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 (see "Update" below). 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!

Update: This genus has now been placed in the family Thynnidae.

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.