Archive for the ‘Prostigmata’ Category

Mites in the News

February 4, 2015

Zerconid_Idaho_3As the Good Book says: “To every thing there is a season, and a time to every purpose under the heaven” (Ecclesiastes 3:1). The last year hasn’t been the season for much new at Macromite’s Blog. Mites, alas, have been getting short shrift and I’ve been chasing platypus and butterflies and littering Facebook with the result. However, while I’ve been trudging around my new neighbourhood under the skeptical gazes of the kookaburras and wallabies, others have taken up the mite-art palette and brush with outstanding success.

Sam Bolton (or ‘Bolten’ as The Guardian misspelled his name) struck first in classic greyscale with his ‘Buckeye Dragon Mite’. Such is the power of a good monster picture that I’m told his paper was the most downloaded from The Journal of Natural History last year. Let’s hope someone also cites the paper in a scientific journal or two.

http://researchnews.osu.edu/archive/newmite.htm

http://smithsonianscience.org/2014/03/new-dragon-like-mite-found-in-ohio-is-gentle-reclusive/

And now, Martin Oeggerli’s long quest to bring the wonders of the acarine world to the public’s attention has been fulfilled. Quite a spectacular feat, both in colour use and in attracting the attention of National Geographic, something that several acarologists that I know of were not able to do. But if you compare Martin’s header image – a zerconid mite – with my more pedestrian zerconid image above, it is easy to understand his success. The text is by Rob Dunn (and The Inquisitive Anystid and I checked it for accuracy).

http://www.micronaut.ch/mighty-mites-micronaut-feature-article-published-by-national-geographic/

http://ngm.nationalgeographic.com/2015/02/mites/dunn-text

For those who are not squeamish (and if you are please don’t go there), y0u can see Rob among others bringing you up-to-date on follicle mite research in this video:

https://www.youtube.com/watch?v=KHDDCySUCIk

Even I am feeling itchy after watching that, but at least the rumour they explode on your face has been put to rest.

 

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Anystis: the race is sometimes to the swift

February 13, 2014

 

An anystid (possibly an Anystis) eating a scale insect (Photo Geoff Waite)

An anystid (possibly an Anystis) eating a scale insect (Photo Geoff Waite)

I was reading an essay on political cant by George Orwell yesterday, “Politics and the English Language” (1946), at Project Gutenberg Australia*. As one exercise he rewrote, into political obfuscation, a famous and lyrical passage from the Bible:

“I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favor to men of skill; but time and chance happeneth.” (Ecclesiastes 9:11 King James Version)

Almost always Orwell makes his points clearly and with passion. I now feel a bit chastised at my writing and terrified of using ‘dying metaphors’, ‘verbal false limbs’, ‘pretentious diction’ and ‘meaningless words’. I especially don’t want to use meaningless words.

That same day, I received a request for help with the etymology of a genus of mites, Anystis von Heyden, 1826. I was at a loss, my books were of no help, and Google failed. I’ve previously posted on the psychic perils of reading Karl von Heyden’s mind. Anystis seemed to be without meaning.

This morning, though, after a long walk taking poor pictures of macropods and beetles, the verse from Ecclesiastes bobbed-up in my memory along-side Anystidae – a family of famously swift runners. Common names include ‘whirligig mites’ in North America and ‘footballers’ in Australia (don’t ask me to explain Australian Rules Football, but even a few minutes of watching will convince you that the players in colourful jerseys spin around with abandon much like the mites). Could Anystis be a name, not from the Latin or Greek, but of something or someone fast in the past?

My friend Bruce Halliday (at what is left of the CSIRO at Black Mountain) had sent on a list of von Heyden genera and from my limited knowledge, his names indicated an interest in Greek history. For example, Cunaxa  a genus of predatory mites may be a reference to the Battle of Cunaxa reported on by the Greek mercenary Xenophon.

With the proper modifiers, Google now came to the rescue with a passage from a delightful book on ‘Running through the Ages’ by Edward Seldon Sears: “The Spartan runner Anystis and Alexander the Great’s courtier Philonides both ran 148 miles (238 km) from Sicyon to Elis in a day.” (Sears 2001). This seems to be derived from Pliny in his Natural History, who thought this run (1305 stadia) was more impressive than the better-known dash of Philippides from Athens to Sparta (1140 stadia) to report on the battle of Marathon.

I take this race as strong inference of what von Heyden was thinking when he proposed the genus Anystis. Anyone who has watched these mites must be impressed with their speed, and although the ancient Anystis exhibited both speed and stamina, I now feel some confidence that I am using the generic name in a non-meaningless way.

