Thursday, August 28, 2014

White-whiskered Grasshopper

One of the most abundant, yet inconspicuous grasshoppers in North America is the little White-whiskered Grasshopper, Ageneotettix deorum. Easily overlooked as just another drab grasshopper, it can be easily recognized by its white antennae and red or orange hind tibia ("shin" segment on the hind leg).

This species is a member of the family Acrididae and the subfamily Gomphocerinae, known as slant-faced grasshoppers. The head of the White-whiskered Grasshopper is not as acutely sloped as its relatives, but it shares other subtle characters in common.

While most slant-faced grasshoppers are found clinging to grasses in the vertical plane, A. deorum is perhaps most often seen on the ground. When flushed from its hiding place it may leap into the middle of a trail where it could either hunker down, hop away again, or crawl rapidly into nearby grass tussocks. Only when it is walking do you easily see those bright red hind legs.

This is not a particularly large grasshopper, males ranging from 11-28 millimeters, female 15-28 millimeters. It is one of the few species in which both genders are nearly identical in size.

The White-whiskered Grasshopper occurs from the Great Lakes (Michigan, south and west to Indiana, Minnesota, and Illinois) through most of Missouri, western Arkansas, and Texas, all the way to the Pacific coast (southeast British Columbia, eastern Washington and Oregon, and much of California). Adult specimens can be found commonly from mid-July through early October.

Ageneotettix deorum frequents dry grasslands with short grasses, so I find it abundantly here in Colorado Springs on the fringe of the Great Plains. I still get confused periodically because of the variability of this species in terms of size and markings. Larger individuals can certainly be mistaken for grasshoppers of other genera. Other grasshoppers can have white antennae, and the White-whiskered Grasshopper can occasionally have darker antennae. The hind tibia is usually hidden under the edge of the hind femur when the insect is at rest, and there are simply few other consistent markings to go by.

The sheer abundance of this species puts it in the category of a rangeland and crop pest. During outbreaks there can be up to 25 adult specimens per square yard; and the species can account for fifty percent or more of the grasshopper fauna. Wheat is particularly vulnerable, but A. deorum also enjoys Kentucky Bluegrass and other kinds of music...I mean....forage. It will even feed on dried, fallen grassblades, seeds, dung, and deceased insects.

Eggs are laid in the soil in the summer and fall, hatching the following spring. Nymphs progress through five instars before reaching adulthood, roughly 40-48 days after emerging from the egg. The adults fly well, but flights are generally short (3-6 feet), and mere inches over the ground.

Sources: Bland, Roger G. 2003. The Orthoptera of Michigan. East Lansing: Michigan State University Extension Bulletin E-2815. 220 pp.
Capinera, John, L., Ralph D. Scott, and Thomas J. Walker. 2004. Field Guide to Grasshoppers, Katydids, and Crickets of the United States. Ithaca, New York: Comstock Publishing Associates (Cornell University Press). 249 pp.
Helfer, Jacques R. 1972. How to Know the Grasshoppers, Cockroaches, and Their Allies. Dubuque, Iowa: Wm. C. Brown Company Publishers. 359 pp.
Pfadt, Robert E. 1996. "Whitewhiskered Grasshopper," Wyoming Agricultural Experiment Station Bulletin 912

Tuesday, August 26, 2014

Scolops Planthoppers

Some insects are so unique that they cannot be mistaken for anything else. The planthoppers in the genus Scolops, family Dictyopharidae, are cute, squat little insects with an elongated "nose." Think of the caricature of Cyrano de Bergerac, shrunk down to about 5-8 millimeters.

a specimen from Colorado

There are currently 32 recognized species of Scolops, and the genus is unique to southern Canada, the U.S., and northern Mexico. Though they feed on plant sap, they are not pests of any crop, so consequently very little is known about their biology. They all look pretty much alike, being straw-colored, brown, or gray with the characteristic horn.

a specimen from Iowa

Some species have short-winged forms in addition to the usual long-winged form. Differences in the venation of the front wings have been used in separating the species. The number, length, and arrangement of spines at the tip of the hind tibia ("shin" segment) has also been a character used to differentiate similar species.

