Wednesday, September 29, 2010

Wasp Wednesday: Neorileya

Most people think of wasps as fairly sizeable, menacing social insects that sting. Nothing could be farther from the truth. The overwhelming majority of wasps are solitary, tiny, and stingless. Collectively, these little creatures are known as “micro-Hymenoptera.” They are chiefly parasites, hyperparasites (parasites of parasites), or parasitoids (parasites that invariably kill their host). I had the good fortune to come across one such wasp recently, when I spied a 2-3 millimeter wasp on a string of eggs laid by a giant mesquite bug, Thasus neocalifornicus. This started quite a sleuthing exercise.

While I recognized the wasp as some sort of egg parasite, I had to narrow the list of suspects down to one of several possible families. My first step was to contact both the Entomo-l listserv and my friend Eric Grissell, an authority on micro-Hymenoptera. Entomo-l is an international e-mail list of professional entomologists, and I was pleased and grateful to get several responses, none of which agreed with one another! One respondent urged me to link to an image, and they did so on Talk Like a Pirate Day, which made for an amusing exchange.

While the dimensions of the wasp stretched the boundaries of my camera’s capabilities (I shoot with a Canon PowerShot SX10 IS), I did link the resulting image in my next post to the listserv, and Dr. Grissell, and this narrowed the focus to two families: Encyrtidae and Eurytomidae, both of which include egg parasites. Eric even suggested a potential genus: Neorileya. He also copied his response to me to another expert, Dr. Michael Gates at the Systematic Entomology Laboratory, Agricultural Research Service, United States Department of Agriculture.

Dr. Gates agreed with Eric and even suggested a possible species: Neorileya ashmeadi. I may try and collect some of the eggs to try and rear out the wasps for specimens I can send him for verification.

According to Gates’ revision of the subfamily Rileyinae (family is Eurytomidae if you recall), the genus Neorileya includes six species that collectively range from central California to Argentina. They are known to be endoparasitoids of the eggs of not only Coreidae (the family to which the giant mesquite bug belongs), but also Pentatomidae (stink bugs), Reduviidae (assassin bugs), and even Tettigoniidae (katydids, totally unrelated to the true bugs).

It is truly mind-boggling to think that an insect can carry out its own entire metamorphosis inside the egg of another insect, but that is just one of the many wonders of the wasp world that I hope to continue sharing with you on “Wasp Wednesday.”

Sources: Gates, M. W. 2008. “Species Revision and Generic Systematics of World Rileyinae (Hymenoptera: Eurytomidae),” University of California Publications in Entomology. 127: 332.
Goulet, Henri and John T. Huber, eds. 1993. Hymenoptera of the World: An Identification Guide to Familes. Ottawa, Ontario: Agriculture Canada. 668 pp.

Friday, September 24, 2010

Brown marmorated Stink Bug Invading Homes

Since this insect is literally making the headlines right now, I am re-publishing this post introducing the “brown marmorated stink bug,” Halyomorpha halys. Special thanks to John R. Maxwell for allowing use of his images of this insect.

Unlike the western conifer seed bug and the boxelder bugs, the brown marmorated stink bug is not native to the North American continent. It was first detected in Allentown, Pennsylvania in September, 1998 but probably arrived at least two years earlier. The insect hails from Asia, being indigenous to China, Japan, Taiwan and Korea.

Thus far, H. halys has amounted to a mere “nuisance pest” that appears in numbers on the exterior of homes as it seeks shelter for the winter. The adult insects fly well, and sometimes manage to creep indoors, much to the consternation of property owners. The fact that they can deploy their scent glands when under duress makes them even more unappealing.

Outdoors, during the spring and summer months, nymphs and adults feed on a variety of plants, shrubs, trees, and fruits. They sip liquid sap and fruit juices through beak-like mouthparts collectively called a rostrum. Their feeding causes mostly cosmetic damage and they have not yet attained pest status for that reason. This is not the case in their native range where they are especially problematic for soybean growers.

Unfortunately, these are non-descript bugs that are easily confused with innocuous native stink bugs like those in the genus Brochymena. Older nymphs like this one do sport distinctive spikes and spines, and black and white-banded legs.

It is the aggregation behavior of the adults in the fall that seems to be their most unique and identifying characteristic.