References:

* http://gutenberg.net.au/ebooks03/0300011h.html#part47

von Heyden, C. H. G. 1826. Versuch einer systematichen Einteilung der Acariden. Isis, 18, 608-613.

Sears, E.S. 2001. Running through the Ages. McFarland: Jefferson, NC.

A Good, but Deviant Stigmaeus

October 9, 2011

Eustigmaeus frigida (Habeeb) - a mite that feeds on mosses

I find the Raphignathoidea (Acariformes, Prostigmata, Raphignathina) one of the more fascinating superfamilies of mites. Many of its members are bizarrely attractive, for example species of Xanthodasythyreus and Dasythyreus (Dasythyreidae) that look like an ambulatory pincushions.

The elongate setae probably act as a defence against predators and are produced in members of several other families. In other raphignathoid families increased degrees of sclerotization are the most obvious trend in predator defence.

A species of Stigmaeus, a typical predatory raphignathoid mite

Armour reaches it apogee in groups such as a the Homocaligidae or the Cryptognathidae. In the latter, the body is completely encased in a dorsal and a ventral shield that fit together rather like a tin and its lid, but with a tube at the anterior end into which the mouthparts can be withdrawn (and hence crypto = hidden, gnatho = jaws).

Gnathosomal capsule with elaborate peritreme in Xanthodasythyreus

Currently, 11 families of Raphignathoidea are recognized and they are highly variable in form from soft-bodied to fully armoured. They all share some characters in common, for example the chelicerae have a needle-like movable digit used to stab and a sheath-like fixed digit that protects the needle when not in use, the genital papillae are not expressed, an ovipositor is not present, prodorsal trichobothria are absent, and the pad between their claws bears tenent hairs. Seven families have stigmatal openings near the bases of their chelicerae and simple to elaborate peritremes, but four families do not, and in any case stigmata and peritremes occur in other superfamilies as do the other character states that have been mentioned. As a result, the superfamily is difficult to key – it shows up at two spots in the current edition of the Manual of Acarology and the second couplet is one of those messy, exception-filled, paragraph-long abominations that are embarrassing to write and a headache to use.

Needle-like stabing digits of a predatory stigmaeid mite (Agistemus sp.)

The 7 families with stigmata and peritremes mostly have fewer than 50 described species and are characteristic of dry habitats (grasslands, deserts) or dry microhabitats (tree trunks, logs) in moister places. In contrast, the four families without stigmata, including the obscurely named Stigmaeidae with well over 300 described species, are found from dry to wet habitats and all types in between. In fact, the largest genus in the family Eustigmaeus (eu = good) Berlese, 1910, repeats this act, being found from deserts to submerged lake margins. Most stigmaeids that have been studied are predators of small arthropods and some are important biocontrol agents. However, Uri Gerson of the Hebrew University of Jerusalem demonstrated that at least some Canadian species of Eustigmaeus feed on mosses.

Eustigmaeus frigida mouthparts, lateral view (arrow = cheliceral digit)

This seems to be true of the species that inhabits the mosses growing along the margin of the lake at my research site: E. frigida (Habeeb, 1958). The cheliceral digits are difficult to observe on a light microscope, even under oil immersion, so I thought I’d check them with the SEM, but this is one of those cases where more magnification is of no help. The mouthparts seem well along the road to becoming a gnathosomal capsule and only the tips of the cheliceral digits protrude from their wrapping. I wonder if the mite simply rasps the leaves of the mosses with the protruding tips of the chelicerae and sucks up the juices? Seems like that would work even under water.

E. frigida mouthparts ventral view (arrow = cheliceral rasp?)

And the answer is …

June 18, 2011

Putative Mycetophagus prepupa with Paracarophenax

Well, Ted gets a point for the adult beetles – they are Mycetophagidae – and a species of Mycetophagus according to Arnett, although if the adult male beetle didn’t have a distinctive tarsal formula, I’m not sure I would have ever keyed it out. A coleopterist now has the specimens and a species identification may be forthcoming. The associated larva is not a Ciidae – I think these are restricted to polypore mushrooms and the habitat was a fleshy gilled mushroom, Pleurotus ostreatus.  My inference that the larvae associated with these adult beetles is the same species is based on co-occurance, appropriate size, and lack of any alternative. I’ll see if I can get a specialist to agree, but larvae don’t seem to be especially well known.

I think I’ll have to give Kaitlin the win here, though, with three points: one for recognising the mite as a member of the Heterostigmatina (aka Heterostigmata), one for a creative (if wrong) story about the life history, and one for boldly guessing where no other acarologist dared.

