Locust

by Jeffrey A. Lockwood

  If the phase transformation process of locusts were applied to humans, we would find that an economic downturn had caused our neighborhoods to smell like a sewer and our fellow commuters were constantly pushing and shoving us on the way to work. These sensory insults would trigger hormonal changes turning us into a mob of anxious, red-faced neurotics with a reduced libido and an intense desire to charter a fleet of planes. As the planes unloaded us along the way (or perhaps our ranks thinned by plane crashes), our population density would decline. The stench and jostling would diminish, and we would revert to reclusive, pale-faced homebodies. Perhaps locusts and humans have more in common than we suppose.

  Although Uvarov did not understand the biochemical mechanisms, he correctly predicted that the capacity of locusts to radically change their form and function was not restricted to the species that he had investigated. He made explicit mention of Faure’s work on the Brown locust of South Africa, noting, “These valuable observations of Mr. Faure’s leave no doubt that L. pardalina has, like L. migratoria, two different phases, which differ in morphology and coloration, but more profoundly in the biology.” So whereas Darwin was reluctant to share the limelight of evolutionary theory with Wallace, Uvarov took pains to credit his colleague: “The above-quoted conclusions of Mr. Jacobus C. Faure concerning the transformation of the solitary phase into the swarming one, at which he arrived quite independently of my work on migratoria, give a very strong support to the theory of phases as a direct cause of the periodicity.”

  Uvarov was not a taxonomist of the sort so stridently despised by Riley forty-five years earlier. Not only was Uvarov happiest when working in the field, but he also cared deeply about the use of his studies in alleviating human suffering from the ravages of locust plagues. His insights into the proper identification of L. migratoria were eventually recognized as “the greatest contribution ever made by a taxonomist in the solution of a major economic problem.” Uvarov immediately understood that his theory would lead to new and powerful means of controlling locusts. Rather than having to wait until they were swarming over the countryside, it would be possible to find and suppress the harmless “grasshopper” (solitary phase) and thereby prevent outbreaks of the rapacious “locust” (gregarious phase). This strategy of preventive control, rather like the suppression of forest fires by finding and quenching lightning strikes before they transform into conflagrations, has come to serve as the foundation for modern locust management programs around the world.

  Uvarov was a scientist far ahead of his time with regard to conceptualizing the natural world. The modern science of complexity with all of its attendant forms (chaos, catastrophe theory, self-organized criticality, etc.) constitutes a beautiful and compelling mathematical formalization of the concept that Uvarov articulated for biology and Karl Marx expressed for political economy: “Quantitative differences beyond a certain point pass into qualitative changes.” Or, as so concisely expressed by the physicist P. W. Anderson, “More is different.” The principle is that in many complex, natural systems, as we increase pressure, size, density, or time, what often emerges is a sudden shift in form or function. With gradually mounting loads, girders instantly snap; with continuously looming intruders, dogs switch from submission to attack; and with slowly decreasing temperature, liquids suddenly solidify. The field of complexity has made exciting progress toward working out the mathematics pertaining to these discontinuities in the natural world. However, it seems somehow arrogant to be declaring that we are creating a “new science,” when the fundamental concept of emergence—the appearance of entirely new forms and processes that were not predictable from, and are not reducible to, smaller and simpler scales—was so elegantly and explicitly stated by our predecessors. In 1921 Boris Uvarov comprehended that beyond a certain point, population density triggered a qualitative change in locusts. Perhaps the notion was pervasive among intellectuals in the 1920s, as a pithy dialogue from Paris suggests. F. Scott Fitzgerald commented, “The rich are different from you and me,” to which a young Ernest Hemingway replied, “Yes, they have more money.”

  The phase theory of locusts would prove to be a phase transition in the life of Boris Uvarov. He rapidly transformed into one of the most powerful, effective, and important figures in twentieth-century entomology. Uvarov developed the Anti-Locust Research Centre and virtually created the locust management unit within the Food and Agriculture Organization of the United Nations, which to this day provides global leadership. His philosophy of locust control echoed the sentiments of C. V. Riley—both men argued in favor of ecologically based pest management, eschewing insecticides. And his personality was reminiscent of Riley’s in some ways. He did not suffer fools gladly but was far more approachable and personable than his predecessor. Uvarov was eminently practical while being well grounded in the principles of the biological sciences. Like Riley, he was intolerant of bumbling bureaucracy—even to the point of biting the hand that fed him, but not to the point of professional self-destruction. As evidence that his up-to-the-edge diplomatic skills were finely honed, the British honored this brilliant scientist with knighthood in 1961. Sir Boris Uvarov left a brilliant two-volume compendium on grasshoppers and locusts, in which he synthesized more than 7,000 scientific papers published between 1950 and 1970. These books still serve as the definitive synthesis for acridology—a term that he coined for the study of grasshoppers and locusts (family Acrididae). And for those who were trying to explain the Rocky Mountain locust’s disappearance, Uvarov’s phase theory would provide one of the most troublesome false leads in the case—and, eventually, one of the most important clues in solving the mystery.

