Influence of selected plant amines on probing behaviour of bird cherry-oat aphid (Rhopalosiphum padi L.)

Functional analysis of Ornithine decarboxylase in manipulating the wing dimorphism in Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

The brown planthopper (BPH, Nilaparvata lugens), a major insect pest of rice, can make a shift in wing dimorphism to adapt to complex external environments. Our previous study showed that NlODC (Ornithine decarboxylase in N. lugens) was involved in wing dimorphism of the brown planthopper. Here, further experiments were conducted to reveal possible molecular mechanism of NlODC in manipulating the wing dimorphism. We found that the long-winged rate (LWR) of BPH was significantly reduced after RNAi of NlODC or injection of DFMO (D, L-α-Difluoromethylornithine), and LWR of males and females significantly decreased by 21.7% and 34.6%, respectively. Meanwhile, we also examined the contents of three polyamines under DFMO treatment and found that the contents of putrescine and spermidine were significantly lower compared to the control. After 3rd instar nymphs were injected with putrescine and spermidine, LWR was increased significantly in both cases, and putrescine was a little bit more effective, with 5.6% increase in males and 11.4% in females. Three days after injection of dsNlODC, injection of putrescine and spermidine rescued LWR to the normal levels. In the regulation of wing differentiation in BPH, NlODC mutually antagonistic to NlAkt may act through other signaling pathways rather than the classical insulin signaling pathway. This study illuminated a physiological function of an ODC gene involved in wing differentiation in insects, which could be a potential target for pest control.

Investigation of Metabolic Resistance to Soybean Aphid (Aphis glycines Matsumura) Feeding in Soybean Cultivars

Simple Summary

This project examined the interaction between soybean aphids and Ontario-grown soybean cultivars to determine which leaf metabolites were most associated with aphid resistance. Tolerance and resistance were determined by measuring the growth and reproduction of aphids and leaf feeding damage over 10-day and 4-week infestation periods. Chromatographic techniques were used for the analysis of legume-specific plant natural products and isoflavonoids, and high-resolution mass spectrometry was used for the identification of free amino acids in aphid-resistant, tolerant, and susceptible soybean cultivars. There was a low correlation between isoflavonoid leaf concentrations and aphid resistance in the soybean varieties studied; however, the aphid-resistant cultivars were determined to have lower free amino acid concentrations, indicating that lower nutrient quality could be responsible for the resistance observed. Identifying these cultivars is important for managing aphid populations and provides an additional tool for soybean integrated pest management.

Abstract

Soybean aphid (Aphis glycines) is a major soybean (Glycine max) herbivore pest in many soybean growing regions. High numbers of aphids on soybean can cause severe reductions in yield. The management of soybean aphids includes monitoring, insecticide applications when required, and the use of resistant cultivars. Soybean aphid-resistant soybean varieties are associated with genes that confer one or more categories of resistance to soybean aphids, including antibiosis (affects survival, growth, and fecundity), antixenosis (affects behaviour such as feeding), and tolerance (plant can withstand greater damage without economic loss). The genetic resistance of soybean to several herbivores has been associated with isoflavonoid phytoalexins; however, this correlation has not been observed in soybean varieties commonly grown in southern Ontario, Canada. Isoflavonoids in the leaves of 18 cultivars in the early growth stage were analyzed by HPLC and the concentration by fresh weight was used to rate the potential resistance to aphids. Greenhouse and growth cabinet trials determined that the cultivars with greater resistance to aphids were Harosoy 63 and OAC Avatar. The most susceptible cultivar was Maple Arrow, whereas Pagoda and Conrad were more tolerant to aphid feeding damage. Overall, there was a low correlation between the number of aphids per leaf, feeding damage, and leaf isoflavonoid levels. Metabolite profiling by high-resolution LC-MS determined that the most resistant cultivar had on average lower levels of certain free amino acids (Met, Tyr, and His) relative to the most susceptible cultivar. This suggests that within the tested cultivars, nutritional quality stimulates aphid feeding more than isoflavonoids negatively affect aphid feeding or growth. These findings provide a better understanding of soybean host plant resistance and suggest ways to improve soybean resistance to aphid feeding through the breeding or metabolic engineering of leaf metabolites.

