immatures

Beetle Collecting 101: How to rear wood-boring beetles

/ Ted C. MacRae / 13 Comments

I’ve been collecting wood-boring beetles for more than three decades now, and if I had to make a list of “essential” methods for collecting them I would include “beating,” “blacklighting,” and “rearing.” Beating is relatively straightforward—take a beating sheet (a square piece of cloth measuring 3–5 ft across and suspended beneath wooden, metal, or plastic cross members), position it beneath a branch of a suspected host plant, and tap the branch with a stick or net handle. Many wood-boring beetles tend to hang out on branches of their host plants, especially recently dead ones, and will fall onto the sheet when the branch is tapped. Be quick—some species (especially jewel beetles in the genus Chrysobothris) can zip away in a flash before you have a chance to grab them (especially in the heat of the day). Others (e.g., some Cerambycidae) may remain motionless and are cryptically colored enough to avoid detection among the pieces of bark and debris that also fall onto the sheet with them. Nevertheless, persistence is the key, and with a little practice one can become quite expert at efficiently collecting wood-boring beetles using this method. Blacklighting is even easier—find the right habitat (preferably on a warm, humid, moonless night), set up a blacklight in front of a white sheet, crack open a brew, and wait for the beetles to come!

Rearing, on the other hand, takes true dedication. One must not only learn potential host plants, but also how to recognize wood with the greatest potential for harboring larvae, retrieve it from the field, cut it up, place it in rearing containers, and monitor the containers for up to several months or even years before hitting pay dirt (maybe!). Despite the considerable amount of effort this can take, the results are well worth it in terms of obtaining a diversity of species (usually in good series), some of which may be difficult to encounter in the field, and identifying unequivocal larval host associations. I have even discovered two new species through rearing (Bellamy 2002, MacRae 2003)! Moreover, checking rearing containers can be a lot of fun—in one afternoon you can collect dozens or even hundreds of specimens from places far and wide, depending on how far you are willing to travel to collect the wood. Because of the effort involved, however, the more you can do to ensure that effort isn’t wasted on uninfested wood and that suitable conditions are provided to encourage continued larval development and adult emergence from infested wood the better. It is with this in mind that I offer these tips for those who might be interested in using rearing as a technique for collecting these beetles.

I should first clarify what I mean by “wood-boring” beetles. In the broadest sense this can include beetles from any number of families in which the larvae are “xylophagous,” i.e., they feed within dead wood. However, I am most interested in jewel beetles (family Buprestidae) and longhorned beetles (family Cerambycidae), and as a result most of the advice that I offer below is tailored to species in these two families. That is not to say that I’ll turn down any checkered beetles (Cleridae), powderpost beetles (Bostrichidae), bark beetles (family Scolytidae), or even flat bark beetles sensu lato (Cucujoidea) that I also happen to encounter in my rearing containers, with the first two groups in particular having appeared in quite good numbers and diversity in my containers over the years. Nevertheless, I can’t claim that my methods have been optimized specifically for collecting species in these other families.

First, you have to find the wood. In my experience, the best time to collect wood for rearing is late winter through early spring. A majority of species across much of North America tend to emerge as adults during mid- to late spring, and collecting wood just before anticipated adult emergence allows the beetles to experience natural thermoperiods and moisture regimes for nearly the duration of their larval and pupal development periods. Evidence of larval infestation is also easier to spot once they’ve had time to develop. That said, there is no “bad” time to collect wood, and almost every time I go into the field I am on the lookout for infested wood regardless of the time of year. The tricky part is knowing where to put your efforts—not all species of trees are equally likely to host wood-boring beetles. In general, oaks (Quercus), hickories (Carya), and hackberries (Celtis) in the eastern U.S. host a good diversity of species, while trees such as maples (Acer), elms (Ulmus), locust (Gleditsia and Robinia), and others host a more limited but still interesting fauna. In the southwestern U.S. mesquite (Prosopis) and acacia (Acacia) are highly favored host plants, while in the mountains oaks are again favored. Everywhere, conifers (Pinus, Abies, Juniperus, Tsuga, etc.) harbor a tremendous diversity of wood-boring beetles. To become good at rearing wood-boring beetles, you have to become a good botanist and learn not only how to identify trees, but dead wood from them based on characters other than their leaves! Study one of the many good references available (e.g., Lingafelter 2007, Nelson et al. 2008) to see what the range of preferred host plants are and then start looking.

I wish it were as simple as finding the desired types of trees and picking up whatever dead wood you can findm but it’s not. You still need to determine whether the wood is actually infested. Any habitat supporting populations of wood-boring beetles is likely to have a lot of dead wood. However, most of the wood you find will not have any beetles in it because it is already “too old.” This is especially true in the desert southwest, where dead wood can persist for very long periods of time due to low moisture availability. Wood-boring beetles begin their lives as eggs laid on the bark of freshly killed or declining wood and spend much of their lives as small larvae that are difficult to detect and leave no obvious outward signs of their presence within or under the bark. By the time external signs of infestation (e.g., exit holes, sloughed bark exposing larval galleries, etc.) become obvious it is often too late—everything has already emerged. Instead, look for branches that are freshly dead that show few or no outward signs of infestation. You can slice into the bark with a knife to look for evidence of larval tunnels—in general those of longhorned beetles will be clean, while those of jewel beetles will be filled with fine sawdust-like frass that the larva packs behind it as it tunnels through the wood. Oftentimes the tunnels and larvae will be just under the bark, but in other cases they may be deeper in the wood. Broken branches hanging from live trees or old, declining trees exhibiting branch dieback seem to be especially attractive to wood-boring beetles, while dead branches laying on the ground underneath a tree are not always productive (unless they have been recently cut).

