In the similar environment on the other side of the world,
scientists in China recognized a potential problem in the 1960s. In Northeastern
China, many non-native ash trees (from the United States) were planted. The
trees were similar to other ashes in Asia, and were planted widely in residential
areas. Soon after, however, outbreaks of EAB followed. Little was known about
the insect because most of its life cycle was hidden under the tree’s bark. EAB
remained “only sometimes an important pest in certain areas in China,” and
didn’t pose a large-scale threat (Wang 2).
The hidden life cycle of the EAB was studied by Chinese
entomologists Xiao-Yi Wang, Zhong-Qi Yang, Juli R. Gould, Yi-Nan Zhang, Gui-Jun
Liu, and EnShan Liu in Journal of Insect
Science article, “The Biology and Ecology of the Emerald Ash Borer, Agrilus
planipennis, in China.” They conducted a study on the velvet ash in Guangang
Forest Park, Dagang District, Tianjin Municipality, China, where “most forests
are monoculture ash plantings” (2).
They found that the beginning of the problem was the most
difficult to detect.
There were rarely any clear symptoms on the surface of
the bark during the initial infestation … It was more difficult to detect an
early stage of infestation for those trees with rough or thick bark (6).
But once EAB has entered a tree, the tree’s life span is
cut short. To study these life cycles, Wang al.
et. cut down infected trees and studied them in two environments, the
laboratory (where each pair of EAB were caged with a log) and in the outdoor
environment. They cut the logs and sealed the ends with wax (so the bugs had to
enter through the bark).
Wang al. et.
report that EAB deposit eggs under the bark and upon hatching from the egg, the
larvae burrow deeper into the bark and into the cambium, then into the xylem
for hibernation around the beginning or middle of September. From June to April
they are in larval stage, around 300 days. They become pupae stage and eat
through the cambium for 20 days to emerge in May (in China). After a week, they
mate, lay eggs and die (Wang 3-18).
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