Wednesday, June 23, 2010

Life cycle of the Giant Mesquite Bug, Thasus neocalifornicus

Photo by Terry Ketron

Lately I have received several inquiries about clusters of colorful 'Beetles' that are clinging to the leaves and seed pods of Mesquite Trees in Southern Arizona. Luckily, photos from omnipresent cellphones cameras accompanied the questions. It turned out that the 'beetles' were actually the nymphs of true bugs, of Giant Mesquite Bugs, Thasus neocalifornicus. (a revision of the genus by Brailovski et al in 1994 states that this is the only species of the genus in the United States, while T. acutuangulatus and T. gigas occur only south of the Mexican border).

How to tell a beetle from a true bug
Beetles and many true bugs are often confused because superficially they can look quite similar, as the picture of Paranthesis Ladybeetle and Harlequin Bug shows. But at closer investigation their morphology and life cycle are very different and they are therefore grouped in different taxonomic orders.

Beetles (Coleoptera) are the largest order of insects. From above, the body of a typical beetle shows three obvious parts:
the head with compound eyes, chewing (in most species) mouth parts, and antennae that can vary in shape and usually have more than 10 antennomeres.
the pronotum, which covers the prothorax.
the hard forewings or elytra which cover the membraneous flight wings and the rest of the body like a shell. A small scutellum may be visible where the two elytra and the pronotum come together.

The mouth parts of True Bugs (a specific group of Hemipterans) form a tubular rostrum in accordance with their piercing sucking function (true bugs suck!). The antennae have only 4 big antennomeres and are long, thin and angular. The pronotum is usually as wide as the base of the wings. A very conspicuous triangular scutellum is located behind the pronotum between the wing-bases. The forewings are hard only in front and membraneous towards the tips. The borders of the scutellum and the dividing line between those wing parts forms a conspicuous X that helps to easily recognize the group.

The Life cycles of beetles and true bugs shows how very different they really are
Both beetles and true bugs hatch from eggs. Beetle larvae are elongate and may superficially resemble caterpillars. They eat voraciously and shed their skin repeatedly to allow for growth. But they still look like grubs until they finally pupate. During the immobile pupa stage their bodies undergo radical changes to become the winged, sexually active adults that we know as beetles (complete metamorphosis).

Even newly hatched True Bug nymphs vaguely resemble their parents in shape, if not coloration. They go through a fixed number of moults ,5 in most cases. Each resulting instar is a step closer to the size and shape of the adults until they emerge from the last moult winged and ready to propagate (incomplete metamorphosis).

Timing is everything
Lets follow the development of a cluster of Giant Mesquite Bug eggs that were deposited by last year's generation, maybe in a protected spot under loose bark of a Velvet Mesquite Prosopis velutina in Sabino Canyon close to Tucson. In late April, mesquite leaves unfold explosively to shroud the somber, deciduous tree in lush fresh green within a couple of days. This is also the major blooming season of the mesquite trees.

At this time little nymphs hatch from the eggs, feed on the leftovers, and almost immediately moult for the first time. If they are not already on their food tree (we found many clusters in the shrubbery underneath the mesquites) it's now time to climb up to those fresh, juicy mesquite leaves.

First instar nymph and first molt

Second instar nymph
The second instar nymph is already recognizable as baby Giant Mesquite Bugs by the characteristic diamond shaped antennal discs of the species.

Third instar nymphs Photo by Tuan Cao
The bright red, black and white pattern becomes even more conspicuous in the third instar. The nymphs are still staying closely together as a group, projecting the appearance of a much bigger animal and probably of a very bad tasting one.

Wing buds are have appeared in the 4th instar Photo Ned Harris

They can afford to stay together because they don't have to compete for food: While the nymphs are getting bigger and hungrier, the tree has begun to put a lot of resources into the production of long, juicy mesquite beans. The pods themselves, not just the seeds, are sugary sweet. Over centuries the people of the southwest have used this abundant resource for flour and to feed countless cattle. Even Coyotes rely on the pods for 80% of their summer diet. Javelina scat is full of them. Sucking the juice of these fast growing seed pods, amazing numbers of mesquite bug nymphs are able to grow quickly to their astonishing adult size without any obvious harm to the tree.

