signals of an EAB infestation just by looking at the tree itself. The canopy of an infested tree begins die-back by thinning its leaves above infested portions of the trunk and major branches. Heavily infested trees exhibit this canopy die-back usually starting at the top of the tree. Up to half of the branches may die in one year. Most of the canopy will be dead within two years of when symptoms are first observed. Sometimes ash trees push out sprouts from the trunk after the upper portions of the tree dies. The D-shaped exit holes on the bark can often help in detection, even though they are difficult to see high in the tree. Bird activity can also be a sign that EAB larvae are within a tree. Woodpeckers and Nuthatches are the more prevalent bird species to look for because they forage into bark for insects.

Current Practices: Traps, Lures, Chemicals and Why They Aren’t Enough

EAB is becoming such a large problem nationally that agencies are beginning to find that it is a lost cause to try and eradicate it. In regions where EAB was first detected, the ash tree populations have been decimated. Discussions have thought that if the ash tree density decreased low enough to where it was tough for EAB to spread, EAB density would drop as well. This is true but the presence of EAB will still be prevalent. EAB will reside in the remaining stands, and ash tree seedlings will grow into susceptible sized trees and start the infestation over. It seems to be a problem that will stay in the ecosystem for some time.

Federal and State government agencies are in charge of dealing with the problematic pest. The regulations currently in place only focus on the detection and prevention of further infestation to unaffected areas. Research funded by these agencies is based mostly on the ecology of EAB and how they can attract it using different traps and lures. The traps and lures have changed multiple times over the years since the first detection. The multiple changes in traps have included the shape of the trap, color, size, placement in tree, means of actually obtaining the insect, and placement of trap in different habitat conditions. Lures have also changed over time by using various alcohol concentrations and oils derived from trees. No use of no lure at all has been tried as well. All of these conditions have been tested in the lab and used in the field over the years.

Currently the primary trap used is called a purple panel trap. Its a piece of flexible plastic folded into a triangular prism that is a certain shade of purple that EAB are supposedly attracted too. The trap is covered in a non-toxic adhesive that is very sticky, that grabs the EAB and any other insect or debris that comes into contact with it. The current lures used now are an alcohol concentration know as Hexenol, and an oil concentration derived from Manuka trees. The Manuka oil has a similar scent to a concentration of Ash tree oil. The reason why they used manuka oil instead is because is it cheaper to manufacture and they are not using the resource of ash trees that we are trying to save. The combination of the manuka oil and hexenol mimics the scent of a distressed or dying ash tree that should attract EAB. The traps are used in areas that have a potential threat of EAB invading. The traps do not attract EAB from a far distance thus bringing them into unaffected areas. The traps are applied when there is thought of a nearby infestation. Mixed results have come back from these now regulated lure traps. The traps have had a positive use in some newly detected infestations, but when applied in known affected areas, the traps don’t always work and don’t catch any EAB. Its not really known yet why the traps work in some areas but not in others. Changes to the trap and lures are being implemented and the placement of traps is being focused on more. With the purple panel traps not working all the time what can we look towards to help us in the detection, monitoring, and possible eradication of EAB.

Emerald Ash Borer (EAB) has various chemical control options, each with their own positives and negatives. Kreutweizer, Good, Chartrand, Scarr, and Thompson (2007) state when applied at higher rates to eradicate leaf shredding insects such as EAB, Imadicloprid can cause as much as 91% control rates. However these high rates raise the concentration of the chemical within the leaves to about 80 ppm. The authors (2007) go on to state that these concentrations in leaves pose a large threat to non-target aquatic organisms or other aquatic microcosms. These aquatic insects develop a toxicity to Imadicloprid at 0.13 ppm, a concentration that has no significant effect on leaf shredding insects. Henceforth great caution must be exercised when applying Imadicloprid near water sources to prevent leaching or leaf fall into these water sources.