One way to target specific beetles species is to selectively cut targeted plant species during late winter, allow the cut branches to remain in situ for a full season, and then retrieve them the following winter or early spring. These almost always produce well. Doing this will also give you a chance to learn how to recognize young, infested wood at a time that is perfect for retrieval, which you can then use in searching for wood from other tree species in the area that you may not have had a chance to cut. I have cut and collected branches ranging from small twigs only ¼” diameter to tree trunks 16″ in diameter. Different species prefer different sizes and parts of the plant, but in general I’ve had the best luck with branches measuring 1–3″ diameter.

Once you retrieve the wood, you will need to cut it into lengths that fit into the container of your choice (a small chain saw makes this much easier and quicker). In the field I bundle the wood with twine and use pink flagging tape to record the locality/date identification code using a permanent marker. I then stack the bundles in my vehicle for transport back home. Choice of container is important, because moisture management is the biggest obstacle to rearing from dead wood—too much moisture results in mold, while too little can lead to desiccation. Both conditions can result in mortality of the larvae or unemerged adults. In my rearing setup, I use fiber drums ranging from 10-G to 50-G in size (I accumulated them from the dumpster where I work—mostly fiber drums used as shipping containers for bulk powders). Fiber drums are ideal because they not only breath moisture but are sturdy and may be conveniently stacked. Cardboard boxes also work as long as they are sturdy enough and care is taken to seal over cracks with duct tape. Avoid using plastic containers such as 5-G pickle buckets unless you are willing to cut ventilation holes and hot-glue fine mesh over them. While breathable containers usually mitigate problems with too much moisture, desiccation can still be a problem. To manage this, remove wood from containers sometime later in the summer (after most emergence has subsided), lay it out on a flat surface such as a driveway, and hose it down real good. Once the wood has dried sufficiently it can be placed back in the container; however, make sure the wood is completely dry or this will result in a flush of mold. I generally also wet down wood again in late winter or early spring, since I tend to hold wood batches through two full seasons.

I like to check containers every 7–15 days during spring and summer. Some people cut a hole in the side of the container that leads into a clear jar or vial—the idea being that daylight will attract newly emerged adults and facilitate their collection. I’ve tried this and was disappointed in the results—some of the beetles ended up in the vial, but many also never found their way to the vial and ended up dying in the container, only to be found later when I eventually opened it up. This is especially true for cerambycids, many of which are nocturnal and thus probably not attracted to daylight to begin with. My preference is to open up the container each time so that I can check the condition of the wood and look for evidence of larval activity (freshly ejected frass on the branches and floor of the container). I like to give the container a ‘rap’ on the floor to dislodge adults from the branches on which they are sitting, then dump the container contents onto an elevated surface where I can search over the branches and through the debris carefully so as not to miss any small or dead specimens. I use racks of 4-dram vials with tissue packed inside each and a paper label stuck on top of its polypropylene-lined cap as miniature killing jars. Specimens from a single container are placed in a vial with a few drops of ethyl acetate, and I write the container number and emergence date range on the cap label. Specimens will keep in this manner until they are ready to be mounted weeks or months (or even years) later. If the vial dries out, a few drops of ethyl acetate and a few drops of water followed by sitting overnight is usually enough to relax the specimens fully (the water relaxes the specimens, and the ethyl acetate prevents mold if they need to sit for a while longer).

I store my containers in an unheated garage that is exposed to average outdoor temperatures but probably does not experience the extreme high and low temperatures that are experienced outdoors. In the past I wondered if I needed more heat for wood collected in the desert southwest, but I never came up with a method of exposing the containers to the sun without also having to protect them from the rain. Metal or plastic containers might have eliminated this problem, but then breathability would again become an issue. I would also be concerned about having direct sun shining on the containers and causing excessive heat buildup inside the bucket that could kill the beetles within them. Now, however, considering the success that I’ve had in rearing beetles from wood collected across the desert southwest—from Brownsville, Texas to Jacumba, California, this seems not to be a big issue.

If anybody else has tips for rearing wood-boring beetles that they can offer, I would love to hear from you.

REFERENCES:

Bellamy, C. L. 2002. The Mastogenius Solier, 1849 of North America (Coleoptera: Buprestidae: Polycestinae: Haplostethini). Zootaxa 110:1–12 [abstract].

Lingafelter, S. W. 2007. Illustrated Key to the Longhorned Woodboring Beetles of the Eastern United States. Special Publication No. 3. The Coleopterists Society, North Potomac, Maryland, 206 pp. [description].

MacRae, T. C. 2003. Agrilus (s. str.) betulanigrae MacRae (Coleoptera: Buprestidae: Agrilini), a new species from North America, with comments on subgeneric placement and a key to the otiosus species-group in North America. Zootaxa 380:1–9 [pdf].

Nelson, G. H., G. C. Walters, Jr., R. D. Haines, & C. L. Bellamy.  2008.  A Catalogue and Bibliography of the Buprestoidea of American North of Mexico.  Special Publication No. 4. The Coleopterists Society, North Potomac, Maryland, 274 pp. [description].

