Arthropoda

Arthropods – insects, arachnids, crustaceans, myriapods, & relatives

Lord of the flies!

/ Ted C. MacRae / 23 Comments

I happened upon a rather interesting scene last week in a soybean field in northern Argentina (Chaco Province). This assassin bug (family Reduviidae) had captured and was feeding on an adult stink bug of the species Piezodorus guildinii—an important pest of soybean in Argentina and Brazil (where it is known by the common names “chinche de la alfalfa” and “chinche verde pequeño”, respectively). Assassin bug predation is always interesting enough itself, but what made this scene especially fascinating was the large congregation of flies surrounding and even crawling upon the predator and its prey. I had not witnessed something like this before, but it seemed clear to me that the flies were engaging in kleptoparasitism—i.e, stealing food. I’ve gotten into the habit of keeping a full set of extension tubes mounted on the camera with my 100mm macro lens—this not only provides the most useful (for me) range of magnification but also serves as a convenient and easy-to-use field microscope. Through the viewfinder I could see that there were at least two markedly different types of flies involved—more abundant, small, brown flies that I presumed (incorrectly, as it turns out) to be some type of drosophilid (vinegar fly), and a few larger, black flies that were completely unfamiliar to me. The flies were apparently feeding on fluids from the stink bug prey but also crawled all over the assassin bug as it fed. The assassin bug seem unencumbered in its feeding by the presence of the flies, but periodically it would slowly wipe its forelegs over its head to dislodge flies that had settled onto it. Just as quickly as they flew away, however, they crawled back.

The assassin bug, on the other hand, I recognized as very likely a species of Apiomerus—a large, exclusively New World genus known in North America as “bee killers” for their habit of sitting on flowers and ambushing visiting bees for prey. The prey selection behaviors of these insects, however, are more generalist than the name implies, as can be seen by these photographs. To verify my generic ID and possibly obtain a species ID, I sent some of these photos to Dimitri Forero at the Heteropteran Systematics Lab at University of California-Riverside. Dimitri is revising portions of Apiomerus (e.g., Berniker et al. 2011) and working on a general phylogenetic hypotheses for the genus. In the past he has been quite helpful in fielding questions from me about these bugs, and within a few hours Dimitri replied to inform me that the assassin bug was, indeed, a member of the genus Apiomerus, likely representing the common, widespread species A. lanipes (ranging from Panama to Argentina), based on its coloration, locality, and relative size. Update 12 March, 3:07 pm—After seeing the last photo in this post (which I did not send to him initially), Dimitri wrote to say the ventral abdominal pattern was not characteristic of A. lanipes. He asked about its size, to which I replied that it was about the same length but maybe a little less robust than A. crassipes (eastern North America). He later added, “I now think that this is A. flavipennis Herrich-Schaeffer, 1848. It is very similar to A. lanipes, but a lot smaller (lanipes is really robust), and with the abdomen with black and white patches, whereas in lanipes the abdomen is always black. I checked some series of specimens that I have here and, I am pretty sure now of the ID. I have material from Argentina as well. In some specimens that coloration of the corium varies, but the original description says it is yellow with a “hairy” pronotum, which fits very nicely your photos.” Apiomerus flavipennis is known from Argentina and Southern Brazil only.

Quite unexpectedly, Dimitri also noted that at least some of the flies could belong to the family Milichiidae. He first became aware of these flies after seeing a photograph of Apiomerus showing something similar and suggested Milichiidae online as a possible source for more information. This remarkably informative  website by milichiid expert Irina Blake, who dubs species in the family as “freeloader flies”, is a model for how websites dealing with obscure insect taxa should be organized and populated (and features on the home page a great photo of ant-mugging flies taken by our favorite myrmecophile). At any rate, I forwarded my photos to Irina and within minutes received her response that the bigger black flies most probably represent the cosmopolitan Milichiella lacteipennis and the smaller flies a species of the family Chloropidae (of “dog pecker gnat” fame) in the subfamily Oscinellinae, noting that she has seen similar (or the same?) chloropids in other photos as well engaging in kleptoparasitism.