Chemical regulations and applications are a good option for an individual to apply if the biocontrols have failed to reduce EAB numbers. However, chemical control is an unrealistic and largely unacheivable goal for the government to force regulations on. Biocontrols are a realistic government regulation because they allow for a natural and self sustaining means of EAB control. Chemical control is a good means for EAB eradication, but it is a poor option for the prevention of large EAB numbers and too costly of a means for government implication. In all, the chemical control options are good for the private or commercial sector, but biocontrols like insects and quarantines are the most realistic means of which the government can assist in reducing outbreak numbers.

Enter Cerceris

Current government practices are only providing data as to what the Emerald Ash Borer is doing. We are not battling Emerald Ash Borer as effectively as we could be.  EAB can be controlled by a few biological methods that are seamless for the environment. Biological controls can vary on what they are and what they do exactly. Usually invasive pest do not have a natural enemy. By introducing an enemy species to the affected ecosystem can affect the unwanted species. Biocontrols can be parasitic, predatory, or fungal to an “invasive” host species, and when the ecological effects come into place, the host species will be affected. Release of biocontrol species can have varying effects. Depending on if the biocontrol species specifically goes after the unwanted pest species of interest determines the effect it will have. Some biocontrols are a generalized control, meaning that they go after a general type of species. Some are species specific, meaning that they only go after a distinct species and that is it. The difference in effect that a generalized or specific control can have is drastic. Generalized species can cause problems outside the scope of controlling a pest. They not only go after the unwanted pest you are trying to rid, but they also go after species that are not a problem. This can cause problems in the ecosystem by affecting even more species in the area. Species specific biocontrols are the preferred type of biocontrol because they only go after the specific pest species of interest and do not cause problems in other areas of the ecosystem.

While we mentioned there are several options of biocontrol,including several bark foraging birds and even some parasitoids, we would like to focus most of our efforts into species specific biological control for EAB by Cerceris fumipennis. This species is a boroughing wasp type insect the creates its home in compacted sandy soil like a baseball diamond or dirt parking lot. The species makes a small cave 7 to 10 cm deep by excavating sand from the hole as it digs deeper (Careless, 2009, pp.16). These wasps then seek out their prey up in their territory feeding zone that is approximately 2 kilometers. They paralyze EAB by injecting them with venom at a joint of the beetle shell. This is how they get the venom around the EAB’s impenetrable shell. Once the beetle is paralyzed, the wasp picks the beetle up and flies it back to the nest. They bring the beetle into the nest alive. The beetle may be stung several times to keep it remaining paralyzed. However, it is always kept alive. This is to keep the prey fresh for the future larvae to eat. Beneath the surface the female wasp creates individual cells throughout the borough. In each individual cell a beetle is stored with eggs laid. She then backfills the cell to keep any other foraging predators from stealing the food (Careless, 2009, pp.16). The Cerceris larvae hatch and feed in this cell area for a period of time before going to pupae stage, then to adult the following summer.

This wasp has a remarkable sense of how to find EAB habitat.  Studies have suggested this extra sensory perception is quite amazing (Careless, 2009, pp.16). Us humans have not been able to figure out how this occurs. We are actually using the findings of these wasps as a detection to figure out where EAB habitats are. These wasps forage primarily on EAB type insects called buprestids, and are constantly searching out and feeding on these insects. They are certainly an excellent form of means to remove many EAB from wildlife. Our government could work to release more Cerceris fumipennis into affected ecosystems. It would be beneficial, for the preservation of Ash trees, for us to release wasps and promote areas for these wasps to flourish in.

The Case for Biocontrols

Biocontrols are the simplest and cheapest means of effectively combating the outbreaks of EAB across the North American continent. While the traps and lures are great tools for monitoring the pest and do have the capacity to collect EAB, thereby “controlling” the population, they lack the large scale effective control that is needed to combat the future problem EAB is posing. To add to that, lures can do equal amounts of harm as good by actually attracting EAB to a region it may not have found in the first place. So while they are great tools for monitoring the progress of the continental EAB infestation, they do very little to actually help to fix the problem at hand.