Copyright © Ted C. MacRae 2014

Stalking tigers in Argentina

/ Ted C. MacRae / 3 Comments
Brasiella argentata

Brasiella argentata | banks of Rio Paraná, Corrrientes, Argentina

Most of you know that I have spent a lot of time in Argentina over the years, and while most of my time there has been for work I have had a fair bit of opportunity to collect insects as well. This includes tiger beetles, and in fact I recall one trip some years ago during which I spent the better part of a week chasing tigers in northeastern Argentina around Corrientes and west into Chaco Province. I think I collected maybe a dozen species or so—some in great numbers and others not, and with the help of tiger beetle expert David Brzoska I’ve managed to put names on most of the material. Despite this, however, I’ve never actually posted any photos of tiger beetles from Argentina here on BitB. I guess the main reason for this is that my efforts to photograph tiger beetles is still a relatively new pursuit (compared to the time that I’ve been going to Argentina), and most of my luck with tiger beetles in Argentina has preceded my time with a camera. The other reason for the delay is that, while I have managed to photograph a few tiger beetles in Argentina, I’ve only recently been able to determine their identity (and you all know how I dislike posting photos of unidentified insects). Well, time to change that, and for this post I am featuring the very first tiger beetle that I was able to photograph in Argentina—the aptly named Brasiella argentata.

Banks of Rio Paraná, habitat for Brasiella argentata.

Banks of Rio Paraná, habitat for Brasiella argentata.

The individuals in this post were photographed on 1 April 2011 during the early part of a week-long visit to Corrientes and neighboring Chaco Province in northern Argentina. Remember, this is the southern hemisphere, so early April is way late in the season and, in this part of Argentina, typically on the back end of a very long dry period. Still, it is far enough north to be borderline subtropical climate, and with the stifling heat it could, for all intents and purposes, have been the middle of summer. I knew tiger beetles could be found along the banks of the Rio Paraná, as I had collected them there during my trip some 10 years previous, so in late morning of my first day after arrival in the city I kitted up and walked down to the river. Sand and mud beaches are not plentiful along the mostly rocky shoreline, and I was perturbed to see the area where I had collected during my last visit had since been “developed.” Nevertheless, I found promising-looking habitat a short distance further north and walked to its moister edges (photo above). I saw nothing at first, but eventually I came to a small, moist drainage where the sand was mixed with more mud, and there they were! It took a little bit of looking, as this species is quite small—adults average only ~7 mm in length, and despite the impression you may get from these photos they are well camouflaged to match the color of the wet, muddy sand and, thus, difficult to see before they take flight and again after they land.

An individual sits long enough to allow a few close, lateral profile shots.

Brasiella argentata is one of the most widely distributed Neotropical species of tiger beetles, occurring from Panama and the West Indies south to Peru and Argentina (Cassola & Pearson 2001). Numerous subspecies have been described from throughout its range, but in truth it seems to actually be a “species swarm” comprised of multiple species, many of which can only be determined by examination of characters contained within the male aedeagus (Sumlin 1979). The genus Brasiella itself, like many others, was until recently considered to be a subgenus of Cicindela, but the distinctiveness of these mostly small (Pearson et al. 2007 refer to them as “Little Tiger Beetles”), cursorial (running) beetles has been recognized in most of the more recent comprehensive treatises (e.g., Cassola & Pearson 2001, Erwin & Pearson 2008). Unlike most of its related genera (subtribe Cicindelina), Brasiella is almost exclusively Neotropical in distribution—only one of its 45 species, B. wickhami, reaches the U.S. in southern Arizona (Pearson et al. 2007).

Brasiella argentata

The only photo I managed looking towards the front of an individual.

If their smallness must be recognized, so must their running abilities. This was one of the most difficult species I’ve ever attempted to photograph, and with those difficulties added to the heat of the day and its “perfect storm” habitat it’s a wonder I got any photographs at all. It was a good half hour before I even got the first photo (top), and another hour and a half of effort was required before I managed to get a selection of photos that included a good, close lateral profile shot (middle). As is often the case with very wary tiger beetles, frontal portraits were almost impossible due to their persistent efforts to flee, so I feel fortunate to have managed the last photo. It’s not as close as I typically like to get, but I am pleased with the composition and also the fact that it shows the species’ truncate labrum—a key character.

REFERENCES:

Cassola, F. & D. L. Pearson. 2001. Neotropical tiger beetles (Coleoptera: Cicindelidae): Checklist and biogeography. Biota Colombiana 2:3–24 [pdf].

Erwin, T. L. & D. L. Pearson. 2008. A Treatise on the Western Hemisphere Caraboidea (Coleoptera). Their classification, distributions, and ways of life. Volume II (Carabidae-Nebriiformes 2-Cicindelitae). Pensoft Series Faunistica 84. Pensoft Publishers, Sofia, 400 pp [Amazon description, book review].

Pearson, D. L., C. B. Knisley & C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp. [Oxford description].

Sumlin, W. D., III 1979. A brief review of the genus Cicindela of Argentina (Coleoptera: Cicindelidae). Journal of the New York Entomological Society 87(2):98–117 [JSTOR].

