I posted this issue in "fungus infection" by Motaarji, but did not get any input... I repost here again, after I can confirm that I have seen some bugs moving around, after I zoom this to hundreds time larger, the bugs can not be seen without this camera with 50 to 1600x zoom.
This is the picture of the cactus, some color changing at the base..


If we zoom it, we can see some brownish thing on it, they are bot moving




Then I tried to look closely the upper area of the cactus which looks healthy.. and I saw some brown bugs that are moving, the spike of the cactus make it impossible to clean it with brush, I put the following pictures to give the perspective of the size



For now I only have the option of spraying the cactus with either:
1. Alcohol
2. Dish soap, I have tried dish soap to clean mealy bugs in other fruits/ flowers, but the size of mealy bugs is hundreds time bigger than this one.

Please help me with recommendation on what to do? I have never spray alcohol on plants before, also worry that if I use dish soap, there will be too much soap in the soil and at the end will kill the cactus. Any suggestion is highly appreciated.

On the second thought, I have a feeling that spraying alcohol may be a better option for me, as it will evaporate into the air, any of you ever us alcohol to treat cactus? if yes, what is the concentration of alcohol you are using, is it 100% or I have to dilute it to 50 or 70% ? Thanks alot

I think dish soap or alcohol would be good. The soap at 1-2% in water (or you can buy insecticidal soap for plants, which I make from a concentrate). The alcohol (ethanol or isopropanol) at 70%. Both have to physically contact the bugs to have an effect on them, so hit the area from all different angles with a fine mist or light spray.

It's true that the soap will not evaporate, but you will be watering in a week or whatever, and watering will flush the soap right out the bottom. So there will be no net accumulation as long as you rinse when you water. The reason I like the dedicated product for horticultural use is because it's the potassium salt of fatty acids, as opposed to the sodium salt typically used to make dish soap, and potassium is kinder to succulents than sodium. I don't think it actually matters as long as you flush when you water.

It's hard to know whether those are "bad" bugs (they are really tiny!) so maybe don't go crazy with lots of extra spraying. One proper treatment, around sundown ideally (direct sun tends to combine poorly with these agents, calm air allows them to persist in liquid form on the plant for longer). Then wait until a couple of days after the next watering and do a repeat treatment if you see anything moving at that point.

Thanks alot Baja, I am ordering some organic pesticide now, hopefully tomorrow I can apply it to the cactus... Too bad, this one is my largest mammillaria, larger than tennis ball, I don't want to lose it

This is another type of bugs that only attack Huernia Schneideriana, when the plant infected, there will be sign of 1 black spot, and the plant will turn yellow to top and to bottom, the top one will always die and can not be rooted even you cut them when they are still green, the bottom part of the huernia will still survive if you manage to cut before it turn yellow, if you do nothing, then the plant will never survive. Since I manage to catch 1 today, might as well share it here, very small but visible, around 1.5 mm in length. Can see the size comparison with hair in the picture.

The bug is quite hard like having shell, can fly, but can easily slapped with hands

This plant has turned yellow all the way down, surely die

Just now I checked again on my mammi beneckei, the pesticide is not working, and sure there are bugs , this time I can get a better picture of it..

When I tried to touch the bug with toothpicks, it can hop like a spring. I sprayed it with alcohol, when I zoom it again after spraying alcohol, then I can also see some very thin spyder web... hope the bugs can be killed by alcohol

Kaktus said:Just now I checked again on my mammi beneckei, the pesticide is not working, and sure there are bugs , this time I can get a better picture of it..

When I tried to touch the bug with toothpicks, it can hop like a spring. I sprayed it with alcohol, when I zoom it again after spraying alcohol, then I can also see some very thin spyder web... hope the bugs can be killed by alcohol

Hi, did the alcohol spray work? How is the plant doing after its treatment?

I think the 70% alcohol works, I sprayed alcohol again 2 days after the first spray, and now the cacti looks healthy, I like the color now as it started to develop a red tone color, maybe during the treatment, I did not let him has access to direct sunlight, now it has full sunlight and stress, as you may see in the picture, or possibly the color change because of the alcohol, no idea.
There are some area near the bottom getting worse, looks like dry out, but I just assume that it is a normal process

Having been drunk, you know how awful and dried out you feel next day, poor thing lol. I sprayed mine yesterday, its a bearded cactus and I'm quite sure I'd already speared every mealy bug with a toothpick lol but I know they lay eggs.
I'm sat looking at him now and wishing I could give them water but I think it's 2 days. I need to go look it up!

Kaktus said:On the second thought, I have a feeling that spraying alcohol may be a better option for me, as it will evaporate into the air, any of you ever us alcohol to treat cactus? if yes, what is the concentration of alcohol you are using, is it 100% or I have to dilute it to 50 or 70% ? Thanks alot

I have. I used 99% and although they evaporate almost immediately I would rinse the plant after about a minute. Killed all the mealy bugs, spider mites, and those tiny flies.