To elucidate the potential for colony growthand the dispersal of aphids in relation to the ant attendance,the mobility, tolerance of starvation, colonygrowth, and dispersal were examined in the ant-tendedAphis craccivora Koch and the non-ant-tended Acyrthosiphonpisum Harris under the absence of predators andants. The increase of the dispersal rate with density wasmore conspicuous in Ac. pisum than Ap. craccivora. Thesuccess rate of dispersal was higher in Ac. pisum than Ap.craccivora. These results would be derived from thehigher ability of dispersal by walking in Ac. pisum thanAp. craccivora. The longer legs, higher walking speed,and stronger tolerance of starvation in Ac. pisum mightresult in a higher ability of dispersal by walking. Thesetraits may have developed in relation to non-ant attendance,because Ac. pisum aphids frequently escape fromnatural enemies by dropping from the host plant. On theother hand, Ap. craccivora have not developed morphologicaland behavioral traits concerning dispersal bywalking, because increasing colony size without dispersalis likely to be advantageous for ant attraction. Escapingbehaviors of Ap. craccivora from natural enemies havenot been well developed due to the ant’s defense againstnatural enemies. The proportion of alatae in Ap. craccivorawas higher than in Ac. pisum instead of a lesserability for dispersal by walking in Ap. craccivora. Thedifferences in ant attendance have been influenced in thedevelopment of morphological and behavioral traits concerningthe dispersal ability, and then, different potentials
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