Since its first appearance in Pennsylvania, the brown marmorated stink bug has been discovered in the following states: Connecticut, Delaware, Idaho, Indiana, Illinois, Iowa, Maine, Maryland, Minnesota, Mississippi, Montana, New Jersey, New York, Nevada, Ohio, Oregon, South Dakota, Tennessee, Utah, Virginia, Washington, West Virginia, Wisconsin, Wyoming, and the District of Columbia. Specimens have also been intercepted by agriculture officials in California and Florida. Should you suspect you have found this species in a state not on this list, you are urged to report your finding (backed up with specimens whenever possible) to your state department of agriculture.

As with all of the insects being profiled in this series, care should be taken to exclude the bugs from entry into structures by repairing worn weatherstripping, mending holes in window screens, and sealing other possible points of entry with silicone caulking and other such materials.

Wednesday, September 22, 2010

Wasp Wednesday: Myzinum

Sexual dimorphism, the graphic physical and morphological differences between genders, can be extreme in the wasp world. One example of this is in the genus Myzinum, members of the family Tiphiidae. They should be common right now in most parts of North America, at least east of the Rockies and in the Southwest where they visit autumn wildflowers like goldenrod (Solidago) and thoroughwort (Eupatorium).

There are currently ten recognized species in the genus north of Mexico, but they have been very difficult to separate, even for experts. There is no such issue when it comes to telling males from females, however. Well, the only problem for non-experts is recognizing that the genders don’t constitute different species, if not different genera or different families.

Male Myzinum species are seemingly more abundant than the females for a number of reasons. They spend more time on flowers and so are more conspicuous. They can also gather in “slumber parties,” bedding down in the early evening in large groups on vegetation in fields and meadows.

The uninitiated assume that they are female wasps because the males sport an intimidating “pseudostinger” at the tip of the abdomen. The curled spine, part of the external genitalia, looks menacing to be sure. The body of the male is very slender, and he has long, straight antennae.

It may sound stereotypical and sexist to describe the female Myzinum as being larger-bodied, but there is no getting around that fact.

Her abdomen is very robust, her legs stouter for digging up the host organism (more on that in a minute), and she has short, coiled antennae. She is built for her lifestyle to be sure. Meanwhile, the male is merely a missile-shaped sperm-delivery animal. (Hoping that gets me off the male chauvinist pig hook).

Myzinum species are parasitoids of scarab beetle grubs, especially the “white grubs” of the May beetle genus Phyllophaga. Parasitoids are parasites that invariably kill their hosts. Female wasps somehow divine the presence of a grub below ground and dig up the beetle larva. The wasp then stings it into a brief paralysis and lays a single egg on it. The beetle grub regains control of its faculties shortly, and quickly buries itself once more, but the damage is done. The larval wasp that hatches from the egg bores into the beetle grub and begins slowly consuming it. The grub still feeds, creating more tissue that its internal wasp parasite will eventually eat. This host-parasite treadmill continues for some time, but eventually the wasp larva kills the beetle grub. The larval wasp then pupates and emerges as an adult wasp the following summer.

Pat yourself on the back if you simply recognize that the male and female Myzinum are two halves of the same organism. You are already ahead of the game. Remember that even entomologists who study this genus are continually boggled by them when it comes to sorting out the different species. Special thanks should go to Dr. Lynn Kimsey for correcting the mistakes of her predecessors and providing revised descriptions and a key for our nearctic fauna, not a simple task!

Sources: Kimsey, Lynn. 2009. “Taxonomic purgatory: Sorting out the wasp genus Myzinum Latreille in North America (Hymenoptera, Tiphiidae, Myzininae).” Zootaxa 2224: 30–50.

Tuesday, September 21, 2010

Update.

Once again I find myself apologizing for the relatively sporadic nature of my posts here lately. No excuses, really, though I have been working rather random hours at the Tucson Botanical Gardens, and consequently eating randomly, sleeping randomly, and writing randomly. Maybe I need to take a class on time management.

I also just concluded a project in which I reviewed chapters for a forthcoming self-published book on the natural history of Virginia Beach, Virginia, by Scott Bastian. He has been a delight to work with, and he will be turning out a pretty unique book that has a wealth of information stretching far beyond the locality of Virginia Beach. You'll hear more about this once it is off the presses.

