Locust (26 page)

For a period of fifteen years, entomologists tacitly accepted Faure’s conclusions, although most writings used phrases such as “believed to be the migratory phase” to describe
spretus,
or “thought to be similar or perhaps identical to the Rocky Mountain locust” to portray
sanguinipes
. But Faure’s evidence supporting the explanation of the locust’s disappearance via a phase transformation was insufficient to convince Charles H. Brett, a professor of entomology at Oklahoma State University.

In 1947, Brett reported the results of his own experiments to definitively transform
sanguinipes
into
spretus
. Rather than just using crowding as the stimulus, Brett manipulated food, temperature, and humidity, hoping that the ghost of an extinct locust would be conjured up through these manipulations. It wasn’t. In fact, many of the environmental conditions in Brett’s experiments yielded creatures smaller than the original stock of
sanguinipes
. Undeterred, he concluded that
sanguinipes
would have consistently changed into the larger
spretus
if not for the interference of complicating factors.

In trying to salvage his hypothesis of phase transformation in the case of the Rocky Mountain locust, Brett creatively interpreted his data as revealing a possible cause of
spretus’
disappearance. In particular, he noted that
sanguinipes
adored alfalfa, a food source that produced stunted and malformed grasshoppers in his studies. From this observation of grasshoppers, Brett hypothesized that the introduction of alfalfa into the West had been deleterious to
sanguinipes
(and hence,
spretus
), leading to the demise of the locust.

Soon, entomologists were beginning to drop the extensive and delicate qualifiers from their language that tend to be so aggravating to the rest of the world. Without any further evidence, they were now stating, “Except for its brighter colors, longer wings, and greater flying ability, the Rocky Mountain grasshopper closely resembled the migratory grasshopper. . . . It was an extreme migratory ‘phase’ of the migratory grasshopper and not a different species.” Although the phase transformation of
sangunipes
into
spretus
had not been demonstrated
by experiment or observation, it was becoming established by dint of repetitive assertion.

 

The various and elaborate measurements of specimens by Faure and Brett may have convinced some entomologists, but taxonomists were not fooled by this numerical necromancy. After all, if we take various measurements of a tuna, a dolphin, and a mouse, we’re almost certain to conclude that the fish and the dolphin are much more closely related than the dolphin and the rodent. Numbers simply fail to reveal the characteristics that are meaningful evidence of a shared lineage—the presence of lungs or gills, scales or hair, milk glands or air bladders. These are the qualities that allow us to properly reflect evolutionary history and determine the degree of relatedness. In entomology in general, and acridology in particular, we often resort to qualitative differences in structures that most people would find peculiar at best, and perverse at worst. We spend a lot of time peering at grasshopper penises.

The genitals of a male grasshopper are elaborate structures, comprising a number of elegantly working parts. The external features include a couple of hinged plates or “doors” at the tip of the abdomen that are the grasshopper’s equivalent of a foreskin, protecting the more delicate internal structures. Also on the exterior of the creature’s abdomen are a pair of small, variously shaped protuberances called
cerci
. Some look like clubs, others like hooks, and some like tiny cowboy boots. The internal or concealed genitalia are a bit more amorphous. We refer to these structures as the
phallic complex,
which is not a psychological condition but a mass of variously membranous, leathery, and hardened features. In grasshoppers, the phallic complex is tucked away inside the tip of the abdomen, being prudently encased by the external plates and extruded only when mating is imminent. The phallic complex includes the penis, or more technically speaking the aedeagus, which is the organ that enters the female and through which sperm pass. Actually, I suspect that there is a bit of prudishness and squeamishness in using the term
penis
in entomology—it sounds more clinical and technical to rename a structure that appears so flamboyant compared to our own. Lying above the aedeagus is the epiphallus, a hardened structure that probably plays a role in ensuring a proper fit of the male and female genitals during copulation.

The explanation of why the male genitals of grasshoppers are so intriguing to taxonomists is fairly simple. To begin, these structures exhibit remarkable consistency within species but spectacular variation among species, even in cases where two kinds of grasshoppers seem to be otherwise similar in size, form, and color. The basis for these differences is probably, at least in part, a function of reproductive isolation. For a species to evolve and sustain genetic integrity, its members shouldn’t be trying to mate with other species. Species often have distinct body forms and colors that allow prospective mates to readily identify their own kind. Some grasshoppers use elaborate courtship rituals to ensure that the prospective mate is the “right one.” Not so for the spurthroated grasshoppers—a subfamily named for the conical protuberance that arises from between their front legs, giving the impression of an enlarged Adam’s apple or “spur throat.” Species in this taxonomic group (of which
spretus
was a member) are similar in appearance and undiscriminating in their foreplay.

For the spurthroated grasshoppers, sex is a lover’s leap. Males often hop onto almost any moving object of approximately the right size and color of a prospective mate, including females of other species and sometimes even other males. In the latter case, consummating the sudden relationship is, of course, hopeless. But in the former case, mistaken matings would seem possible. However, with his weirdly contorted genitals, the male is not able to insert his aedeagus into just any female. When a mismatched male is not summarily kicked off by the female, he spends long minutes tediously probing with his genitalia. But the elaborately sculpted tip of his penis simply doesn’t align properly with her genital tract. The result is that the tube that is extruded from the aedeagus in order to transfer the sperm doesn’t thread properly into the duct of the female that opens into her pouch that receives and stores the sperm. The system is a bit like a key-and-lock and without the male’s “key” finding a matching “lock” in the female, the effort ends in frustration. And so, one might ask, why don’t taxonomists use the female genitalia, the “lock” rather than the “key”? The explanation might reflect male chauvinism in science, but there is a more simple answer. Consider your front door—it is much easier to examine and describe the structure of your key than it is the inner form of your lock.

