Preference of aphids (Hemiptera : Aphididae) for lucerne, maize, soybean and wheat and their potential as prospective border crops for Potato virus Y management in seed potatoes

Aphid landing rates, species composition and abundance on lucerne (Medicago sativa), maize (Zea mays), soybean (Glycine max), wheat (Triticum aestivum) and potato (Solanum tuberosum) were determined in a small-scale field trial to identify potential crops as prospective border plants for seed potatoes to reduce the spread of Potato virus Y (PVY) in South Africa. Aphids were sampled using green bucket traps to estimate aphid landing rates, whereas leaf counts and sweep-netting were used to identify colonizing species. Of the 34 species or species groups collected with green bucket traps, 18 were previously known vectors of PVY. The most abundant vector species or species groups were Acyrthosiphon pisum, Macrosiphum euphorbiae, Metopolophium dirhodum, Myzus persicae, Rhopalosiphum padi and Sitobion spp. The only other species that occurred in high numbers, but whose vector status is unknown, were Acyrthosiphon kondoi and Tetraneura fusiformis. Landing patterns suggest that A. kondoi, A. pisum and M. dirhodum may be able to discriminate between plant species and select their preferred host plant, if available within a habitat patch, in the pre-alighting phase, whereas other species such as R. padi seemed less selective. Results on aphid landing together with colonization of the crops evaluated suggest that maize and wheat show the highest potential as possible crop border plants in regions where aphids colonizing Poaceae, and lucerne in regions where aphids colonizing Fabaceae are abundant. Soybean appears to be less suitable because cultivars with a high trichome density, which reduces colonization by aphids, are preferentially planted in South Africa.Potatoes South Africa (PSA), the University of Pretoria and a grant from the Technology and Human Resources for Industry Programme (THRIP) of the National Research Foundation of South Africa. (TP2005101300009). The research was undertaken as part of M.L. Fourie’s (Schröder) M.Sc. degree."http://www.journals.co.za/ej/ejour_ento.html2016-03-30am201

Visual cues and host-plant preference of the bird cherry-oat aphid, Rhopalosiphum padi (Hemiptera: Aphididae)

Alate aphids respond to short (UV) and long (green-yellow) wavelength stimuli during host-plant searching behaviour. Although many aphids are attracted to yellow, the bird cherry-oat aphid, Rhopalosiphum padi, is attracted to green. As part of identifying suitable plant species for crop border plants for seed potatoes, the attraction of R. padi to different shades of green in relation to differences in spectral reflectance of three cultivars of a non-host, potato, and two host-plant species, maize and wheat, were determined. Choice experiments were carried out under laboratory conditions to evaluate aphid landing preference for stimuli of different colours. Rhopalosiphum padi alates preferred to land on the colour targets with the highest reflectance. Significantly more alates landed on yellow and lime colour targets with a maximum wavelength reflectance of 46 % from 600-610 nm and 26 % from 525-531 nm, respectively. The peak light reflectance of the crop plants ranged between 12 % (potato; 532-555 nm) and 20 % (wheat; 537-553 nm). The results on aphid landing preference for different colour targets suggest that R. padi will land in higher numbers on the wheat plants, compared to potato, due to their higher peak percentage reflectance. In addition, the study indicates that the wavelength reflectance curves of plants can be used as a characteristic to select possible crop border plants when making choices between seemingly equally suitable plant species/cultivars.Potatoes South Africa (PSA), the Technology and Human Resources for Industry Programme (THRIP), the National Research Foundation (NRF) and the University of Pretoria.http://www.journals.co.za/ej/ejour_ento.html2016-07-30am201

Olfactory responses of Rhopalosiphum padi to three maize, potato, and wheat cultivars and the selection of prospective crop border plants