A relative lack of rain this year in Arizona (except for the area immediately adjacent to the Mexican border) has meant that many insects have been lacking, or at least less numerous, than usual. Perhaps because the Tucson Botanical Gardens is heavily watered, I have found a surprising diversity of things there, and expect the trend to continue through October.

Best wishes to my readers for a fruitful fall of exploring, image-taking, and enjoyment of autumn colors.

Wednesday, September 15, 2010

Wasp Wednesday: Bicyrtes

Among the most commonly encountered members of the “sand wasp” guild are the eight North American species in the genus Bicyrtes (By-SIR-teez). Two species in particular are widespread in the U.S. and adjacent southern Canada. They are much more sedate and easier to approach than most other members of the subfamily Bembecinae (family Crabronidae), and their predatory habits earn them some respect as well.

Female Bicyrtes actively hunt the nymphs of stink bugs in the family Pentatomidae as food for their larval offspring. The next time your child turns up their nose at Brussels sprouts, let them know it could be a lot worse. Actually, the accepted prey of these wasps includes equally odorous leaf-footed bugs (Coreidae), and shield bugs (Scutellaridae) and assassin bugs (Reduviidae) have also been recorded.

Wasps that burrow in the soil are termed “fossorial,” and a female Bicyrtes is an excellent digger. She can nest in soil of a more coarse texture than most other sand wasps. I imaged this Bicyrtes quadrifasciata excavating a nest in South Deerfield, Massachusetts in fairly rocky soil on the site of a former pickle factory, long since razed but with pavement fragments and pebbles in abundance.

While many sand wasps nest in dense aggregations of dozens (if not hundreds) of individual females, I find that Bicyrtes tends to be more of a loner. The wasp uses a “tarsal rake” of spines on the segments of her front tarsi (“feet”) to tunnel about 15-20 cm down into the soil at a shallow angle. Depending on the species the burrow terminates in a single cell, or several cells branching from the main tunnel. She closes the burrow while she goes off hunting prey.

When returning from a successful hunt, the wasp uses subtle landmarks to relocate her hidden nest. Meanwhile, we can’t remember where we parked the car.

Most sand wasps practice “progressive provisioning,” feeding their larval offspring as they grow, but Bicyrtes stockpiles prey, laying an egg on the first victim to go into a given underground cell. Once she completes a nest, she sets out to repeat the process, having cached enough food ahead of time that she needn’t hang around to spoon feed her children.

Both male and female Bicyrtes are very fond of nectar, and become distracted enough at flowers that they can be closely approached. Look for them on the blooms of Dogbane (and the related Indian Hemp) as well as milkweeds, white sweet clover, wild carrot (Queen Anne’s Lace), and a variety of other weeds.

Bicyrtes can easily be told from similar wasps by the very boxy appearance of the back of the thorax. The angular hind corners of the thorax are often white. Plus, if you are able to get close enough to see that character, you are looking at something other than sand wasps like Bembix and Steniolia that stick around for about a millisecond before zipping off to parts unknown.

I leave you with a parting shot of a female Bicyrtes from Bentsen Rio Grande Valley State Park in Mission, Texas that I have yet to identify to species. Maybe one of you can solve the mystery. In any event, keep an eye out for these wonderful wasps that stick it to our stink bug foes.

Sources: Evans, Howard E. 1966. The Comparative Ethology and Evolution of the Sand Wasps. Cambridge, Massachusetts: Harvard University Press. 526 pp.
Krombein, Karl V. et al. 1979. Catalog of Hymenoptera in America North of Mexico. Washington, DC: Smithsonian Institution Press. Vol. 2, pp 1199-2209.

Wednesday, September 8, 2010

Wasp Wednesday: Northern Paper Wasp

When I lived in Cincinnati, Ohio I found the Northern Paper Wasp, Polistes fuscatus, to be among the most abundant of the social wasps. This has changed recently as the European Paper Wasp, Polistes dominula, has overtaken its native counterpart to become the dominant wasp, especially in urban areas. Still, most people living in the eastern United States and adjacent southern Canada are familiar with P. fuscatus.

