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Keywords:

  • insect herbivore;
  • MYB transcription factor;
  • transgenic red apple leaves;
  • insect behaviour;
  • preference;
  • visual cues;
  • leaf phenolics;
  • larval feeding;
  • life cycle;
  • Rosaceae;
  • Lepidoptera;
  • Tortricidae

Abstract

Anthocyanins have diverse roles in plant reproduction and in response to both abiotic and biotic stress. By over-expressing the apple MYB transcription factor, MYB10, we have generated apple trees, Malus × domestica Borkh. (Rosaceae), with highly pigmented red foliage due to the presence of high concentrations of cyanidin-based anthocyanins. In this study, we investigated the impact of the high anthocyanic apple leaves on the behaviour, feeding, and life cycle parameters of the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), a widespread herbivorous pest of apples. Behaviour of 1- to 3-day-old larvae towards red anthocyanin-rich and green apple leaves was studied in choice and no-choice trials, and survival, growth, and development of larvae feeding on red and green apple leaves from the neonate to pupation were compared. First-instar E. postvittana showed a statistically significant preference for green over red leaves from three transgenic red apple lines and a preference for the less red old leaves over the bright red new leaves. This was significantly different from their behaviour towards wild type green leaves, where new leaves were selected over old. In complete darkness, first-instar E. postvittana showed no significant preference for the green leaves, indicating that visual cues were important. Although larval survival was not greatly affected by feeding on the red foliage, larval growth and development were significantly affected by feeding on leaves from some of the transgenic red apple lines. Liquid chromatography-mass spectrometry analysis of leaf phenolics showed that both anthocyanins and quercetin glycosides were significantly raised in the red transgenic lines compared with wild types.