Understanding host plant volatile – aphid interactions can facilitate the selection of crop border plants as a strategy to reduce plant virus incidence in crops. Crop border plant species with attractive odours could be used to attract aphids into the border crop and away from the main crop. As different cultivars of the same crop can vary in their olfactory attractiveness to aphids, selecting an attractive cultivar as a border crop is important to increase aphid landing rates. This study evaluated olfactory responses of the bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), to three cultivars each of maize [Zea mays L. (Poaceae)], potato [Solanum tuberosum L. (Solanaceae)], and wheat [Triticumaestivum L. (Poaceae)] with the aim of selecting an attractive crop border plant to reduce the incidence of the non-persistent Potato virus Y [PVY (Potyviridae)] in seed potatoes. Volatiles emitted by the crop cultivars were collected and identified using coupled gas chromatography/ mass spectrometry. Quantitative and qualitative differences were found among cultivars. Behavioural responses of alate R. padi to odours of the cultivars and synthetic compounds identified from the plants were determined with a four-arm olfactometer. Rhopalosiphum padi was attracted to odours emitted from maize cultivar 6Q-121, but did not respond to odours from the remaining eight crop cultivars. Volatile compounds from maize and wheat cultivars that elicited a behavioural response from R. padi and contributed to differences in plant volatile profiles included (Z)-3-hexenyl acetate (attractant) and a-farnesene, (E)-2-hexenal, indole, and (3E,7E)-4,8, 12-trimethyltrideca-1,3,7,11-tetraene (TMTT) (repellents). We conclude that maize cv. 6Q-121 is potentially suitable as a crop border plant based on the behavioural response of R. padi to the olfactory cues emitted by this cultivar. The findings provide insight into selecting crop cultivars capable of attracting R. padi to crop border plants.National Research Foundation (NRF), the University of Pretoria and the Swedish Foundation for Strategic Environmental Research (MISTRA) through the Plant-ComMistra programme. MISTRA and Carl Tryggers Stiftelse.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1570-74582016-11-30hb201

Reproductive compatibility of a newly imported Australian population of the biocontrol agent Anaphes nitens with an existing South African population

Introductions of natural enemies in classical biocontrol programs potentially cause genetic bottlenecks which can be detrimental for biocontrol. This can be mitigated by introducing multiple populations of a natural enemy, but thorough pre-release testing is needed to ensure compatibility. In this study compatibility between an established population of Anaphes nitens in South Africa and a newly imported A. nitens population from Australia was tested. Anaphes nitens is an egg parasitoid of Gonipterus sp. n. 2, an important pest in Eucalyptus plantations. South African and Australian A. nitens lineages were compared to two admixed lineages, which were reared from the F0 to the F2 generation. No differences were found in the proportion of replicates producing offspring overall, or female offspring specifically, indicating there was no sexual isolation between the populations. The typical symptoms of cytoplasmic incompatibility in haplodiploids, namely male biased sex ratios, were not observed. The lack of significant differences in fecundity and development time between the lineages suggested that there was no hybrid vigour or outbreeding depression. We conclude that a field release of the imported A. nitens population poses a low risk of disrupting the existing biocontrol program due to reproductive barriers or outbreeding depression. Whether there is a benefit of adding the newly imported Australian A. nitens population to the existing biocontrol system in South Africa needs to be studied further, for example by performing a field release combined with post-release assessments for determining establishment and spread.https://www.elsevier.com/locate/ybconhj2024BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant PathologyZoology and EntomologySDG-15:Life on lan

Distribution of Gonipterus species and their egg parasitoids in Australia : implications for biological control

Gonipterus species are pests of Eucalyptus plantations worldwide. The egg parasitoid wasp Anaphes nitens is used in many countries for the biological control of Gonipterus spp. Recent taxonomic studies have shown that the three invasive Gonipterus spp., which were previously considered as G. scutellatus, form part of a cryptic species complex. These taxonomic changes have implications for the biological control of Gonipterus spp. The aims of this study were to understand the species composition and distribution of Gonipterus spp. and their egg parasitoids in Australia. Gonipterus spp. adults and egg capsules were collected in south-eastern Australia and Tasmania. Adult Gonipterus were identified using morphology and DNA barcoding. Parasitoids were reared from Gonipterus egg capsules and identified. Thirteen Gonipterus species were collected: twelve species were found on the Australian mainland and one species in Tasmania. These included three described species, four previously recognized but undescribed species, two undescribed species and four unidentified species. Five egg parasitoid species that attack Gonipterus spp. were identified. Anaphes nitens, Centrodora damoni and Euderus sp. were identified on the Australian mainland and A. tasmaniae and A. inexpectatus were identified in Tasmania. The results from this study will contribute to the improvement of Gonipterus biological control in the future.An Australia Awards Fellowship (Australian Department of Foreign Affairs and Trade), the University of the Sunshine Coast, South African Department of Science and Technology—Sector Specific Innovation Fund, the Tree-Protection Cooperative Programme (TPCP) at the Forestry and Agricultural Biotechnology Institute (FABI) of the University of Pretoria, Forest and Wood Products of Australia, and the Biological Control of Eucalypt Pests Alliance (BiCEP).https://www.mdpi.com/journal/forestsam2022BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant PathologyZoology and Entomolog

