D e s e r t E x p o s u r e
October 2011
What's Bugging You?
The answer may range from voracious aphids to the colorful cochineal, the tricky blister beetle to the villainous assassin bug. In the insect world of the Southwest, variety is indeed the spice of life.
Jay W. Sharp
The population of insects in the desert basins and mountain ranges of the Southwest falls far short, in terms of sheer numbers, of that in many other parts of the United States, such as in the densely vegetated and humid estuaries along the Gulf Coast. The diversity of species across the Southwest, however, may equal or exceed that of any place else in the country. As Floyd G. Werner notes in Insects of the Southwest, which he co-authored with Carl Olson, "The Southwest has a concentration of diversity that is unbeatable in the United States."
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Ladybird beetle, which preys on aphids and cochineal insects. |
The 100,000 or more insect species in the Southwest amount to a small percentage of the possibly 10 million species throughout the world. The ever-changing mix within our various insect communities and the variability among the species, however, reflect a wide variety of ecological and environmental conditions. These range from hot desert basins (where summer temperatures climb well above 100 degrees Fahrenheit) with sparse vegetation or almost barren sand dunes; to widely separated river bottoms with dense shrub and thick woodlands; to mountain slopes and valleys with pygmy woodlands and park-like forests; to towering peaks (where winter temperatures can fall well below zero) with subalpine forests. The insects have adapted to every ecological niche in the Southwest, making their homes in the rocks, soils, air, plants and animals.
The insects vary almost unimaginably in terms of size, form, color, range, habitat, diet and environmental roles and in almost science-fiction life cycles and behaviors. But for all their differences, they are bound together by certain common characteristics. Every species has a head, a thorax and an abdomen. The head has eyes, antenna and mouthparts. The thorax, or middle body segment, bears wings and six jointed legs. The abdomen contains the heart, the digestive tract and the reproductive organs. Every species has an exoskeleton that encases vital organs.
A few examples suggest the breadth of the diversity within these basics:
Aphid
"Of all the bugs, the aphids are probably the most interesting," William Atherton DuPuy wrote in his Our Insect Friends and Foes, first published in 1925.
In southwestern New Mexico, for instance, the aphids, or "plant lice," comprise various species that come in a range of sizes (all small, from one- to three-sixteenths of an inch in length, according to Werner and Olson) and in a variety of colors (from green to bright yellow to black to brown). Soft and pear-shaped, the typical aphid has a distinctive pair of cornicles, or "honey tubes," protruding from the rear of its abdomen. When called to move, perhaps due to overcrowding or declining plant forage, the aphid may dress itself in wings, which will take it to new fields.
The aphid, well represented across the Southwest, often gets very choosy in selecting the plant on which it will feed. One species may dine just on your roses or another of your garden plants. A yellow and black species lives solely on milkweeds or oleanders, note Werner and Olson, who add, "The brown aphids that make a shiny mess under arbor vitae trees [a species of conifer] can't even live on the related junipers."
In feeding, the aphid inserts its straw-like proboscis, or "bill," through the plant skin and sucks up the fluid, causing leaves to shrivel and, sometimes, the plant to die. Because the plant fluids lack amino acids essential to life, the aphid calls on a bacterium, which lives within specialized cells, to provide supplementary nutrients — the insect's way of taking vitamins.
Prodigiously reproductive, the adult female aphid of the early spring may carry within her body not one, but two, generations — or a pregnant daughter. It amounts to a kind of biological telescoping of the reproductive process, with no need for males. An aphid population, all female from spring into the summer, can explode almost overnight. The male aphid finally makes an appearance in the fall, as the sunlight wanes and the temperatures fall. It and the female mate. The female now produces an egg that can survive through the winter, yielding a larva that renews the aphid's reproduction cycle come spring and summer.
Fortunately, aphids serve as a banquet for ladybird beetles and their voracious larvae as well as for parasitic wasps and aphid lions. Otherwise, aphids would soon engulf us all.
