Poplar Tree Response to Feeding by the Petiole Gall Aphid Pemphigus spyrothecae Pass

Changes in Biologically Active Compounds in Pinus sylvestris Needles after Lymantria monacha Outbreaks and Treatment with Foray 76B

Due to climate warming, the occurrence of Lymantria monacha outbreaks is predicted to become more frequent, causing repeated and severe damage to conifer trees. Currently, the most effective way to control the outbreaks is aerial spraying with the bioinsecticide Foray 76B. The present study aimed to determine the impact of both: (i) L. monacha outbreaks and (ii) treatment with Foray 76B on tree resistance through the synthesis of polyphenols (TPC), flavonoids (TFC), photosynthetic pigments (chlorophyll a and b, carotenoids), lipid peroxidation (MDA), and soluble sugars (TSS) in Pinus sylvestris needles. Samples were collected from visually healthy (control), damaged/untreated, and damaged/Foray 76B-treated plots in 2020 and 2021 (following year after the outbreaks). The results revealed that L. monacha outbreaks contributed to the increase in TPC by 34.1% in 2020 and 26.7% in 2021. TFC negatively correlated with TPC, resulting in 17.6% and 11.1% lower concentrations in L. monacha-damaged plots in 2020 and 2021, respectively. A decrease in MDA was found in the damaged plots in both 2020 and 2021 (10.2% and 23.3%, respectively), which was associated with the increased synthesis of photosynthetic pigments in 2021. The research results also showed that in the following year after the outbreaks, the increase in the synthesis of photosynthetic pigments was also affected by the treatment with Foray 76B. Moreover, the increase in the synthesis of TPC and photosynthetic pigments in the damaged plots in 2021 illustrates the ability of pines to keep an activated defense system to fight biotic stress. Meanwhile, a higher synthesis of photosynthetic pigments in Foray 76B-treated plots indicates a possible effect of the treatment on faster tree growth and forest recovery after L. monacha outbreaks.

Population Development of Alien Gall-Forming Aphid Tetraneura nigriabdominalis on Ulmus minor and Ulmus glabra

Tetraneura (Tetraneurella) nigriabdominalis (Sasaki, 1899) is a holocyclic and heteroecious species widely distributed throughout the world. Its primary hosts are various elm species, on which it forms galls. The results of this study complement those of previous research on the development of T. nigriabdominalis on primary hosts. Our research was conducted on two elm species, Ulmus minor and Ulmus glabra, at three locations and for three successive seasons between 2017 and 2019. Fundatrices hatched between 27 April and 12 May. The first galls were observed 6–8 days after the hatching date of the fundatrices. On average, there were 1–7.5 galls on one leaf. The highest abundances of T. nigriabdominalis galls were found in the medial and basal parts of the leaf blades. The fundatrices matured within 12–21 days after hatching and produced nymphs within 2–3 weeks. The fecundity of the fundatrices was influenced by the temperature in April, the size of the laminae, and the size of the galls. The females developing on U. glabra were more fecund (2–58 nymphs), whereas those developing on U. minor produced 1–29 nymphs. The winged migrants of the second generation appeared between late May and late June, when the first cracks on the galls were also observed. The entire development of two aphid generations on the primary host was temperature-dependent and lasted from four to almost six weeks. Our results show that U. glabra and U. minor are suitable hosts for T. nigriabdominalis. The development of aphids proceeded similarly on both tree species. Temperature, especially in April, significantly influenced the duration of individual developmental phases and the fecundity of fundatrices.

The Variation of Selected Physiological Parameters in Elm Leaves (Ulmus glabra Huds.) Infested by Gall Inducing Aphids

Three aphid species, Eriosoma ulmi (L.), Colopha compressa (Koch) and Tetraneura ulmi (L.) induce distinct gall morphotypes on Ulmus glabra Huds.; opened and closed galls. Because the trophic relationship of aphids and their galls shows that throughout the gall formation aphids can elicit multiple physiological regulations, we evaluated the changes of hydrogen peroxide content (H₂O₂), cytoplasmic membrane condition, expressed as electrolyte leakage (E_L) and concentration of thiobarbituric acid reactive substances (TBARS), as well as, the activity of catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) in gall tissues, as well as, in damaged and undamaged parts of galled leaves. All aphid species increased E_L from gall tissues and significantly upregulated APX activity in galls and galled leaves. Alterations in H₂O₂ and TBARS concentrations, as well as GPX and CAT activities, were aphid- and tissue-dependent. The development of pseudo- and closed galls on elm leaves did not have a clear effect on the direction and intensity of the host plant’s physiological response. The different modes of changes in H₂O₂, TBARS, CAT and GPX were found in true galls of C. compressa and T. ulmi. Generally, physiological alterations in new plant tissues were quite different compared to other tissues and could be considered beneficial to galling aphids.

Physiological response of Populus nigra 'Italica' to galling aphids feeding

Although gall-inducing aphids, namely Pemphigus bursarius (L.) and P. phenax Börner et Blunck, are widely known as serious pests for their secondary hosts (lettuce and carrot, respectively), the physiological mechanism of their gall induction on Populus L. trees still requires a better understanding. In this study, we compared physiological parameters, i.e. H₂ O₂ , electrolyte leakage (E_L ), MDA, APX and GPOD. Changes in physiological parameters were analysed in foliar tissues with galls and in the gall tissues themselves and compared to leaves without galls. Significantly higher H₂ O₂ levels were observed in P. phenax galls when compared to leaves with galls. In turn, the highest E_L of cells and MDA content was in P. bursarius galls. Other samples had lower or similar oxidative stress marker levels to leaves without galls. APX and GPOD had similar activity profiles in galls of both aphid species. Their activity decreased significantly in gall tissues, where it was even ten-fold lower than in leaves without galls. Data generated in this study indicate that patterns of the physiological features, e.g. ROS accumulation and cell membrane integrity, of Populus leaves with galls and galls alone depends on the gall-inducing aphid species. Where decreased APX and GPOD activity, especially in gall tissues, indicated a reduction in the antioxidant potential of these neoformed structures.

Reactive Oxygen Species in Plant Interactions With Aphids

Reactive oxygen species (ROS) such as hydrogen peroxide and superoxide are produced in plants in response to many biotic and abiotic stressors, and they can enhance stress adaptation in certain circumstances or mediate symptom development in others. The roles of ROS in plant-pathogen interactions have been extensively studied, but far less is known about their involvement in plant-insect interactions. A growing body of evidence, however, indicates that ROS accumulate in response to aphids, an economically damaging group of phloem-feeding insects. This review will cover the current state of knowledge about when, where, and how ROS accumulate in response to aphids, which salivary effectors modify ROS levels in plants, and how microbial associates influence ROS induction by aphids. We will also explore the potential adaptive significance of intra- and extracellular oxidative responses to aphid infestation in compatible and incompatible interactions and highlight knowledge gaps that deserve further exploration.