This year spring came late to the foothills of the Catalina Mountains north of Tucson. So the mesquite beans are still growing and the bug nymphs are still in their last, 5th, instar close to the end of June.

5th instar (left)Last molt (right) Photos Ned Harris

By the time the monsoon moisture rolls up from the Golf and the July heat begins to pile up huge thunderheads over the Catalinas, the mesquite beans will be ready to fall to the soaked ground to be swept away by running washes until the pods rot and set the seeds free to germinate. By then the mesquite bugs will have turned into huge adults with strong legs that can cling to branches during afternoon storms and fly to disperse and meet their mates in the heat of the day. The adults are about 2 inches long.

Female (left) and male (right) adult Giant Mesquite Bug
mating group (below)

They often congregate to mate
A collage of the nymphal instars and an adult male

Sunday, June 20, 2010

Dichelonyx truncata in Sedona

At the beginning of June I was visiting my friends Kathleen O'Neil and Peter Tilman in Montezuma Wells. They took me to get reacquainted with the breathtaking beauty of the Red Rocks of Sedona and of the West Fork of Oak Creek Canyon in particular. We arrived just before sunset and the canyon lay already in deep shadow. No better light to best appreciate the deep colors of the landscape.

The trail first crosses the orchards and gardens an old hotel or lodge that burned down long ago. Some walls and chimneys are still standing. An lone fireplace exhibits the great skill of stone masons who used the natural local stone. Left behind ornamental plants make botanists wonder. We found thriving Vinca major, Spirea, Apple and Plum Trees and gorgeous but out of place Blue Iris.

Typical western Pinacate Beetles Eleodes obscurus were doing their head-down acrobatics or were mating everywhere on the sandy path. They looked nearly out of place in these genteel surroundings.

An old cave or mine shaft in the vertical red rock cliff must have served as a root cellar for the lodge. Peter, a geologist and prospector, was taking a closer look when the first beetle landed on his sleeve. Green, small, flighty, it looked at first like a Chrysomelidae. On closer inspection its antennae characterized it as a Scarab. Soon there were more - on my shirt and hat. In fact, I didn't find them on anything else at first.

It was Dichelonyx truncata. Two species of the genus occur in Arizona. Their distribution is very local. In fact, Pat Sullivan's field notes indicated that he found his only specimens also on the West-Fork Trail in Sedona in the seventies.

For any proper bug person everything after this discovery should have been anticlimactic. But I'm also an artist at heart. With two nice beetles in my pocket I could really enjoy the drama of the narrowing sandstone gorge and the great company of my friends.

I loved the contrast of complimentary reds and greens, the deep shadows and the last filtered light, and the delicate columbines, monkey flowers and ferns against the sheer cliffs.

This late in the day, we had the sandy beaches and completely quiet, mirror-still water all to our selves until a bouncy, exuberant Pitbull set another interesting counterpoint.

Thursday, June 17, 2010

Sisenes championi at Carr Canyon in the Huachuca Mountains

Last weekend a naturalist friend spotted a red elongated beetle with long antennae on the Wait-a-minute bushes in Carr Canyon. On Tuesday Patrick Sullivan (left) invited Fred Skillman (right) and me to join him on an expedition to find it again - Fred as a Cerambycid specialist and me as a photographer because we thought it might be Elytroleptus rufipennis, a predatory Long-horned Beetle, Cerambycid.

Wait-a-minute Bush, Mimosa biuncifera, grows along the lower canyon for at least half a mile. First, we found very few insects at all, just some bees and cryptocephaline leave beetles of the Clytrini tribe. I think these Mimosas rely mainly on wind pollination. When I was beating for beetles, clouds of pollen rose into my nose, mixed with dust from the dirt road. After our nice rainy spring Arizona is getting tinderbox-dry very quickly again.

