The cactus mealybug Atrococcus mamillariae (formerly known as Spilococcus cactearum) is a pest of cacti and other succulents. It was first described in England but its origin is not clear. It is now found on many greenhouse-grown succulents around the world as it was probably distributed by the trade in ornamental plants.
The cactus mealybug usually infests stems but can occasionally be found on crowns, roots. and flowers. Depending on the host plant species, infestations with cactus mealybug cause discoloration of the plants and later necrosis of the tissue. Plant deformations can also occur. Heavily infested plants stop growing and will eventually die.
Mealybugs get their name from the fact that the body of the females from the third nymphal instar onwards are covered with a white waxy material in the form of powder, threads, spiky projections or platelets. Eggs are laid in a sticky, foamy mass of wax threads, called an egg sac. First instar nymphs of the cactus mealybug are yellow-brown and not yet covered with wax. They are actively mobile and known as ‘crawlers’.
From the second instar on, they are covered with white waxy exudate and become more sedentary and only move occasionally. After the second instar, the males form a pupa. After a complete metamorphosis, a winged male emerges from this pupa. The males lack mouth parts and are incapable of feeding. They have a brief lifespan during which they are wholly engaged in seeking females to fertilize.
The female second instar nymph, on the other hand, moults into a third instar, and then into the adult female without a complete metamorphosis. Third instar nymphs and adult females are oval and covered by wax. The adult female is 1.7-3.3 mm long.