The value of the male genitalia for discriminating among species of grasshoppers was pioneered by Theodore Huntington Hubbell. Having earned his bachelor’s degree at the University of Michigan, he pursued graduate studies at Harvard. However, Hubbell left before earning his degree at the behest of a friend to teach at the University of Florida. While teaching, Hubbell managed to earn his doctorate at the University of Michigan and returned to his alma mater as the Curator of Insects in the Museum of Zoology in 1946. Hubbell became the museum director in 1955 and built a collection of Orthoptera (grasshoppers, crickets, and katydids) that now requires hundreds of drawers stacked into towering cabinets filling more than 5,000 square feet of floor space. Within this bonanza of biodiversity, Hubbell discovered the taxonomic Rosetta Stone of these creatures—the size and shape of the various knobs, spines, and twists of male genitals.

To be precise, Hubbell’s innovation was based on a rather simple insight, that different species had remarkably unique internal genitalia. Of course, the existence of the aedeagus was well known prior to his work. Plenty of morphologists had illustrated these graceful—and sometimes wickedly armed—structures, but nobody had thought of systematically comparing them among different species. It was here that Hubbell made his contribution by providing spectacular evidence of the diagnostic value of the concealed genitalia of grasshoppers. Soon, the entomological world came to accept this bizarre but effective approach to deciphering the identity of grasshoppers. And when the “gold standard” of taxonomy was applied to settling the identity of the Rocky Mountain locust, the answer was unequivocal. The phase theory had very nearly made the Rocky Mountain locust disappear as a species, but it was to be brought back into existence through its reproductive organ, a fitting means for perpetuating the life of a species.

In 1959, armed with Hubbell’s insights regarding the informative power of the male genitalia, the federal government’s foremost expert on orthopteran taxonomy declared in utterly unambiguous terms that the Rocky Mountain locust was not simply the migratory phase of
sanguinipes
(then
mexicanus
) but a separate species altogether. Not many scientists have the standing to settle such long-standing debates by fiat, but Ashley Gurney had earned the authority through a lifetime of deep devotion to entomology. He had served as a malariologist in
World War II, and friends recounted his annoyance at having the Japanese interrupt his mosquito collecting through their incessant shooting. Having earned a doctorate in entomology at the University of Massachusetts, he was hired by the USDA and became affiliated with the Smithsonian Institution. The Smithsonian is in the big leagues of taxonomy and by the 1950s, Ashley Gurney had ascended to a position that allowed him to carry on with the job that God had given Adam—naming the creatures.

In one short sentence—backed by pages of diagrams and analyses—Gurney and his colleague, Arthur Brooks from Canada’s Department of Agriculture, established the taxonomic standing of the Rocky Mountain locust that has held for nearly half a century: “Our study of the aedeagus indicates that
spretus
is a distinct species.” They invited continued tests of their conclusion, but the genitalic evidence was unambiguous. Although similar in size, the genitals of
mexicanus
resembled a soft cotton mitten whereas those of
spretus
were more like a tough leather sheath. They examined the specimens that Brett claimed to have transformed into a
spretus-
like creature a decade earlier, and they found that there was “no approach to the aedeagus of
spretus
.”

This work by Gurney and Brooks became the new standard. They clearly understood the implications of their findings: The disappearance of
spretus
was not simply a matter of a biological variant of an existing species having been somehow suppressed. Rather, the disappearance was the extinction of the most abundant form of life ever to sweep across the continent. It could not be “re-created” in the laboratory by the rearing of an extant species under particular conditions. The Rocky Mountain locust was gone forever.

But with the taxonomic status of the Rocky Mountain locust being as resolved as such matters get in classical taxonomy (molecular analyses were yet to come), entomologists were left to face an even more compelling problem. If extinction is like an ecological murder, then we had finally identified the victim. There was no multiple personality, no switched identities, none of the oh-so-clever feints used in detective stories—just a body. So, how did a species that once blackened the skies, sweeping across a continent in swarms larger than any known biological phenomenon on earth, disappear forever in less than twenty-five years?

E
VEN THOUGH CHARLES BRETT HAD FAILED TO resurrect
spretus
from
sanguinipes
through alterations in temperature, humidity, and food, his experiments left no doubt that a steady ature, humidity, and food, his experiments left no doubt that a steady diet of alfalfa produced wimpy grasshoppers. And in light of these findings he proposed the first clear hypothesis for the demise of the Rocky Mountain locust. According to Brett:

Brett’s logic was simple: If
spretus
were the robust phase of
sanguinipes
, then a widespread plant that caused a sickly form could account for the disappearance of
spretus
. If
spretus
had been the Superman of grasshoppers, maybe we’d planted a botanical kryptonite across its landscape. Brett’s proposal stimulated some of the first systematic thinking about the causes of the Rocky Mountain locust’s demise. Although it turned out that
spretus
was not the gregarious phase of
sanguinipes
, alfalfa remained a viable suspect. Could it be that both species fared poorly on alfalfa and thereby began to decline in the West?