Insect invasion

The em­er­ald ash borer, an in­sect from Asia, has mi­grated to the area and could dev­ast­ate the city's ash tree pop­u­la­tion.

  • The emerald ash borer. PHOTO COURTESY OF WIKIMEDIA

  • Bug bites: Curtis Helm, from the Department of Parks and Recreation, walks through a forest by the Fairmount Park Horticulture Center and points out trees threatened by the emerald ash borer. The invasive insect has been observed in Warrington, Bucks County. MARIA POUCHNIKOVA / TIMES PHOTO

  • Bug bites: Curtis Helm, from the Department of Parks and Recreation, walks through a forest by the Fairmount Park Horticulture Center and points out trees threatened by the emerald ash borer. The invasive insect has been observed in Warrington, Bucks County. MARIA POUCHNIKOVA / TIMES PHOTO

A glisten­ing green in­sect no lar­ger than a penny is poised to wipe out an en­tire spe­cies of Phil­adelphia’s trees, and people may be power­less to stop the his­tor­ic on­slaught, ac­cord­ing to a Fair­mount Park for­est­er.

The in­si­di­ous em­er­ald ash borer will likely be here be­fore we real­ize it and could dev­ast­ate 126,000 ash trees in all parts of the city, said Curtis W. Helm, the pro­ject man­ager for urb­an forestry and eco­sys­tem man­age­ment with the city’s De­part­ment of Parks and Re­cre­ation. There are ac­tu­ally two primary spe­cies of ash in the city, green and white. Both are vul­ner­able to the borer.

“It’s been de­scribed by for­est­ers in the Mid­w­est as a tid­al wave,” Helm told the North­east Times dur­ing a Ju­ly 25 walk around the Fair­mount Park Hor­ti­cul­tur­al Cen­ter. “Trees get over­whelmed and killed al­most sim­ul­tan­eously in an area.”

Last year, Helm au­thored the 30-page Em­er­ald Ash Borer Man­age­ment Plan for the city, which iden­ti­fied the in­sect as an in­vas­ive pest that ori­gin­ated in Asia. Amer­ic­an sci­ent­ists first ob­served the fly­ing bug in De­troit in 2002. It prob­ably had made its way over­seas in wooden ship­ping pal­lets. Since then, it has spread to at least 16 U.S. states and three Ca­na­dian provinces. It’s been seen in at least 31 Pennsylvania  counties and was de­tec­ted in War­ring­ton, Bucks County, in March 2012. Helm de­scribed the bug’s ar­rival in Phil­adelphia as “im­min­ent.”

People are largely re­spons­ible for its mi­gra­tion.

“The in­sect on its own wouldn’t move very fast, a couple of miles a year maybe, whichever way the wind is blow­ing,” Helm said. “But people pick up fire­wood, put it in their campers, drive hun­dreds of miles and set up their camps. Then the in­sects emerge.”

The in­sect thrives on all North Amer­ic­an ash spe­cies, of which there may be 126,000 or more in the city’s 11,407 acres of wa­ter­shed parks (in­clud­ing Pennypack, Ta­cony Creek and Poquess­ing Creek parks in the North­east) and smal­ler de­veloped parks, as well as privately owned res­id­en­tial and com­mer­cial prop­er­ties. Based on a dec­ade-old U.S. Forest Ser­vice study, park of­fi­cials be­lieve that ash trees ac­count for up to six per­cent of the city’s tree cov­er. A new sur­vey is in pro­gress. Be­cause the in­vas­ive borer evolved in­de­pend­ently from nat­ive ash trees, the plants are de­fense­less to the in­sect.

“In Asia, there’s a bal­ance between the in­sect and the tree. [In Amer­ica], there’s no re­la­tion­ship that’s been es­tab­lished over the mil­len­nia,” Helm said.

Ac­cord­ing to the for­est­er, the borer lit­er­ally chokes the life out of ma­ture ash trees, which typ­ic­ally grow up to 80 feet tall and can live for hun­dreds of years. In early sum­mer, the fe­males lay their eggs on the trunk, usu­ally in the up­per por­tion of the trees where the bark is thin­ner. The eggs hatch with­in a couple of weeks, then the lar­vae bore through the bark to feed on the cam­bi­um lay­er. That’s the re­l­at­ively thin lay­er of the tree that pro­duces new bark and where nu­tri­ents and mois­ture cir­cu­late.

