Biology and Larval Morphology of Agrilus subcinctus (Coleoptera: Buprestidae), with Comparisons to the Emerald Ash Borer, Agrilus planipennis

Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an exotic invasive pest of ash (Fraxinus spp.) trees that was first discovered in North America in 2002. There has been concern that surveyors could confuse immature stages of EAB with A. subcinctus Gory, an ash borer native to North America. We conducted studies in 2006-2009 in southern Michigan to determine biological and morphological characters for distinguishing immature A. subcinctus and EAB life stages. Agrilus subcinctus adults were captured on yellow sticky cards from late May through mid-August, with peak flight occurring in June. Agrilus subcinctus egg laying began in late May to early June. Agrilus subcinctus eggs were smaller than EAB eggs. Agrilus subcinctus eggs and immature stages were found only on dead ash twigs, while EAB primarily infests live stems and branches. We determined that A. subcinctus has four larval instars, with 4th instar A. subcinctus being similar in size to 2nd instar EAB. Shape of abdominal segments, pronotal groove, and urogomphi can be used to distinguish larvae of A. subcinctus from EAB. The following hymenopteran parasitoid species were reared from immature A. subcinctus stages: Avetianella sp. (Encyrtidae), Ecphylus sp. (Braconidae), Eurytoma sp. (Eurytomidae), near Hadrotrichodes (possible undescribed genus; Eulophidae), Heterospilus sp. (Braconidae), Metapelma sp. (Eupelmidae), and Oodera sp. (Pteromalidae).