Not long after receiving the first reply from Dimitri, I got another message from him with a link to a very interesting paper by Eisner and colleagues (1991), who recorded freeloader flies in Florida preferentially attracted to stink bugs and leaf-footed bugs (family Coreidae) being preyed upon by the orb-weaving spider Nephila clavipes. Olfactory stimuli were already suspected to be involved in attraction of milichiids and also chloropids (Sivinski 1985); however, Eisner et al. (1991) experimentally demonstrated that milichiid attraction was tied to specific components of defensive sprays in several pentatomid and coreid species (including P. guildenii, the prey species in this series of photographs). The defensive sprays of the bugs were generally ineffective at preventing predation by the spiders (and apparently this is the case for A. lanipes and other reduviids as well), thus serving as a signal to milichiids and chloropids not only of the presence of a food source but perhaps also assisting search for mates in a density dependent fashion (Sivinsky 1985). Milichiid attraction to hymenopteran prey, richly endowed with integumental glands themselves, has also been documented; the Eisner study raises the question whether these types of prey are also detected from chemical cues.

REFERENCES:

Berniker, L., S. Szerlip, D. Forero and C. Weirauch. 2011. Revision of the crassipes and pictipes species groups of Apiomerus Hahn (Hemiptera: Reduviidae: Harpactorinae). Zootaxa 2949:1–113.

Eisner, T., M. Eisner & M. Deyrup. 1991. Chemical attraction of kleptoparasitic flies to heteropteran insects caught by orb-weaving spiders. Proceedings of the National Academy of Sciences of the United States of America 88:8194–8197.

Sivinski, J. 1985. Mating by kleptoparasitic flies (Diptera: Chloropidae) on a spider host. Florida Entomologist 68(1):216–222.

Copyright © Ted C. MacRae 2012

Sharpshooter

/ Ted C. MacRae / 1 Comment

Pawiloma victima | Buenos Aires Province, Argentina

With around 20,000 species worldwide, leafhoppers (family Cicadellidae) are not only the largest family of true bugs (order Hemiptera) but also one of the top ten largest families of all insects. My favorite are “sharpshooters” (subfamily Cicadellinae)—large, distinctive, brightly colored species, and the individual shown in the photo above is no exception. I found it today in a soybean field in western Buenos Aires Province. Leafhoppers do have a reputation for difficult taxonomy due to their diverse numbers and often similar appearance (many can only be distinguished by examination of male genitalia); however, the distinctive color patterns of sharpshooters make many of them relatively easy to identify. The best resource for doing this is Sharpshooter Leafhoppers of the World (Wilson et al. 2009), an excellent website with a searchable photo database of nearly all 2,400 recognized species in the subfamily. According to that site, there are 64 species of sharpshooters recorded from Argentina, with the individual in this photo being a dead ringer for Pawiloma victima.

REFERENCE:

Wilson M. R., J. A. Turner & S. H. McKamey. 2009. Sharpshooter Leafhoppers of the World (Hemiptera: Cicadellidae subfamily Cicadellinae). Amgueddfa Cymru – National Museum Wales. Available online at http://naturalhistory.museumwales.ac.uk/Sharpshooters [accessed:  8 March 2012 ].

Tucuras, langostas, y saltamontes

/ Ted C. MacRae / 10 Comments

Staleochlora viridicata | Cordoba Province, Argentina (March 2011)

Tucuras, langostas, and saltamontes are names in Argentina for what we in North America call grasshoppers (order Orthoptera, superfamily Acridoidea). Argentina certainly has its share of species, some of which can only be described as “gigantes”! During my first week out in the field at my home base here in western Buenos Aires Province, I encountered the hefty-bodied female in the photo below and was immediately reminded of a similar-looking individual I had photographed in neighboring Córodoba Province during my March 2011 visit. Both had short but well-developed wing pads that at first suggested they might be mature nymphs of an incredibly large species. However, when I noted both were females I decided they likely represented adults of some type of lubber grasshopper (family Romaleidae), many of which—especially the females—are brachypterous (short-winged) and heavy-bodied as adults. A little searching revealed that both belong to the genus Elaeochlora, each looking very much like the species pictured on an Argentine postal stamp and identified as E. viridis (update 9 Mar 2012 – Sam Heads has identified these as Staleochlora viridicata).

