The relationship between pre-flight reproduction and migratory urge in alatae ofAphis fabaeScopoli (Hemiptera: Aphididae)

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Abstract
Alatae of Aphis fabae Scop. which reproduced before their first flight (flyers) were compared in the laboratory with those which did not (migrants) in order to test whether this difference in behaviour could be taken as an expression of migratory urge. No difference in live weight or dry weight could be found between the two groups. Flyers, however had a higher wingloading than migrants after the final moult but not after pre-flight reproduction. Flyers also had a lower fat/dry weight ratio than migrants and appeared to have more embryos, including a greater number in an advanced state of development. The significance of these observations is discussed in relation to two hypotheses which could account for the different behaviour of migrants and flyers. The results support the hypothesis that migrants have an innately greater urge to take off than flyers, mediated by their crowding experience during development, and that this is likely to result in migratory as opposed to trivial flight.