Scale insects
Pest insect
- Presence of a few scale insects
- Presence of numerous immobile scale insects
- Sticky substance on leaves and stems
- Plant growth halted or slowed down
- Yellowing and leaf drop
- Black mold on leaves and stems
| Difficulty High |
| Frquency High |
| Reproductive rate Up to 250x |
| Lifecycle Up to 60 days |
Scale insects, or armored scales, form a family of pest insects that cause damage to plants by piercing plant tissues to feed on their sap. Several thousand subspecies are referred to by one of these names based on the appearance and rigidity of their carapaces.
Host plants
These scale insects can be found on almost all types of indoor plants. They particularly favor fruit trees of the citrus family.
Screening
Armored and scale insects are mostly immobile and are even more difficult to identify as their appearance varies greatly depending on the species. They cluster together, easily camouflage on stems and leaves, and often go unnoticed there. Honeydew is a sticky, transparent substance that accumulates on leaves and stems. When honeydew is secreted in sufficient quantity, it can cause a form of black mold called sooty mold. When yellowing and leaf drop occur, the phenomenon is usually concentrated at the base of the plant.
A sufficient population can slow down or halt the growth of affected plants.
Prevention
Although some species of armored and scale insects are present in most climates, those affecting indoor plants are of tropical origin. They are not adapted to continental climates, and their spread always occurs from one indoor culture to another through people, plants, or other contaminated objects.
Treatment
Foliar treatments with insecticidal soap can be effective against nymphs but will have little effect on adult females protected by their carapaces. Thorough cleaning and manual removal of scale insects remain the best option. Green lacewings may help control the infestation. Thermal treatment through heat or cold is possible for plants that can tolerate it.
In severe cases, treatment may be very difficult, if not impossible, and plant elimination, complete pruning, or cloning should be considered.
Morphology
Among the numerous varieties of armored and scale insects, Coccus hesperidum is one of the most commonly found in indoor plants. The adult female resembles a small flat scale of brown or amber color. In other species, they resemble galls or even shells. Male individuals are winged, much smaller, and only live for a few hours, the time for fertilization.
Behaviour
Adult females of most species permanently position themselves to feed and remain immobile.
Lifecycle
Each species has a distinct reproductive cycle influenced by temperature, and some can reproduce in the absence of males. Nymphs spend some time under the mother before dispersing and attaching to the plant in turn.