immatures

Working with Cerceris fumipennis—Part 2

/ Ted C. MacRae / 19 Comments

During the 6-week period from late May to early July this year, I collected ~400 jewel beetle specimens representing at least 20 species (see Working with Cerceris fumipennis—Part 1). A final accounting of the species represented won’t be done until this winter, but the genera represented include Acmaeodera, Actenodes, Agrilus, Anthaxia (Haplanthaxia), Buprestis (Knulliobuprestis), Chrysobothris, Dicerca, Poecilonota, and Spectralia. Perhaps two-thirds of the specimens were “ground-picked”¹, while most of the remaining third were “stolen” directly from wasps by netting wasps in flight as they returned to their nest carrying prey.

¹ It’s not clear to me why I found so many abandoned buprestids at nest entrances. The wasps are known to drop prey when threatened and, rather than search for and relocate the prey, fly off to look for a new beetle(Careless et al. 2009). I observed this myself in several cases when I missed netting the wasp but swiped the net close enough to scare it, at which time it dropped the beetle and flew off (and I popped the beetle in a vial). However, the bulk of the beetles I found on the ground were not only at the nest entrance, but even mixed within the diggings surrounding the nest. My first act when checking each field was to check each nest, pick up any adults lying on top of the burrow diggings, and then carefully spread out the diggings with a knife or trowel to collect the beetles hidden within them. One nest contained as many as 13 Agrlus obsoletoguttatus inside the diggings. I wondered at one point if the wasps were leaving the beetles at the burrow entrance and then digging out the burrow before coming back to retrieve them, but I never actually witnessed this. On the other hand, I observed numerous wasps approaching their burrows while carrying prey, and every time the wasp dropped directly into the burrow. In fact, I could even predict what beetle species I was likely to find inside the nest based on the species I found around the entrance (more on that below).

This ball field with contains several dozen Cerceris fumipennis nests.

There is a third method that I used to collect beetles that I haven’t yet discussed, and that is digging them out of nests. In the latter part of the survey period (late June and early July), beetle numbers dropped rapidly, as did apparent wasp activity. As mentioned in the previous post, this drop off in activity came precisely at the time of season when I have observed buprestid beetle activity to decline in Missouri. As the drop off in activity was taking place, I began wondering what I would find if I tried digging up some of the burrows. Of course, digging up a nest takes much more effort than netting wasps or picking beetles up off of the ground, so it becomes important not only to identify whether a nest actually belongs to C. fumipennis and if it is active and likely to contain freshly captured beetles.  In addition, I observed the burrows of a variety of other insects in these fields as well, some of which are shown here and which might be confused with burrow entrances of C. fumipennis.

Cerceris fumipennis nest with Chrysobothris sp. adult left on diggings.

Cerceris fumipennis burrows exhibit perfectly circular, pencil-sized entrances surrounded by a symmetrical mound of diggings with a fine rather than granular texture. There are other Cerceris species that make nearly identical burrows, but they prey on other insects rather than buprestid beetles. At my site I found C. bicornis, a weevil specialist, almost as common as C. fumipennis. Their burrow entrances on the whole seemed slightly larger, but I could not use this as consistent distinguishing character. What I could use, however, was the presence of weevils rather than buprestids lying on the ground near the nest entrance. (I also observed this species returning to its nest and noted a rather faster, more powerful flight that made them even more difficult to capture than C. fumipennis). In contrast, there can be no doubt that the burrow above, with a buprestid beetle lying on the ground near the entrance, belongs to C. fumipennis.²

² The white plastic tag marks the burrow to facilitate locating nests on subsequent visits. It is secured with a golf tee and also can be rotated so that the hole covers the entrance. The hole is large enough to allow the wasp to leave but too small for a returning wasp to enter while carrying a beetle. The idea was to rotate the tags when I first entered a field to cover all the burrow entrances, watch for wasps returning with prey, and then net the wasps as they tried (in vain) to enter the burrow. However, I never actually observed a wasp trying to enter a covered burrow, even after leaving a field and returning 20–30 minutes later.

I presume this nest to be that of Bembix americana (sand wasp).