The mite is, in fact, an undescribed species of Paracarophenax Cross, 1965 (Acariformes: Heterostigmatina: Acarophenacidae). Of the five described species in the genus (Magowski 1994), Paracarophenax dermestidarum (Rack, 1959) seems to be the only species that has been studied in any detail – it is a parasitoid of the eggs of a dermestid beetle. However members of other genera in the family are of considerable interest as biocontrol agents of stored product beetles.

For example, Acarophenax lacunatus (Cross & Krantz, 1964) is an egg parasitoid of a number or grain-infesting beetles (Oliveira et al. 2003a,b) including the Lesser Grain Borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). Adult female mites are phoretic on adult beetles. The mites detach from the beetle as eggs are laid. A mite attaches to the egg, swells up (physogastry), and as it kills the egg up to two dozen offspring develop inside the body of the mother mite (Faroni et al. 2000). One or two of these internal young are males and they mate their sisters before they pop open the mother and start looking for new eggs or new beetles to hitch rides on.

This seems to be the general life style of these mites, including those in the genus Adactylidium Cross, 1965 on thrips eggs and Aeithiophenax Mahunka, 1981 on the eggs of scolytine bark beetles. So, we may assume that our Paracarophenax does something similar. I’m not aware of reports of these mites attaching to larvae, but the three ‘Mycetophagus‘ larvae with mites were all large, plump, and probably prepupae (smaller larvae did not harbour mites). In the swampy morass of a decomposing oyster mushroom, I think it makes sense that the mites hang on (they were not feeding) to the late stage larva. One wonders where pupation takes place, but for the mites to have another generation, they need to hitch a ride on an appropriate insect.

Further reading:

Cross EA, Krantz, GW. (1964) Two new species of the genus Acarophenax Newstead and Duvall 1918
(Acarina:Pyemotidae). Acarologia, 6, 287-295.

Faroni LRD’A, Guedes RNC & Mathioli AL. (2000) Potential of Acarophenax lacunatus (Prostigmata:Acarophenacidae) as a biological control agent of Rhyzopertha dominica (Coleoptera: Bostrichidae). Journal of Stored Products Research, 36,  55-63.

Magowski WL. (1994) Discovery of the first representative of the mite subcohort Heterostigmata (Arachnidae:
Acari) in the Mesozoic Siberian amber. Acarologia, 35, 229±241.

Oliveira CRF, Faroni LRD’A, Guedes RNC. (2003a) Host egg preference by the parasitic mite Acarophenax lacunatus (Prostigmata: Acarophenacidae). Journal of Stored Products Research, 39, 571–575.

Oliveira CRF, Faroni LRD’A, Guedes RNC, Pallini A. (2003b) Parasitism by the mite Acarophenax lacunatus on beetle pests of stored products. BioControl, 48, 503–513.

Rack G. (1959.) Acarophenax dermestidarum sp.n. (Acarina, Pyemotidae), ein eiparasitic yon Dermestes arten. Z.  Parasitenkunde, 19, 411-431.

Three-in-one Phoresy Photon Challenge

February 28, 2011

Name the insect and its hitch-hikers for full credit

This is the first Challenge using a light micrograph, but the usual rules apply – name the beasts as well as you can and Macromite fame may be yours. If the task proves too daunting, well then here’s a meander through the illustrated behavior to keep you entertained.

Phoresy is a behaviour, or rather a set of behaviours, exhibited by many small animals and especially by mites. The word is a bit confusing. The root, phor– is from the Greek word phoros which means to bear, to carry or refers to movement (not phor, a thief or kind of bee), but phoresy actually requires an absence of movement and it is usually not (but not always) the mite that does the carrying. Thus, the usage is a bit inverted from similarly derived jargon, e.g. the conidiophores that bear fungal spores or electrophoresis where an electrical field is used to carry charged particles through a gel or other medium. In the case of phoresy, it is the mite that is carried, usually by some lucky, larger, and more vagile arthropod.

Hypopi have no mouths but do have sucker plates

Nature is full of interesting interactions, but to study them first requires defining them. Well, perhaps not, but that is what scientists like to do – and tying them up with definitions and tagging them with a name derived from Greek or Latin (or both) is always great fun. The term phoresy was first proposed by French entomologist and bostrichid specialist Pierre Lesne in 1896 and to quote from a delightful paper (read the pdf – the web text is full of errors) by the famous myrmecophile and ant acarologist W.M. Wheeler (1919): “In 1896 Lesne called attention to a number of small insects that habitually ride on larger insects. To this phenomenon he applied the term “phoresy” and showed that it is distinguished from ectoparasitism by the fact that the portee does not feed on the porter and eventually dismounts and has no further relations with the latter.”

