Thursday, September 30, 2010

Hockeria rubra and host Harrisina brillians, a wasp and her host

This post is about one of the images of the slide show of the last blog chapter. Some Annual Sunflowers, Helianthus annuus along the Santa Cruz River attracted all kinds of flies, wasps, beetles and grasshoppers. Most of them congregated on the wilting leaves and seemed to gorge themselves on some oozing sap.

Among them was this reddish wasp with those over-sized thighs that indicated even to me that it is a  Chalcid wasp. Through our great multimedia network, Ron Meldetz, Henry Hespenheide, and Dennis Haines all identified it for me as Hockeria rubra (Ashmead, 1894). They even agreed!

Dennis added: 'The genus utilizes two separate groups as hosts. The females with pointed abdomens like H. rubra are lep larval parasitoids. Those with rounded abdomens like H. bicolor and eriensis utilize antlions. H. rubra's only recorded host is the Western Grapeleaf Skeletonizer, Harrisina brillians. I've collected both male and female nectaring on Eriogonum flowers.'

 Western Grapeleaf Skeletonizer, Harrisina brillians

The location of the wasp was not too far as the crow (and hopefully the wasp) flies from Charles (weevil specialist) and Lois (fulgorid specialist) O'Brien's backyard garden in Green Valley. This summer, Lois has had her hands full with the biological control (hand picking pregnant females) of the Grapevine Skeletonizer to protect a vine that has provided nourishment and refreshment to entomologists on countless field trips. So this find should make her happy.

Tuesday, September 28, 2010

Santa Cruz River to Montosa Canyon in the Santa Rita Mountains

Phillip Kline and Rich Hoyer introduced me to Montosa Canyon a couple of years ago. The beautiful landscape and the diversity of plant and animal life make it attractive all year round.  For my post-monsoon trip (or so I thought) on September 22nd I crossed the dry the Santa Cruz River in Amado and  followed Mnt Hopkins Rd into the canyon, spending most of my time in the lower part that has the lusher vegetation. There are very dry areas with small yellow blooming Acacias,  a creek, now dry, that supports a small riparian community, Desert Broom bushes that are oozing sap, and blooming Asteraceae along the road.

Click here to see more and larger images. On the images, click the upper right corner to make information visible

Later in the afternoon, a spectacular storm moved up from Mexico and provided breathtaking vistas. Official statistics indicate that the monsoon lasts till the end of September, and I guess sometimes that's true.

The storm and the associated drop in temperature cut my collecting time short. Under the lights of the Amado I 19 Rest Stop, where I usually find a plethora of beetle species, there was only one lonely beetle crawling on the wall. But this was my very first Arizona Nicrophorus species. Characteristically, these guys are much more common in cold, wet environments than in the desert.

Nicrophorus marginatus

Friday, September 24, 2010

Color-changing Leaf Beetles

The coloration of leaf beetles or Chrysomelidae is fascinating. Their colors do not only range from highly aposematic to extremely cryptic and from opaque to transparent or metallic-reflective, some leaf beetles can even change colors. 

While some species go through reversible changes repeatedly and quickly probably in a reaction to exogenous factors like light, temperature or humidity, others experience one irreversible color change that coincides with their ‘attainment of sexual maturity’ as Knab described it in 1909. He referred to the resulting mature color as ‘nuptial color’.
This color change is distinctly different from the chitinization and pigmentation process  right after eclosion (hatching from the pupa) and usually happens weeks or months later.
Most Chrysomelidae are single brooded and become sexually mature only after they have aestivated or hibernated. The same physiological changes that lead to sexual maturity seem to induce the color change. The resulting new look is so different that the two stages have sometimes been described as different species.
This blog chapter will concentrate  on  two Arizona leaf beetle species from two different sub-families, one cassidine and one chrysomelinae.

The Canyon Ragweed Tortoise Beetle, Physonota arizonae Schaeffer, 1925
For several years, towards the end of the monsoon season in late August, I found the freshly hatched adults among many last instar larvae and pupae on the leaves of Canyon Ragweed. At this time the perennial plant produces several feet-high stems with rich leaves. 

The newly enclosed, and presumably sexually immature beetles have a striking pattern of cream and brown spots. Surprisingly, they blend in well with the scar tissue of ragweed leaves that were damaged by larval feeding. 

On the 3rd of July 2009, before the non-mosoon of that year began, I finally found a single 'mature' individual. I only recognized it by its size and the three spots on the pronotum. It helped that I was actively looking for this type. At this stage, the beetles are metallic brown-green and somewhat camouflaged on undamaged leaves. I assume that this was a mature beetle that had over-wintered because we hadn't been able to find any larvae til then and also none of their very obvious frass pattern.

 Two color forms of  P.arizonae Photo by Rick Williams

Later that year a  friend sent me a picture of the two forms together, taken on September 8th . So the change seems to happen not too long after eclosion, before the winter pause.

