Cactus mites

[Pattock]

I thought this could make a separate thread, as so little seems to be known about a false spider mite that is a common pest of cultivated cacti. They are known as Brevipalpus russulus. They have also been called Acarus russulus, Hystripalpus russulus and Tenuipalpus cactorum.

I thought it would be easy to find out if they are nocturnal, as some people say they are to be found at soil level but they clearly feed on the whole of the stems. I can't find anything in scientific journals. I can find physical descriptions of the mite. Several sources repeat that little is known of the biology or control of this mite.

It is only slightly smaller than the two-spotted red spider mite, which may be 0.3 to 0.5 mm. This species has both males and females. The female is slightly larger than the male, from 0.2 to 0.33 mm. They seem to be flatter than spider mites. If it is found on the upper stems during the day, it may be well-camouflaged due to its russet colour. It may fluoresce under UV light like other arachnids, if anyone wants to try spotting them at night.

However, these pictures show a distinct difference in colour, the mites being quite bright red. One paper called them crevice mites, presumably because they like to tuck themselves away. http://dimetris.com.ua/wiki/%D0%BA%D0%B ... s_russulus

The male is haploid, having only one set of chromosomes. The female is diploid, having two sets of choromosomes, one from each sexual parent.

The first description of the species was in 1867¹ and it was already known as a pest to cactus enthusiasts:

Acarus roussâtre . Acarus russulus.

Ce petit acarus, qui a probablement été importé du Mexique ou de quelque autre contrée de l'Amérique centrale, ne se trouve que sur les Cactées, particulièrement sur les mamillaria, les echinocactus et genres voisins; il est connu des amateurs de plantes grasses sous le nom de rouget. Cette petite arachnide d'un roux ferrugineux est presque microscopique; elle fait beaucoup de tort aux plantes sur lesquelles elle s'établit, et si l'on n'y apporte pas un prompt remède, elle ne tarde pas à les faire périr.
Les fumigations de tabac peuvent, en pareil cas, être employées avec succès. M. Landry, de Passy, détruit cet acarus en saupoudrant ses plantes avec du tabac.

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This little acarus, which was probably imported from Mexico or some other country in Central America, is found only on the Cacti, particularly on the mamillaria, the echinocactus and allied genera; it is known to lovers of fat plants under the name of rouget. This small rusty-red arachnid is almost microscopic; it does much harm to the plants on which it grows, and if we do not bring a prompt remedy, it does not take long to destroy them.
Tobacco fumigations may in such cases be employed with success. Mr. Landry, of Passy, destroys this acarus by sprinkling his plants with tobacco.
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The French word "rouget" simply means "reddish"² as does the specific name "russulus"³. Rouget also refers to the fish we call a red mullet, a type of swine-fever and a harvest bug or large red insect-parasitic mite called Trombidium.

So, does anybody have any other clues? Perhaps the BCSS should promote research into this mite?

¹ Boisduval, Jean Alphonse "Essai sur l'entomologie horticole : comprenant l'histoire des insectes nuisibles a l'horticulture avec l'indication des moyens propres a les éloigner ou a les détruire et l'histoire des insectes et autres animaux utiles aux cultures" (1867, Librairie d'Horticulture de E. Donnaud) 89-90

² A dictionary.
https://archive.org/details/in.ernet.dl ... 7/mode/2up

³ Another dictionary
http://www.perseus.tufts.edu/hopper/tex ... 3Drussulus

I am starting to itch far too much now. I am going to stop.

[RAYWOODBRIDGE]

There was a very good zoom talk on this very subject not long ago, by a young German gentleman his name escapes me at the moment, but I am sure someone will remember the name.

[Mike P]

There have also been threads about this in the past although I don’t recall quite how long ago.

[Davey246]

Sounds like northern mite (in habit).
Poultry can get infested with depluming/red mite which stay on the bird and suck blood, and irritate like mad so the birds over-preen and hence lose feathers. They are treated by dusting or spraying the birds, often with a pyrethroid.
Northern mite got its name because it frequently appeared as the migrating birds arrived in the UK in autumn, from the north and the two events became linked (many, many moons ago).
Northern mite are active at night, sucking blood, but hide during daylight in any nooks and crannies. Traditionally, or since it was introduced anyway, Duramitex has been sprayed around housing - originally this was malathion, then changed to cypermethrin when malathion was banned for amateur use, but reverted to malathion under derogation for poultry use (which may have recently been recinded).

[iann]

Every time this topic is raised, there is a chorus of amazement about this incredible yet unknown mite. And yet the topic is raised so often and much information is offered. Then people seem to immediately forget about it again. Granted, most popular sources continue to talk only about the "red spider mite" as being the (non-red) web-spinning pest of yore, but in my experience cacti are far more likely to have the Brevipalpus flat mite than the true spider mite. Real spider mites, for me, are a pest primarily of mesembs and occasionally some columnar cacti. Maybe the Brevipalpus eat them! It probably doesn't help that Brevipalpus are effectively invisible to the naked eye, like to lurk deep between areoles and at the base of cacti, and don't have huge population explosions like spider mites. Small numbers do cause significant damage though, easily mistaken for corking at first.

[Pattock]

Every time this topic is raised, there is a chorus of amazement about this incredible yet unknown mite. And yet the topic is raised so often and much information is offered. Then people seem to immediately forget about it again.

Which is precisely why I thought it worth collating the latest, cumulative knowledge to try to get it to stick in people's minds. Clearly, even seasoned growers are still identifying the cactus mite as red spider mite. The fact that both are reddish does not help. Though the carmine spider mite is redder. I only had that once, on a Salvia amarissima cutting I received. The lack of webbing is pretty obvious with the cactus mite.

The important part for growers is, of course, the control. From a brief dip into the forum here and the internet more generally, my impressions are:

Cactus mites are particularly resistant to pesticides, probably because of the practices of the commercial nurseries. I have also seen people recommending you just douse them with whatever is the favoured pesticide of the day.

Phytoseiulus persimilis predator mites appear to ignore them. Less specialist Amblyseius predator mites may help control or eliminate them. No scientific studies have been done into the control of this species that I can find.

One source suggested oily soap sprays were effective. You would have to make sure they contacted the mite, of course. Tricky when they hide.

[SimonT]

If we can't ID the mite and we just call all the mites RSM, "Red Spider Mite", then how can proper control of the mite be obtained? You might see this in the preference of predators for mites of different species, efficiencies of different sprays, or even the different response of different species of mite to misting with water! So how is best to ID mites? Is it sufficient just to split them between Red Spider Mites, spinning webs, and flat mites than are smaller and without webs?

I agree with Pattock that it would be good to bring together the current best practice. I've been lucky with mites so far. But I think it is still good to be ready to deal with this problem, rather than getting caught out some time in the future.

[Nick_G]

My collection has suffered over the years from both RSM and Brevipalpus but for the last few years regular spraying (once a month) with a rape seed oil spray or SB seems to have them well under control. The kiss of death writing that of course . I did my May spray just this morning.

For Brevipalpus you do have to make sure you heavily spray the whole plant from the soil line upwards.

[Herts Mike]

Is that what has caused this? I couldn’t see any RSM at the time.

[Tina]

Blimey Mike, put the paper bag back on its scaring the plants