Scale insects primarily spread to new plants during their mobile 'crawler' stage.
Scale infestations on plants spread when crawlers walk or are blown by the wind to nearby plants or plant parts. These tiny, mobile stages are the primary means by which scale colonizes new host plants.
The Mobile Crawler Stage
Unlike adult scale insects that become sessile (immobile) and remain fixed in one spot, the initial phase after hatching is the 'crawler' stage. These crawlers are small, active, and possess legs, making them capable of movement.
Methods of Movement
Based on their capabilities, crawlers move from one plant to another through two main methods:
- Walking: Crawlers can actively walk short distances to adjacent leaves, stems, or entirely different plants located nearby.
- Wind Dispersal: Due to their small size and light weight, crawlers can be blown by the wind across greater distances, landing on other plants or plant parts. This is a significant factor in the spread of scale infestations, especially in closely planted areas.
After a crawler successfully finds a suitable feeding site and begins to feed, it settles down. As described in the reference, it becomes very flat and covered with a clear wax shell, remaining beneath its waxy armor as it grows. At this point, the scale insect loses its mobility and cannot move to another location on its own. Therefore, the spread relies entirely on the transient crawler stage.
