A Weekend of Rare Cerambycids

This week a visit of my friend and co-author of the Arizona Beetle Book in preparation, Dr. Arthur Evans, and Pat Sullivan's annual Infestation party for entomologists promised a lot of fun field work and the probable discovery of more species to photograph for our book  (is that good or bad by now?) But the first exciting news came actually from a herpetologist and facebook friend in Clinton, Greenlee County, AZ. Terry Johnson informed us that 5 specimens of a striking looking Longhorn Beetle had been found there, and he got photos for us and promised me a specimen. It later turned out that there was only ONE specimen, not 5. But I did get it.

Megaderus bifasciatus, found in Clinton, Greenlee County, AZ

 Robert Velton identified the beetle as Megaderus bifasciatus. There were some few reports of this mainly Mexican and central American species from SE Arizona and from Texas. So I was quite happy, looking forward to adding this striking species to the AZ Beetle Book. But Terry's discovery coincided with the reviewing process of a paper whose authors were doubting that any of those old observations were valid. Luckily our community is small and close-knit so they were informed of the find and right now they are asking good questions about the provenance.. Five living specimens in situ are not easily explained as mislabeled or misidentified,  but were they maybe found right next to a pile of imported logs? That would raise the suspicion that they were recent adventives. I will report the result of this interesting story as soon as I know it. edit: only one pristine, newly hatched looking specimen in a residential development of 5 year old houses. Dan Heffern is now doing detective work to find out how our bug got there. Home Depot wood delivery for fences seems to be under suspicion.

 Meanwhile, we had our potluck feast at Pat's and I was working off some calories in his beautiful garden that slopes up the side of Ramsey Canyon behind his house.  I  picked mainly small leaf beetles from his perennials, all chosen for their attractiveness to insects I am sure. The diversity was delightful, even if they were all old friends.

But then I came across a little grey Cerambycid wit anulated antennae.

Mecas menthae. on  Salvia leucantha

  If it had been on a sunflower leave, I would have disregarded it as  the well-known Dectes texanus. But I have learned to trust the botanical knowledge of bugs implicitly.  I also remembered that lately a friend had compared species in the two Flat-faced Longhorn genera Dectes and Mecas because they resemble each other. Bingo! Genus Mecas! I showed it to Steven Lingafelter and with the help of Pat's house-synoptic collection, we had the species: Mecas menthae. Sure enough, not only did the plant turn out to be Salvia leucantha (Mexican Sage) in the Mint Family (Labiaceae) but we found 5 more specimens on the bush, making it clear that the beetles do consider it their host plant.

After a trip to Copper Canyon where our lights were inundated with scarabs from tiny Diplotaxis to sturdy  Phileurus truncatus and Strategus aloeus and a restful night's sleep in the back of my Subaru
I visited the garden again. This time I found a nice number of leaf beetle species on Sacred Datura and some morning glories whose leaves were just about skeletonized.

Elytroleptus luteus in situ

But then a little streak of orange on a leave of a tall evening primose where I had been watching pinhead sized jumping weevils. Another Cerambycid? Or a very narrow Netwing? From the expert came the e mail shout 'Holy cow, that is a fascinating beetle! ' We both tentatively talked of Elytroleptus sp., but none that we knew.  What Steven Lingafelter then found looked all wrong at first glance: A beetle not red, but yellow and even called E. luteus. But as an experienced collector and taxonomist he knows that dried specimens may change from red to yellow, and that species are sometimes described from dry museum specimens. Maybe the author was never lucky enough to see our bug alive and beautifully contrasted by a green leaf.  The other details, like proportions, leg coloration, and costae on the elytra fit very well. So I guess he got the correct id!

Elytroleptus luteus

 
Check out the distribution for this beetle: it just makes it across the Mexican Border into Arizona, but it's found all through Central America.

Longhorns in the genus Elytroleptus are considered mimics of toxic beetles in the family Lycidae whom they closely resemble.
Close to the Longhorn imitator, I found a Jumpingspider that was trying to take down one of the toxic Lycids. It released the beetle unharmed. I do not know if my camera disturbed it or if it found the beetle unpalatable.

Does the Palo Verde Rootborer really kill Palo Verde Trees?

Check your porch lights: It's Palo Verde Rootborer season in Tucson. The huge, up to 4 in long beetles emerge from the ground, mate at night, and lay eggs into or close to dead Palo Verde roots (and probably other trees, too).  
Like every year, friends tell me that 'tree people' claim that the beetles are responsible for the demise of many trees. I don't think these 'tree experts' have done much conclusive research to base this opinion on. What they see is a downed Palo Verde tree with beetle grubs around its roots. 

Palo Verde Root Borer Pupa

 Some larvae are big enough or already pupated to make an identification possible, and they are indeed Palo Verde Rootborers. But did the beetle larvae even really damage the tree roots? Palo Verde Rootborers are prionins. Most (not all) of this subfamily of Longhorns feed on dead wood, mostly even on decaying substrate like old stumps, not on living tissue. 

When water is very scarce, branches die and break off, decreasing the evaporative surface area. Note that for this tree leaves are a luxury, only present right after a very good rain fall. Photosynthesis is performed in the green bark of trunk and branches.

 For Palo verde trees, leaves are a luxury that they only enjoy right after productive rains. Most of the year, they rely for their photosynthesis on the green bark of trunk and branches. That means that the bark also has pores that cause evaporation. During droughts, there are no leaves to drop. So Palo verdes famously react to adverse conditions by dropping whole branches. The branches are dead before they break off, but the main trunk survives with the potential to regrow when the drought finally ends. Maybe under ground, roots that aren't reaching any water source are also cut off  and left to die. Carl A. Olson and several other knowledgeable folks assume that the Palo Verde larvae are primarily feeding on those dead or dying roots.
Consider that desert trees and desert beetles evolved together and the trees survived the onslaught of the beetles just fine for eons. Of course,  climate change could  make the trees more susceptible and tilt that equilibrium. It's possible.

Even the competition of a saguaro that used it as a nurse tree might eventually kill a Palo Verde if there is not enough water for both

Still, most of the trees probably primarily succumb to drought damage, competition for resources, attacks by CA root rot, wrong irrigation, overheated surroundings of asphalt and concrete, or other human induced factors. Besides, Palo Verde Trees do not live as long as Ironwoods, for example, anyway.

Notopleurus lobigenis, a cousin of Derobrachus hovorei, shares its appetites

 But the activity of the ominously big beetles happens under ground, out of sight. So, when a tree finally falls over and we can see pulled-up roots, it's usually a dead or dying tree. Which naturally has plenty of rotting roots, and  Palo Verde Root Borer larvae feeding on those. But what's the hen and what's the egg here? Nobody is any wiser.