The fourth-instar nymphs of at least some Scolops species produce wax from glands near the rear margin of some of the abdominal segments. Most planthoppers in the superfamily Fulgoroidea produce waxy secretions that help repel predators, or disguise the 'hopper as cottony plant debris.

a specimen from Arizona

In my own experience, Scolops are most common in arid habitats, especially dry fields, prairies, and grasslands, even in otherwise moist climates. There are a few host plant records for these planthoppers, compiled on the University of Delaware website cited below. Most host plants seem to be in the families Asteraceae and Chenopodiaceae.

I call Scolops "rhinoceros planthoppers," but there appears to be no formal common name for the genus. One species, S. perdix, is known as the "Partridge Scolops." They certainly can "hop," and this habit may make it difficult to know whether a given specimen is feeding on a particular plant, or simply landed there after hopping to escape your approach.

another Colorado specimen

Sources: Bartlett, C.R. 2014. "Genus Scolops Schaum, 1850," Planthoppers of North America. College of Agriculture & Natural Resources, University of Delaware.
Lawson, Paul B. and R.H. Beamer. 1930. "Some New Scolops (Homoptera, Fulgoridae) with Notes on Other Species," J. Kans. Entomol. Soc. 3(3): 67-72.
Liang, Ai-Ping and Michael R. Wilson. 2002. "Wax-secreting, Cuticular Structures in Nymphs of Scolops abnormis Ball (Hemiptera: Fulgoromorpha: Dictyopharidae)," J. Kans. Entomol. Soc. 75(2): 132-137.
Osborn, Herbert. 1938. "The Fulgoridae of Ohio," Ohio Biol. Survey Bull. 35, 6(6): 283-357.

Friday, August 22, 2014

Colorado's State Insect: Colorado Hairstreak Butterfly

You can't say that the Colorado state legislature has never done anything good. Back in 1996 it passed a bill making the Colorado Hairstreak, Hypaurotis crysalus, the state insect. Heidi and I finally got to see this magnificent butterfly this past Monday, August 18, in North Cheyenne CaƱon Park here in Colorado Springs, after looking in vain for the last 3-5 years.

Just why this insect is so elusive is something of a mystery to me, though we noticed that the butterflies favored healthy oak trees free of most galls and other signs of weakness. The Gambel's Oak, Quercus gambeli, is the host plant for the larva. The oak is widespread at elevations from about 6,500 ft. to 7,500 ft., so the butterflies should be equally abundant one would think.

These are fairly large butterflies for members of the hairstreak family Lycaenidae, with a wingspan of 32-38 millimeters. They normally rest with wings closed, and their dull gray underside, striped with white and brown lines, a little orange and blue trim, make it easy to overlook them. When they open their wings to bask, however, they reveal their full glory. The dorsal surface of the wings is largely vivid purple, with black margins and a black patch or band on the forewing. Bright orange spots along the edges, and delicate "tails" on the hind wings add some pizzazz.

Males, like most hairstreaks, are territorial and will defend a given oak tree from rivals. We witnessed several instances of one male chasing another on a south-facing slope in the park at an elevation of slightly more than 7,000 ft.

This species rarely, if ever, visits flowers for nectar. Instead, it feeds on fermenting sap from wounds in trees, on the exudates of developing acorns (see image above), and on the honeydew secreted as a waste product by aphids and scale insects.

The larval stage of the butterfly is yellowish green, slug-like in form, and exceedingly cryptic. We may want to go looking for that stage next spring to complement our images of the adults. In late summer and fall, the female butterflies lay their eggs individually on branches and twigs of the host tree, where they overwinter. The caterpillars that hatch then consume the new oak foliage as it develops.

The story of the rise of this butterfly to the status of State Insect involves the usual lobbyists: School children. In this case, it was thanks mostly to the fourth grade class of teacher Melinda Terry at Wheeling Elementary in Aurora, Colorado.

There is but one generation of this butterfly annually, and while specimens have been recorded from May to November, they reach peak abundance in July and August. Besides Colorado, this insect is found in Utah, Arizona, New Mexico, the southeast edge of Wyoming, and extreme eastern edge of Nevada, barely inching across the border.

The "type" specimen, from which the species was described, was collected at Palmer Lake in El Paso County, Colorado (just north of Colorado Springs), in 1873. At least, that was the year of publication of the description, by W.H. Edwards.

Look for the butterflies to be active even on cloudy days, and right up until dark. Indeed, we encountered them after a thunderstorm skirted the Seven Bridges Trail in the park, on our way back to our car.