The most glaring comparisons between chemical and biological controls are the costs and sustainability of each type. As previously stated biological controls have initial costs, but once acted on are virtually self sustaining and operate with biological pinpoint precision . After the initial costs it comes down to monitoring and keeping an eye out for fluctuating EAB numbers. Chemical controls along with the danger described above, have many considerations and a higher cost for a control that must be reapplied in most cases every year.According to Herms, McCullough, Smitley, Sadof, Williamson, and Nixon (2009) there are several ways to apply insecticides to Ash trees, each of which coming with their own considerations and drawbacks (p. 4). The authors (2009) state low pressure trunk injections are a viable means of control, but they are expensive and a waste until the EAB numbers have been researched and established (p. 4). Herms, McCullough, Smitley, Sadof, Williamson, and Nixon (2009) go on to explain that soil drenches are a good way for the systemic insecticide to reach the roots in the soil, but they require perfect soil and climate conditions to be readily absorbed by the tree’s roots (p. 6). All these must be considered as well because there is often a concept of “putting good into bad” with chemical application. In other words, the tree is beyond saving. In cases like this other costs and considerations come into play like the value and costs in removing and potentially replacing the infected the tree. These considerations do come into play with biological control, however they are an after thought because the biocontrol agents would have been introduced to the habitat and will have done all they could have to this point.

The use of biocontrols in our ecosystems go back to the early nineteenth century. Winter Moth was a big problem in the Northeast of America in the early part of the century. These moths came from Europe and were causing trees to die. On the island of Nova Scotia in Canada, a very successful introduction of a species specific parasitic fly to winter moth took place. Stocks of this parasitic fly were released on the island and within 7 years there was 90% parasitism in the winter moth. The moth’s populations dropped dramatically and the moth is no longer a major threat to the island’s trees. Success using biocontrols vary in degree and size depending on where and what they are trying to protect, but there are examples of huge success using biological controls (Elkinton, Personal Communication, 2013).

What Needs to Change

Government agencies are currently only fighting half of this battle. Federal agencies fund monitoring and trapping practices to identify and document the progress that EAB is making, but take no actions in slowing the spread down.  The EAB is dominating the Ash trees and it is destroying a lovely tree species. The Ash tree has not had a significant threat until of recent, with the invasion of EAB. This new threat is one that needs to be properly dealt with to save what remains of the nation’s beautiful Ash tree populations from invasive destruction.

The wasp can consume the EAB with the right influx of numbers in the right conditions.  The wasps must be released profoundly in the proper habitat within range of a nearby newly developed EAB outbreak.  This is the way to fight EAB.  We need to attack new outbreaks before trees have suffered irreparable damage.  We need to send government employees out who can locate new outbreaks, assess the likelihood of a Wasp release being an efficient control method, then make the executive decision as to whether or not intervention is deemed a worthy cause.  In certain scenarios such as inner wooded areas with high populations, it may not be logical to pursue eradication. However it would be practical to pursue intervention to stop the spread of the EAB outbreak into uninfected areas. In other situation where the trees serve as an icon, such as city curb lining for streets or in parks where the Ash is a prominent fixture, controls should be in place with the resources available.  Controls can be setup in areas where there are sandlots or parking lots.

The costs associated with this new control method would not be substantial.  Government employees are already in place and they are spending time looking at this issue.  We are proposing that federal agencies make better use of them by implementing a goal oriented plan that is working toward an outcome. These government employees already spend time in forests monitoring EAB progress. The federal agencies employing these monitors should equip them with the capabilities to act on their findings. Using our paid government employees with righteous intent will lead to outstanding results under appropriate situations.  Employees would need specific training in the evaluation procedure as to whether or not an efficient logical plan will have a high percentage of success at each specific location.  This is all certainly doable.  We are already almost paying for the costs associated with this plan, so why not give it a shot.  The Ash tree is worth saving.

A New Invasive?

There are some that say that the release of species into a natural environment is tampering with our environment.  The folk that resist our intervention must look at our proposal logically. We are having a cause and effect on the environment by a non-native species but we can understand this and make good decisions for the environment.  These wasps we plan to release and potentially build small habitats for do not cause any environmental impact except a positive one.  They do not sting humans and their daily task is to seek out buprestids and return to their nest with them to procreate.  They use the destructive insect as food for their larvae. There is no big impact here because Cerceris naturally occur here on the North American continent and is species specific so environmentalist should rest at ease.  We have assessed our proposal and would not be implementing this practice if it would be temperamental to symbiotic environments.

