by Piter Kehoma Boll
It’s time for our next beetle and this time our fellow is a species that spent its first century after discovery without calling much attention but then something happened. Its name is Agrilus planipennis and is commonly known as the emerald ash borer.
Native from East Asia, the emerald ash borer is found in southeastern Russia, Mongolia, northern China, Korea and Japan. Adults measure about 8.5 mm in length and have a metalic green color on the head, pronotum and elythra, and an iridescent-purple metalic color on the dorsal side of the abdomen, seen when the wings are open. They live in the canopy of ash trees (Fraxinus spp.) during spring and summer and feed on their leaves.
After about a week as adults, the emerald ash borers start to mate. Females remain on the trees and males hover around looking for them. Once a female is located, the male drops over her and they start to mate. After mating is concluded, females live for some more weeks and typically lay about 40 to 70 eggs, although some live longer and may lay up to 200 eggs.
The eggs are laid between crevices or cracks of the bark and hatch about two weeks later. The newly hatched larvae chew through the bark, reach the inner tissues of the trunk and start to feed on them. They reach up to 32 mm in length in the fourth instar, more than three times the length of the adult, and pupate during spring, emerging as adults soon after. In China, adults emerge from the trees in May.
In its native area, the emerald ash borer can be a nuisance but is not highly problematic to ash trees because it occurs in low densities. However, in 2002, the species was found in the United States feeding on local ash species. Since the emerald ash borer has no natural predators in North America and the ash species in this continent did not evolve to be resistant to infection, it started to spread very quickly. In less than two decades, the beetle has killed millions of ash trees and is a serious threat to the more than eight billion ash trees found in North America. With the death of ash trees, North American forests become vulnerable to more invasive species, which will only worsen the scenario.
In order to control the spread of the emerald ash borer, ash trees are treated with pesticides. Four parasitoid wasps from China known to attack only the emerald ash borer have also been released in North America to help control the spread and their success is still being assessed. Traps, such as glue-covered purple panels, which are visually attractive to the beetles, are also used to capture the animals and determine the extent of the invasion.
Once more, a completely fine species has led to an ecological disaster due to human influence and now we are running to find ways to avoid an ecosystem collapse throughout an entire continent.
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Francese JA, Mastro VC, Oliver JB, Lance DR, Youssef N, Lavallee SG (2005) Evaluation of colors for trapping Agrilus planipennis (Coleoptera: Buprestidae). Journal of Entomological Science 40(1): 93-95.
Liu H, Bauer LS, Miller DL, Zhao T, Gao R, Song L, Luan Q, Jin R, Gao C (2007) Seasonal abundance of Agrilus planipennis (Coleoptera: Buprestidae) and its natural enemies Oobius agrili (Hymenoptera: Encyrtidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae) in China. Biological Control 42(1): 61-71. doi: 10.1016/j.biocontrol.2007.03.011
Wang XY, Yang ZQ, Gould JR, Zhang YN, Liu GJ, Liu ES (2010) The biology and ecology of the emerald ash borer, Agrilus planipennis, in China. Journal of Insect Science 10(1): 128. doi: 10.1673/031.010.12801
Wikipedia. Emerald ash borer. Available at < https://en.wikipedia.org/wiki/Emerald_ash_borer >. Access on 9 December 2019.
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