  THE SEARCH FOR THE DR. JEKYLL OF NORTH AMERICAN LOCUSTS

  Even before Uvarov’s work, entomologists in the United States had a vague impression that perhaps the Rocky Mountain locust was an insect changeling. A report on the grasshoppers of Minnesota in 1913 noted that to “the student who wishes an idea as to the appearance of the Rocky Mountain locust, we may say that, with a rather large and somewhat light-colored specimen of [the migratory grasshopper] in hand, by extending the tegmina and wings somewhat in imagination, he may have a very good idea of the pest of the early days.” Such suspicions took on new life with Uvarov’s phase theory. Perhaps the Rocky Mountain locust was not extinct, only quiescent. Could it be that this locust was the migratory phase of a species still living right under our noses?

  If Melanoplus spretus was a migratory Mr. Hyde, there were two candidates for Dr. Jekyll. These suspects were the grasshoppers that had apparently filled the niche vacated by the Rocky Mountain locust at the turn of the century. The long-shot candidate for the role of Dr. Jekyll was the redlegged grasshopper, which had become a nuisance in the years following the decline of the Rocky Mountain locust. This species, M. femurrubrum (femur referring to the creature’s legs and rubrum alluding to the reddish coloration of the tibiae—the long, thin, spiny shanks of a grasshopper), was similar in size and shape to the locust. Femurrubrum was identified and named in 1773 by a French entomologist, Charles De Geer. This poor fellow’s name was so often butchered in scientific papers that a ten-page scientific paper was published in 1956 entitled “On the Rendering of Charles De Geer’s Surname.”

  Such details of spelling matter to taxonomists, who are both fastidious in their attention to minutiae and possessed with what, to the rest of the world, might seem to be a misplaced sense of self-importance. That is, when scientists first use the name of a species in technical writing, the creature’s Latin name is usually followed by that of the person who first named it—and in some cases the year of naming is added. So the full and proper name of the redlegged grasshopper is Melanoplus femurrubrum De Geer 1773. If the person who named a species placed it within a genus and the species is later moved to a different genus, then the person’s name is retained but put in parentheses. Thus, when one is the first to name a species there is a historical legacy, a kind of immortality that forever links the scientist to the creatur
e. The only impermanence in this system comes if a taxonomist discovers that a species has been given two or more different names, in which case only the oldest name is retained and the other—along with the associated name of the errant human—is abandoned. For example, L. danica was erased from the catalog of earth’s creatures by Uvarov’s revision.

  The naming of things is a powerful act, given the fundamental importance of language to humanity. Most taxonomists might give some sort of rational explanation for their exactitude, but within Western culture, the Judeo-Christian emphasis placed on the Word plays into the sense that theirs is important, even sacred, work. Taxonomists half-jokingly refer to themselves as the only scientists with a divine mandate. God’s first assignment to Adam was to name the creatures, a task that is probably no more than 10 percent completed today.

  And so, getting the name of the species—and the person who named it—right takes on an importance that runs deeper than a simple aversion to typographical error. Charles De Geer named a whole mess of species, so his name was rendered in many creative ways. It seems that there were no less than seven versions of his name, including de Geer, DeGeer, Degeer, and Geer. In an exhaustive historical critique that included analyses of the Frenchman’s signature, it was concluded that De Geer (with a space between De and Geer) was the correct form. Ironically, the rendering today is almost universally DeGeer (no space), suggesting either that entomologists are just plain contrary or that not many folks read the Bulletin of the Brooklyn Entomological Society, where the definitive paper was published. Alas, both the spelling of the Frenchman’s name and the grasshopper he named failed to sustain great scientific interest in resolving the identity of the Rocky Mountain locust. Although femurrubrum bore a certain resemblance to spretus, this modern-day grasshopper faded as a suspected alter ego. The attention of entomologists became riveted on a more compelling species.