Habitat Helpers

A group of individuals that could have an equally high impact on the current nesting practices of Cerceris fumipennis that must be addressed are groundskeepers.  It is logical that people will be annoyed by wasps.  When people see wasps, they have a natural fear toward the insects because they believe all bees and wasps sting.  This is not factual.  There are several species of bees and wasps that do not sting even when provoked and Cerceris fumipennis happens to be one.  It is critical that these wasps are able to nest in the hard packed sand a ball field withholds.  Another prime breeding ground would be a worn out picnic area with little grass cover.  These wasps thrive in environments where the sand is hard and compacted with little grass cover.  Baseball field greenskeepers can be reassured that these bees are harmless.   Our professional approach would be allowing them to flourish in areas where they are making an efficient impact on EAB.  In situations where they are a nuisance and are not making a significant impact on our cause, then eradication or displacement methods could be discussed.  These wasps will make the difference under appropriate situations. The wasps in populated colonies can dominate the EAB thus doing the work to save our Ash trees.

However logical the allowance of wasps to develop a habitat may seem, there are obviously some instances of EAB outbreaks where this simply would not apply. For outbreaks that have the possibility of being intervened with that are in more deeply wooded areas, we are suggesting something different. For forested areas we are suggesting the possibility of not only releasing Cerceris fumipennis into that environment, but also creating a micro environment in which the wasp can create a habitat. Simulating the soil types of compacted sandy areas such as a baseball infield is not something that is terribly difficult or costly to do. Matching that with how small this habitat would need to be, the scheme of habitat construction paired with wasp release seems logical if anything.

Conclusion

Biocontrols are not only a viable means of protection from EAB, but a financially and environmentally responsible solution to stopping the spread of the invasive insect. As we stated previously, the government currently employs forestry professionals to monitor EAB numbers by setting traps and collecting data. We are proposing the government fund an addition to that program by setting thresholds and implementing biocontrols in regions where EAB numbers have reached those thresholds. While we discussed the benefits of cautious pesticide use, we suggest that such use be only on an as-needed basis in which there are no alternatives to saving a tree that is of high importance to a private owner or the community. Similar to the Dutch Elm Disease pandemic that has changed the look of the American suburb across the country, if left unchecked EAB could change the way we see and use a valuable timber product. The benefits of preventing EAB spread far outweigh the downfalls of inserting stingless wasp populations into high density EAB areas. With that in mind, the government should continue to monitor the spread of EAB with their current practices or monitoring and quarantine but should put into action a manageable threshold with biocontrol action ready in the waiting to halt the spread of the Emerald Ash Borer.

Reference List :

Careless, P.D., Marshall, S.A., Gill, B.D., Appleton, E., Favrin, R., & Kimoto, T. (2009). Cerceris fumipennis – a biosurveillance tool for emerald ash borer. Canadian Food Inspection Agency. (pp. 16).

Herms, D., McCullough, D., Smitley, D., Sadof, C., Williamson, R., & Nixon, P. (2009). I insecticide options for protecting ash trees from emerald ash borer. North Central IPM Center Bulletin. (pp. 1-12).

Kreutzweiser, D., Good, K., Chartrand, D., Scarr, T., & Thompson, P. (2007). Non-target effects on aquatic decomposer organisms of imadicloprid as a systemic insecticide to control emerald ash borer in riparian trees [Abstract]. Ecotoxicology and Environmental Safety. (pp. 315-325).

Personal Experience- Eric DeLeo, Massachusetts Department of Conservation and Recreation (DCR), Summer 2013

Personal Communication- Entomology Professor Joseph Elkinton – University of Massachusetts Amherst, Spring 2013

United States Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine Program. (2009).  Non-Flight period zones for emerald ash borer throughout the continental United States. Washington D.C.

United States Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine Program. (2014). Emerald ash borer federal regulatory overview for Massachusetts. Washington D.C.