Copyright Ted C. MacRae 2013

Hooray for iStock—I finally have an ID for my photo

/ Ted C. MacRae / 16 Comments

I was all set to make a “One-Shot Wednesday” post today, but sometimes big news strikes and plans must change. The news today was in the form of a random tweet by Alex Wild:

iStock-caption_Wild-20131120

The link in the tweet led me to the following photo on iStock by Getty:

bedbug has captured worm

I was stunned—the photo depicted a scene almost identical to one that I had photographed back in September while visiting soybean fields in Louisiana. For two months I sat on the photo with no idea what I was looking at, but now thanks to Alex I have my answer! Compare the above photo with mine below, and you’ll see that everything matches perfectly—I had photographed a “bedbug” that had captured a “worm”!

Podisus maculiventris preying on Chrysodeixis includens larva

bedbug captures a worm

I considered myself to be fortunate, because there was not just one but two different subjects in the photo, and both of them matched perfectly with the subjects shown in the iStock photo. Gotta love the internet—nowadays names for even the most hard-to-identify bugs are just a click away if you know where to look!

</snark>

Of course, the aggressor in both photos is not a “bedbug” [sic for “bed bug”] (order Hemiptera, family Cimicidae) but a stink bug (family Pentatomidae), specifically Podisus maculiventris, or “spined soldier bug”—perhaps the most common predatory stink bug in North Amerca and ranging from Mexico and parts of the West Indies north through the U.S. into Canada. It is a well-known predator of crop pests and, as such, has been imported to several other countries as part of classical biological control efforts. As for the “worm,” in my photo it is a late-instar larva of Chrysodeixis includens, or “soybean looper, and while I haven’t been able to identify the exact species in the iStock photo it is definitely a lepidopteran caterpillar that appears to related to if not in the same family as the soybean looper (Noctuidae). Now, I concede that “worm” is sometimes used for lepidopteran larvae, but one must also concede that in it’s broadest sense “worm” can refer to members of several disparate phyla such as Nematoda (roundworms), Platyhelminthes (flatworms), or Annelida (segmented worms).

This case, of course, just screams for application of the Taxonomy Fail Index (TFI), which scales the amount of error in a taxonomic identification in absolute time against the error of misidentifying a human with a chimpanzee—our closest taxonomic relative. For example, when TFI = 1 the error is of the same magnitude as mistaking a human for a chimp, while  TFI > 1 is a more egregious error and TFI < 1 a more forgivable one. In the case shown here, one must go back to the common ancestor that eventually gave rise to all of the worm phyla and noctuid moths (~937.5 mya). In addition, since there are two subjects in the photo, one must also go back to the divergence of the main hemipteran groups that contain bed bugs and stink bugs (mid-Triassic, ~227.5 mya). This results a whopping 1.165 billion total years of divergence between the identifications assigned to the subjects in the iStock photo and their actual identity. Assuming that chimps and humans diverged approximately 7.5 mya, this gives a TFI for the iStock photo of 155! I haven’t searched thoroughly to determine whether this is a record for the highest TFI in a single photo, but surely it is a strong contender!

Copyright © Ted C. MacRae 2013

Quick Guide to Armyworms on Soybean

/ Ted C. MacRae / 5 Comments

Throughout the soybean growing areas of the southern U.S. and South America, lepidopteran caterpillars are the most important pest complex affecting the crop. Millions of pounds of insecticides are sprayed on the crop each year in an effort to minimize their impact—a practice that is not always successful and entails significant exposure risks to the environment and farm workers alike. A variety of lepidopteran species occur in soybeans, and proper identification is essential to ensure adequate control and avoiding unnecessary applications. While the most important and commonly encountered species are velvetbean caterpillar (Anticarsia gemmatalis) and soybean looper (Chrysodeixis includens), others include soybean podworms (Helicoverpa zea in the U.S.; H. gelotopoeon and—now—H. armigera in Brazil and Argentina), sunflower looper (Rachiplusia nu), bean shoot moth (Crocidosema aporema), and armyworms of the genus Spodoptera. The last group contains several species that can affect soybean, and while they have traditionally been considered minor pests of the crop a number of species have increased in importance during the past few years.

I have been conducting soybean field trials in both the U.S. and South America for many years now and have had an opportunity to photograph most of the species known to occur on soybean in these regions. Identification of armyworm larvae can be rather difficult due to their similarity of appearance, lack of distinctive morphological differences (e.g. number of prolegs), and intraspecific variability in coloration. Conclusive identification is not always possible, especially with younger larvae; however, the different species do exhibit subtle characters that can usually allow for fairly reliable identification of large larvae. Considering the dearth of direct comparative resources—either in print or online—I offer this quick guide to the six armyworm species that I’ve encountered in soybean.

Spodoptera frugiperda (fall armyworm) | Jerseyville, Illinois

Spodoptera frugiperda (fall armyworm) | Jerseyville, Illinois

Spodoptera frugiperda (fall armyworm). This is not the most important armyworm pest of soybean, in contrast to its great importance in other crops such as corn and cotton. It is, however, the most widely distributed of the species, occurring in both the southern U.S. and throughout soybean growing areas of Brazil and Argentina. When problems do occur on soybean they are usually a result of larvae moving from grassy weeds to small soybean plants in late-planted or double-crop fields. Larvae can damage all stages of soybean, from seedlings (cutting them off at ground level) to later stages by feeding primarily on foliage and even pods. Larvae are somewhat variable in coloration but are distinctive among armyworms by virtue of the pinaculae (sclerotized tubercles) visible over the dorsum, each bearing a single stout seta. Four pinaculae are present on each of the abdominal segments, with those on the eighth abdominal segment forming a square, and larvae also exhibit a pronounced inverted, white, Y-shaped mark on the head.