Lestes damselfly (male) with parasitic water mite larvae (red blobs)

As classically defined in the mid-20th Century, phoresy required an animal to stop its normal behaviours (e.g. seeking food or members of the opposite sex), seek out a carrier, mount the carrier and refrain from doing anything other than holding on, and then after a time to dismount from the carrier and resume normal behaviours. Taking a bite out of the carrier was considered a no-no – and animals that did so were banned from phoresy and sent to parasite prison. The heteromorphic deutonymph of Astigmatina (aka hypopus) is a classic phoriont – it lacks functional mouthparts, has no foregut (and so feeding would seem to be verboten), and has a ventral sucker disk formed from modified setae for holding onto an insect or other larger arthropod (sometimes even other  mites).

So, in an evolutionary ecology sense, classical phoresy can be thought of as an ectosymbiosis in the commensal category where the mite gets a free ride and the carrier doesn’t really care. Dispersal is assumed to be at the root of the evolution of these behaviours in the mites (although phoresy may actually concentrate, rather than disperse the mites). But are things really so simple?

Again the jargon is a bit confusing: ‘commensal’ implies eating together, and the mite can’t eat while on the carrier or it wouldn’t be considered phoretic. Consider the case of water mite larvae – they use adult aquatic insects to ‘disperse’, but since they take a bite while doing so, they are considered parasites, not phorionts. Then there are the strange hypopi of Hemisarcoptes cooremani which hitch rides under the elytra of ladybird beetles in the genus Chilochorus. Since Chilochorus beetles like to eat mites, this seems like a dangerous thing to do – but hypopi of H. cooremani that do not find a beetle die. Those that do find a beetle hang on for 5-21 days and swell up before leaving the beetle. Marilyn Houck (1994), who has studied this interaction, has suggested that beetle hemolymph (reflexive bleeding is a defense of many ladybird beetles – pick them up and noxious yellow blood oozes from their leg joints) may provide critical nutrients, possibly via the anal vestibule of the mites (which connects to a hindgut).

Another point to consider is how the porter really feels about the portees. When I look at insects covered in phoretic mites, e.g. the Photon Challenge above, I find it difficult to believe the bug is having a good time. But some bees and wasps have special mite pockets (acarinaria) that appear to have evolved to encourage mites to hitch a ride. I’ll post on acarinaria some day, but for now I will just note that some of these hymenopters do much better with their mites than without them.

Lisa Hodgkin and her colleagues at the University of Melbourne published an excellent paper last year with some interesting experimental data. They studied a bark beetle (Ips grandicollis) introduced into Australia and its phoretic mites and demonstrated that ‘phoresy’ can be both dynamic and complex. Phoretic mites were associated with both negative (adults) and positive (larvae) effects on beetle reproduction and development. Heavy mite loads were not good for female beetles, but having mites in the galleries resulted in bigger and healthier offspring. Perhaps when we are considering defining complex interactions like phoresy we should remember what Hamlet pointed out to Horatio: There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy.

References:

Lisa K. Hodgkin, Mark A. Elgar and Matthew R. E. Symonds. 2010. Positive and negative effects of phoretic mites on the reproductive output of an invasive bark beetle. Australian Journal of Zoology, 2010, 58, 198–204. http://www.publish.csiro.au/paper/ZO10034

Houck, M.A.  1994.  Adaptation and transition into parasitism from commensalism: a phoretic model. In: (Houck, M.A., ed.), Mites. Ecological and evolutionary analyses of life-history patterns. Chapman and Hall, New York: 252-281.

P. Lesne. 1896. Moeurs du Limosina sacra. Phenomenes de transport mutuel chez les animaux articules, Origine du parasitisme chez les insectes Dipteres. Bull. Soc. Ent. France 45, 1896, pp. 162-165.

WM Wheeler. 1919. The phoresy of Antherophagus. Psyche Boston Volume: 26: 145-152.
http://psyche.entclub.org/26/26-145.html

The Macromite Before Christmas

December 24, 2010

Water-skating Homocaligus adorned with Roynortonella pustules

The winter solstice (adorned with a full lunar eclipse on an almost clear night here in Edmonton) is several days past and my brief Albertan ‘mid-winter’ holiday season has just commenced. In Australia the first month of summer is almost over – Australia begins its summer on the first day of December, presumably out of the usual nonconformity or some other reason that was never clearly explained to me – but their summer solstice is just past and it is also the holiday season (with snow in the mountains, but otherwise warmer than here). Celebrating the longest night of the year makes a certain sense. Although I still have 4-5 months before green returns to the landscape, I can optimistically assume that the sun will be shining longer and longer each day, even if it is on clouds that are dumping snow on me, and eventually the winter will end, at least officially. So, in the spirit of my holiday season, I wish my readers, wherever they are and whatever their holiday or not, a happy Christmas and productive, healthy, and intellectually stimulating New Year.

