RESPONSE TO INTRACLONAL SELECTION FOR ADAPTION TO RESISTANT WHEAT IN THE ENGLISH GRAIN APHID (HOMOPTERA, APHIDIDAE)

There are many reports of variation and changes within parthenogenetic lineages of aphids that are not clearly related to environmental fact ors. This suggests that intraclonal as well as interclonal genetic var iation must be a priori considered when studying the evolution of an a phid population. To investigate intraclonal genetic variation in host use in the English grain aphid, Sitobion avenae F., 3 fines were found ed by a single female and maintained for 2 yr on either a susceptible wheat genotype. Triticum aestivum L. 'Arminda', or highly resistant Va rieties of wheat, T. monococcum L. lines 'Tm44' and 'Tm16', We examine d possible changes in the intrinsic rate of natural increase and feedi ng behavior (electronic monitoring) of the 3 isofemale lines on their rearing plant over the 2-yr course of the selection Experiment (60-70 successive aphid generations). No response to selection for increased survival or increased ability to feed on resistant wheat was detected, suggesting that S. avenae clones are not genetically variable for the se traits. These results support the idea, still controversial of a ge netic stability of parthenogenetic lineages of aphids and show that on ly the interclonal variability must be taken into account when examini ng the evolution of the ability to overcome plant resistance in S. ave nae populations.