Spodoptera exigua (beet armyworm) | Stoneville, Mississippi

Spodoptera exigua (beet armyworm) | Stoneville, Mississippi

Spodoptera exigua (beet armyworm). This species is better known as a pest of vegetables but will occasionally damage soybean in the southern U.S. In soybean larvae prefer to feed on foliage of seedling plants but will, if present during reproductive stages, also feed on blossoms and small pods. Late-instar larvae can be rather variable in appearance, but most tend to be green above and pinkish or yellowish below with a white stripe along the side. Larvae can be confused with Spodoptera eridania (southern armyworm) because of a dark spot that might be present on the side, but in southern armyworm the spot is on the first abdominal segment while in beet armyworm (when present) it is on the mesothorax.

Spodoptera ornithogalli (yellowstriped armyworm) | Jerseyville, Illinois

Spodoptera ornithogalli (yellow-striped armyworm) | Jerseyville, Illinois

Spodoptera ornithogalli (yellow-striped armyworm). This species is widely distributed throughout North and South America, but its status as an occasional pest of soybean is limited practically to the southeastern U.S. It is often encountered in soybean in low numbers but can reach pest status in double-crop fields with small plants that have been planted after wheat (similar to fall armyworm). Compared to other species in the genus the larvae are rather uniform in appearance, exhibiting paired, black, triangular spots along the back of each abdominal segment with thin to prominent yellow stripes running lengthwise adjacent to and not interrupted by the spots. Larvae oftentimes have an almost black velvety appearance with distinctly contrasting bright yellow stripes.

Spodoptera eridania (southern armyworm) | Jerseyville, Illinois

Spodoptera eridania (southern armyworm) | Jerseyville, Illinois

Spodoptera eridania (southern armyworm) | Union City, Tennessee

Spodoptera eridania (southern armyworm) | Union City, Tennessee

Spodoptera eridania (southern armyworm). This species is, like fall armyworm, widely distributed from the southern U.S. through Brazil and Argentina. In the U.S. it occurs only sporadically on soybean, usually causing “hot spots” of damage by groups of many larvae hatching from a single egg mass and skeletonizing the nearby foliage before dispersing as they grow larger. In Brazil and Argentina this species has emerged during recent years as one of the most important armyworm pests of soybean, especially in regions where cotton is also grown. Larvae can be somewhat variable in appearance and, in South America, can be easily confused with those of the black armyworm (S. cosmioides), both of which often exhibit prominent black markings on first and eighth abdominal segments and a subspiracular light-colored line along the length of the thorax and abdomen. Southern armyworm, however, rarely exhibits an additional black marking on top of the mesothoracic segment. Additionally, when the subspiracular line is present it is interrupted by the black marking on the first abdominal segment and is less distinct in front of the spot than behind, and if the line is not present then the black spots on top of the first abdominal segment are larger than those on top of the eighth abdominal segment.

Spodoptera cosmioides (black armyworm) | Acevedo (Buenos Aires Prov.), Argentina

Spodoptera cosmioides (black armyworm) | Acevedo (Buenos Aires Prov.), Argentina

Spodoptera cosmioides (black armyworm) | Chaco Prov., Argentina

Spodoptera cosmioides (black armyworm) | Saenz Peña (Chaco Prov.), Argentina

Spodoptera cosmioides (black armyworm) | Acevedo (Buenos Aires Prov.), Argentina

Spodoptera cosmioides (black armyworm) | Acevedo (Buenos Aires Prov.), Argentina

Spodoptera cosmioides (black armyworm). No accepted English common name exists for this strictly South American species that was previously considered a synonym of the North and Central American species Spodoptera latifascia. In Brazil it has been referred to by such names as “lagarta preta” (black caterpillar) and “lagarta da vagem” (pod caterpillar). The latter name has also been applied to other soybean pests, including southern armyworm, so to me “black armyworm” seems the most appropriate English name to adopt. Like southern armyworm, this species is a sometimes pest of cotton and in recent years has become increasingly important in soybean throughout Brazil and northern Argentina. Larvae often resemble and can be easily confused with those of southern armyworm; however, there is almost always a dark spot on top of the mesothoracic segment that is lacking in southern armyworm. Additionally, the light-colored subspiracular line, when present, is not interrupted by the black spot on the first abdominal segment and is equally distinct in front of and behind the spot. When the line is not present the black spots on top of the first abdominal segment are smaller than than those on top of the eighth abdominal segment.

Spodoptera albula

Spodoptera albula (gray-streaked armyworm) | Saenz Peña (Chaco Prov.), Argentina

Spodoptera albula (unbarred or gray-streaked armyworm). While known to occur in extreme southern U.S., this species has been cited as a pest of soybean only in Brazil, although its importance has not matched that of southern or black armyworm. Like most armyworms it is polyphagous, but this species seems to prefer amaranth (Amaranthus spp.). Larvae of this species can be distinguished from other South American armyworms that feed on soybean by the trapezoidal black marking on the mesothorax (usually semicircular to slightly trapezoidal in black armyworm), the black marking on the first abdominal segment not larger than that on the sixth abdominal segment, both of which are smaller than those on the seventh and eight abdominal segments, the white-only rather than white and orange dorsolateral stripe, and the triangular black markings on the abdominal segments each with a small white spot in the middle or at the apex of the marking.

