Emerald ash borer, Agrilus planipennis, is an invasive borer from northeast Asia threatening North American ash trees (Fraxinus).
Life Cycle
Females lay eggs 2 weeks after emergence. Eggs are initially light-yellow, turning to brownish-yellow before hatching. Eggs hatch in 1-2 weeks, and the tiny larvae bore through the bark and into the cambium and phloem. The creamy white larvae are 1–1.25 in. (2.5-3.2 cm) long with flat, broad, segmented bodies. Adults begin emerging in mid-June leaving 0.1–0.2 in. (0.25-0.5 cm) “D” shaped emergence holes. The life cycle in Michigan takes between 1-2 years depending on the climate. Larvae feed on phloem and make serpentine galleries that girdle and kill trees when the larval densities are high. Mature larvae tunnel into sap wood to pupate. In northern areas (e.g., Michigan), a single generation may require two years, but in mid-Atlantic states (e.g., Maryland), a generation can be completed each year.
Distribution
It was first detected near Detroit, Michigan and likely was introduced in the 1990s. It is now found in 14 other states and two Canadian provinces, and the infested range is expanding rapidly. Emerald ash borer attacks and kills healthy ash trees from ones several inches in diameter to mature trees. Massive mortality to ash of several species has occurred since the species' invasion in both landscape plantings and natural ash-dominated communities, especially in riparian areas.
Control Efforts
Three species of biocontrol have been researched and are currently being deployed. They include Spathius agrili (Hymenoptera: Braconidae), Oobius agrili (Hymenoptera: Encyrtidae), and Tetrastichus planipennisi (Hymenoptera:Eulophidae). This is a long-term management method rather than one targeted at immediate control. In dense populations, woodpeckers consume many larvae.