For the first few weeks, I thought the burrows such as that shown in the above photo also belonged to C. fumipennis. However, I never found beetles lying on the ground near the entrance, nor did I ever observe a wasp to enter or leave the burrow. I eventually noticed several distinct differences in burrow architecture—the burrow entered the ground at an angle rather than straight down, the diggings were distributed asymmetrically to one side of the entrance, and the latter seemed consistently a little larger than those of C. fumipennis. In addition, these burrows always seemed to be in the sandier portions of the fields. While I never associated any insect directly with these burrows, I did observe sand wasps (perhaps Bembix americana) in the vicinity and have seen similar-looking burrows dug by these wasps at Sand Prairie Conservation Area.

Larval burrows of Cicindelidia punctulata and other tiger beetles lack diggings around the entrance.

Tiger beetle larval burrows might also be confused with C. fumipennis burrows, especially after rain or high winds which can wash/blow away the diggings from around the entrance. I found adults of the punctured tiger beetle, Cicindelidia punctulata, fairly commonly at the site and presume the numerous tiger beetle larval burrows that were also present belong to that species. Larval tiger beetles burrows also enter the ground straight down and are, at first appearance, also perfectly round, but they are usually a little too small for C. fumipennis (those of Tetracha spp. being an exception)—the presumed C. punctulata burrow in the above photo measures about 5 mm in diameter. In addition, closer examination reveals a slight “D” shape to the burrow entrance (upper right in the above photo—the tiger beetle larva rests its jaws against the flat side) and, more distinctively, beveling of the ground around the rim of the burrow entrance. Cerceris fumipennis nests lack the slight D-shape and distinctive beveling.

Use a grass stem as a guide while carefully digging away the surrounding soil.

Years of practice digging up tiger beetle burrows prepared me well for my first attempts at digging up C. fumipennis burrows. While it might seem an easy task to follow a hole into the ground while digging soil away from it, in practice the burrow can be quickly lost after even a few inches due to falling soil covering the hole and making it impossible to relocate. I use a thin, flexible but sturdy grass stem to preserve the burrow path, inserting the stem into the burrow and down as far as it will go and then removing the soil carefully from around the hole with a knife or trowel. I try to avoid letting soil fall over the hole by prying the soil away from the hole, but if the hole does get covered the grass stem allows it to be easily relocated.

This nest contained a single Buprestis rufipes…

Cerceris fumipennis burrows are not very deep—only 10–15 cm, and angle to one side a few cm below the surface before leveling out near the bottom. I noticed the nest in the above photo because I saw a wasp fly into it. When I went over to look at it I found a Buprestis rufipes lying on the ground near the entrance and so decided to dig it up. As I expected, I found another B. rufipes at the bottom of the burrow (two above photos courtesy of Madison MacRae).

…while this one contained a cache of seven Agrilus quadriguttatus.

The above photo shows a cache of seven Agrilus quadriguttatus that I found at the bottom of another burrow. In this case, the prey is rather small compared to large prey such as Buprestis and Dicerca. While nests provisioned with species in these latter genera often contained only a single beetle in them, I nearly always found multiple beetles in nests provisioned with the smaller Agrilus species. One nest contained as many as 13 Agrilus obsoletoguttatus, among the smallest of the species I found utilized by C. fumipennis at this site.

Buprestidae taken from five different Cerceris fumipennis nests.

Some of the nests I dug up contained multiple species of beetles, but far more commonly I found only a single species in a given nest. The photo above shows the diversity and number of beetles found on one date after digging up five different nests. From top left the beetles are: 1) 1 Buprestis rufipes; 2) 2 Agrilus quadriguttatus and 1 A. obsoletoguttatus; 3) 2 A. quadriguttatus and 1 A. obsoletoguttatus; 4) 8 A. obsoletoguttatus; and 5) 2 Poecilonota cyanipes, 2 A. quadriguttatus, and 1 A. pseudofallax. It would make sense for wasps to provision nests with greater numbers of smaller beetles to ensure adequate food for their larvae to complete development. How the wasps actually locate their prey, and why this species has specialized almost exclusively on buprestid beetles, is a mystery (at least to me); however (and here comes the speculation du jour), I suspect the wasps may have keyed in on volatiles used by the beetles—either those released by suitable hosts or by each other to facilitate mate location. Use of buprestid pheromones or freshly dead host volatiles would allow wasps to more efficiently locate buprestid prey and, once locating a source (a tree harboring a particular beetle species), could return repeatedly to provision their nest fully. It seems less likely that wasps rely exclusively on visual location of prey, as this would involve a large amount of random searching through trees and passing up numerous, seemingly equally suitable prey.