Effect of Neuroterus quercusbaccarum (L.) galls on physiological and biochemical response of Quercus robur leaves

Gall formation is associated with multiple changes in plant cells, which still requires a better understanding. In this study, galls caused by sexual generation (♀♂) of Neuroterus quercusbaccarum (L.) (Hymenoptera: Cynipidae) on pedunculate oak trees (Quercus robur L.) were used as a model. Cytoplasmic membrane condition, concentration of hydrogen peroxide (H2O2), the activity of antioxidant enzymes and amino acid decarboxylase as well as chlorophyll fluorescence parameters were determined. Changes in physiological and biochemical parameters were analyzed in foliar tissues with galls and gall tissues themselves and compared to control. The presence of galls on oak leaves caused an increase of lipid peroxidation level. A significant decline in H2O2 and TBARS content with the reduction of guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) activity were observed in gall tissues. The activity amino acid decarboxylase, i.e., LDC, ODC and TyDC varied between samples, which may affect the content of amino acids. The presence of N. quercusbaccarum galls caused an insignificant increase of the chlorophylls, carotenoids and anthocyanin contents, while the content of pigments and their ratios in gall tissues was extremely low. Moreover, photosynthetic parameters (F0, Fm, Fv/Fm, Y, qP) were significantly decreased. Data generated in this study indicate that the development of N. quercusbaccarum galls on pedunculate oak leaves has a negative effect on host plant related to the disruption of cell membrane integrity, disturbance of photosynthesis and reduction of the antioxidant potential of the host plant.

The identification and expression analysis of candidate chemosensory genes in the bird cherry-oat aphid Rhopalosiphum padi (L.)

The bird cherry-oat aphid Rhopalosiphum padi (L.) is one of the most important wheat pests with polyphagia and autumn migrants. And, chemosensory genes were thought to play a key role in insect searching their hosts, food and mate. However, a systematic identification of the chemosensory genes in this pest has not been reported. Thus, in this study, we identified 14 odorant-binding proteins, nine chemosensory proteins, one sensory neuron membrane protein, 15 odorant receptors, 19 gustatory receptors and 16 ionotropic receptors from R. padi transcriptomes with a significantly similarity (E-value < 10-5) to known chemosensory genes in Acyrthosiphon pisum and Aphis gossypii. In addition, real-time quantitative polymerase chain reaction (RT-qPCR) was employed to determine the expression profiles of obtained genes. Among these obtained genes, we selected 23 chemosensory genes to analyze their expression patterns in different tissues, wing morphs and host plants. We found that except RpOBP1, RpOBP3, RpOBP4 and RpOBP5, the rest of the selected genes were highly expressed in the head with antennae compared with body without head and antennae. Besides that, the stimulation and depression of chemosensory genes by plant switch indicated that chemosensory genes might be involved in the plant suitability assessment. These results not only provide insights for the potential roles of chemosensory genes in plant search and perception of R. padi but also provide initial background information for the further research on the molecular mechanism of the polyphagia and autumn migrants of it. Furthermore, these chemosensory genes are also the candidate targets for pest management control in future.

The effect of Tetraneura ulmi L. galling process on the activity of amino acid decarboxylases and the content of biogenic amines in Siberian elm tissues

Tetraneura ulmi (L.), a member of Eriosomatinae subfamily, is one of the gall-forming aphids occurring on elms. Sap-sucking behaviour of founding mothers results in the formation of new plant organs. This study documents the changes in the content of plant biogenic amines (putrescine, cadaverine, spermidine, tryptamine, spermine and histamine) and key enzymes of their biosynthesis: lysine decarboxylase (LDC), tyrosine decarboxylase and ornithine decarboxylase (ODC) in galls and other parts of Siberian elm (Ulmus pumila L.) leaves during the galling process. The direction and intensity of these changes for particular amines and enzymes were dependent on the stage of gall development and part of the galling leaf. Generally, the amine content tended to increase in gall tissues during the 1st and 2nd period of the galling process and decreased in later phases. LDC and ODC activities were markedly enhanced, especially in gall tissues at the initial stage of the galling process.