Copyright © Ted C. MacRae 2013

Twig tethered to a twig

/ Ted C. MacRae / 1 Comment
Geometrid larva (subfamily Ennominae?) | Plymouth, North Carolina

Geometrid larva (subfamily Ennominae?) | Plymouth, North Carolina

In September I visited soybean field trials across the southeastern U.S. It’s a trip I’ve done every year for the past I don’t know how many years and one that I enjoy immensely due to the opportunities it gives me to see the country, kick the dirt with academic cooperators, sample the local cuisine… and photograph insects. New for me this year was the Carolinas, and in a soybean field in Plymouth, North Carolina I encountered this geometrid larva on the stub of a soybean leaf petiole. Geometrid larvae are known variously as inchworms, cankerworms, spanworms, measuring worms, loopers, etc., depending on the species. Most of the common names refer to the same thing that the family name does—the larval method of locomotion whereby the caterpillar—possessing legs only at the two extremes of its body—”inches” its way along as if measuring the ground it walks on (Geometridae is derived from the Latin geometra, or “earth-measurer”). The resemblance of the larvae of many species to dead twig stumps is nothing short of remarkable, and had it not been for the contrasting coloration I may never have noticed the larva in the first place. I also did not notice until looking at it through the macro lens of my camera the tether attached by the larva to the tip of the twig—invisible to the naked eye but providing energy-saving stabilization for the larva to hold its cryptic position.

I’ve not encountered a geometrid larva in soybeans before, and my impression has been that they are largely deciduous tree feeders (perhaps due to the periodic occurrence in my area of outbreak species such as fall cankerworm). In trying to determine the species, I found no geometrids covered in the Higley & Boethel (1994) handbook on U.S. pests, and when I consulted the Turnipseed & Kogan (1976) and Kogan (1987) global reviews of soybean pests I found reference only to a few minor pests in India and southeast Asia. Hmm, time for BugGuide. Of course, lepidopteran larvae are not nearly as well represented as the adults, but it seemed most similar to species of the subfamily Ennominae, so I turned to Google and searched on “Ennominae soybean.” This turned up Passoa (1983), who reported larvae of Anacamptodes herse as pests of soybean in Honduras (and mentioned references to several other geometrid species associated with soybean in Brazil). Back to BugGuide, where I found the genus Anacamptodes listed as a synonym of Iridopsis, but the species I. herse was not among the list of species represented in the guide. Checking the link provided at the site to a revision of the genus by Rindge (1966) revealed that I. herse is strictly a Central American species. Perhaps another, North American species of the genus also favors soybean, which led me to Wagner (2005) who mentions soybean as a favored food plant for I. humilis. However, the contrasting purple-brown/yellow-green coloration and relatively thickened body of that species are quite unlike this individual. I don’t have Wagner’s book (only his smaller one on caterpillars of eastern forests—no match in there, either), so it may be that my only remaining option is to post the photo at BugGuide and hope that David Wagner encounters it (actually I should get David’s book anyway)¹.

¹ Update 10/5/13 11:30 am CDT—or hope that Brigette Zacharczenko runs into the post via Facebook and offers to pass it along to Dave during their lab meeting on Monday.

REFERENCES:

Higley, L. G. & D. J. Boethel [eds.]. 1994. Handbook of Soybean Insect Pests. The Entomological Society of America, Lanham, Maryland, 136 pp. [sample pages].

Kogan, M. 1987. Ecology and management of soybean arthropods. Annual Review of Entomology 32:507–538 [pdf].

Passoa, S. 1983. Immature stages of Anacamptodes herse (Schaus) (Geometridae) on soybean in Honduras. Journal of The Lepidopterists’ Society 37(3):217–223 [pdf].

Rindge, F. H. 1966. A revision of the moth genus Anacamptodes (Lepidoptera, Geometridae) (1966). Bulletin of the America Museum of Natural History 132(3):174–244 [pdf].

Turnipseed, S. G. & M. Kogan. 1976. Soybean entomology. Annual Review of Entomology 21:247–282 [pdf].

Wagner, D. L. 2005. Caterpillars of Eastern North America: A Guide to Identification and Natural History . Princeton University Press, Princeton, New Jersey, 496 pp. [Google eBook].

Copyright © Ted C. MacRae 2013

Ceti Eel offspring?

/ Ted C. MacRae / 5 Comments
Nicrophila americana

Nicrophila americana (American carrion beetle) larva | Sam A. Baker State Park, Wayne Co., Missouri.

If this creature was a tad bit slimier, you might think it had just been plucked from underneath the armor of an adult Ceti Eel and was looking to slip inside the ear of Chekov or some other human to wrap itself around the unsuspecting victim’s cerebral cortex. In reality, this creature lives not on Ceti Alpha V., but right here on earth, and while it’s natural history may not include making human hosts “extremely susceptible to suggestion“, it does include an appetite for dead flesh and the maggots that try to compete for it. Say hello to the larva of Nicrophila americana (American carrion beetle), a member of the family Silphidae (carrion and burying beetles) (not to be confused with the endangered Nicrophorus americanus, or American burying beetle). Like most beetles, the larvae can be difficult to recognize as such due to its very different form compared to the adult. However, the one-segmented tarsi, distinct head, presence of chewing mouthparts, and presence of spiracles along the sides of the body give the clues to its identity.

Necrophila americana

While not the offspring of a Ceti Eel, its habits are almost as… er, disgusting!