Sources: Brock, Jim P. and Kenn Kaufman. 2003. Kaufman Field Guide to Butterflies of North America. Boston: Houghton Mifflin Company. 384 pp.
Cranshaw, Whitney and Boris Kondratieff. 2006. Guide to Colorado Insects. Englewood, Colorado: Westcliffe Publishers. 232 pp.
Ferris, Clifford D. and F. Martin Brown. 1981. Butterflies of the Rocky Mountain States. Norman: University of Oklahoma Press. 442 pp.
Lotts, Kelly and Thomas Naberhaus. 2014. "Colorado Hairstreak," Butterflies and Moths of North America (BAMONA).

Wednesday, August 20, 2014

Aphid Killers: Pemphredon Wasps

Aphids are the insect equivalent of the wildebeest: they exist in vast numbers, and pretty much everything else eats them. Some other insects even specialize on aphids as prey. Chief among those are the "aphid wasps" in the genus Pemphredon, family Crabronidae (formerly a part of the family Sphecidae).

Not surprisingly, aphid wasps are not very large. Most are only ten millimeters in length if not smaller. They are solid black, and look a bit like a miniature thread-waisted wasp, the abdomen being on a short stalk (petiole) attached to the thorax. They have a cubical (square) head. These wasps are forever on the move, so it is very difficult to observe them, let alone get images.

The genus Pemphredon includes 20 recognized species in North America north of Mexico. Collectively, they range over most of the continent.

© Judy Jay in Bohart & Menke, 1976

Aphids are most abundant in spring and fall, so it is no surprise that Pemphredon are most commonly seen in May, then again in August and September. Pay attention to any aphid colony on a tree or weed, and eventually you will see these little wasps hunting. It is likely they also feed on aphids as adult wasps. Aphid wasps will visit flowers, but are only occasionally seen on blossoms.

Pemphredon are solitary wasps, each female making her own nest. She uses pre-existing cavities in wood, hollow stems, or she tunnels through the pith of broken twigs or berry canes. In fact, stems with thorns may be preferred because they are not likelyto be consumed by vertebrate herbivores.

I once spotted an uncharacteristically motionless Pemphredon on the side of a log. It was unmoved as I took images, until....a female made a hurried exit from a tunnel. Both wasps landed so close to me that I managed only one half-focused image of the pair, male on top, before they split. He had been waiting just outside her nest tunnel in hopes of mating with her. You can see her two antennae protruding from her hole, just in front of the male wasp in the above image.

The female wasp hunts aphids in their colonies, plucking them off stems and leaves with her jaws, stinging them into paralysis or simply crushing them, and then flying them back to her nest. She will stockpile ten to several dozen victims. One industrious female Pemphredon lethifer in England harvested 89 aphids for one cell! She will lay an egg after the last victim is gathered, but the egg may be placed at the back of the cell or halfway to the front.

Once she completes a cell, she then creates a partition, usually of chewed plant pith or sawdust, to close the cell, and create the bottom of the next cell. These partitions can be very thick, over 25 millimeters in some cases, perhaps the better to discourage parasites from digging through. She thus fills the tunnel from bottom to top, with as many cells as it will acoomodate. In situations where a twig is wide enough, some Pemphredon species will create branching tunnels instead of a single linear one.

Sometimes, the female wasp will guard the front of her completed nest to chase off potential parasites or competitors. Small carpenter bees (Ceratina spp.), compete for the same pithy-twig nesting sites as Pemphredon, and are not above destroying the wasp's nest to create their own living space.

Tiny cuckoo wasps (Omalus spp.) are parasites of Pemphredon nests, as are ichneumon wasps (Perithous mediator), bee flies (Anthrax irroratus), satellite flies (Senotainia trilineata), and other wasps and flies.

You can create housing for aphid wasps simply by drilling small diameter holes in a block of wood and hanging it off the ground under a protected place, like the eave of a garden shed. There are also ready-made lodges sold commercially for solitary bees that can be modified to suit the wasps, too.

Sources: Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.
Dollfuss, H. 1995. "A World Revision of Pemphredon Latrielle 1796 (Hymenoptera, Sphecidae)," Linzer biol. Beitr. 27(2): 905-1019.
O'Neill, Keven M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca, NY: Comstock Publishing Associates (Cornell University Press). 406 pp.