Further up the canyon the Mimosa flowers looked fresher and there were more insects. Of course, it was also getting later in the day and warmer.

Fred found the first of the beetles and minutes later Pat had a couple as well. They fit the description we had, but they were no Cerambycids. They looked and behaved like Lycids, but the pronotum was too narrow and the elytra had no net-like texture.

Finally, Pat identified them as Oedemeridae. While that family bears the English name False Blister Beetles, in German they are Scheinbockkaefer, which translates into False Long-horned Beetle. I don't know whether that information would have cheered up Fred who was looking for 'Bycids'.Thanks to Vassili Belov on Bug guide we found out that we had Sisenes championi Horn 1894. It is an Arizona specialty that occurs nowhere else in the US. Vassili of the Bug guide and Carl Olson of the University of Arizona both call it 'a very good bug'. So it is quite exciting. I'm also glad to finally have one clearly identified Arizona Oedemerid for my digital collection. My records of that family so far consisted of more than half a dozen unidentified species mostly in the genus Oxacis.

At Carr Canyon, we continued to the top parking area where Fred proved his incredible eye for bycids by spotting several Neoclytus irroratus on some freshly dead branches of white-leaf oak. They were extremely cryptic when sitting still. When moving, their long legs and short antennae and make them look very much like wasps. I had one in my beating sheet at Mount Lemmon last week and it nearly fooled me.

From the very arid highpoint of the canyon, where only White-leaf Oak and Manzanita grow, we descended into the lush and varied vegetation the along the creek.

There were dozens of the little Psyllobora vigintimaculata. I had been looking forward to photographing them on this trip (left).
I still needed this more common species after I found the rarer Psyllobra plagiata (right) at Molino Basin in the Catalinas this spring.

On low growing oaks I found a Hispine Beetle that turned out to be Baliosus ferrugineus, a species described by C. L. Staines in 1996 with a Holotype from neighboring Miller Canyon.
There had been bear sightings on our trail last weekend, and I swear Pat and I heard the voice of at least one bear in the underbrush. But Fred was out on his own at the time, so who knows what we heard.
Here's what we missed by staring only on the ground, looking for beetles. My friend Tommy Peck took this picture last year at the same location.

Thanks to Pat and Fred for inviting me to a very memorable and fun trip, even without any bear sightings.

Tuesday, June 8, 2010

Cowbirds chicks and their foster parents

Since early March we've been hearing the flowing silvery song of Cowbirds in our backyard in the Tucson Mountains. We have two species here. The Brown-headed Cowbird has increased its breeding range from the Grasslands of middle North America to include now most of the US and Canada. The Bronzed Cowbird reaches us from its main distribution in Central America.

Bronzed Cowbird by NetSearchMedia

Brown-headed Cowbird by Ned Harris

Both species are brood parasites. Females lay their eggs in the nests of other species and leave it to the foster parents to raise the brood. Thus saving a lot of energy, female Brown-headed Cowbirds can lay more than three dozens eggs per summer. The nestlings hatch early and grow fast, so they have a competitive advantage over their nest mates and are usually the only ones to survive. Though foster species have some strategies to get rid of these brood parasites, they mostly just get conned into caring for the impostor.

Birds, like most animals (and humans for that matter) are programmed to react to certain signals with fixed behavioral patterns. Most of these signal are early evolutionary developments and therefore shared by many related species. Famous is the 'Kindchenschema' (big round forehead, big, wides-paced eyes, closely arranged features) that evokes maternal behavior across species lines in a wide variety of mammals. As kitschy dolls, Chihuahua dogs, and many cartoon characters demonstrate, these imprinted signals can be exaggerated to become even more effective, even to the point of corrupting the originally survival-based instinct.


The following anecdote illustrates this point. Last year I observed a cowbird chick following around after a female Hooded Oriole. The foster mother couldn't provide fast enough, the father seemed to be just watching, and she decided to feed the chick at one of our bird feeding stations (hummingbird feeders, fruit, water, and a quail block).