REFERENCE:

Careless, P. D., S. A. Marshal, B. D. Gill, E. Appleton, R, Favrin & T. Kimoto. 2009. Cerceris fumipennis—a biosurveillance tool for emerald ash borer. Canadian Food Inspection Agency, 16 pp.

Copyright © Ted C. MacRae 2012

One-Shot Wednesday: two-striped grasshopper nymph

/ Ted C. MacRae / 3 Comments

Melanoplus bivittatus (Two-striped Grasshopper) nymph | Jerseyville, Illinois

As the heat of summer solidifies its chokehold over the middle and southern latitudes of North America, grasshopper nymphs will begin to ramp up their development. I see grasshoppers commonly in my soybean field trials, where their feeding presents more of an annoyance to me than an actual threat to yields.

I photographed this particular individual on almost this same date last year in one of my Illinois soybean trials, not knowing for sure which species it represented. There was no particular reason for only taking this one single photograph, other than it was perched nicely when I saw it and that I did not feel like taking the time to chase it into another good pose after my first shot disturbed it.

Later in the season I saw numerous adults representing Melanoplus differentialis (differential grasshopper), a common species in this area, and assumed this was its nymph. However, a closer look at the photo suggests it represents the closely related M. bivittatus (two-striped grasshopper). While adults of these two species are easily distinguished based on coloration, the nymphs can look very similar (especially in their earlier instars) and are distinguished on the basis of the black femoral marking—more or less solid in M. bivittatus and broken into chevrons that create a “herringbone” pattern in M. differentialis.

Wing pad size and relative body proportions suggest this is a fourth-instar nymph.

Copyright © Ted C. MacRae 2012

The “Big 3” of corn in Argentina

/ Ted C. MacRae / 8 Comments

While leafcutter ants are one of the more unusual pests that Argentina corn farmers must deal with, the three most important confront farmers throughout the Western Hemisphere: stalk borers, earworms, and armyworms. In the U.S. the primary stalk boring pest of corn is the European corn borer (Ostrinia nubilalis), while in Argentina it is the sugarcane borer (Diatraea saccharalis). Corn earworm (Helicoverpa zea) and fall armyworm (Spodoptera frugiperda), on the other hand, are common to both countries. Here are some recent photos of the three species in Argentina – the first two on corn and the latter on soybean.

After you look at the photos, I have a funny story…

Diatraea saccharalis eggs ready to hatch | Buenos Aires Prov., Argentina

Helicoverpa zea egg on corn silk | Buenos Aires Prov., Argentina

Spodoptera frugiperda mid-instar larva on soybean | Buenos Aires Prov., Argentina

Learning to speak a foreign language via immersion can result in some embarrassingly funny moments. This afternoon I made an unplanned visit to the field with some colleagues. There has been much rain recently so the ground was rather muddy. Not having my boots with me, I picked my way through as best I could, and afterwards as I was cleaning the mud off my shoes, I commented (in Spanish) to one of my Argentine colleagues (a young female) that this was my only pair of clean shoes. I said everything okay but messed up the word for shoes—instead of saying “calzados” I said “calzones.”

In Argentina, calzones means “underwear.”

I’m really glad the shocked look on her face quickly gave way to hysterical laughter once she figured out what I was trying to say.

