What's eating my sun cup cactus?

Sun Cup Cactus (Mammillaria microhelia) is a small globe cactus whose dense tubercles and wool-filled axils are ideal mealybug hiding spots — this is by far its most common pest problem. Root mealybugs and spider mites also occur. Inspect axil wool between tubercles at every watering.

White woolly masses in the axils between tubercles and at the growing tip; honeydew; yellowing or pitting of nearby tubercles Apply 70% isopropyl alcohol with a fine-tipped cotton swab to each colony; spray the whole plant with diluted neem oil; repeat every 10 days

Softening or slow collapse of body despite appropriate watering; white powdery coating on roots at repotting Unpot, clean roots, dry the plant; repot in fresh gritty mix and water with diluted neem solution; treat monthly for three months

Webbing among spine clusters; faint pale stippling on the tubercle surfaces; worsens in winter dry heat Gently rinse the plant; apply insecticidal soap or neem spray; ensure good airflow and avoid placing near heating vents