Staleochlora viridicata| Buenos Aires Province, Argentina (March 2012)

Getting at least a genus name for these individuals then prompted me to go back to photographs I had taken last year of other types of grasshoppers. One of these, Eutropidacris cristata, is truly one of the largest grasshoppers I have ever seen (update 9 Mar 12 – Sam Heads notes that Eutropidacris is now a synonym of Tropidacris). This individual was seen in a soybean field in the northern Argentina province of Chaco. These insects, known in Argentina as “La tucura quebrachera,” apparently occur in outbreak numbers periodically and, understandably owing to their monstrous size, generate a lot of attention. In Brazil the sepcies is known as “gafanhoto-do-coqueiro” (coconut tree grasshopper),

Tropidacris cristata | Chaco Province, Argentina (March 2011)

One of the more colorful grasshoppers I have seen in Argentina is Chromacris speciosa. The individual below was photographed last March in eastern Córdoba Province, also on soybean. It’s tempting to presume that the green and yellow coloration has a cryptic function, but apparently the nymphs of this species are brightly colored red and black and have the habit of aggregating on foliage. This is classic aposematism (warning coloration) to indicate chemical protection from predation, so perhaps there is a similar function to the adult coloration as well.

Chromacris speciosa | Cordoba Province, Argentina (March 2011)

Copyright © Ted C. MacRae 2012

Crazy Eyes 2

/ Ted C. MacRae / 4 Comments

Buenos Aires Province, Argentina | March 2012

While the eyes of this female horse fly (family Tabanidae) aren’t quite as striking as those of Tabanus lineolus (the wonderfully dimorphic males and females of which were made famous by Thomas Shahan and Ralph Holzehthal), they still managed to catch my eye as I was scouting for more pedestrian types of insect in a soybean field in central Argentina this past week. We know this is a female due to the separated eyes (males have larger eyes that meet at the middle of the head—supposedly the better to see females with); and by the obvious, blade-like mouthparts, which the females use to slice mammal skin so they can lap the blood that their eggs need for development prior to being laid while males forego specialized mouthparts and concentrate on using their huge eyes to look for females.

Female horse flies have well-separated eyes and distinct, blade-like mouthparts.

 

I suspect this individual had recently emerged from the soil (where many horse flies pupate) and was still hardening off, as she was very calm sitting on the leaf and allowed me to steady the leaf with one hand as I snapped a few photos with the other. I would have loved to have switched out the 100mm lens I was using and put on my 65mm 1-5X lens to really zoom in on those striking eyes. Unfortunately, I don’t think my field companions shared or understood my fascination with this little insect. If anybody has a clue about the identity of this species please let me know.

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

Leafcutter ants on corn

/ Ted C. MacRae / 7 Comments

Leafcutter ants attacking corn | western Buenos Aires Prov., Argentina

North American corn farmers certainly have their share of insect pests to worry about. Between corn borer, earworm, armyworm, and rootworm, there isn’t much of the plant that isn’t vulnerable to attack by at least one of these insects. Argentina corn farmers have all this and more—have you ever seen ants attacking corn? I took these photographs yesterday in a corn field in western Buenos Aires Province showing leafcutter ants dining on the developing kernels of late-planted corn. Okay, “dining” may not be the proper word, as they are not actually eating the kernels, but rather harvesting them to bring them back to their “hormiguera” (ant nest) for cultivation of the fungi on which they feed. The four pairs of spines on the pro-mesonotum and narrow distal antennal segments suggest this is a species of Acromyrmex, three species of which are mentioned as pests of corn in Argentina (A. lundii, A. striatus, and A. lobicornis). Of these, the individuals in these photos seem to best match AntWeb’s photos of Acromyrmex lundii, but that is just my guess.

Acromyrmex sp. poss. lundii?

Copyright © Ted C. MacRae 2012

To the land of Gauchos

/ Ted C. MacRae / 10 Comments

Today I leave for an extended stay in Argentina. Many have asked me if my trip is for work or fun, and my standard response has been, “It’s for work, and it will be fun!” For the next eight weeks, I’ll be helping out with field trials and speaking to farmers (while sampling a few Malbecs as well). Of course I would rather it be an 8-week collecting trip, but I consider myself fortunate even to have an opportunity such as this. I’ll pick up a few insects along the way, but what I really hope to bring back in large quantity is photographs.

It’s a little difficult to predict how reliable and consistent I’ll have internet access or the time to take advantage of it, so postings over the next few weeks may be a little less regular than what has become my usual custom. The trip is also heavily front-loaded with work activities as I get my bearings and spend time getting to know my new colleagues, so I’m not sure when I might have new photos to show here. Not to worry, I have plenty of material that I haven’t yet shown. Until then, I leave you with this photograph I took last November at  in Buenos Aires. These tiny bugs seem to be early-instar leaf-footed bug (family Coreidae) nymphs, their bright red and black coloration and aggregating behavior indicating ample chemical protection against predation.