Copyright © Ted C. MacRae 2012

Cycloalexy in tortoise beetle larvae

/ Ted C. MacRae / 13 Comments

One of the first insects I encountered during my visit this past November to  in Buenos Aires, Argentina were these tiny beetle larvae grouped together on a single leaf of an unidentified shrub.  The presence of fringed lateral appendages and exuvial-fecal debris masses held by caudal appendages immediately identifies them as larvae in the leaf beetle subfamily Cassidinae, known commonly in North America as “tortoise beetles” due to the appearance of the adults.  With nearly 3,000 species distributed throughout the world, tortoise beetles are easily recognizable as a group; however, species identifications can be much more difficult, especially in the Neotropics where the group reaches its greatest diversity (Borowiec and Świętojańska 2002–2011). Identification of larvae can be even more challenging, as the larvae of many species remain unknown, and I was unable to find adults in association with the larvae to aid my identification.

Anacassis sp. (poss. exarata) early-instar larvae on Baccharis salicifolia | Buenos Aires, Argentina

Nevertheless, host plant can be an important clue to leaf beetle identity, as most species in the family limit their feeding to a single plant genus or group of related plant genera. The shrub on which the beetles were feeding looked familiar to me, and while perusing a list of plants that have been recorded from the Reserve (Burgueño 2005) I had an “Aha!” moment when I spotted the asteraceous genus Baccharis. I decided the plant must represent Baccharis salicifolia because of its narrowly lanceolate, willow-like leaves with fine apical serrations (Cuatrecasas 1968) (see first photo). The only tortoise beetles known to feed on Baccharis are species in the genus Anacassis (McFadyen 1987), several species of which are known from Argentina, and one (Anacassis exarata) looking very much like the larvae in these photos.

Note the circular, heads-directed-inward orientation of all larvae around the periphery

The manner in which these early-instar (perhaps even newly hatched) larvae were feeding as a group while working their way down the length of the leaf towards its base is not something I had observed before. Larvae of most tortoise beetles are solitary feeders (Borowiec and Świętojańska 2002–2011), and I was further intrigued by the deliberate circular formation that the larvae had assumed.  The larvae around the periphery were all facing inward, tightly packed against each other and with their exuvial-fecal debris masses directed outward. Additional larvae were seen inside the circular formation. As I manipulated the leaf for photographs, the larvae would occasionally raise their debris masses up and outward, presumably a defensive reaction to disturbance and a perceived threat. It was clear to me that the larvae had deliberately “circled their wagons” for defensive purposes.

Close body contact allows exuvial-fecal debris masses to form a protective barrier against predators

In fact, this type of defensive strategy has been reported in a number of South American cassidines, as summarized by Jolivet et al. (1990), who coined the term “cycloalexy” (from the Greek κύκλος = circle, and αλεξω = defend) to describe such strategies. Cycloalexy can either be “heads in, tails out” or vice versa and is usually associated with other repellent activities such as coordinated threat movements, regurgitation, or biting. The strategy is intended to provide protection from predators such as ants and true bugs and parasitioid wasps, although some parasitoids seem to have thwarted the strategy by depositing their eggs where they can be ingested (thus avoiding direct confrontation with the prey). Cycloalexy has been described primarily among chrysomelid beetles and tenthredinoid hymenopterans (sawflies); however, examples from a few other insect orders (e.g., Diptera, Neuroptera, Lepidoptera) are known as well (Jolivet 2008).  All known cycloalexic insects are subsocial in the larval stage and often also exhibit maternal protection of eggs or newly hatched larvae.

This and several other older larvae had become solitary, presumably protected in part by greater size

In addition to this single group of early instar larvae, I noted also a few larger individuals—all of whom were feeding on the plant in a more solitary fashion. Presumably as the larvae grow larger they are more able to defend themselves, or perhaps larger larvae simply demand more “elbow room” because of the larger amounts of leaf tissue they require for feeding. If cycloalexy is beneficial for small cassidine larvae but less so for larger larvae, perhaps this behavior is actually more common than is currently realized.

REFERENCES:

Borowiec, L., and J. Świętojańska. 2002–2011. Cassidinae of the world – an interactive manual (Coleoptera: Chrysomelidae). http://www.biol.uni.wroc.pl/cassidae/katalog%20internetowy/index.htm [accessed 3 Dec 2011].

Burgueño, G. 2005. Manejo de la vetación en reservas naturales urbanas de la region metopolitana de Buenos Aires. Aves Argentinas, Asociación Ornitológica del Plata, Proyecto Reservas Naturales Urbanas, 16 pp.