The genus name (literally meaning “attracted to corpses“) is a perfect descriptor of this beetle’s natural history. Adults are attracted to animal carcasses, where they lay their eggs and prey on maggots (fly larvae) as they hatch to give a competitive advantage to their own larvae once they hatch. The larvae also will eat maggots and other larvae within the carcass, along with the carcass itself. This larva had completed its development and was searching the ground for a suitable spot to dig a burrow for pupation and eventual emergence as an adult.

Copyright © Ted C. MacRae

Raining spit

/ Ted C. MacRae / 1 Comment
Cephisus siccifolia

Cephisus siccifolia 3rd instar nymph | Buenos Aires, Argentina

Even though it was November (and thus spring in Argentina), conditions were already unusually dry—a portent of the worst drought that would hit Argentina in 70 years. Because of this, I found the occasional wet spot on the pavement as I walked the trails in La Reserva Ecológica Costanera Sur rather odd. At first I thought they were spit—the trails were popular on this day for runners and bike riders, but I quickly realized that those would have to be some truly ginormous spit wads based on the size of the splatter. It wasn’t long before I thought to look up, and this is what I saw on the branch directly above me:

Cephisus siccifolia

Cephisus siccifolia spittle mass on unknown species of tree.

I knew right away this was the work of a froghopper, or “spittlebug,” a true bug (order Hemiptera) in the family Cercopidae. Spittlebugs are common in the eastern U.S. where I live and are famous for the spit-like wads of froth (“cuckoo spit” to some) within which the nymphs conceal themselves until they reach adulthood. Our eastern U.S. species, however, are most commonly seen on herbaceous plants rather than in trees, and the frothy masses they produce are fairly small—about the size of a real wad of spit (at least, according to my direct comparison when I was 12 years old). The spittle masses I was seeing today were enormous, frothy, liquid masses that literally dripped from the trees by their own weight—raining spit!

Cephisus siccifolia

Nymphs produce bubbles by siphoning air into a channel under the abdomen.

I was about to move on when I noticed some movement in the spittle mass. A closer look through the macro lens revealed the tip of the abdomen of a nymph slowly circling around near the surface of the spittle and creating new bubbles as it did this. As one can imagine, living inside a mass of bubbly liquid presents a challenge to breathing, and the nymphs get around this problem by protruding the tip of the abdomen outside the spittle mass and taking in air through a tubelike canal below the abdomen (Hamilton & Morales 1992). Strong contractions of the abdomen inside the spittle mass eject air from the canal, resulting in bubble formation.

Cephisus siccifolia

Nymphs partially exposed by removal of spittle mass.

I sent these photos to Andy Hamilton (Canadian National Collection of Insects, Arachnids and Nematodes), specialist in world Cercopidae, to see if there was any chance he might recognize the genus or species based on these photos. I noted that these were the biggest spittlebug nymphs I had ever seen (the individual in the first photo measuring ~10mm in length). Not only did he recognize them as belonging to the genus Cephisus, but he was actually in the process of finishing up a revision of the New World members of the tribe Ptyelini—Cephisus being the sole New World genus to represent the tribe. Based on its white coloration and occurrence as far south as Buenos Aires, Argentina, he suggested this must be C. siccifolia—a species that can sometimes achieve economic pest status (Ribeiro et al. 2005) but which still apparently needs to be properly recorded from Argentina (Hamilton 2012). Based on degree of wing pad development, Andy surmises the individual in Photo represents a 3rd instar (if the 3rd instar measures 10 mm, can you imagine the size of the 5th instars?!). Andy asked me if I would grant him use of the photos in his soon-to-be-published revision (of course I agreed), and here is the plate with the photos (as well as an adult photographed by someone else) as it appears in his paper:

Hamilton_2012_Cephisus

As Andy notes in his paper, it seems rather unusual that Cephisus is the only tribal representative in the New World despite having successfully colonized all of its tropical and subtropical mainland areas. There are several other genera in the tribe in Africa, which would suggest that the Ptyelini arose prior to the late Cretaceous rifting that separated South America and Africa into two continents. It is thus puzzling why the tribe went on to further diversify in Africa but not in the New World.

A tight crop of Photo above was featured in , for which Ben Coulter was the hands-down winner. Honestly I thought this might end up being a slam dunk challenge—people have gotten very good at designing Google search strings to come up with answers that in pre-internet days might have been impossible to find. Nobody stumbled upon the magic search string for this challenge—”MacRae Cercopidae” which pulls up the Hamilton paper and above plate as the very first result. Still, Ben used good old fashioned intuition based on the locality tag to correctly surmise the species and take the early lead in BitB Challenge Session #7. Congratulations, Ben!

REFERENCES:

Hamilton, K. G. A. 2012. Revision of Neotropical aphrophorine spittlebugs, part 1: Ptyelini (Hemiptera, Cercopoidea). Zootaxa 3497:41–59.

Hamilton, K. G. A. & C. F. Morales. 1992. Cercopidae (Insecta: Homoptera). Fauna of New Zealand 25, 40 pages.

Ribeiro, G. T., M. da Costa Mendonça, J. Basílio de Mesquita, J. C. Zanuncio G. S. & Carvalho. 2005. Spittlebug Cephisus siccifolius damaging eucalypt plants in the State of Bahia, Brazil. Pesquisa Agropecuária Brasileira 40(7):unpaginated.