There the chick got in the way of a hungry Curved-billed Thrasher. Thrashers are among the most aggressive visitors, even picking and winning fights with big Gilded Flickers (below) and White-winged Doves.

The Thrasher aggressively started towards the chick to chase it away. The chick hunkered down, flared its stubby wings, opened the huge yellow-lined beak, chittered excitedly - it begged. The Thrasher hesitated, then approached as if to feed the chick, then just turned away. Not exactly feeding, definitely not chasing, obviously confused and disarmed. Normally, a bird only feeds chicks that hatched in its own nest and that it is bonded with. The ueber-chick had nearly succeeded in crossing this line. I assume that Cowbird chicks are equipped with exaggerated begging-attributes, both visual and behavioral that make them simply irresistible.

This year we are watching the plight of a very small, but extremely energetic pair of Black-tailed Gnat Catchers. Their cowbird chick is already twice their size but still much smaller than last years Oriole fosterling. This time the male seems to be the more devoted parent, or maybe he's less camera shy than the female.

Individual Cowbird females seem to return to the host species that raised them. Some researchers believe that their eggs show similarities to those of the host. Last year, our Orioles were hit at least twice probably by the same female.
Now we have at least one new Cowbird lady around that likes Gnat Catchers.

Even though the Gnat Catcher female spent a lot of time in Creosote bushes full of seed pods, I don't think she figured out that she could just stuff the chick with those. She kept looking for insects instead. Cowbird chicks seem to thrive on a lot of different diets. As adults they return to a fairly vegetarian life stile, similar to that of other related Blackbird species.

I was first introduced to the intriguing behavior of Cowbirds as a postdoc at the biology department of the University of Trondheim, Norway. Researchers Arne Mosknes and Eivin Roskaft had turned from their brood parasitism studies of European Cuckoos to the American example, the Cowbird. Cowbirds are far more common than the more solitary Cuckoos and Eivin and Arne got to do research in a far warmer climate.

Saturday, June 5, 2010

Granit Creek, Yavapai County

For many years on Memorial Day Weekend, my watercolors have been part of the annual Western Fine Art Show of the Phippen Museum in Prescott. The show closes daily at five pm and I use the evening hours to explore. This year the nights are still too cold to find anything but roaches at the lights in town and it hasn't rained for a while, so riparian areas are the best places to find wildlife.

On Saturday evening, I walk from the Watson Woods Riparian Preserve along Granite Creek to the east shore of Watson Lake. I carry a flashlight, important to avoid snakes and helpful to check for bugs.

Most day-active insects have retired for the night in closing flowers and in leaf axels.

Scores of Ladybugs for example, Wasps (Horntail Tremex columba above left), Grasshoppers (Green Bird Grasshopper, Schistocerca shoshone above right), Dragonflies (Meadowhawk below right), and the first Cicadas (Platypedia sp.) of the season.

I'm not sure whether the big Carpenter Ant is licking sweet juice from the blooming oak or is preparing to sleep.

The little Soft-winged Flower Beetle Collops sp. seems to have found the softest bed of all in a tuft of willow cotton caught in a weed.

The beautiful Blacktailed Rattlesnake, Crotalus molossus is turning in for the night as the temperature will go down into the forties. As the summer temperatures get hotter, he will shift his activity phase to the cooler nights. Bullfrogs drone from the lake shore after sunset and several Woodhouse's Toads, Bufo woodhousii are crossing the road.

Night active weevils, Dorytomus inaequalis remind of spiders with their long legs and jerky motions as they appear on the bark of Cottonwood trees.

Some Hyaline Grass Bugs, Liorhyssus hyalinus, land on the flowers of Evening Primrose that seem to glow in the dark.

Over all there is much less activity than last year at this time when it was warmer and we also had to cope with an unseasonal down-poor during the show.

Tree Swallows are stirring sleepily on their perches. Maybe they ate all the bugs.