Life Cycle
A. planipennis may take one or two years to complete its life-cycle depending on 1) the timing of egg deposition, 2) the health and stress level of the tree, and 3) local temperatures. The one-year EAB life-cycle is described below.
Adults The adult beetle is dark metallic green, bullet-shaped and about 8.5 millimetres (0.33 in) long and 1.6 mm in) wide. The body is narrow and elongated, and the head is flat with black eyes. Adults begin to emerge from the trunks of ash trees after the accumulation of 400-500 growing degree days base 50°F (GDD). Peak adult emergence occurs at ~1000 GDD. After emergence, adults fly into the ash canopy where they feed on leaves throughout their lives. EAB adults start mating one week after emergence, and females begin laying eggs 2–3 weeks later. In the field, EAB adults are readily observed mating and egg-laying on the trunks of ash trees on warm, sunny afternoons and evenings. The adults of both sexes are strong fliers.
Eggs A female EAB may lay >100 eggs in her lifetime, depositing them individually or in groups on the bark along the trunk and portions of the major branches. Eggs are laid in areas where the bark is rough, and between bark layers or in bark crevices. Eggs are approximately 1.0 mm long x 0.6 mm wide and creamy white when laid; fertile eggs gradually turn amber after a few days. The eggs hatch after about two weeks.
Larvae Newly hatched larvae bore through the bark to the phloem and outer layer of new sapwood where they feed until the weather gets too cold in the fall. There are four stages of larval development (instars). As they feed, the larvae create long serpentine galleries filled with frass, which enlarge in width as they grow. Larvae are creamy white, and dorso-ventrally flattened. When fully mature, fourth-instar larvae are 26 to 32 mm long. Their head is mostly retracted into the prothorax with only the dark brown mouthparts visible. The prothorax is enlarged, with the mesothorax and metathorax more narrow. Larvae have 10 bell-shaped abdominal segments and a pair of small brown structures called urogomphi, which are characteristic of all larvae in the genus Agrilus.
Overwintering larvae, pre-pupae, pupae, and adults In the fall, mature fourth-instar EAB larvae excavate pupal chambers in the sapwood or outer bark where they fold into overwintering “J-shaped larvae”. In the spring, the J-shaped larvae shorten into prepupae then shed their cuticle to become naked pupae. Pupae are initially creamy white, but the eyes turn red and the body begins to darken as they develop. To emerge from ash trees, adults chew D-shaped exit holes through the bark and are capable of immediate flight upon emergence. EAB larvae that are immature as cold weather arrives in the fall will simply overwinter in their larval gallery. Larger larvae complete development the following spring, whereas smaller larvae may require another summer of feeding to complete development.
Read more about this topic: Emerald Ash Borer
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