An undescribed, but checklist making, Annerossella from Queensland

Over the last few years I have gotten into the habit of tarting up one of my mites for a Christmas card. This year I picked an unidentified Albertan species of Homocaligus – one of the two genera of the raphignathoid family Homocaligidae. This mite is a festive bright red in life and skates over the shallow margins of lakes among emergent vegetation and aquatic mosses. Eggs are probably laid on vegetation as in Annerossella knorri Gonzalez, a homocaligid described from the leaves of water lettuce (Pistia stratiotes) near Bangkok, Thailand. I suspect it is a predator, perhaps of the springtails (Podura aquatica) that hop along in this habitat. I once kept an undescribed Australian species of Annerossella in a small aquarium, but other than watching it skate across the water, I was unable to add anything to the knowledge of its ecology (at about 0.5 mm in length, it is difficult to observe). However, I did make one of my early coloured SEMs of the mite and posted it on the Mite Image Gallery at the University of Queensland. Much to my surprise this was the first record of the family in Australia and my friend Bruce Halliday, putting aside his doubts about the validity of ephemeral web publications, cited the image in his Mites of Australia, a checklist and bibliography (1998, CSIRO Publications). Interestingly, the image at the top of a species of Homocaligus is probably the first record of the family from Alberta.

A pustule from the gymnodamaeid Joshuella agrosticula at 40,000x

Although festive enough for the holiday in itself, I thought the Homocaligus needed more adornment. The pine cone-like bulbs on the mite are cerotegumental pustules from another mysterious Albertan mite, Roynortonella gildersleeveae (Hammer, 1952). This mite used to reside in the genus Nortonella Paschoal, named after the great oribatologist Roy A. Norton. Unfortunately, in 1908 a certain Rohwer had already used Nortonella for a genus of tenthridinid sawflies; thus, the name was preoccupied. I suggested the new name as a replacement that was in keeping with the author’s original intentions. Like other members of its family (Gymnodamaeidae), the surface of the adult mite has scattered fields of strange and intriguing Bucky Ball-like pustules. The pustules arise as the cerotegument dries after the adult moult in what must be some interaction between microfibers and wax. Their elaborate form and species-to-species variants keep me, if not tied to a particular belief in the nature of the Universe, at least still amazed by how rewarding the study of even the smallest parts of Nature can be.

For more on Homocaligidae and Gymnodamaeidae see:

Fan Q-H. 1997. The Homocaligidae from China, with description of two new species (Acari: Raphignathoidea). Entomol. Sin. 4: 337-342.

Gonzalez RH. 1978. a new species of mite on water lettuce in Thailand (Acari: Homocaligidae). International Journal of Acarology 4:221-225.

Walter DE. 2009. Genera of Gymnodamaeidae (Acari: Oribatida: Plateremaeoidea) of Canada, with notes on some nomenclatorial problems. Zootaxa 2206: 23–44.

Wood TG. 1969. The Homocaligidae a new family of mites (Acari: Raphignathoidea), including a description of a new species from Malaya and the British Solomon Islands. Acarologia (Paris): 11: 711-729.

Seeing Red & Being Blue: Polymorphus

April 16, 2010

A carotenoid mite (UV protected) feasting on spider eggs

Waiting for an answer to a Macromite Electron Raster Challenge is a bit like waiting for a warn spring day in Edmonton: patience may be rewarded, eventually. But warmth is predicted for today (although along with a brisk wind) and I decided to take the day off work and catch up at home. First up is awarding points, or rather first up is fitting a mite into this somehow, and I offer a red Queensland Charletonia mite eating spider eggs while baby spiders look on in horror in honour of the Queenslander with the best answers. In the mite’s case, UV-protection and perhaps an advertisement of bad taste are thougth to be the reasons it is red.

 Without a doubt, Snail’s Eye View was there the firstest with the mostest (although Adrian should get some kind of prize for ketchup). So, congratulations to Bronwen Scott from the beautiful and diverse Atherton Tablelands where I used to spend many a happy day plucking mites from rainforest canopies.

 No one really knows why Polymorphus marilis sequesters carotenoids and no one got the species correct – hardly surprising since  the worm, a specialist on its definitive host the Lesser Scaup Aythya affinis (Bush & Holmes 1986), is nowhere near as well known as P. minutus, P. paradoxus, or a host of other carotenoid blazing acanthocephalans that adorn the pages of various scientific journals. Most cystacanths of Acanthocephala lack colour, but the more famous ones shine through their intermediate hosts’ cuticle as bright yellow-orange to red spots.