Cuatrecasas, J. 1968. Notas adicionales, taxonómicas y corológicas, sobre Baccharis. Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales 13(50):201–226.

Jolivet, P. 2008. Cycloalexy. In: J. L. Capinera [Ed.], Encyclopedia of Entomology, Springer Science+Business Media B.V.

Jolivet, P., Vasconcellos-Neto, J., and Weinstein, P. 1991. Cycloalexy: A new concept in the larval defense of insects. Insecta Mundi 4(1–4) (1990):133–141.

McFadyen, P. J. 1987. Host-specificity of five Anacassis species [Col.: Chrysomelidae] introduced into Australia for the biological control of Baccharis halimifolia [Compositae]. Entomophaga 32(4):377–379.

Copyright © Ted C. MacRae 2011

“Sunflower looper” – Rachiplusia nu

/ Ted C. MacRae / 11 Comments

Rachiplusia nu ''oruga medidora'' | Santa Fe Province, Argentina

With a planted area approaching 20 million hectares, soybean has become Argentina’s most important agricultural crop.  Most of the planted area is located within the so-called “Humid Pampas” region of central Argentina (Buenos Aires, Córdoba, Santa Fe and Entre Rios Provinces), but the crop continues to expand in the northestern part of the country as well (Chaco, Tucumán and Salta Provinces).  More than any other crop in Argentina (except perhaps cotton), soybean is attacked by a tremendous diversity of insects.  The most important of these are the defoliating Lepidoptera, primarily species in the family Noctuidae.  Anticarsia gemmatalis (velvetbean caterpillar) is the most consistent and widespread defoliator, but an increasingly important species in Argentina is Rachiplusia nu (“oruga medidora del girasol,” or sunflower looper).

Eggs are laid primarily on the undersides of leaves

Rachiplusia nu belongs to the noctuid subfamily Plusiinae, the larvae of which can be recognized by having three pairs of prolegs and the “looping” manner by which they walk.  Chrysodeixis includens¹ (soybean looper), much better known because of its status as a major pest of soybean in the southeastern United States (and of growing importance in Brazil as well), also belongs to this group, and in fact the larvae of the two species are quite similar in appearance.  While R. nu is the primary plusiine species affecting soybean in Argentina, C. includens has appeared with increased frequency on soybean in Argentina in recent years, primarily in the more northern, subtropical growing regions adjacent to those areas in Brazil where it is now a major pest of the crop.

¹ Although still widely referred to in the literature as Pseudoplusia includens, the genus Pseudoplusia was synonymized under Chrysodeixis some eight years ago by Goater et al. (2003).  More recently the synonymy was accepted and formally applied to the North American fauna by Lafontaine and Schmidt (2010). 

Neonate larva on soybean

Despite their similarity of appearance, larvae of the two species can be rather conclusively distinguished by the shape of their spinneret (Angulo and Weigert 1975).  This is not a very convenient character for use in the field, however, leading to misidentifications in areas where the two species co-occur.  This is not an insignificant problem, as the two species exhibit differing susceptibilities to pesticides labeled for their control (C. includens especially having become resistant to a number of pesticides).  The result is control failures and subsequent application of even more pesticides in an effort by farmers to protect their crops.  While not as conclusive as the shape of the spinneret, in my experience R. nu larvae (at least older larvae) tend to have a darker, smoky-blue cast to the color (compared to the bright yellow-green of C. includens) and rather distinct patches of tiny black asperites on the thoracic ventors that are not apparent in C. includens.

Younger larvae consume only the lower surface between veins, resulting in ''window paning''

As the common name implies, soybean is not the only crop attacked by R. nu.  Early season infestations tend to occur in alfalfa and flax, after which the populations spread to soybean and sunflower.  The latter crop especially is heavily attacked by this insect, primarily in the drier western regions in Córdoba Province.  Dry conditions seem to favor an increase in the populations of this species, while moist conditions promote increased incidence of pathogenic fungi that are very effective at suppressing R. nu larval populations.

