Posts Tagged ‘phoresy’

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

Two, four, no, ten pests in one!

May 15, 2009
Nine Broad Mites hitch a ride on a whitefly
Nine Broad Mites hitch a ride on a whitefly

I guess I’m getting giddy from too much time humped over a computer or a microscope and a lack of sun and warmth (it’s a cold, late spring here in Alberta).  So here is something from a sunnier clime, or rather somethings.  The Bemisia whitefly in this image was sent to me by some colleagues in Toowoomba, Queensland (currently with a clear 8C autumn night and a weekend with predicted highs of 23 C, beating the May Long Weekend in Edmonton by 4-5 degrees).  Unfortunately, the whitefly was not covered with parasites, but with the infamous Broad Mite Polyphagotarsonemus latus (Banks) (Prostigmata: Tarsonemidae), a plant pest with, as you might guess from the generic name, a broad host range.  However, I think the common name comes from it being rather tubby (0.17 x 0.10 mm).

 Like many mites, the life history of the Broad Mite is amazing.  For one thing, they have reduced their life cycle to the almost the bare minimum – egg, larva, adult – cutting out all three nymphal stages.  At a constant temperature of 27 C, this mite can go through a complete generation, egg to egg, in 3 days and summer generation times in the field are typically 4-5 days.  As the larvae and adults feed, they distort leaf tissue into folds and bumps that protects them from weather and predators – not quite as fancy as the gall mites in the Eriophyoidea, but on their way there.

 Male Broad Mites have a large sucker-like genital capsule sticking out their rear end and they use this to hold onto inactive larvae – pharate females that are finishing up their development within the larval skin.  This looks a bit strange – the pharate female crosses the male T – and has fooled several entomologists into thinking they were observing an act of predation.  Nope, just males that want to make sure they alone go on a female’s first date.  This type of precopulatory guarding has evolved numerous times within the Acari, and in this case is associated with a male aedeagus and a female secondary sperm transfer system.  This makes quite a contrast to the oribatid mites with which I am currently working.  Male oribatids wander around depositing spermatophores on the substrate wherever they feel like it, whether or not females are around, and make no effort to contact, let alone guard, a female.  Perhaps that is one reason that 10% of oribatid mite species appear to be thelytokous (i.e. all female and parthenogenetic).

 As you may know, whiteflies are rather small, but not so small that a heap of broad mites can’t hitch a ride.  Mites lack wings, so if they want to get between patchy habitats, they have to come up with an alternative means of transportation.  A surprising number, including many members of the Broad Mite’s family (Tarsonemidae), simply orient to a stiff breeze and let go to become part of the aerial plankton.  That seems pretty inefficient if you have a specific place you’d really like to get before you dehydrate or starve, but I don’t know that climbing on such a tiny and seemingly inefficient flier as a whitefly is much better.

A mite with a mite problem

April 28, 2009
5 hypopi hitching a ride on an Athiasiella

5 hypopi hitching a ride on an Athiasiella

This morning Myrmecos Blog, the place to go for spectacular ant pictures, links to a picture on Flickr by Brian Valentine of a couple of red ants from a compost heap covered with mites. I especially like the ones sticking to the foreground ant’s eye. These look like the dispersal stage of another Astigmatina, possibly a species of the acarid genus Sancassania, as they are common in decomposing material, but then so are several other families. If the compost is very wet and stinky, then they may be Histiostomatidae. The dispersal stages are technically called ‘heteromorphic deutonymphs’, but an older term ‘hypopus’ (plural – hypopi) is easier on the tongue. Hypopi are bizarre for a number of reasons. For example, most have some of their posterior ventral setae modified into a sucker plate that allows them to latch onto surfaces such as insect cuticle – or that of larger mites for that matter. Actually anthing with an appropriate surface that wanders through a compost heap can become covered with [these] little hitchhikers – the famous Australian medical acarologist, Bob Domorow, once published a picture in Acarologia of a skink absolutely encased in [hypopi] CORRECTION – deutonymphs, yes, but of a uropodid mite, not astigmatine hypopi.  See Domrow, R. 1981. A small lizard stifled by phoretic deutonymphal mites (Uropodina). Acarologia 22:247–52

Hypopus underside - note tiny 'head' and sucker plate (bottom)
Hypopus underside – note tiny ‘head’ and sucker plate (bottom)

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