Mealybugs cause damage to several crops in the horticultural sector. The most important species occurring in glasshouses belong to the genera Planococcus and Pseudococcus. Within the Planococcus genus, the citrus mealybug, Planococcus citri, is a particular problem. Several species within the Pseudococcus genus occur in glasshouses.
The mealybug has five stages in its life cycle. The females go through the stages of egg, three nymphal stages and adult insect; the males go through egg, two nymphal stages, false pupa and adult insect. Mealybugs derive their name from the third larval stage onwards when the female's body is covered with a white wax-like substance in the form of powder, filaments, projections or plates.
- Nymphs and female adults feed on plant sap. This reduces growth and causes deformation and/or yellowing of the leaf; sometimes leaves may drop off the plant. This can reduce yield or cause cosmetic damage. Infested plants often drop flowers or leaves if present.
- Mealybugs excrete honeydew on which dark sooty moulds develops. Together with the whitewax-like secretions, these soil the plants. Photosynthesis of the leaves is reduced, causing production to decrease.