Visual orientation in the greenhouse whitefly ( Trialeurodes vaporariorum Westwood, Hemiptera: Aleyrodidae) is the result of 9wavelength-specific behaviours9. Green-yellow elicits 9settling behaviour9 while ultraviolet (UV) radiation initiates 9migratory behaviour9. Electroretinograms of the photoreceptors9 spectral efficiency showed peaks in the green and the UV range and whitefly vision was said to be dichromatic. In order to study the visual behaviour of T. vaporariorum , nineteen narrow-bandwidth LEDs covering the UV-A and visible range were used in combination with light scattering acrylic glass screens in a small-scale choice arena under greenhouse conditions. Multiple-choice and dual-choice assays were performed, resulting in LED-based behavioural action spectra of settling (green) and migratory behaviour (UV). A potential inhibitory blue-green chromatic mechanism was studied by combining yellow with different blueish LEDs. Intensity dependencies were illustrated by changing LED intensities. Regarding the 9settling response9, highest attraction was achieved by a green LED with a centroid wavelength of 550 nm, while a blue LED with 469 nm proved to be most inhibitory. Behaviour was distinctly intensity dependent. 9Migratory behaviour9 was elicited the most by the UV LED with the shortest available wavelength of 373 nm. The results clearly prove the presence of a green and a yet undescribed blue sensitive photoreceptor and a blue-green opponent mechanism. Furthermore, empirical colour choice models were built and receptor peaks were estimated around 510 - 520 nm (green), 480 - 490 nm (blue) and 340 - 370 nm (UV). Consequently, Trialeurodes vaporariorum possesses a trichromatic receptor setup.

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Blue–green opponency and trichromatic vision in the greenhouse whitefly (Trialeurodes vaporariorum) explored using light emitting diodes

Summary Aphids secrete diverse repertoires of salivary effectors into host plant cells to promote infestation by modulating plant defence. The greenbug Schizaphis graminum is an important cereal aphid worldwide. However, the secreted effectors of S. graminum are still uncharacterized. Here, 76 salivary proteins were identified from the watery saliva of S. graminum using transcriptome and proteome analyses. Among them, a putative salivary effector Sg2204 was significantly up‐regulated during aphid feeding stages, and transient overexpression of Sg2204 in Nicotiana benthamiana inhibited cell death induced by BAX or INF1. Delivering Sg2204 into wheat via the type III secretion system of Pseudomonas fluorescens EtAnH suppressed pattern‐triggered immunity (PTI)‐associated callose deposition. The transcript levels of jasmonic acid (JA)‐ and salicylic acid (SA)‐associated defence genes of wheat were significantly down‐regulated, and the contents of both JA and SA were also significantly decreased after delivery of Sg2204 into wheat leaves. Additionally, feeding on wheat expressing Sg2204 significantly increased the weight and fecundity of S. graminum and promoted aphid phloem feeding. Sg2204 was efficiently silenced via spray‐based application of the nanocarrier‐mediated transdermal dsRNA delivery system. Moreover, Sg2204‐silenced aphids induced a stronger wheat defence response and resulted in negative impacts on aphid feeding behaviour, survival and fecundity. Silencing of Sg2204 homologues from four aphid species using nanocarrier‐delivered dsRNA also significantly reduced aphid performance on host plants. Thus, our study characterized the salivary effector Sg2204 of S. graminum involved in promoting host susceptibility by suppressing wheat defence, which can also be regarded as a promising RNAi target for aphid control.

The salivary effector protein Sg2204 in the greenbug Schizaphis graminum suppresses wheat defence and is essential for enabling aphid feeding on host plants

In the past, breeding for incorporation of insect pest resistance or tolerance into cultivars for use in integrated pest management schemes in oilseed rape/canola (Brassica napus) production has hardly ever been approached. This has been largely due to the broad availability of insecticides and the complexity of dealing with high-throughput phenotyping of insect performance and plant damage parameters. However, recent changes in the political framework in many countries demand future sustainable crop protection which makes breeding approaches for crop protection as a measure for pest insect control attractive again. At the same time, new camera-based tracking technologies, new knowledge-based genomic technologies and new scientific insights into the ecology of insect-Brassica interactions are becoming available. Here we discuss and prioritise promising breeding strategies and direct and indirect breeding targets, and their time-perspective for future realisation in integrated insect pest protection of oilseed rape. In conclusion, researchers and oilseed rape breeders can nowadays benefit from an array of new technologies which in combination will accelerate the development of improved oilseed rape cultivars with multiple insect pest resistances/tolerances in the near future. 

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Perspectives for integrated insect pest protection in oilseed rape breeding

Abstract BACKGROUND Plant resistance to insects can be reduced by crop domestication which means their wild ancestors could provide novel sources of resistance. Thus, crossing wild ancestors with domesticated crops can potentially enhance their resistance against insects. However, a prerequisite for this is identification of sources of resistance. Here, we investigated the response of three wild potato (Solanum stoloniferum Schltdl.) accessions and cultivated potato (Solanum tuberosum) to aphid (Myzus persicae Sulzer) herbivory. RESULTS Results revealed that there was a significant reduction in aphid survival and reproduction on wild potato accessions (CGN18333, CGN22718, CGN23072) compared to cultivated (Desiree) potato plants. A similar trend was observed in olfactometer bioassay; the wild accessions had a repellent effect on adult aphids. In contrast, among the tested wild potato accessions, the parasitoid Diaeretiella rapae (M'Intosh) was significantly attracted to volatiles from CGN18333. Volatile analysis showed that wild accessions emitted significantly more volatiles compared to cultivated potato. Principal component analysis (PCA) of volatile data revealed that the volatile profiles of wild and cultivated potato are dissimilar. β‐Bisabolene, (E)‐β‐farnesene, trans‐α‐bergamotene, d‐limonene, (E,E)‐4,8,12‐trimethyl‐1,3,7,11‐tridecatetraene (TMTT), and p‐cymen‐7‐ol were the main volatiles contributing to the emitted blends, suggesting possible involvement in the behavioural response of both M. persicae and D. rapae. CONCLUSION Our findings show that the tested wild accessions have the potential to be used to breed aphid‐resistant potatoes. This opens new opportunities to reduce the aphid damage and to enhance the recruitment of natural enemies. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/ps.6957