The Second Transmembrane Domain of P2X7 Contributes to Dilated Pore Formation

Activation of the purinergic receptor P2X7 leads to the cellular permeability of low molecular weight cations. To determine which domains of P2X7 are necessary for this permeability, we exchanged either the C-terminus or portions of the second transmembrane domain (TM2) with those in P2X1 or P2X4. Replacement of the C-terminus of P2X7 with either P2X1 or P2X4 prevented surface expression of the chimeric receptor. Similarly, chimeric P2X7 containing TM2 from P2X1 or P2X4 had reduced surface expression and no permeability to cationic dyes. Exchanging the N-terminal 10 residues or C-terminal 14 residues of the P2X7 TM2 with the corresponding region of P2X1 TM2 partially restored surface expression and limited pore permeability. To further probe TM2 structure, we replaced single residues in P2X7 TM2 with those in P2X1 or P2X4. We identified multiple substitutions that drastically changed pore permeability without altering surface expression. Three substitutions (Q332P, Y336T, and Y343L) individually reduced pore formation as indicated by decreased dye uptake and also reduced membrane blebbing in response to ATP exposure. Three others substitutions, V335T, S342G, and S342A each enhanced dye uptake, membrane blebbing and cell death. Our results demonstrate a critical role for the TM2 domain of P2X7 in receptor function, and provide a structural basis for differences between purinergic receptors. © 2013 Sun et al

Secondary organic aerosol production from local emissions dominates the organic aerosol budget over Seoul, South Korea, during KORUS-AQ

Organic aerosol (OA) is an important fraction of submicron aerosols. However, it is challenging to predict and attribute the specific organic compounds and sources that lead to observed OA loadings, largely due to contributions from secondary production. This is especially true for megacities surrounded by numerous regional sources that create an OA background. Here, we utilize in situ gas and aerosol observations collected on board the NASA DC-8 during the NASA–NIER KORUS-AQ (Korea–United States Air Quality) campaign to investigate the sources and hydrocarbon precursors that led to the secondary OA (SOA) production observed over Seoul. First, we investigate the contribution of transported OA to total loadings observed over Seoul by using observations over the Yellow Sea coupled to FLEXPART Lagrangian simulations. During KORUS-AQ, the average OA loading advected into Seoul was ∼1–3 µg sm−3. Second, taking this background into account, the dilution-corrected SOA concentration observed over Seoul was ∼140 µgsm−3ppmv−1 at 0.5 equivalent photochemical days. This value is at the high end of what has been observed in other megacities around the world (20–70 µgsm−3ppmv−1 at 0.5 equivalent days). For the average OA concentration observed over Seoul (13 µg sm−3), it is clear that production of SOA from locally emitted precursors is the major source in the region. The importance of local SOA production was supported by the following observations. (1) FLEXPART source contribution calculations indicate any hydrocarbons with a lifetime of less than 1 day, which are shown to dominate the observed SOA production, mainly originate from South Korea. (2) SOA correlated strongly with other secondary photochemical species, including short-lived species (formaldehyde, peroxy acetyl nitrate, sum of acyl peroxy nitrates, dihydroxytoluene, and nitrate aerosol). (3) Results from an airborne oxidation flow reactor (OFR), flown for the first time, show a factor of 4.5 increase in potential SOA concentrations over Seoul versus over the Yellow Sea, a region where background air masses that are advected into Seoul can be measured. (4) Box model simulations reproduce SOA observed over Seoul within 11 % on average and suggest that short-lived hydrocarbons (i.e., xylenes, trimethylbenzenes, and semi-volatile and intermediate-volatility compounds) were the main SOA precursors over Seoul. Toluene alone contributes 9 % of the modeled SOA over Seoul. Finally, along with these results, we use the metric ΔOA/ΔCO2 to examine the amount of OA produced per fuel consumed in a megacity, which shows less variability across the world than ΔOA∕ΔCO

Chemical transport models often underestimate aerosol acidity in remote regions of the atmosphere

The inorganic fraction of fine particles affects numerous physicochemical processes in the atmosphere. However, there is large uncertainty in its burden and composition due to limited global measurements. Here, we present observations from eleven different aircraft campaigns from around the globe and investigate how aerosol pH and ammonium balance change from polluted to remote regions, such as over the oceans. Both parameters show increasing acidity with remoteness, at all altitudes, with pH decreasing from about 3 to about −1 and ammonium balance decreasing from almost 1 to nearly 0. We compare these observations against nine widely used chemical transport models and find that the simulations show more scatter (generally R2 \u3c 0.50) and typically predict less acidic aerosol in the most remote regions. These differences in observations and predictions are likely to result in underestimating the model-predicted direct radiative cooling effect for sulfate, nitrate, and ammonium aerosol by 15–39%