Older larvae consume entire tissues but still avoid veins, resulting in a ''skeletonized'' appearance

Like many defoliating lepidopterans, eggs tend to be laid on the undersides of leaves, where the larvae begin feeding after they hatch.  Young larvae consume only the lower epidermal layer of the foliage between the veins, leading to an appearance in the foliage called “window paning”.  As they larvae grow they begin consuming the entire tissue layer but still preferentially avoid vascular tissue, resulting in a skeletonized appearance to the foliage.  A single larvae can consume more than 100 cm² of soybean foliage, which translates to several trifoliates.  As a result, it doesn’t take many larvae to cause significant loss of foliage on the plant.  Soybean has the ability to compensate for loss of foliage due to increased photosynthesis in lower foliage exposed by feeding in the upper part of the plant, but losses exceeding around 15% during the later reproductive stages of plant growth are enough to significantly reduce yields (and it is during these reproductive stages of growth that R. nu infestations tend to occur).

Rachiplusia nu adult | Buenos Aires Province, Argentina

Rachiplusia nu is the most widely distributed of three South American species in the genus, occurring in Argentina, Bolivia, Brazil, Chili, Paraguay, Peru and Uruguay, while a fourth species, R. ou, is widely distributed throughout North and Central America (Barbut 2008).  Unlike R. nu, its North American counterpart R. ou has not gained status as a pest of soybean or other crops.

In a BitB Challenge first, nobody was able to correctly ID the larva of this species beyond the level of subfamily.  This, despite the huge Argentina hint bomb that I dropped when I posted the challenge and my well-known vocation as a soybean entomologist.  I figured the answer would be forthcoming as quickly as one could Google the search phrase “Argentina soybean Plusiinae” (which, in fact, shows the following except for the very first result “Pseudoplusia includens is the most common soybean Plusiinae in the Americas (Herzog, 1980). Rachiplusia nu in southern Brazil, Uruguay and Argentina, and…” [emphasis mine]). Most participants guessed, predictably, soybean looper, while only a few were fooled into guessing Geometridae (the true loopers, and distinguished by having only two pairs of prolegs).  As a result, I’m not declaring a winner for ID Challenge #14, although the appropriate points will still be awarded (when I get around to assigning them, that is.  Hey, I’m working in Argentina right now—it was enough for me just to get this post out!).

REFERENCES:

Angulo, A. O. and G. T. H. Wiegert. 1975. Estados inmaduros de lepidópteros noctuidos de importance economica en Chile y claves para su determinación. Sociedad Biologico Concepción, Publicación Especial 1:1–153.

Barbut, J. 2008. Révision du genre Rachiplusia Hampson, 1913 (Lepidoptera, Noctuidae, Plusiinae). Bulletin de la Société entomologique de France113(4):445–452.

Goater, B., L. Ronkay and M. Fibiger. 2003. Noctuidae Europaeae. Vol. 10, Catocalinae, Plusiinae. Entomological Press, Sorø, 452 pp.

Lafontaine, J. D. and B. C. Schmidt. 2010. Annotated check list of the Noctuoidea (Insecta, Lepidoptera) of North America north of Mexico. ZooKeys 40: 1–239.

Copyright © Ted C. MacRae 2011

Brazil Bugs #16 – Royal Moth Larva

/ Ted C. MacRae / 4 Comments

Citheronia laocoon? 1st instar larva | Campinas, Brazil

I was sure Super Crop Challenge #6 would be a win for the house, but Troy Bartlett scored an impressive points sweep by correctly deducing that the structures shown were the spines of an early instar caterpillar of “something akin to a hickory horned devil (Citheronia regalis).”  I found this caterpillar feeding on the foliage of a small tree in the Ciudad Universitaria (Distrito Barão Geraldo) area of Campinas, Brazil last January.  I must confess that I spent considerable time trying to identify it myself before I finally threw in the towel and called on the experts for help.  The spines made me think it must be some kind of nymphalid butterfly larva, although I had never seen such “fly swatter” clubs at the ends of the spines, so I sent the photo to Phillip Koenig, a local butterfly expert who has collected extensively in Ecuador.  He, too, was puzzled and forwarded the photo to Charley Eiseman, who himself didn’t know what to make of it and forwarded it on to Keith Wolfe, a lepidopterist who specializes in butterfly immatures.  After stumping his Brazilian contacts, Keith had the idea that perhaps it wasn’t a late-instar larva—as we all had assumed (this larva was a good 15–20 mm in length), but rather one in an early stadium.  A quick search of several standard websites revealed this to be the L1 or L2 larva of a species of Citheronia (Saturniidae, Ceratocampinae).  To support his ID, he provided links to larval photos of C. splendens (Arizona) and C. lobesis (Central America).  The L1 larva of both of these species bears the same “fly swatter” spines, and the latter is remarkably similar in color pattern as well.