 Photoshop aside, one could claim that the reason these cystacanths are red is that they sequester carotenoids from their intermediate hosts, and this does seem to be true, but why? Well warning colouration and protection from ultraviolet light are two common uses of carotenoids, but neither makes sense here – the worms want to get eaten (at least by the definitive hosts) and one would think (perhaps incorrectly) that they are protected from UV under the cuticle of the amphipod intermediate host. So what is going on?

Mallard bum with amphipods & Amphipod with acanthocephalan

 Well, one definite effect of this red pigmentation has been to cause quite a few scientists to paint red spots on uninfected amphipods to see if they are more likely to be eaten by definitive hosts (usually ducks or fish) than unpainted amphipods. The results have been mixed (see Ted’s link and the Bakker et al. paper listed below for two contrasting fishy examples, and Bethel & Holmes and the citations therein for the fowl truth). Peter links to a paper that reports that European P. minutus appear to cause sterility in an another amphipod, and perhaps, the sequestering of carotenoids is related to failure to produce eggs. Zohar & Holmes (1998) also demonstrate that Polymorphus-infected Gammarus lacustris males are less likely to pair up or guard mates. But, more interesting associations between red acanthocephalans and their various hosts are changes in amphipod colour (loosing their camouflage brown) and behaviour (losing their fear of light so that they swim near the surface, tending to cling to anything they touch).

Gammarus lacustris with & without carotenoids in cuticle

 Amphipods that are not infected by an orange acanthocephalan maintain carotenoids in their cuticle, and thus, acquire UV protection, a brownish hue that blends in with lake bottoms, and the typical reddish shell of a boiled crustacean when they die. This is wonderfully illustrated by a concise and informative letter to Nature by Ole Hindsbo – again on P. minutus, but this time in New Zealand. In less than one page, Hindsbro elegantly demonstrates that most (but not all) infected Gammarus lacustris are pale because their blue blood shows through their carotenoids deficient cuticle, that the pale amphipods are more likely to swim in sunny spots where they would be easily seen by a definitive host, and that in the lab a duckling is more likely to eat the pale, infected amphipods. He also cites M. Denny’s PhD thesis (from UA no less) showing that Gammarus lacustris infected with Polymorphus paradoxus tend to cling to floating objects (see mallard picture). Dabbling ducks like a mallard may not be proficient at hunting arthropods in the water column, but Bethel & Holmes (1977) demonstrated that clinging to a mallard bum is a good way to get a mallard to eat amphipods infected with P. paradoxus. Scaup do hunt and consume a lot of amphipods, so one might hypothesize that those infested with P. marilis would be less likely to cling and more likely to paddle palely through the water column.

 So why are some acanthocephalans red? I vote for ‘because they make their hosts blue’.

 Thanks to all those students of red acanthocephalans who have provided me with so many hours of interesting reading. Special thanks to John Holmes for a sparking discussion on worms, ducks, and muskrats at the Strickland dinner and to Leo Balanean for many interesting stories about amphipods and their worms on those early morning bus rides and for the use of his picture. When Leo’s thesis is finished, the world will know just how red Polymorphus marilis and paradoxus really are.

 References (also see links in comments):

Bethel WM & Holmes JC. 1977. Increased vulnerability of amphipods to predation owing to altered behavior induced by larval acanthocephalans. Can. J. Zool. 55: 110-115.

 Bush AO & Holmes JC. 1986. Intestinal helminths of lesser scaup ducks: patterns of association. Can. J. Zool. 64: 132-141

 Bakker TCM, Mazzi D & ZalA S. 1997. Parasite-induced changes in behavior and color make Gammarus pulex more prone to fish predation. Ecology 78(5): 1098–1104.

 Hindsbo, O. 1972. Effects of Polymorphus (Acanthocephala) on colour and behaviour of Gammarus lacustris. Nature 238: 333.

Zohar S & Holmes JC. 1998. Pairing success of male Gammarus lacustris infected by two acanthocephalans: a comparative study. Behavioural Ecology 9: 206-211.

Sellnickia: Details & Enhancements

January 17, 2010

Sellnickia anterior with details: sp. A, sp. B

Here’s some more on the predatory labidostome mite from the previous post – a closer and greener view of the anterior end. It’s greener, because I distinctly remember a live collection of a species of Sellnickia with unusually greenish mites running around, many with startlingly white Folsomia-like springtails crushed in their chelicerae. A reliable memory or a dream? I do dream of outlandish mites every now and then, some of my favourite dreams I might add, although my absolute favourite was when I discovered a giant trigonotarbid in a deep, misty, tree fern and liverwort covered canyon. Since trigonotarbids (allegedly) haven’t been around for a couple of hundred million years, I suppose this indicates one should be skeptical of their dreams.

In any case, this reminds me that Adrian has asked for more details on the time it takes to make these mite portraits.  Warning – what follows is lengthy.