Calligrapha serpentine (Rogers, 1854)
Is a very attractive leaf beetle living on Narrow-leaf Mallow (Sphaeralcea angustifolia) Desert Globe Mallow  (Sphaeralcea ambigua), and probably some related Malvaceae species in Mexico and in the US from Texas to Arizona. 

I have found mating adults in the grass land of Cochise County, AZ in early to mid July and in Grant County New Mexico in early August. Their elytra showed a distinct black linear pattern on a vividly iridescent green base color.

On September 4 September 2010 I went back to a patch of Mallows 2 miles north of Lochiel, Cochise Co. where I had seen the beetles last year in late July. I was quite surprised to find bright red leaf beetles with exactly the same black pattern on one plant and only hairy red and black leaf beetle larvae on other Mallows.

 A post by Sheri L. Williamson from Oct. 2009 on confirmed that the green and the red beetles were indeed the same species. She also connected me to the delightful True Confessions of a Citizen Scientist by S. A. Russel who had followed C. serpentina from the egg to larva, pupa and early red imago and to mature green nuptial beetledom. 

Since this change from red to its total complementary opposite, green, seems particularly interesting, I decided to observe its progress in the five beetles that I had collected.

   September 10. All  5 beetles are still red
The problem was to provide appropriate food because Globemallows are spring flowers in Tucson and have just about no leaves in summer. My beetles had to spend the first three days without food in the fridge and then lived for a couple of weeks on an unusually diverse diet of several Mallow and Hibiscus species that I brought home from field trips to the Tucson Mountains, Mount Lemmon and Kitt Peak.

 September 15. All beetles are showing patches of green

After 5 days one beetle was still mainly tomato-red. The others showed patches of green, mostly on the lateral portions of the elytra. The biggest, roundest beetle (probably one of  the  females) appeared more green than red.
September 16. The big female is nearly all green, one male is still mostly red. 

September 18. All beetles have green elytra but the four smaller ones are still a little paler than the big female. 

September 19. All beetles are bright green
The color change had taken about 8 days. It didn't happen gradually, but patches switched from red to green rather abruptly, first in the lateral areas of the elytra and then moving towards the center seam.

I'm still curious about the physiological changes and how the colorshift is correlated with the process of reaching sexual maturity. I did not observe any mating attempts.  Little is known in which form these beetles overwinter. The post-monsoon season is dry and a lot of herbaceous plants are already starting to shrivel up. So my guess is that the adult beetles will enter a resting phase now, and new larvae will grow up during the vegetation seasons of he next year.

Due to the lack of food I had to end my own observations here. 

Friday, September 17, 2010

Velcro bug, el Torrito, Mesquite Twig Girdler, or Oncideres rhodosticta: the most abundant beetle in Arizona after the monsoon

It’s Velcro-bug time again!
Anywhere between Green Valley and Sierra Vista, Arizona, and probably all over New Mexico and far into Texas, border patrol agents, gas station and supermarket employees, and everyone else who leaves his porch lights on at night is familiar with those half-inch long beetles that cling to every surface as if glued to it. They hold on with little hooks on their feet and even with their mouth parts. For a good reason, as in nature being picked up usually means being eaten by a bird, a grasshopper mouse or a lizard.

Male (left) and female (right) Mesquite Girdler
During the day the beetles rest motionless clinging to the bark of a tree, mostly well hidden by their cryptic wing pattern. Observed closely, the shades of dark-brown and silver-grey and the raised reddish dots are very attractive. The scientific species name Oncideres rhodosticta refers to those markings which distinguish this very common species from the related rarer Oncideres quercus and the much larger cousin Lochmaeocles marmoratus, all found in Arizona.

Arizona members of the tribe Onciderini. Mesquite Girdler on the right

Like most adult longhorn beetles, adult O. rhodosticta feed on plant material. The chew leaf buds and the green bark of fresh mesquite twigs. Sometimes the nightly feeding frenzy of the beetles leaves the ground under a tree littered with chewed-off leaf-matter and twigs.

Life cycle of the Mesquite Twig Girdler Oncideres rhodosticta :
Adult twig girdlers eclose from late August to early November. 
Towards the end of our summer monsoons, the female beetles create the most well-recognized sign of O. rhodosticta 'infestation' when they prepare a nursery for their off-spring: Dead or dying finger-thick mesquite (or sometimes Acacia) branches that stay connected to the tree and usually carry the wilted, bleached leaves like flags into the winter months.
The common name, Mesquite Twig Girdler, hints at the story: Before she lays her eggs, the female chews a precise, complete circle around a finger-thick twigs. This task can take up to two days. She bites all the way through the Xylem and Phloem of the bark and thus disconnects the branch from its water source. Then she chews a separate shallow grove for each of about 8 eggs in the distal, dying part of the branch. The larvae will hatch and live in the wood until they are grown, pupate, go through their metamorphosis and hatch as adult beetles by the end of the next monsoon season to restart the cycle.

