What's eating my selenicereus pteranthus?

Selenicereus pteranthus (princess of the night) is a vigorous climbing cactus most troubled by mealybugs, which cluster at the deep ribs and branch nodes. Spider mites can cause pale scarring on the fleshy stems in low-humidity rooms. Scale insects are a secondary pest. Root mealybugs strike in waterlogged compost.

White cottony masses at rib grooves, stem joints, and the growing tip; feeding slows elongation and can abort flower buds Apply isopropyl alcohol with cotton buds to all colonies; follow up with neem oil spray over the full plant; repeat every 10 days

Fine pale stippling or russeting across the green stem surface; tiny mites visible with a hand lens; worse in heated indoor air Shower the plant with tepid water; apply insecticidal soap; ensure good air circulation and avoid placing near heating vents

Brown disc-like scales fixed to ribs; produce honeydew that drips onto lower leaves and grows sooty black mould Scrub off scales with a damp cloth or toothbrush; treat with horticultural oil; check plant monthly during the growing season