Maricopa County Cooperative Extension Home Horticulture:
Gardening & Landscaping in the Low Desert
Caterpillars are approximately 2 cm long, hairy reddish pink. Pupal casings, 5 - 6 cm long, 1 cm in diameter, amber to light brown in color. The mature moth is mottled brownish gray, 5 cm in length. A mature larva may be up to 14 mm in diameter, greenish white except for the dark brown head with distinct abdominal prolegs. The larvae pupate and begin to emerge in early April. The emergence continues for about 2 months followed by egg laying which lasts about 1 month. The carpenterworm, Prionoxystus robiniae, requires 3-4 years to complete its life cycle.
Borer damage is always secondary to tree decline or stress. While most borers feed on dead wood - the carpenterworm moth larvae is a LIVE WOOD borer that was first reported in Stanfield (near Maricopa) where Shamel Ash trees were affected. So far, it has been isolated to southeast Maricopa County. This moth's caterpillars enter the tree near the crotches of branches where the female lays 300-600 eggs. Tunnels formed by the larvae may extend into the heartwood of the tree and exceed 15 cm in length and be up to 18 mm in diameter. Found in 15 -20 year old Shamel Ash trees in Mesa. Sample of wood from tree shows holes in branches and tunneling into the wood. Sawdust was found near the holes and on the ground near the tree.