Response to intraclonal selection for adaptation 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 factors. This suggests that intraclonal as well as interclonal genetic variation must be a priori considered when studying the evolution of an aphid population. To investigate intraclonal genetic variation in host use in the English grain aphid, Sitobion avenae F., 3 lines were founded by a single female and maintained for 2 yr on either a susceptible wheat genotype, Triticum aestivum L. 'Arminda', or highly resistant varieties of wheat, T. monococcum L. lines 'Tm44' and 'Tm46'. We examined possible changes in the intrinsic rate of natural increase and feeding 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 these traits. These results support the idea, still controversial, of a genetic stability of parthenogenetic lineages of aphids and show that only the interclonal variability must be taken into account when examining the evolution of the ability to overcome plant resistance in S. avenae populations