What's eating my selenicereus anthonyanus?

Selenicereus anthonyanus (fishbone cactus) indoors is most commonly attacked by mealybugs sheltering along its distinctive fishbone stem margins. Spider mites cause silvery stippling in dry rooms. Scale insects can appear on older stem segments. Fungus gnats indicate the bark mix is staying too wet between waterings.

White fluffy deposits in the deep lobes of the flat fishbone stems; heavy infestations yellow the stem margins and prevent flowering Dab every colony with a 70% isopropyl alcohol swab; spray neem oil solution weekly; isolate from nearby houseplants promptly

Pale, dry silvery speckling across flat stem surfaces; faint webbing may link adjacent lobes; population spikes in low winter humidity Raise ambient humidity; apply insecticidal soap to all stem surfaces; move plant away from radiators or heat mats

Tan or brown crusts along the stem midrib and older segments; cause sticky honeydew and eventual yellowing of affected portions Scrape off with a soft brush; wipe with alcohol; treat with horticultural oil spray if scales return after manual removal