To give even a general answer to ‘how long’, one needs to first decide how the image is going to be put to use. If the purpose is to illustrate morphology for a scientific publication, then the less time spent manipulating the image, the better. For example, the detail of the cuticle from sp. B in the image above was simply selected, copied and pasted. To illustrate why: I was once told a story about an early photographic plate of fossil aquatic scorpions. Although aquatic chelicerates typically have compound eyes (think horseshoe crab), modern terrestrial scorpions are typical ‘arachnids’ with at most lateral clusters of simple ocelli. No eyes were obvious on the aquatic rock scorpions in the photo plate, but I am told that the actual impressions in the rock have lateral compound eyes. Apparently, since scorpions weren’t supposed to have compound eyes, the ‘artefacts’ had been airbrushed out by the author so as not to confuse the reader. Once you start ‘improving’ an image, you run the risk of producing misinformation.

The time required to prepare a SEM for a scientific publication is primarily a function of specimen preparation time. For example, to produce a grayscale SEM suitable for publication of the Sellnickia sp. A above took less than 3 hours including selecting the mite, drying it through a series of solvents to eliminate its water content, placing it on a stub, sputter coating in gold, putting it into the electron microscope and achieving the proper vacuum, focusing and fiddling with astigmatism etc., and taking the images. Three hours is a lot of time to take one picture, so I always do lots of specimens on the same stub. Mites are excellent in this way – lots more fit on a stub (~10 mm diameter) than could dance on the head of a pin. So, 2-4 hours of preparation can result in 30-60 images in a 4 hour SEM run, depending on time needed to focus, resolution (the more resolution the longer the raster time for each image grab), software or hardware problems (all too frequent), and the quality of the specimens (finding specimens on the stub without dust, goo, dents, or broken bits).

The reasons this mite was easy are: (a) it is hard shelled (little or no deformation on drying) and relatively large (much easier to transport onto a stub) and (b) relatively flat (not much depth of field in a dorsal view).

The image in this post is from a single grab – if you look closely, some of the ornamentation and many of the setae are not in sharp focus and the blow-up of the detail (A) is a bit blurry.

The image of the full mite in the previous post is a composite of 4 – I divided the mite into quadrants and took four separate SEMs and then pasted them together in Photoshop – mostly to get a large image size (the camera was only capable of relatively low resolution grabs).

Masking – separating the image from the background – takes the most time. In the case of the full body image in the previous post, it took 7-8 hours to put together and mask – that is not bad and is a function of the outline of the animal – few setae and other protuberances to mask around.

In contrast, the anterior view in the image in this post took about an hour to mask this morning (including erasing the legs that were bunched up and out of focus on either side). Masking out artefacts (e.g. cracks and bubbles in the glue) or unwanted detail (e.g. the out of focus legs in this picture) can dramatically improve the quality of a greyscale image in a paper – but it takes a lot of time. It would probably be a good idea to mention in the legend of the figure that the legs have been removed.

Once the animal is masked, then you can decide it you want to colour it. I don’t think that a morphologial study needs colour, but a field guide or poster could benefit from colouring.  The problem with a grayscale SEM is that we have colour vision and when we see these mites they look bright yellow to green. Colouring can be simple – the full dorsal habitus view in the previous post took only about 20 minutes to do after masking, because I relied on the shade differences in the original SEM to be reflected in the final picture and used a single colourizing level in Photoshop. If I wanted to show more detail, then I would have to laboriously select the areas needing the different colours one by one.

I actually did this on this morning’s image – the anterior view in this post. I decided to give the mite a more greenish cast in parts of the cuticular design by selecting pixels within the reticula. I also decided to lighten the setae – the setae usually lack the colour of the body in life and appear white. This took way too long – especially trying to select the feathery bothridial sensilla that are overlain on the body. Finally, I decided make the tips of the chelicerae a slightly different shade. All of these changes should be making the mite look more realistic, or at least make it easier to see the different parts, but even these fairly simple selections took about an hour and a half.

So, the total time to prepare the image in this post was about two and a half hours on a Sunday morning. Getting the original image was a similar investment in time. I would consider this a low value for the average SEM that I colourize – the average is about one full day of manipulation of the original grayscale image(s). The maximum is about a full week – the extremely complex  image posted near thebeginning of this blog.

Data-free Ornamentation: Sellnickia

January 6, 2010

 

Collembola Beware: More than just a pretty picture

 Hi all and apologies to any who have been hoping for more frequent postings (special apologies to Bill Bartlett who was left rotting in the spam filter for who knows how long Ha – well written spam, so apologies are to the Spam filter). It was a busy summer/fall and I did publish lots of new mite SEMs, but you will have to trawl Zootaxa and the web to find them. Rather than worry about gray areas in the intellectual property arena and my current employer’s fear of the web, herein I’m sticking to images that I make on my own time and since work has been so all consuming, my time has been limited. However, some Polish colleagues recently convinced me to contribute images to their chapters on soil animals and I spent a few minutes polishing up this very ornate predatory mite for showing. 

