Late summer and early fall is not normally a very good time to go looking for woodboring beetles, which for the most part are found in their greatest diversity and abundance during spring and early summer. This is especially true in the drier western U.S., although notable exceptions occur in the so called “Sky Islands” of southeast Arizona (where most species have shifted their adult activity periods to coincide with late summer “monsoons”) and the lower Rio Grande Valley of south Texas (where spring and fall rains have resulted in bimodal patterns of adult activity for many species). Across the rest of the U.S. a rather limited assemblage of late-season species is found, mostly longhorned beetles associated with fall-blooming composites such as Megacyllene (e.g., M. decora) on goldenrod (Solidago) and Crossidius (e.g. C. hirtipes immaculatus) on rabbitbrush (Chrysothamnus and Ericameria) and snakeweed (Gutierrezia). Late-season jewel beetles are even less common, but one of the few species that does prefer the latter part of the season is also among North America’s most striking species—Agrilus walsinghami.
This sexually dimorphic species occurs broadly across the western U.S., from British Columbia (Davies 1991) south to Baja California (Hespenheide et al. 2011) and east to Colorado (Nelson & MacRae 1990). Adults are encountered almost exclusively on gray rabbitbrush, Ericameria nauseosa (formerly Chrysothamnus nauseosus, Asteraceae), which despite the lack of any rearing records is nevertheless presumed to serve as the larval host (Hespenheide et al. 2011). I was hoping I would encounter this species on my recent Great Basin Collecting Trip (GBCT), as I’ve only seen it once previously (in southeast Arizona). The timing seemed right, as most published dates of collection range from mid-July to mid-September, and in fact I encountered and was able to photograph both male and female on the very first day of the trip (23 August) at the very first locality we visited (Davis Creek Park, Washoe Co., Nevada). As it turned out, I would see this species at perhaps a dozen localities or more during the course of the trip, although never in great numbers at any one locality nor with the sky conditions that allowed for the unusual background colors in these photographs (more on that in a future post).
The notable feature of this species is, of course, its sexual dimorphism, and it is remarkable that no author even mentioned such until Fisher (1928) discussed it in his revision of the genus in North America. Males have the head and pronotum bronzy brown with faint coppery reflections and the elytra brassy with slight purplish tints, while females are larger and more robust and are uniformly blue to greenish blue above. Both sexes have the underside strongly bronzy green with prominent white densely pubescent patches along the lateral portions of the thorax and abdomen and more or less coppery legs, making them truly one of the more spectacular species of Agrilus.
All told I probably collected between two and three dozen specimens across the localities we visited in western Nevada and southeastern California. Too bad I don’t have more of a commercial mind, as I later discovered that somebody actually purchased one of these beetles on ebay for $16.38! All I would have needed was ~100 specimens of this “very uncommon!” (not!) species and I could have paid for the entire trip!
Davies, A. 1991. Family Buprestidae (metallic wood-boring beetles), pp. 160–168. In: Y. Bousquet [ed.], Checklist of the Beetles of Canada and Alaska. Agriculture Canada Publication 1861/E, Ottawa.
Fisher, W. S. 1928. A revision of the North American species of buprestid beetles belonging to the genus Agrilus. Bulletin of the United States National Museum 145:1–347.
Hespenheide, H. A., R. L. Westcott & C. L. Bellamy. 2011. Agrilus Curtis (Coleoptera: Buprestidae) of the Baja California peninsula, México. Zootaxa 2805:36–56.
Nelson, G. H. & T. C. MacRae. 1990. Additional notes on the biology and distribution of Buprestidae (Coleoptera) in North America, part III. The Coleopterists Bulletin, 44(3):349–354.
Copyright © Ted C. MacRae 2013