Paper wasps belong to the same family as yellowjackets, true hornets, and potter and mason wasps: Vespidae. Whereas the yellowjackets tend to be wasps of northern North America, most diverse in boreal regions and cooler habitats, paper wasps are decidedly tropical, with only a handful of species ranging north into the U.S., and fewer still reaching Canada.

Paper wasp colonies are on the small side, rarely exceeding about 200 individual wasps. They build unprotected paper combs they suspend from twigs, stems, the eaves of homes, and other semi-protected locations. The stalk (pedicel) from which the nest hangs is sturdy and often coated with a dark substance that repels ants, the chief threat to the larvae and pupae inside the cells of the comb.

In North America, the life cycle of the nest begins when overwintering female wasps emerge from torpor and begin construction of nests. There is no apparent “worker” or “queen” caste in paper wasps, but recent studies have revealed that in fact some females are destined to become “gynes,” the reproductive females. Others will become subordinates to gynes. This is likely determined in their larval stage. More than one gyne may act as the “foundress” of a nest, but one individual eventually asserts her dominance, and the subordinate wasp leaves.

The gyne performs all roles as the nest founder, building the nest as well as securing food for her developing larval offspring. She makes the nest by harvesting fibers from wood surfaces, be it dead trees, dead woody stems, or fence posts. The fibers she scrapes she then chews into a saliva-soaked ball of pulp. Back at the nest she deftly plies the pulp into a strip of paper added to the existing comb.

Paper wasps are well worth having in the garden. They prey heavily on other insects, especially caterpillars. The Northern Paper Wasp has even been observed entering the silken tents of Fall Webworms to grab the hairy caterpillars. The wasp butchers her kill on the spot, stripping off any irritating hairs or spines that could not be easily consumed by the larvae back in the nest.

Once back at the nest, the wasp either feeds the larvae directly, or shares parts of the “meatball” with fellow workers that in turn distribute the food to the larvae. One larva occupies each hexagonal paper cell. Once the larva reaches maturity, it spins a silken dome over the top of the cell and then molts to the pupa stage. Shortly thereafter, an adult wasp chews its way out of the cap to freedom.

Late in summer, or in early autumn, the colony produces males. The male’s sole function is to fertilize the next generation of gynes. Watch a colony in August or September and see if you can tell the males from the females. It is actually pretty easy:

  • Males have long antennae, usually curled at the tips (females have shorter, straight antennae, though both genders have an “elbow” in each antenna)
  • Males have square, yellow faces (females have dark, triangular faces)
  • Males have a blunt tip to the abdomen (the abdomen of females tapers to a point)

Males and females both are abundant on flowers of goldenrods (Solidago) and throughworts (Eupatorium) at this time of year. With so many wasps easily visible at the same time, it becomes evident that the Northern Paper Wasp exhibits an extreme degree of variability in color and pattern. Most specimens will have a pair of large, deep red blotches on the second abdominal segment, but the yellow markings vary considerably.

Recent DNA analysis is adding mud to the situation instead of clarifying it, but chances are that the western “species” Polistes aurifer, shown below, is going to be lumped back in with Polistes fuscatus.

Enjoy watching these wasps. Their season is short, and unless you antagonize the ones on a nest (and they will give a threat display by standing on tip-toe and raising their wings), they make perfectly peaceful neighbors.

Saturday, September 4, 2010

(Wild) Butterfly Magic

Anyone visiting the Tucson Botanical Gardens lately who is disappointed to learn that the Butterfly Magic event begins in October hasn’t been paying enough attention to the butterflies that are flying freely around the garden outside of the tropical greenhouse. I tallied twenty-two species over the past month, most of those seen in the last week or so. Here’s the list:

  • Pipevine Swallowtail, Battus philenor
  • Giant Swallowtail, Papilio cresphontes
  • Checkered White, Pontia protodice
  • Southern Dogface, Colias cesonia
  • Sleepy Orange, Eurema nicippe
  • Dainty Sulphur, Nathalis iole
  • Cloudless Sulphur, Phoebis sennae
  • Gray Hairstreak, Strymon melinus
  • Leda Ministreak, Ministrymon leda
  • Marine Blue, Leptotes marina
  • Western Pygmy-Blue, Brephidium exile
  • Reakirt’s Blue, Hemiargus isola
  • Fatal Metalmark, Calephelis nemesis
  • Palmer’s Metalmark, Apodemia palmeri
  • Gulf Fritillary, Agraulis vanillae
  • Variegated Fritillary, Euptoieta Claudia
  • Empress Leilia, Asterocampa leilia
  • American Snout, Libytheana carinenta
  • Queen, Danaus gilippus
  • Common Sootywing, Pholisora Catullus
  • Fiery Skipper, Hylephila phyleus
  • Orange Skipperling, Copaeodes aurantiaca