All the members of the early derivative prostigmatan family Labidostomatidae are ornate, but Australian members of this genus are my favourites. All that I have seen also are somewhere between golden and greenish yellow – and very fast moving. In a live extraction, one often sees them carrying around some unfortunate springtail – which they mash up in their massive ice-tong-like chelicerae, suck-up the juices, and spit out the empty shell. 

Labidostomatidae is based on the genus Labidostoma – and subject to numerous spelling variants for those who aren’t sticklers for Greek grammar, e.g. Labidostomidae, or stutter on the ‘m’, e.g. Labidostommatidae, or think that Nicoletiella should have precidence. I’m sure that I’ve made all of the mistakes myself over the years, but this is the currently correct version according to the 3rd Edition of The Manual of Acarology – another place you can see many of my and other superb SEMs, although only in B&W. 

Beetles in the Bush is starting up a blog carnival on, not too surprisingly, beetles, and called An Inordinate Fondness. Mites are inordinately fond of many habitats and beetles are one of them. So, even though I’m in the midst of describing a mite from an ant, I think I’ll take a break next time and put together something on the real beetle mites.

Does a fly itch?

June 18, 2009
A couple of larvae from the Cohort Parasitengonina

A couple of larvae from the Cohort Parasitengonina

Trombiculoidea are mites with a dubious distinction – most languages have one or more common names for them.  In Australia we would tend to call the hexapod larval stage ‘scrub itch mites’ for the intensely annoying rash-like erruptions they leave after biting – an all too common result of a pleasant stroll through the bush.  In North America they are better known as chiggers, red mites, or harvest mites (i.e. common in the Fall).  I imagine readers of this blog with a knowledge of non-English languages could supply a host of other sobriquets.  Anyone with actual experience of scrub itch, or as it is technically known – trombiculosis,  might be tempted to add some colourful modifiers.

Because a large wheal may develop at the spot that a chigger bites, some think that they are burrowing in the skin.  Alas, no, they are ectoparasites that digest our skin and lymph for their feed.  There’s nothing to dig out to reduce the itch and the best thing you can do is not scratch and help avoid secondary infections.  The first scratch is probably good, since it will crush or dislodge the mite, but the mite leaves behind all the enzymes it has been injecting into your skin, and that can take a week or two for your body to deal with.  The more you scratch, the longer it will take to heal. 

If you live in an area where the rickettsial disease scrub typhus is endemic, then it is a good idea to watch out for any large black scabs that form on a chigger bite.  A large black scab or eschar is a sign of infection and all it takes is one infected bite.  In Queensland scrub typhus is a problem, but one good thing about Edmonton is that both chiggers and scrub typhus seem to be absent.

It may be of some comfort to know that only two families of chiggers feed on vertebrates – about a dozen other families of related mites feed on insects, millipedes, spiders, harvestmen, scorpions, and the like.  The two-winged flies (Diptera) seem to be especially lucky when it comes to collecting chiggers.  A possible example of one is above on the viewers right (Microtrombidiidae?).

Only the larval stage (i.e. the first active stage which has only 3 pairs of legs) is parasitic in the Cohort Parasitengonina (chiggers and their relatives and the water mites).  The nymphs and adults are predators – and they may have common names too.  In English, the terrestrial species are often called Red Velvet Mites and they can be quite large (up to 16 mm – the largest known mites outside the ticks) and are covered in a dense pelage of hairs, typically red but sometimes red & white patterned, orange, or another colour or combination.  Alex Wild at MyrmecosBlog has posted a striking picture of one of the red species.

A headless mite - adult Calyptostoma sp.

A headless mite - adult Calyptostoma sp.

I don’t have any good SEMs of a red velvet mite – they are as hairy as a mammal and one would go bonkers trying to mask around all the hairs.  However, I do have an adequate picture of a member of the Subcohort Erythraiae, a species of Calyptostoma (Calyptostomatidae) with short setae.  These rather sluggish mites are thought to be predators of fly larvae as nymphs and adults.  The mouthparts (capitulum or gnathosoma) are retracted into the body and can be shot out to impale a maggot.  The mite larvae are parasites of adult Diptera (BugGuide has some good pictures of craneflies infested with the larvae).  So, the next time you come home with a case of scrub itch, think about all those poor flies out there that couldn’t scratch even if they wanted to – and emulate them, don’t scratch.