Copyright © Ted C. MacRae 2013

How to collect larvae of Amblycheila cylindriformis

/ Ted C. MacRae / 19 Comments
Amblycheila cylindriformis larval burrow | Major Co., Oklahoma

Amblycheila cylindriformis larval burrow | Major Co., Oklahoma

Step 1. Go to your favorite grassland habitat in the western half of the Great Plains anywhere from Texas north to South Dakota and look for barren soil amongst the vegetation. Clay banks near streams or in ravines and even vertical clay bluff faces are also good (although I have not myself observed the latter). “My” spot is in the Glass Mountains of northwestern Oklahoma, where talus slopes in mixed-grass prairie beneath flat-topped mesas and the ravines that cut through them provide just enough slope for this species’ liking.

Burrow diameter of ~8mm identifies this as a 3rd instar larva.

Burrow diameter of ~8mm identifies this as a 3rd instar larva.

Step 2. Look for large, almost perfectly round burrow entrances that go straight down from the surface. By large, I mean approximately 6–8 mm in diameter—as large a burrow as any tiger beetle in North America will make. Many other insects create burrows, but tiger beetle burrows are generally recognizable by their almost perfectly circular shape and clean, beveled edge. Look closely, and the burrow will be seen to actually be slightly D-shaped to match the shape of the tiger beetle larva’s head—the large, sickle-shaped, upward-facing jaws resting against the flat part of the D. In the case of this species, they tend to be found in clusters of several burrows in close proximity to each other. The burrow in these photos was found at the upper edge of a drainage ravine on the upper part of the talus slopes (see diagram in this post).

Dig around the burrow, carefully excavating along the grass stem, until the larva is reached.

Dig around the burrow, carefully excavating along the grass stem, until the larva is reached.

Step 3. Try this first—chew the end of a long, narrow grass stem (frayed and sticky will be easier for the larva to grab hold of) and stick it down the burrow until it hits bottom, tap lightly a few times to entice a bite, then yank (and I mean yank!) the stem out. With luck, the larva will come flying out of the burrow and land somewhere on the ground in front of you. (By the way, if you have never done this, you are missing one of the greatest treats that insect collecting has to offer. If you have done it, you owe it to yourself to show this to somebody else who has not ever seen it—their shocked reaction at the sight of the flying larva is beyond priceless!) Larvae are not always in the mood to bite, however, so if the so-called “fishing” technique does not work then you will have to dig. Stick the grass stem back down the burrow and begin excavating around the burrow, carefully prying away the soil adjacent to the burrow to prevent it from falling into and obscuring the burrow. Keep excavating as you follow the grass stem down until, at least, you reach the larva. In the photo above you can see in the lower right-center area the burrow with the grass stem protruding from it and the larva placed on a clump of soil in front of the shovel (for sense of scale). It seems I had an easy time of it with this larva, as literature sources report larval burrows extending down to depths of a meter or more.

Amblycheila cylindriformis 3rd instar larva.

Amblycheila cylindriformis 3rd instar larva.

Step 4. Behold the beast! There is nothing more that can be said—these larvae are ginormous! This particular larva measured a full 62 mm from the tips of its mandibles to the tip of its abdomen—that’s 2½ inches! No other tiger beetle larva in North America reaches this size, except perhaps the related A. hoversoni (South Texas Giant Tiger Beetle).

The distinctly smaller 2nd pair of eyes confirm this is not Tetracha or Cicindela (sensu lato)...

The distinctly smaller 2nd pair of eyes confirm this is not Tetracha or Cicindela (sensu lato)…

Step 5. If size alone isn’t enough, you can confirm that the larvae does indeed belong to the genus Amblycheila by looking at its eyes—their are two pairs, and the 1st pair (closest to the mandibles) are distinctly larger than the 2nd pair. This isn’t clearly visible in the photo above because I doused the larva with water to remove the mud and dirt that encrusted it upon removal from its burrow.

...and the well-separated hooks on the 5th abdominal segment confirm it is Amblycheila.

…and the distinctly separated hooks on the 5th abdominal segment confirm it is Amblycheila.

Step 6. Another way to distinguish larvae of the genus Amblycheila is by looking at the hooks on the hump of the 5th abdominal segment, best done with a hand lens (or, even better, with an MP-E65 lens!). All tiger beetle larvae have several pairs of large hooks that the larva uses to brace itself against the wall of its burrow when capturing prey to prevent the struggling prey from pulling the tiger beetle larva out of its burrow. Larvae in the genus Omus, restricted to the Pacific region of North America, have three pairs of hooks (referred to as the outer, middle, and inner hooks), while all other North American tiger beetle genera have two (having lost the outer pair). In Amblycheila and Tetracha the hooks are simple and thornlike, while larvae of all other North American genera have much longer middle hooks that are curved and sickle-shaped (e.g., Cylindera celeripes in this post). Amblycheila larvae can be distinguished from Tetracha larvae by the middle and inner hooks on each side being distinctly separated rather than touching at the base (e.g., Tetracha floridana in this post). There is also a cluster of short, stout hairs around the base of each hook in Amblycheila that is missing in Tetracha (e.g., Tetracha virginica in this post).

The numerous stout setae are also characteristic of the genus.

The numerous stout setae are also characteristic of the genus.

Step 7. Lastly, don’t forget to look at the hump in lateral profile—it is as alien a structure as any in the insect world. In the case of Amblycheila larvae, the bed of hairs posterior to the hooks is comprised of much shorter, stouter, and more densely placed hairs than larvae of Tetracha.

Copyright © Ted C. MacRae 2013