Aphids, the phloem sap feeders, probe into leaf tissues and activate a complex network of plant defence responses. Phytohormonal signaling plays a major role in this network; however, the dynamics of the signals spreading is yet to be clarified. Despite the growing knowledge about transcriptomic changes upon infestation, results often differ due to sampling, varying strongly between the tissues collected at the single feeding site, individual leaves, pooled infested leaves, or whole plant rosettes. This study focuses on activation of salicylic and jasmonic acid signals in Arabidopsis leaves during infestation by cabbage aphid (Brevicoryne brassicae) in high spatio-temporal resolution. We used genetically encoded fluorescent biosensors, histochemistry and qRT-PCR to precisely map activation of distinct branches of phytohormonal signaling. We found a rapid induction of salicylic and jasmonic acid signaling markers in cells surrounding stylet puncture, co-localizing with callose deposition. For both PR1 and JAZ10 we detected activation at 24 hpi, increasing and spreading along the veins until 72 hpi and, to a lesser extent, within the epidermal pavement cells. The SA signaling wave appeared in parallel with JA-associated, and continued to increase in time. Our results first show a local activation of SA- and JA-related responses after stylet penetration of Arabidopsis leaves and bring a detailed insight into the spatio-temporal complexity of plant defence activation during specialist aphid attack.
Over the course of three years (2016–2018), the effects of insecticides on stem-mining weevils [(Ceutorhynchus pallidactylus (Marsham, 1802), Ceutorhynchus napi (Gyllenhal, 1837)] were assessed under field conditions. The dates for spraying were determined on the basis of the recorded percentages of weevil females carrying mature eggs in their ovaries (timing I: the first females with mature eggs present in yellow water traps; timing II: more than 50% of the females with mature eggs present). Delaying the first spring insecticide application till timing II made it possible to combine the control of the stem weevil along with the control of the pollen beetle, Brassicogethes aeneus (Fabricius, 1775). However, the poor effectiveness of the tested insecticides on the stem-mining weevils, regardless of the date they were sprayed, indicates it is impossible to successfully control the insect pests with one insecticide application during the seasons with prolonged egg-laying periods.
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