What's eating my echinocereus rigidissimus?

Echinocereus rigidissimus (Arizona rainbow cactus) grown outdoors or in a greenhouse can suffer mealybugs, scale insects, and spider mites on the plant body, plus fungus gnats in damp compost. Outdoors in warm climates it may attract grasshoppers or ground beetles. Slugs and snails rarely trouble it due to its formidable spine coverage.

White waxy tufts at areoles and the crown; honeydew deposits; stunted growth or wilting in heavy infestations Apply isopropyl alcohol with a cotton swab or fine brush; follow with neem oil spray; repeat weekly for 3–4 treatments

Hard brown or grey disc-like bumps on ribs; tissue pitting and yellowing below the scales Scrape off physically; spray with horticultural oil; treat again after 10 days to eliminate crawlers

Fine webbing across spine clusters; stippled, dull, or bronzed patches on the cactus epidermis Rinse with water spray; apply insecticidal soap or neem oil solution; ensure good air movement around the plant

Larvae feed on root hairs in wet compost; adult gnats swarm around the plant Allow soil to dry fully between waterings; use yellow sticky traps; drench with Bacillus thuringiensis israelensis (Bti) to kill larvae