Beetle Could Pose New Threat to Olive Trees

Researchers have discovered that olive trees are the only non-ash species of tree vulnerable to attack from the invasive Emerald Ash Borer beetle with potentially devastating consequences.

Jun. 19, 2017
By Mary Hernandez

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A team of researchers from Ohio’s Wright State University has dis­cov­ered that the inva­sive Emerald Ash Borer (EAB) is capa­ble of com­plet­ing devel­op­ment on olive trees, mak­ing it the sec­ond offi­cial non-ash species of plant that can host the insect. While EAB pre­vi­ously only posed a threat to forests and land­scapes, this lat­est dis­cov­ery reveals that it could have neg­a­tive con­se­quences for olive trees should an inva­sion occur.

Research into EAB’s abil­ity to make a home out of the cul­ti­vated olive (or Olea europaea) was led by Don Cipollini, pro­fes­sor of plant phys­i­ol­ogy and chem­i­cal ecol­ogy at Wright State University.

The find­ings were pub­lished in the Journal of Economic Entomology. It builds off pre­vi­ous stud­ies first ini­ti­ated in 2014, where the team explored its attacks on white fringe­tree (Chionanthus vir­gini­cus), which is a rel­a­tive of the ash tree.

Cultivated olive trees are a close rel­a­tive of the white fringe­tree and are known to grow in areas where sus­cep­ti­ble ash trees have been cul­ti­vated and grown. In ini­tial stud­ies, tests were done on the tree using EAB eggs sourced from insects with no pre­vi­ous expo­sure to either olive or white fringe­tree in order to reveal the true innate poten­tial of the EAB to use alter­na­tive hosts with­out hav­ing an adap­tive advan­tage.

The cur­rent study involved the researchers using the Manzanilla cul­ti­var of olive and plac­ing eggs directly on cut stems. It was dis­cov­ered that lar­vae were capa­ble of feed­ing and grow­ing to adult­hood on the tree, although not at the same level as that seen on most North American ash trees or white fringe­tree.

The find­ings revealed that the poten­tial host range of EAB is broader than pre­vi­ously thought and if the insect can detect and uti­lize olive trees, it could make the leap to become a pest of the crop. As olive trees are already vul­ner­a­ble to sev­eral pathogens and insects, it could make them more vul­ner­a­ble to EAB. This would make its poten­tial spread and per­sis­tence more likely.

According to Cipollini, the out­comes of the EAB becom­ing a pest of the olive tree would require seri­ous action from all involved par­ties. If the EAB can detect and uti­lize olive trees in the field, then it could have neg­a­tive con­se­quences on growth and pro­duc­tiv­ity of olive trees. Treatment and man­age­ment pro­to­cols will need to be estab­lished for it,” he said.

If the EAB will not attack olives in the absence of any ash trees in the area, then the removal of ash trees becomes part of a man­age­ment strat­egy. Olives are treated chem­i­cally for some pests. If they will need a sep­a­rate pes­ti­cide treat­ment for EAB then many of the sys­temic pes­ti­cides used for EAB on ash trees would be off the table, and other non-sys­temic treat­ments will have to be opti­mized. If olives can indeed serve as a host in the field, there would also be impor­tant reg­u­la­tory impli­ca­tions.”

Cipollini said his team is cur­rently repeat­ing the study with sev­eral other cul­ti­vars. They are also explor­ing the adult EAB’s attrac­tion and will­ing­ness to lay eggs on olive trees, the lar­val use of the phloem tis­sue and tree defenses to it and whether or not the EAB can com­plete their sex­ual mat­u­ra­tion feed­ing exclu­sively on olive leaves.

However, he stressed that genetic and envi­ron­men­tal influ­ences could affect the vul­ner­a­bil­ity of the olive tree to the EAB and that fur­ther test­ing on the inter­ac­tions between the EAB and com­mer­cially grown olives were needed.



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