Evaluation of Greenbug and Yellow Sugarcane Aphid Feeding Behavior on Resistant and Susceptible Switchgrass Cultivars

Switchgrass (Panicum virgatum L.) is an emerging biofuel crop that serves as host for aphids. To discern the effects of plant age and possible resistance mechanisms, the feeding behavior of greenbugs (Schizaphis graminum Rondani.) and the yellow sugarcane aphid (Sipha flava Forbes.) was monitored on three diverse switchgrasses by the electrical penetration graph (EPG) technique. Callose deposition and genes associated with callose metabolism were also analyzed to discern their association with plant resistance. There was a strong host effect on greenbugs feeding on lowland cultivar Kanlow at the V3 stage of development, as compared to the greenbug-susceptible upland cultivar Summer and plants derived from Kanlow (♂) × Summer (♀) (K×S) crosses. These data confirmed that Kanlow at the V3 stage had antibiosis to greenbugs, which was absent in the Summer and K×S plants. In contrast, similar effects were not observed for yellow sugarcane aphids, excluding significant differences in the time to first probe on Kanlow plants at the V1 stage and reduction in time spent on pathway processes on Kanlow plants at the V3 stage. These data demonstrated that Kanlow plants may have multiple sources of resistance to the two aphids, and possibly some were phloem based. Microscopy of leaf sections stained with aniline blue for callose was suggestive of increased callose deposition in the sieve elements in Kanlow plants relative to Summer and K×S plants. RT-qPCR analysis of several genes associated with callose metabolism in infested plants was equivocal. Overall, these studies suggest the presence of multiple defense mechanisms against aphids in Kanlow plants, relative to Summer and K×S plants

Hypermetamorphosis in a leaf-miner allows insects to cope with a confined nutritional space

International audienceHypermetamorphosis has been described in several Lepidoptera leaf-miner species (mostly Gracillariidae, Epipyropidae, and Phyllocnistidae) and can be defined as a strong modification of the larval morphology associated with a switch in its feeding mode. Evolution of this larval feeding strategy presumably influences nutritional resources that can be exploited and has strong consequences for plant morphology. The following studyfocuses on Phyllonorycter blancardella (Lepidoptera: Gracillariidae), a leaf-miner developing on Malus domestica. We characterize the morphology of larval mouthparts and the resulting morphological impact on leaf tissues. Our results show that first instars do not strongly affect the leaf anatomy and leave most plant cells intact, while later instars significantly disrupt leaf tissues. Additionally, young larvae are ‘‘fluid-feeders’’ and feed on plant cell fluids resulting from the progression of the larvae through the lower layer of the leaf spongy parenchyma. They occupy a feeding niche clearly distinct from later instars that are ‘‘tissue-feeders’’. Hypermetamorphosis in P. blancardella most likely allows insects to cope with a confined nutritional space by partitioning the limited feeding resources, and may help leaf-miners to optimize their nutritio