In trying to determine what species of Citheronia occur in southeast Brazil, I came across this link with photos of a caterpillar from southern Brazil—the L1 looking nearly identical—that was eventually identified as the common Brazilian species C. laocoon.  Troy suggested C. brissotii—another good possibility as that species is found from southeastern Brazil through Uruguay to Argentina.  However, in perusing a number of online sources, it appears there are several other species of Citheronia that also occur in Brazil, so a species ID for the larva in this photo may not be possible.

Troy’s win vaults him into 3rd place in the current session overalls, but steady Tim Eisele took 2nd place with 6 pts and takes over the session lead.  Newcomer Roy rounds out the podium in 3rd place with 5 points.  Dave’s pity points are nothing to sneeze at, as they helped him retain sole possession of 2nd place in the overall standings (let that be a lesson to those who don’t play because they’re “stumped”!).  There will be at least two more challenges in the current session before a winner is crowned, so look for an opportunity to shake up the standings in the near future.

Copyright © Ted C. MacRae 2011

Pardalophora phoenicoptera – Orange-winged grasshopper

/ Ted C. MacRae / 13 Comments

For some reason, I’ve found myself increasingly fascinated with certain grasshoppers—not just any grasshoppers, but band-winged grasshoppers (family Acrididae, subfamily Oedepodinae).  And not just band-winged grasshoppers, but band-winged grasshopper nymphs.  It began last year when I found adults and nymphs of Trimerotropis latifasciata in the Glass Mountains of northwestern Oklahoma.  I believe it has something to do with the combination of their frequent association with the same habitats where I look for my beloved tiger beetles and their marvelously cryptic coloration.  Adults themselves are cryptic enough—that is, until they flash their brightly colored hind wings, but the nymphs are positively invisible until they move.  Moreover, many species show a wonderful range of intraspecific diversity in their crypsis—Ronald Reagan may have thought every redwood tree looked the same, but when you’ve seen one band-winged grasshopper nymph, you most certainly have not seen them all.


These two band-winged nymphs were seen at St. Joe State Park (St. Francois Co., Missouri) in the vast central “sand flats” of the park (actually waste areas of crushed limestone tailings left from lead mining operations during the previous century).  At first I assumed they each represented a different species, but based on comments at BugGuide I take both of them to represent Pardalophora phoenicoptera (orange-winged grasshopper)—distinguished from Xanthippus by having only one notch in the pronotal crest and unusual amongst most grasshoppers in that the winter is passed as a nymph rather than egg.  This leads to well-developed nymphs at the beginning of spring and adults much earlier in the season than many other grasshoppers.  These photos were taken on April 28, and the size of the wing pads suggests they are not quite full-grown yet, maybe 3rd or 4th instars.  Acridoid aficionado David J. Ferguson has found this species in the Ozarks on rocky/gravelly hilltops (e.g., “cedar glades”) and on gravelly or stable sandy slopes in sunny openings in Oklahoma. He places the species (particularly the green ones) high on his favorite hopper list, and I’d have to say I agree with him (so far).

One of these days, I’m going to find and photograph the king of all green oedepodines—Trimerotropis saxatilis!

Update 6/8/11: Dave Ferguson has kindly confirmed the ID, writing:

…yes these are identified correctly.  Assuming 5 instars, they look like 4th (where there are 6 instars, numbers 4 and 5 look a lot alike).