Early-instar coreid nymphs | Buenos Aires, Argentina

Copyright © Ted C. MacRae 2012

Chrysobothris viridiceps

/ Ted C. MacRae / 9 Comments

Chrysobothris viridiceps on dead branch of Quercus alba | Baxter Co., Arkansas

Despite their general popularity among beetle collectors, jewel beetles (family Buprestidae) have an admittedly deserved reputation for difficult taxonomy. Part of the reason for this is the existence of several highly speciose genera. In North America, for example, nearly half of its described species belong to just three genera—Acmaeodera, Chrysobothris, and Agrilus (the latter, with nearly 3,000 described species and many more awaiting description, being possibly the most speciose animal genus in the world). Identification of species within these genera is difficult enough due to their sheer numbers and is further complicated by the existence a number of “species-groups”—i.e., groups of very closely related species that have only recently become reproductively isolated from each other (likely in response to host partitioning) but have not yet evolved obvious unique morphological characters. Perhaps the most famous of these is the “Chrysobothris femorata species-group.” A dominant component of hardwood forests throughout North America, members of this group have confounded taxonomists, collectors, and foresters alike for many years. Fortunately, the recent revision of the group and formal description of several species by Wellso and Manley (2007) have brought much needed clarity to the group. While problems still remain (C. femorata sensu novo probably still encompasses several undescribed species), most individuals can now be identified with some confidence.

Males and females both exhibit completely divided post-median fasciae

I have previously discussed three of the seven now recognized species occurring broadly in eastern North America—the nominate C. femorata, still regarded as an important pest of ornamental and fruit tree plantings, C. caddo, one of the new species described by Wellso and Manley (2007) and associated with dead hackberry (Celtis spp.), and C. quadriimpressa, mostly associated with dead branches of oak (Quercus spp.). The individuals shown here, photographed on branches of a dead white oak (Quercus alba) in north-central Arkansas this past June, represent a fourth species in the group, Chrysobothris viridiceps. Unlike most members of the C. femorata species-group, C. viridiceps can be readily recognized in the field  due to the uninterrupted costa (raised narrow ridge) that completely bisects the posterior fovea (rounded pit) on each elytron. In all other species this costa is interrupted by the fovea. Moreover, this species is the only one in the group in which the males (easily distinguished from females by the bright green frons, or face) exhibit bicolored antennal segments, with the outer portion of each segment yellow and the remainder bright metallic green. While the species name is Latin for “green face,” this character is useless for species identification, as males of all species in the group exhibit a more or less green face.

Males sport not only the green face for which the species is named, but also distinct yellow areas on the antennal segments

Females are a little more difficult to distinguish in the field because, like those of other species of the group the antennae are more uniformly reddish. Likewise, the face also lacks the green coloration of the male, and although still useful for species identification the differences among females between the different species are more subtle and require microscopic examination. However, as in the male the elytral foveae are completely divided, allowing even females to be recognized relatively easily.

Females tend to be more reddish on the legs, antennae and face

One thing I have noticed about the different members of the C. femorata species-group is the usefulness of host plant association in distinguishing the different species. Of the seven species occurring in my region, I’ve seen C. femorata associated mostly with stressed but still living trees in genera other than oak or hickory (e.g., maple, sycamore, apple, poplar, ash, etc.), C. adelpha associated exclusively with dead hickory (Carya spp.), and C. caddo associated almost exclusively with hackberry (Celtis spp.). The remaining four species are all associated primarily or exclusively with oaks, but even these species often segregate according to branch size, with C. viridiceps occurring mostly on the smallest branches, C. quadriimpressa on somewhat larger branches, C. rugosiceps on very large branches and the upper trunk, and C. shawnee on large trunks and even stumps. Not surprisingly, these size preferences reflect the relative size of the beetles, with C. viridiceps (7–13 mm in length) generally being the smallest of the four species and C. shawnee (9–18 mm in length) the largest.

Okay, now to get photos of C. adelpha, C. rugosiceps and C. shawnee!

REFERENCES:

Wellso, S. G. and G. V. Manley. 2007. A revision of the Chrysobothris femorata (Olivier, 1790) species group from North America, north of Mexico (Coleoptera: Buprestidae). Zootaxa 1652:1–26.

Copyright © Ted C. MacRae 2012