Stubborn pest - mite or possibly aphid - Orchid Board

harpspiel · #1 03-01-2015, 07:23 PM

I am just about at my wit's end here. My enclosure is slowly getting overrun with some kind of tiny pest, which I often see crawling all over the roots and leaves of my orchids - it seems to especially like Schoenorchis fragrans. It could be benign since I haven't seen much damage yet, but I am seeing a few brown pock marks on the bottoms of leaves. The critter is white or cream colored, about 1 mm long and when I've looked with a magnifying glass seems to have two antennae and around six legs, a little round body and no wings. My two best guesses are either some kind of aphid, or some sort of white spider mite. There are no webs, though, and the tank is around 90% humidity and gets down to 59F every night, so that's not supposed to be conditions that spider mites thrive in.

So far, I have tried spraying the plants and the whole tank with insecticidal soap for a few weeks, which seemed to have no effect.

Yesterday I tried the dry ice method, sealed off the tank and completely filled it for about 4 hours. That killed off all the fungus gnats which I didn't care about, but today the critters are out and about just as happy as they were before.

I don't know what to do from here or how to identify them. Do I try dry ice again, but for longer this time? Do I try to introduce some sort of beneficial predatory insect to control the population? Do I tear the whole tank apart and submerge all the plants and try to bake the soil? I have a shipment coming in next week from Andy's, and I can keep the plants in a short-term setup briefly, but I really need to fix the problem. Any suggestions at this point are appreciated!

Tindomul · #2 03-01-2015, 09:39 PM

Hi, from your description I would say you have a healthy population of springtails. These are insects that break down dead plant material. Sometimes your substrate has enough food for them to provide a boost to their population. They do no harm to living plants.
If you blow on them gently can you see them spring/hop away? That will tell you for sure. Otherwise you can look them up on the web. Springtails or Collembola. Let us know.
If you have damage on the plants, I suggest you keep looking for the culprit.
Also, mites are smaller than springtails and therefore much harder to see. Aphids are much bigger and don't move around much.

harpspiel · #3 03-01-2015, 10:08 PM

I have tapped plants they are on, and had them on my hands after handling plants, and they do move quickly but have never jumped or sprung away. They also seem to have little round bodies, not the elongated springing part in back. They are just on the edge of being big enough to observe - maybe even smaller than 1 mm, and I don't have a good enough camera to get a decent picture. It's entirely possible that what I thought were antennae were legs.

I do see them crawling all over sphagnum and wood as well as the plants, and I'm not seeing active damage to the tops or undersides of leaves - should I just not worry until I do see damage? There are often as many as 10 at a time on a single Schoenorchis.

---------- Post added at 10:08 PM ---------- Previous post was at 09:47 PM ----------

I don't know if that helps much, but at least it gives scale and sort of a hint of legs if you really zoom in. There are two in the magnifying glass.

Tindomul · #4 03-01-2015, 10:50 PM

They could be springs, but I have never seen them crawl on glass. How fast do they move? Aphids move pretty slow and mites are so small that inch takes them forever. I really don't think these are mites, just too big. Could be aphids I just can't see them that well from the pic.
Also I have never seen white aphids.
Also, aphids would not waste time on the glass, they would be on the plants, unless the plants were so infested that they were forced look for new food.

harpspiel · #5 03-01-2015, 11:26 PM

I do regularly see them on the glass. It takes one about 10 seconds or less to travel an inch. I'll borrow my dad's SLR tomorrow and see if I can get a better shot.

camille1585 · #6 03-02-2015, 04:41 AM

Not aphids, they're way too big to be that, and as pointed out, you wouldn't see them on the glass unless the plants were so infested that they were searching for more food. Aphids don't move around much, if that's what they were you'd simply see large colonies of them immobile on the plants and/or roots.

As to the dry ice treatment, were you using enough of it to displace all the air? And perhaps you need to leave it longer. Check out this member article on the topic, if you haven't seen it yet.
Eliminating terrarium pests - Orchid Board

Last fall I treated some plants with CO2, and left them in a sealed container overnight each time I treated them.

harpspiel · #7 03-02-2015, 01:55 PM

Ok, thanks to a loupe and my dad's SLR, here are I think the closest shots I'll be getting. These little guys are all hanging out on one of my Schoenorchis fragrans, and as you can see they spend a lot of time on the top of the leaves, but there is no apparent damage to the leaves. In the first image, the focus is on a critter on the leaf to the right - I show the whole plant for perspective.

---------- Post added at 01:55 PM ---------- Previous post was at 01:38 PM ----------

With these close-up photos, these rather look to me like Neoseiulus californicus or N. cucumeris- two species of <1mm predatory mites used to control spider mites and thrips.

Thoughts?

Tindomul · #8 03-02-2015, 05:30 PM

Mites!
Sorry to id them wrong from your description. Also, springtails don't hang out on the plant's leaves. You probably have both anyway, but you want to treat your plants for the mites.

The Antennas are actually the first pair of legs, giving a grand total of 8 legs. That makes them mites. Great photos!
Good catch.

PS... I didn't know mites came that big, unless these are some kind of plant tick?

camille1585 · #9 03-02-2015, 05:49 PM

Mites do come that big, especially predatory ones. Some scientists in my research group study Phytoseiulus persimilis which is a pretty big mite. Even its favorite prey, the 2 spotted spider mite, is quite big.

Tindomul · #10 03-02-2015, 05:57 PM

Quote:

Originally Posted by camille1585

Mites do come that big, especially predatory ones. Some scientists in my research group study Phytoseiulus persimilis which is a pretty big mite. Even its favorite prey, the 2 spotted spider mite, is quite big.

THat is so cool!