'Dandruff' like dust on moss and medium

[Liodoro]

Hi. I have just had a 'rescue' Zygopetalum delivered by post from a supplier new to me. I opened the package outside and was alarmed to see white dust particles on the damp medium which seems to have quite a lot of moss in it. I am very new to all this and all my other plants are in bark with some Leca. Is this a pest or just the effect of moisture on the moss. I have kept it apart from my collection until I can be sure. Should I repot it immediately?

[Shadeflower]

what you are describing sounds like shed aphid skins.

If you rub your fingers along the underside of the leaves, you should be able to spot aphids. They can camouflage themselves but they are fairly big for a pest and sit on the underside of the leaves. f you look with a torch they will look like little droplets sitting on the undersides.

Have a look.

[estación seca]

It could be small white spots of fungus on medium that was moist and tightly enclosed during shipping. If so it will go away in your home environment. I would not repot until assessing the plant and the medium further. Without photos I can't help with that.

[YetAnotherOrchidNut]

If its aphids as shadeflower suggests (which was my thought too) check new growth especially closely. A lof of orchids are fairly robust to aphids with thick leafs and stuff like that so they home in on the sensitive new growth. The particularly like Dendrobium or Oncidum new pseudobulbs in my experience. No idea about Zygopetalum, i have no experience there.