Dispersal strategy

In a dioecious holocyclic species, three periods in the development of alates, and therefore of migration, are usually observed:

1. The first flight period takes place in spring and corresponds to the departure of the alate fundatrigenia from the primary host to settle on the secondary hosts: this is the emigration flight (E).
2. During the summer, a series of small-scale flights are observed corresponding to alate virginoparae which move from secondary hosts to secondary hosts: these are the dispersal flights (D).
3. Finally, in the autumn, we see the flight of the precursors of sexual forms (sexuparae (type 1) or gynoparae (type 2)) or males that return to the primary host: this is the return flight (R).

In the case of anholocyclic species or populations, the different flights observed in the course of the year correspond to the aphids’ movements to seek out the most suitable plants for their proliferation.
Depending on the species, their life cycles, the geographical situation or environmental conditions, many more types of flight activity are seen than those outlined above. This variability is shown in the number of flight periods, how early or late they take place or the relative length or scale of the flights.
Monitoring of alate populations by trapping during such movements yields useful information on the dates, periods and scales of these biological phases where populations move around and prepare to colonize new cultivated or wild plants.