Strangely, the aphid, secreting honey dew from its cornicles, also serves as a kind of milk cow, or more specifically, a "honey cow," for some ant species. DuPuy wrote, "Ants follow these aphids about and lap up this honey. They even have flocks of them and milk them regularly."
Cochineal Scale
The cochineal, or "crimson," scale has played what is perhaps a unique role for insects on the world stage, having parts in textile manufacturing, territorial conquest, international commerce, cosmetic production, food processing and even science and art.
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Cochineal insect's fungus-looking coating on prickly pear cactus. |
It seems too small a creature for such an outsized task. The female cochineal insect, colored by red pigment, measures only some one-sixteenth to one-quarter of an inch in length; the male measures about half the female's length. She has neither wings nor legs; he has both. She has the shape of an engorged tick; he has more the look of a typical insect, with the addition of two distinctive filaments extending from the rear of his abdomen.
The cochineal covers much of the lower elevations in the western United States and Mexico, including our desert basins in southwestern New Mexico. According to the Arizona Wild Flowers website, the cochineal feeds almost solely on the pads of selected prickly pear cacti species. Like the aphid (a related insect) the female drives her tubular proboscis through the cactus skin, where she will remain affixed for the rest of her life, sucking out the juice. Simultaneously, she produces a white, waxy, fungus-looking coating that will help protect her from predatory insects and birds and shade her from the desert sun. She nevertheless sometimes falls prey to a rare carnivorous caterpillar and, more commonly, to our good friend, the ladybird beetle. Over time, a heavy cochineal infestation can kill its resident plant.
As she feeds, the immobile female cochineal produces eggs beneath her abdomen. When the eggs hatch, the legged juveniles, females and males, called "crawlers," make their way to the edge of their home cactus pad. Wingless females produce long, ethereal filaments, which lift the insects into the desert wind. Some descend onto new host prickly pear cacti, where they will breed, make a new home, set a new dining table, molt and shed their legs, their traveling life over and done. Winged males take flight, searching for mates so they fulfill their role in nature's plan. They die within a few days.
As the Spanish discovered when they conquered Mexico in 1521, the cochineal scale insect, when crushed, yields a supreme scarlet dye, which the Aztecs had long used in the production of exquisite textiles. The dye would become an added incentive for Spain in its Mexican conquest; the Spanish held the source of the dye secret for years. The cochineal produced a major cash export for Mexico, second only to silver.
Over time and across Europe, it would, according to Werner and Olson, bring the color scarlet to royal garments, military uniforms, national dress, cosmetics, various foods and even Michelangelo's palette. It may have been incorporated in the cloth that Betsy Ross supposedly used in making the red stripes for the first flag of the United States. The cochineal still serves as the source of the dye that microbiologists use to stain slide specimens, although it pays a heavy price for the privilege: Some 70,000 cochineal insects are required to manufacture a single pound of the dye.
Blister Beetle
The blister beetle — named for its ability to exude from its joints a liquid that causes painful blisters on your skin — ranks close to the top of the list as one of the insect world's most clever and odious imposters, even if it is often colorful and relatively innocent looking.
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Blister beetle on bloom |
According to Donald J. Borror and Richard E. White in A Field Guide to the Insects of America North of Mexico, the typical blister beetle has an elongated and pliable body. It measures about a half inch to an inch and a half in length. The beetle, says New Mexico State University entomologist Charles R. Ward, in "Blister Beetles in Alfalfa," has thread-like antenna, non-bulging compound eyes, a bowed head and relatively long legs. "Primary body colors," Ward writes, "include black, brown or gray; different species have spots or stripes of yellow red, brown orange, black or white," depending on the species.
Of the more than 300 species of blister beetle that occur in the United States, several dozen make their home in the Southwest, where the adults feed, sometimes voraciously, on both wild and cultivated plants, often favoring honey mesquites. One of the Insects of the Southwest authors says, "I have seen stripped [by blister beetles] trees in a straight line several hundred feet long." If inadvertently harvested and bailed in large numbers with alfalfa, the blister beetle, which contains a toxic chemical compound called "cantharidin," can poison domestic animals, especially horses, that eat the hay.