Tuesday, August 4, 2015

Featured Diagnosis: Honey locust Agrilus (Agrilus difficilis)

A composite photo of the insect, Agrilus difficilis. The photo on the left shows the top of the insect and the photo on the right shows the underside of the insect.
Upper and lower surfaces of adult Honey Locust Agrilus.
Actual size, ~ 3/8” long Photo:
J. Shaughney NMSU Arthropod Collection
Agrilus difficilis, the ‘honey locust Agrilus’ and a close relative of ‘Emerald ash borer’ was identified in Central New Mexico infesting honey locust (Gleditsia triacanthos). The tree canopy was leafless and apparently lifeless down to some green sucker growth near the ground. Upon closer examination there were D-shaped emergence holes in the bark, peeling bark with multiple larval feeding trails on its inner surface and small, very thin, blackish beetles that died in their attempts to escape their host. All of these beetle-related observations are similar to those caused by ‘emerald ash borer,’ an exotic, invasive ash-tree killer not known to occur yet in New Mexico. Dr. Carol Sutherland presumptively identified the insect as  Agrilus difficilis, the ‘honey locust Agrilus’ and this was later confirmed by Dr. Zablotny of the United States Department of Agriculture. 

Image of D-shaped emergence holes on a tree trunk caused by Agrilus difficilis
Emergence hole (D-shaped) made by an adult
 leaving the tree. 
R. Husted, Sandoval Co. MG. 

Photo of damage under the bark. There are adult insects stuck in the emergence holes.
Inside of honey locust bark – severe vascular damage from
larval stage. The black objects are adult A. difficilis that died
 before it could chew its way through the bark.
Photo C. Sutherland NMSU-PDC
Image of the woman standing by a nearly dead tree
This infested honey locust died
from the top down note the green
 sucker growth at the bottom.
Photo: R. Husted, Sandoval Co. MG.

Photo showing two white larvae with dark heads and two sharp spikes at the rear
A. difficilis larvae extracted from honey locust. The two little
dark brown ‘splinters’ on the rear are characteristic
of certain Agrilus species. Photo C. Sutherland NMSU-PDC

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