In high-value crops such as apple, Malus X domestica (Borkh.), insecticidal pest control is of high relevance. The use of resistant apple cultivars can increase the sustainability of pest management in apple orchards. Besides variation in plant chemistry that may influence plant resistance by antibiosis or antixenosis, plant growth characteristics also can affect plant susceptibility to pests such as aphids. Variable susceptibility to the apple aphid, Aphis pomi De Geer (Hemiptera: Aphididae), has been described for different apple cultivars. These observations were based on phenotypic surveys and no information on genetically based apple resistance to A. pomi is yet available. The objective of this study was to relate shoot growth characteristics with aphid population development, and to assess the genetic background of apple antibiosis-based resistance to A. pomi by quantitative trait loci (QTL) analysis. Aphid population development was repeatedly studied in the field in sleeve cages attached to 200 apple trees of different genotypes. Aphid population development was positively correlated to shoot length and growth, and it also was affected by climatic conditions. Indications for antibiosis-based resistance to A. pomi remained weak in the studied apple genotypes, and the only detected putative QTL on linkage group 11 of'Fiesta' apples was not stable for the different replications of the experiment. This lack of quantifiable resistance may be partly explained by environmental conditions related to aphid development in sleeve cages.