Wild potato ancestors as potential sources of resistance to the aphid Myzus persicae

Plants have evolved a number of different chemical defenses, covering nearly all classes of (secondary) metabolites, that represent a major barrier to herbivory: some are constitutive; others are induced after attacks from herbivores (HIPVs) and may elicit the attraction of predators and parasitoids. Here, we studied how the female solitary endoparasitoid Aphelinus varipes responds to plant and host aphid volatiles in a series of experiments on five commercially important vegetables that were either healthy or infested with the aphid Myzus persicae: chili pepper, eggplant, crown daisy, Chinese cabbage and cabbage. The results for the olfactory responses of A. varipes showed that the presence of M. persicae increased the attraction of the endoparasitoid to the infested plants. In a second experiment, volatiles from highly attractive and repellent plants were obtained via headspace collection to investigate volatiles from healthy and aphid-damaged plants. The results for the differences in volatile profiles in response to aphid infestation in chili pepper cultivar were dominated by the volatile blends, including α-pinene, decanal and phthalic acid, while in cabbage they were dominated by isophorone. Moreover, when HIPVs with different concentrations were compared, α-pinene at a dose rate of 100 ng/μL attracted more parasitoids, and the comparison was useful to understand the mechanisms of plant secondary volatiles during aphid infestation and to provide new resources to control this insect pest. Overall our study shows how HIPVs can bolster tritrophic interactions by enhancing the attractiveness of parasitoids.

/pdf/plant-volatiles-and-herbivore-induced-plant-volatiles-from-172exr3x.pdf

Plant Volatiles and Herbivore Induced Plant Volatiles from Chili Pepper Act as Attractant of the Aphid Parasitoid Aphelinus varipes (Hymenoptera: Aphelinidae)

The greenhouse whitefly Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) is a pest of a wide range of vegetable and ornamental crops in greenhouses around the world. Yellow sticky traps are highly attractive to flying adults and so are frequently used to monitor the pest. Our aim was to test whether changes in trap translucency or the addition of printed black patterns could increase the catch on yellow sticky traps in greenhouses. Field trials were carried out in commercial crops of strawberry and tomato under glass over three years. Reduced trap translucency increased trap catches by a factor of 1.5 to 7.0 and the catch increased significantly for both females and males. Spectrometer measurements showed that the increased catch was consistent with an increased landing stimulus from a colour opponency mechanism i.e. the ratio of energy from 500–640 nm to the energy from 300–500 nm. Printed black patterns increased trap catches on specific types of trap, by a factor of 1.4 to 2.3, and the catch increased significantly for both females and males. The patterns increased trap catch on moderately translucent traps, but decreased trap catch on less translucent traps. The evidence points to a contrast/edge effect of pattern, but laboratory experiments are needed to clarify this. Exploitation of these translucency and pattern effects could improve the efficacy of yellow traps for monitoring and mass trapping in crops.

/pdf/reduced-translucency-and-the-addition-of-black-patterns-37kyqf4gfh.pdf

Reduced translucency and the addition of black patterns increase the catch of the greenhouse whitefly, Trialeurodes vaporariorum, on yellow sticky traps.

There is a need to develop new ways of protecting plants against aphid attack. Here, we investigated the effect of a plant defence activator, cis-jasmone (CJ), in a range of cultivars of Brassica napus, Brassica rapa and Brassica oleracea. Plants were sprayed with cis-jasmone or blank formulation and then tested with peach potato aphids (Myzus persicae Sulzer) (Hemiptera: Aphididae) and their parasitoid Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae). CJ treated plants had significantly lower aphid settlement than control plants in a settlement bioassay. Conversely, in a foraging bioassay, D. rapae parasitoids spent a significantly longer time foraging on CJ treated plants. Our results reveal that CJ treatment makes plants less attractive to and less suitable for M. persicae but more attractive to D. rapae in a range of brassica cultivars. It is likely that these effects are due to changes in volatile emission indicating activation of defence and presence of conspecific competitors to aphids but presence of prey to parasitoids. Increases in volatile emission were found in CJ induced plants but varied with genotype. Among the synthetic volatile compounds that were induced in the headspace of CJ treated brassica cultivars, methyl isothiocyanate, methyl salicylate and cis-jasmone were most repellent to aphids. These results build on earlier studies in Arabidopsis and show that tritrophic interactions are influenced by CJ in a wide range of brassica germplasm. The implication is that CJ is a promising treatment that could be used in brassica crops as part of an integrated pest management system.

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Anca D. Covaci

Papers

Reduced translucency and the addition of black patterns increase the catch of the greenhouse whitefly, Trialeurodes vaporariorum, on yellow sticky traps.

Effects of cis-Jasmone Treatment of Brassicas on Interactions With Myzus persicae Aphids and Their Parasitoid Diaeretiella rapae.