Last June, after spending the day collecting insects at Sand Hills State Park in south-central Kansas with Mary Liz Jameson, Jeff Huether and I setup our blacklights at the edge of the dunes. We were hoping to attract males of the genus Prionus, following a hunch that maybe the dunes—a popular historical collecting site—would prove to be the habitat for the enigmatic Prionus simplex (known only from the type specimen labeled simply “Ks.”). We knew it was a long shot, made even longer by a bright moon and the unseasonably cool temperatures that settled over the dunes as the sun dipped below the horizon, and in the end no Prionus would be seen. We did see, however, some other interesting insects, one of the more interesting being males of Hammond’s lined June beetle—Polyphylla hammondi. Almost immediately after sunset a number of these large, chunky-bodied beetles resembling super-sized versions of their far more diverse and commonly encountered relatives in the genus Phyllophaga (May beetles) began arriving at the lights—each one noisily announcing its visit by its loud, buzzing, flight and bumbling thud onto the ground nearby.
I’ve encountered beetles in the genus Polyphylla only occasionally over the years, almost always at night as a result of their attraction to lights. The genus is most diverse in the southwestern U.S., and many species are found only in specific sand dune habitats (Young 1988, LaRue 1998). Their large size, relatively more restricted distributions, and less common occurrence make them interesting enough, but what made this encounter particularly interesting for me was the way the beetles—all males—held their fan-like antennae splayed out. Male Polyphylla have greatly enlarged antennae that they use to detect sex pheromones emitted by the female (Lilly and Shorthouse 1971). Many female Polyphylla are flightless, especially those restricted to sand habitats, and are rarely collected, and for some species they still remain unknown. In fact, the best way to find females is to listen for the sound of the males hitting the ground or vegetation once they have located a female (Skelley 2009).
It was clear to me that these males were actively searching for females. The greatly elongated antennomeres provide lots of surface area for sensory pores to detect female pheromones at low concentrations. I’d not seen this before and didn’t know how long it would last—many beetles have narrow windows of activity for mating that can be affected or restricted further by environmental cues such as temperature. I figured I’d better get some photographs on the spot while I could, and this was a smart decision as it wasn’t too long after I took these photos that the males stopped coming to the lights and those that were already there became inactive and no longer held their antennae so impressively splayed.
In a recent paper describing a new western species of the genus, La Rue (1998) provided detailed notes on behavior that probably pertain to other sand dune inhabiting species as well. Males were observed to begin flying in late afternoon, making rapid, irregular flights several meters above the sand surface. However, as dusk approached, their flights became less erratic and more purposeful as they flew rapidly upwind and then returned in a slow zig-zag flight (indicative of osmoclinotaxic orientation). Mating occurred after they located a female sitting on the sand and alighted within a few centimeters of her. Several males were attracted to each female, further supporting the use of pheromones by the female to attract males. Males were also attracted abundantly to lights after dusk and ceased activity shortly to several hours after sunset, presumably because females cease releasing pheromone to attract them and burrow back into the sand.
LaRue, D. A. 1998. Notes on Polyphylla Harris with a description of a new species (Coleoptera: Scarabaeidae: Melolonthinae). Insecta Mundi 12(1–2):23–37 [pdf].
Lilly, C. E. & J. D. Shorthouse. 1971. Responses of males of the 10-lined June beetle, Polyphylla decemlineata (Coleoptera: Scarabaeidae), to female sex pheromone. The Canadian Entomologist 103:1757–1761 [abstract].
Skelley, P. E. 2009. A new species of Polyphylla Harris from peninsular Florida (Coleoptera: Scarabaeidae: Melolonthinae) with a key to species of the pubescens species group. Insecta Mundi 0085:1–14 [pdf].
Young, R. M. 1988. A monograph of the genus Polyphylla Harris in America north of Mexico (Coleoptera: Scarabaeidae: Melolonthinae). Bulletin of the University of Nebraska State Museum 11(2):vi+115 pp. [BioQuip preview].
© Ted C. MacRae 2016