What's eating my marble houseleek?

Marble Houseleek (Sempervivum marmoreum) as a houseplant is most at risk from mealybugs, which exploit the layered rosette structure to hide and feed. Root mealybugs are a silent secondary pest. Fungus gnats appear when the plant is overwatered, which also risks root rot. The marbled leaf patterning can initially camouflage early mealybug cottony deposits — inspect closely.

Cotton-like wax deposits between rosette leaves and along stems; sticky honeydew and slowed growth. Treat with isopropyl alcohol on a swab; spray the plant with diluted neem oil or horticultural soap; repeat after one week.

Plant declines steadily; white waxy clusters coat the roots and base of stem when removed from the pot. Wash roots thoroughly; allow to dry; repot in fresh gritty compost; a neem root drench helps prevent re-infestation.

Root tip feeding by larvae in wet soil; tiny dark flies emerge from the soil surface. Water very sparingly; use a top dressing of horticultural grit; apply Bti drench to eliminate larvae.