What's eating my myrtillocactus geometrizans?

Myrtillocactus geometrizans (blue myrtle cactus) indoors is most at risk from mealybugs hiding in its tightly packed areoles. Scale insects can colonise the blue-waxy ribs and spider mites cause stippling in dry indoor air. Overwatering encourages root rot and fungus gnat larvae, which damage feeder roots.

Cottony white tufts at areoles and branch joints; heavy feeding yellows the waxy blue-green skin and reduces the plant's vigour Dab infestations with isopropyl alcohol on a swab; follow up with neem oil spray over the whole plant; repeat fortnightly

Hard or soft bumps adhering to ribs; produce sticky honeydew that triggers black sooty mould growth on the stem Scrape off manually, then swab with alcohol; apply horticultural oil; check branch forks where scales concentrate

Adults are harmless but larvae (in overwatered compost) chew fine roots, causing wilting and yellowing despite moist soil Allow top 5 cm of compost to dry fully between waterings; apply yellow sticky traps for adults; drench with Bacillus thuringiensis var. israelensis (Bti)