Host monitoring by aphid migrants: do gynoparae maximise offspring fitness?

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Abstract
Gynoparae (autumn migrants) of the bird cherry-oat aphid,Rhopalosiphum padi (L.), were not found to land randomly on their primary host,Prunus padus L. Some trees, although within a few metres of heavily infested trees, were not colonized at all. This phenomenon occurs regularly from year to year. The reasons for this non-random landing pattern are examined in terms of the success of subsequent generations, special attention being paid to the reproductive rate of the oviparae and fundatrices and the success of the developing populations in the spring of the following year. Trees in Scotland and Finland were examined in this manner and the hypothesis developed that the gynoparae ofR. padi show maternal care in selecting hosts that favour their offspring's survival and reproduction. Aphids were reared under controlled conditions in the laboratory on twigs cut from trees of known previous infestation levels. Aphids on twigs from preferred trees had better survival rates and produced more offspring than those aphids on twigs from non-preferred trees.