The TBG has a dedicated butterfly garden, but there is such a diversity of plants on the grounds that something is blooming somewhere almost all the time. Water and shade are also plentiful, which benefits both the butterflies and the comfort of human patrons.

Please visit the Tucson Botanical Gardens whenever you can. There is literally something for everyone, from a Children’s Garden to a Zen Garden, to the Tropical Greenhouse. You can even bring the dog on Tuesday mornings, or stay late on the Third Thursday when you can hear a musical performance.

Wednesday, September 1, 2010

Wasp Wednesday: Evaniidae

It is always a challenge to select a wasp to profile on “Wasp Wednesday,” in part because there are so many to choose from, but also because I don’t have that many images of wasps…yet. I was thrilled today (August 31, 2010) to find an unusual and wonderful wasp to profile, right at my workplace at the Tucson Botanical Gardens. Right there inside the tropical greenhouse were flitting little ensign wasps.

Ensign wasps of the family Evaniidae get their common name from the tiny, flag-like abdomen that they habitually “wave” as they walk. They have a start-and-stop gait, bobbing their abdomens as they go.

Globally, evaniids are represented by 20 genera and 435 species. There are eleven species in the family Evaniidae in North America north of Mexico, in four genera. Two of those species are not native, and one of those immigrants is the one in the greenhouse at the Tucson Botanical Gardens: Evania appendigaster. It is large for an evaniid, adults measuring up to eleven millimeters in body length. Perhaps the most striking feature of the insect is its bright turquoise compound eyes, at least in living specimens.

Evania appendigaster may be native to Asia, but is widespread in tropical and subtropical regions. Here in the U.S. it is exclusively associated with urban areas, and mostly inside buildings. There is good reason for this strange habitat. This species is a parasite of the egg capsules of cockroaches. Its hosts include the American Cockroach, Periplaneta Americana, Australian Cockroach, P. australasiae, and Oriental Cockroach, Blatta orientalis. Those roaches are also aliens to North America, probably having crossed the Atlantic Ocean on slave ships from Africa.

The first U.S. record of Evania appendigaster (it has no common English name, sorry) was probably on June 5, 1879, from Washington, DC, as represented by a specimen in the collection of the Smithsonian Institution. Today, this species is most common along the Atlantic Seaboard and the Gulf Coast, as well as here in Arizona.

What is the life cycle of this wasp? Females search for the egg capsules (oothecae) of the roaches. Once it locates a capsule, the female wasp inserts her ovipositor into one of the eggs in the package and lays her own egg. She then departs in search of another ootheca. Her egg eventually hatches inside the roach capsule and the larva that emerges then consumes the cockroach eggs. It eventually pupates and the adult wasp chews its way out of the roach ootheca a week or so later.

I have observed the adult wasps feeding on honeydew secreted by aphids, like here on a cottonwood leaf in the Sweetwater Wetlands in northwest Tucson. Indoors, perhaps they will feed on spilled beverages? Who knows?

Excellent images and phylogenetic information can be found at the Tree of Life Web Project, courtesy of Andrew R. Deans. Deans is also the driving force behind another internet project, ”Evanoidea Online”. This resource covers not just the Evaniidae, but also related families of equally interesting wasps. There are also “keys” at that website that allow you to identify the North American Evanoidea.

Ensign wasps are not commercially available for cockroach control, at least to my knowledge, but it might be a venture worth considering. I know that I would sooner employ a non-toxic, mobile pest-control device to eradicate roaches instead of reaching for some kind of chemical at the local hardware store. The wasps are far more engaging, too.

Sources: Smith, David R. 1998. "Evaniidae in the Mid-Atlantic States: Seasonal Occurrence and Identification," Proc. Entomol. Soc. Wash., 100(2): 275-285.