Effects of population density on alienicolae of Aphis fabae Scop.

II. The effects of crowding on the expression of migratory urge among alatae in the laboratory



Apterae reared at different population densities produced alatae among their progeny, but not all these alatae behaved in the same way. Some flew before depositing nymphs (here called migrants), others flew after parturition (flyers) and some never flew (non-flyers). The proportions of alatae, among the progeny from both uncrowded (‘U’) and crowded (‘C’) parents, that flew before depositing nymphs increased as the population density in which they were reared increased. Both crowded and uncrowded apterous parents produced similar numbers of larvae but, on average, ‘C’ apterae produced 17% more migrants. The proportions of migrants among alate progenies were closely correlated with the proportions of alatae among progenies.