  The prime Jekyllian candidate was the migratory grasshopper, M. sanguinipes. This was also one of the species that seemingly replaced the Rocky Mountain locust, into the present day. But at the time in which the phase theory was being applied to the Rocky Mountain locust, the migratory grasshopper had an entirely different name. This species was originally named by Riley as atlanis, in reference to its being first found along the Atlantic seaboard. It takes only a moment to notice that a t is apparently missing from the species’ name. In a weird twist of the rules of zoological nomenclature, the species’ name as first printed serves as the immutable spelling, with provisions for egregious errors. It turns out that Riley had intended the name to be atlantis, a name that a few people understandably, but inappropriately, adopted in later years. However, the perfectionist Riley blundered into an irreversible error by inadvertently omitting the letter t in his original description, thereby creating a name that was a typographical error within a geographic allusion.

  Such oddities are rare, and they can create even weirder problems of interpretation and pronunciation than atlanis. Yponomeutidae is the family name for the ermine moths, a very diverse group with many beautiful and pestiferous species. The name apparently was intended to be Hyponomeutidae. The prefix hypo makes sense. It means “under” or “beneath,” as in hypothermia, which is a subnormal body temperature. But it seems that the prefix ypo has no meaning other than as a testimony to the importance of proofreading.

  In 1917, a taxonomic revision revealed an earlier name for the migratory grasshopper and the species became known as mexicanus, and a subsequent analysis arrived at the name bilituratus. Not until 1962 was the complete history of this creature’s name fully revealed. The earliest—and hence “correct” according to the rules laid down in the International Code of Zoological Nomenclature—name was sanguinipes . This name was derived from the Latin word meaning “blood,” and perhaps referring to the red tibia of this species, a feature often shared with femurrubrum, as if the situation was not otherwise sufficiently confusing. Johann Christian Fabricius, a student of Linnaeus and founder of insect taxonomy, named this species in 1798. This original name came to light after a taxonomist reported that he had seen an old specimen with an identifying label during a visit to Copenhagen, where Fabricius had worked. The pinned insect had been collected by Julius Philip Benjamin von Rohr, an adventurer and collector for Fabricius. Oddly though, there was no record of Rohr’s having spent time in North America. However, he traveled from London to Central America and the West Indies, and it is likely that this journey took him first to the east coast of the United States, where he made the fateful collection during the layover. He was lost at sea in 1792, but not before having transferred possession of his collected material to Sehestedt and Tønder Lund, pupils of Fabricius, who then presumably passed the specimen on to their mentor and into history.

  And so, the three creatures—spretus, femurrubrum, and sanguinipes— were discovered, named, and renamed over the course of two centuries. In the 1930s, Uvarov’s theory had become widely recognized and generally accepted, and American entomologists began to wonder whether spretus might be masquerading as one of the two similar species. An entomologist from the U.S. Department of Agriculture, Robert L. Shotwell, reviewed the taxonomic history and available evidence and concluded that the three were distinct species. A year later, Norman Criddle arrived at precisely the opposite conclusion, maintaining that spretus was “merely a long winged phase of mexicanus [now known as sanguinipes].” This position was also held by Morgan Hebard, an eminent taxonomist specializing in grasshoppers. Sides were chosen, lines were drawn in the sand of taxonomy, and the battle was on. However erudite the various arguments based on dead, pinned specimens might have been, a resolution needed living proof. And the phase transformation camp hoped that the definitive evidence would be a simple matter of inducing the phase transformation in living grasshoppers. If Criddle and Hebard were right, it ought to be possible to resurrect spretus from the grave. This challenge fell to Faure, the South African entomologist who had very nearly beaten Uvarov to the discovery of locust phase transformations.

  Jacobus Faure was entranced by phase variation, and he was convinced that this phenomenon could solve the identity, and hence the disappearance, of the Rocky Mountain locust. He came to St. Paul, Minnesota, in 1932 to conduct the experiments necessary to re-create spretus. Using methods that had successfully induced phase transformations of the brown locust in South Africa, he reared sanguinipes under crowded conditions hoping that spretus would appear. It didn’t. However, Faure managed to hedge his interpretations and qualify his conclusions to such an extent that with a bit of scientific sleight-of-hand he was able to argue that, despite his own data, the two organisms were really the same species.

  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 i
n 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.