Copyright © Ted C. MacRae 2011

A thrips is a thrips…

/ Ted C. MacRae / 7 Comments

Caliothrips phaseoli (bean thrips) - adults | Fontezuela, Pcia. Buenos Aires, Argentina

The critter in ID Challenge #6 is, as most surmised, a thrips¹, and although the black-and-white banding of the elytra make the predaceous “banded thrips” (Aeolothrips sp. of the family Aeolothripidae) a logical ID choice, the species in the photograph is actually the phytophagous “bean thrips” (Caliothrips phaseoli of the family Thripidae).  The individuals in that photo and the additional photos shown here were encountered in several soybean fields during my visit to Argentina last week.  The species seems to be having a bit of a population surge on soybeans in the Humid Pampas – Argentina’s main soybean growing region – due to the dry conditions they’ve had as of late.  Their short life cycle (egg to egg in 2 weeks) and preference for generally protected lower leaf surfaces, along with the lack of any registered chemical insecticides labeled for their use on soybean, makes control of this insects especially problematic.

¹ Yes, that’s “a thrips” – not “a thrip” (similar to deer, species, sheep, etc.).  Personally, I’ve always had trouble with singular use of this definitely plural-looking word – it must be the “s” at the end and the completely natural sound of the word “thrip” in singular use.  Then again, one “specie” doesn’t sound right, so who knows?  At any rate, I’ve managed to force myself to say “a thrips” (although I still wince a little bit inside whenever I do).

Caliothrips phaseoli (bean thrips) - nymphs | Oliveros, Pcia. Santa Fe, Argentina

Thrips are tiny – the adults in the above photo (only slightly cropped) measure no more than ~1 mm in length, testing the limits even of my MP-E 65mm 1-5X macro lens at full magnification.  There are some interesting features about the morphology and life history of thrips – namely their “rasping-sucking” mouthparts and life history that seems somewhat intermediate between the incomplete metamorphosis exhibited by other exopterygote insects (egg, nymph, adult) and the complete metamorphosis of the endopterygotes (egg, larva, pupa, adult).  Thrips actually have only a single mandible (the other aborting development during embryogenesis), which they use to “rasp” a hole into the plant tissues upon which they feed.  The remaining mouthparts then form a sort of siphon, that is used to imbibe the liquids that accumulate within the hole.  This seems to represent – at least functionally – an intermediate step in the evolution of the true piercing/sucking mouthparts exhibited by other hemipteroid insects.  Life history-wise, only the first- and second-instar nymphs (2nd photo above) feed, the third- and fourth-instars becoming quiescent stages termed the propupa and the pupa, respectively.

Reader question: I presume the shiny, black globs on the hairs of the plant are fecal deposits, but why are they placed as such? Does it help avoid spoilage of the leaf feeding surface – I’m not aware of any other insects that are so fastidious (except perhaps ants). Maybe there is a defensive function? I’ve searched and found nothing about this, so please let me know if you have any insight.

There seems to be some difference of opinion regarding the actual species name for these insects.  Most applied economic literature dealing with thrips in soybeans calls these Caliothrips phaseoli – a widespread species occurring in North, Central, and South America.  However, a number of references (both economic and taxonomic) recognize South American populations as a distinct species, C. brasiliensis (or C. braziliensis, depending on the source), based on the solid dark rather than medially lightened elytral band.  I also found some references that seem to regard C. phaseoli as s a synonym of C. fasciatus (although this comparison at Pests and Diseases Image Library seems to show distinct differences in abdominal sculpturing between the two species).  I’m going with C. phaseoli over C. brasiliensis based on a checklist of Brazil Thysanoptera (Monteiro 2001) and the Argentina checklist at the World Thysanoptera website, and the general lack of mention of C. fasciatus as a pest of soybean in Argentina in the literature also makes me go with C. phaseoli.  Congratulations to Ben Coulter, who wins this challenge with a clean sweep of the ID and host plant, and to HBG Dave, whose 4 pts moves him into the lead in the current BitB Challenge session.
 
REFERENCE:

Monteiro RC. 2001. The Thysanoptera fauna of Brazil. Pp. 325–340 in Marullo, R. & Mound, L.A. (eds) Thrips and Tospoviruses: Proceedings of the 7th International Symposium on Thysanoptera. Australian National Insect Collection, Canberra.

Copyright © Ted C. MacRae 2011