Female Mesquite Girdler at her girdling site
Most wood boring insects attack sick, injured or dead wood rather than a living tree. This is partly because of the ability of healthy trees to fight intruders by ‘gumming’ them up, that is by drowning and encapsulating them in sticky resin rich tree sap. So the female Mesquite Girdler protects her eggs by cutting off the tree’s defense lines. A glob of fresh tree sap often hangs from the girdling cut: the trees attempt to fight the parasite which didn't reach its target. The nursery that the longhorn beetle creates is so attractive that several other insect species infest the girdled branches. I have raised more wasps, buprestids, anobiids, bostrichids and dermestids from collected girdled branches than O. rhodosticta adults.
Of course, the pruning-activity of  the beetles comes as a cost to the trees. They lose the carbohydrates stored in the girdled twigs and a part of their photosynthesis-machinery.  However, a study of Texas Tech. University showed no conclusive results concerning the use of the beetles to control the mesquite tree overpopulation of the grass lands.  Natural girdler infestation can cause an over 30% reduction of the canopy, which does not seem to harm the mesquite trees but instead to induce healthy re-growth in the following season.

Living and dead Mesquite Girdlers under the lights of the I 19 border patrol check point
Photo by Joyce Gross Sep. 2008 
Mass occurrences of members of a single species that last for more than a couple of vegetation cycles, as observed in the Mesquite Girdlers in southern Arizona since 2007, usually indicate a disturbance of the natural balance. In this case the overabundance of mesquite trees on former grass lands is certainly a contributing factor. The mesquite tree was introduced into the grass lands through the widespread practice of feeding mesquite beans to cattle. While the nutritious pods are digested, the seeds pass the bovine digestive system not only intact, but with an increased capacity to germinate. But the trees have been with us at least for several decades and the Girdlers seem to proliferate more than ever since 2007. A climate changing to drier and hotter summers seems to have favored this species, while its predators, parasites and diseases are still lagging behind. But there is no doubt among entomologists that these factors will eventually catch up to collapse the population explosion of the girdlers.

PS: The numbers of Mesquite Girdlers did indeed collapse in 2011. Since then I have not seen more than 3 to 5 on my nightly light trap, even during the prime season and in mesquite areas. I was wrong about one thing though: the summers from 2005 to 2009 were not particularly hot or dry in hindsight. It only got hotter and drier from then on.

Wednesday, September 8, 2010

Mohave Rattlesnake revisited

Ten days ago, Frodo, our youngest dog and son of a feral coyote half-breed got his fourth snakebite in as many years. He started his snake encounters as a tiny pup. To him, most bites do not seem much worse than a nasty bee sting, hardly interrupting his play. This time however, he was distraught enough to leave his breakfast to Montana the Husky, so we took him to the vet, just in case. When we got there his hugely swollen head was already returning to normal (I didn't have the heart to document his misery on film) and all he needed was an antibiotic and a painkiller. Presumably all four bites were administered by Western Diamondbacks. Two of them we caught just after the attacks.

Frodo, Tana and a day-time visitor. Nocturnal ones are much more ominous.

Three days ago, at four in the morning, the snake alarm went off again: Frodo’s sharp rhythmic barks. All three outdoor dogs were pointing at a snake from a save distance this time. I’d just returned from an exhausting two day field trip the evening before. Getting out of bed and keeping my eyes open proved rather difficult. The first attempt to noose the snake with the snake-stick failed. The sudden notion that this was no ordinary Diamondback, but probably a Mohave Rattler gave me enough of an adrenalin boost to reopen the noose and place it safely this time. By then, Randy had arrived with the transport bin. The snake securely stored, we went back to bed.

Mohaves are rare here. Some 15 miles further south the herpetologists of the Arizona Sonora Desert Museum have been keeping records for years, and they never got anything but Western Diamondbacks.

When I mentioned a Mohave Rattlesnake in one of my earlier blog chapters, some readers correctly pointed out that I couldn’t be completely sure of the identification just by looking at the relative width of the tail-bands alone. So while I’m still not getting close enough to a rattler’s head to count the scales between the eyes, this time I took some pictures to enlarge the details later. Yes, it’s clearly a Mohave Rattler Crotalus scutulatus. Where this one has two big scales, the Western Diamond-backed Rattlesnake Crotalus atrox has a row of 4 or more small ones.

Thinking about the possibility that this snake is not only producing hemorrhagic venom (which is bad enough by itself) but also a more deadly neurotoxin, we felt our resolution to simply remove snakes from the premises waver. But finally Randy carried him just especially far away from the house to an out-of the way part of the State Trust Land and the border of an old lime-stone quarry. Laika, our wolf-dog, trotted along on his heals. When he released the snake she respectfully stood aside. She’s much too smart to get too close to any snake that she’s aware of.

Note the wide white bands of the tail, another characteristic of the Mohave Rattler that is less reliable but easier to see than the facial scales.