Fresh off our unexpected success at finding Prionus integer in the shortgrass prairie of southeastern Colorado, field mate Jeff Huether and I made our way down into northeastern New Mexico to see if the prionic acid lures we used to attract that species would bring us success with other species of Prionus. Several species in this genus are known to occur in the Great Plains, and we had records of three from the area around Gladstone (Union Co.). Based on our experience from the previous day, we stopped at several sites that had sandy/loam soil and searched exposures along the roadsides for burrows that bore any resemblance to those that we had found associated with P. integer. Frustratingly, we saw no such burrows or evidence of the presence of Prionus beetles in any of the spots that we searched.
Eventually, with day’s end drawing near, we decided to play a hunch and set traps at two sites with soil exposures that seemed most similar to those seen the day before. As Jeff set the last pair of traps in place, I occupied myself photographing a dusty hognose snake (Heterodon nasicus gloydi). While photographing the animal, I happened to look down to my side, and what did I see but a male Prionus crawling through the vegetation! I recognized the species immediately as P. fissicornis—represented in my cabinet by a single specimen. This species is distinguished by the highly segmented antennae (up to 30 segments or more) that place it in the monotypic subgenus Prionus (Antennalia). I called out to Jeff, and for the next half an hour or so we scoured the surrounding area; however, our searches were in vain as we failed to find another individual.
We cast an eye towards the north and watched late afternoon thunderstorms roll across the expansive landscape. Rain is normally a downer on an insect collecting trip. However, considering the numbers of P. integer that came to the traps after rain the previous day, we actually found ourselves hoping that the skies would open up. Whether they would and if this would lead to success with P. fissicornis (or other Prionus species), however, would have to wait until the next morning when we returned to check the traps.
Around 10 a.m. the next morning our reward was revealed—traps brimming with P. fissicornis males! Each trap contained more than a dozen individuals, and males were still actively crawling around in the vicinity of the traps as well.
We spent about an hour at the site determining the extent of their occurrence, and like P. integer the previous day the males were found almost exclusively in a small area adjacent to (and upwind from) the traps. As we searched, we also found a few females, one of which seemed to be in the act of ovipositing into the soil at the base of a plant. I carefully excavated the hole into which the ovipositor had been inserted once the female withdrew it, but I was unsuccessful in finding an egg. Perhaps she was only probing to search for a suitable oviposition site and did not find this one to her liking.
There are some interesting similarities and differences with this species compared to our experience with P. integer the previous day. Males of both were highly attracted to the prionic acid lures that we used and were effectively trapped in cans over which the lures were suspended. It is also interesting that both species were found in rather large numbers directly after a rain event, and it seems logical to presume that rain might trigger adult emergence—as is the case with many insects that inhabit dry habitats with seasonal rains. However, we did not find P. fissicornis adults associated with burrows as with P. integer, making me even more intrigued with the burrowing behavior in the latter and its possible function. Also, it is interesting that we found P. fissicornis adults most active during the morning hours and P. integer most active during early evening, but since we did not visit both localities at both times of day it is not possible to say for sure that the two species differ in their adult daily activity.
© Ted C. MacRae 2014