A single tree can be in­fes­ted with hun­dreds of lar­vae, which de­vour the cam­bi­um in ser­pent­ine pat­terns and block the tree’s cir­cu­lat­ory sys­tem.

“Be­cause so many [in­sects] feed on the tree sim­ul­tan­eously, they block its abil­ity to move what it needs through its sys­tem,” Helm said.

After win­ter­ing in­side the out­er lay­ers of the tree, the ma­ture in­sects will bore out of the tree in the spring, leav­ing D-shaped exit holes in the bark. They can fly im­me­di­ately and mate, re­start­ing the re­pro­duc­tion cycle. People may not no­tice the in­fest­a­tion of an area for a few years be­cause the in­sects of­ten do their work high over­head and the signs of de­cline in the tree are subtle at first.

Healthy ash trees are re­cog­niz­able for their com­pound leaf struc­ture. It has five, sev­en or nine leaves on each peti­ole or stalk, sim­il­ar to wal­nut trees. Also, the bark has an elong­ated-dia­mond-shaped pat­tern, while the limbs and branches have an op­pos­ite-branch­ing pat­tern, mean­ing that branches sprout in pairs dir­ectly op­pos­ite from one an­oth­er.

The trees are noted for pro­du­cing a lot of seeds, which feed loc­al wild­life, and are crit­ic­al com­pon­ents to the urb­an forest can­opy. They help re­duce flood­ing and pro­duce oxy­gen. In ad­di­tion, they provide raw ma­ter­i­al for base­ball bats.

An in­fec­ted tree will have stun­ted growth. Its can­opy won’t be as dark green as a healthy tree and the leaf cov­er­age will be spars­er. It will have dead or dy­ing branches and dead twigs that will fall to the ground. New sprouts will shoot from un­usu­al places on the tree, such as the base of the trunk. This in­dic­ates that nu­tri­ents are not reach­ing the up­per, in­fec­ted area of the tree. Re­mov­ing the bark in an in­fec­ted area of a tree will re­veal ser­pent­ine mark­ings cre­ated by the in­sect’s feed­ing pat­tern. Also, there may be an in­crease in wood­peck­er activ­ity around in­fec­ted trees. The birds feed on the lar­vae.

“It’s like a smor­gas­bord for wood­peck­ers. That’s how these in­fest­a­tions get dis­covered,” Helm said.

In re­cent weeks, the De­part­ment of Parks and Re­cre­ation has de­ployed a team of gradu­ate in­terns in­to city parks, in­clud­ing Pennypack Park in the North­east, to sur­vey and tag ash pop­u­la­tions. The tags are in­di­vidu­ally numbered medal­lions and are cru­cial to the city’s ef­forts to mon­it­or and re­spond to the threat. There are no vast forests of ash in the city. Rather, the trees gen­er­ally grow in small clusters or in­di­vidu­ally.

“If my in­terns find a cluster of trees that looks sus­pi­cious, they’ll no­ti­fy me,” Helm said.

The city’s street tree main­ten­ance work­ers are also on the lookout.

“The prob­lem in Pennypack Park is that some­body has been re­mov­ing tags [from the trees],” Helm said.

The city has not be­gun to identi­fy any trees for pre-empt­ive re­mov­al, ac­cord­ing to the park man­ager. But if and when in­fest­a­tion oc­curs, crews will likely have to re­move trees that pose a safety threat to people and prop­erty if they fall.

“The ones we’re most con­cerned about are the ones that could be a prob­lem if they die,” Helm said. ldquo;If you’re a homeown­er, it’s the same [con­cern].”

For the long term, the city in part­ner­ship with the state’s De­part­ment of Con­ser­va­tion and Nat­ur­al Re­sources plans to in­tro­duce or­gan­isms known as para­sit­oids that con­sume or kill the borers without harm­ing nat­ive in­sects. But that can’t be done un­til the borers ar­rive. Spray­ing in­sect­icides is not a prac­tic­al op­tion in the city. Oth­er in­sect­icides can be ap­plied one tree at a time, but the pro­cess is costly and time-con­sum­ing. In case of near-total de­struc­tion of the ma­ture ash tree pop­u­la­tion, pub­lic agen­cies have been col­lect­ing and pre­serving ash tree seeds in hope of re­in­tro­du­cing the spe­cies to the parks once the threat has passed.

“It’s noth­ing that we can really do much about oth­er than to re­act to,” Helm said. “We’re just try­ing to plan for it.” ••

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