Aphid Populations Research Articles

Model fitting of the seasonal population dynamics of the soybean aphid, Aphis glycines Matsumura, in the field

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is one of the greatest threats to soybean production, and both trend analysis and periodic analysis of its population dynamics are important for integrated pest management (IPM). Based on systematically investigating soybean aphid populations in the field from 2018 to 2020, this study adopted the inverse logistic model for the first time, and combined it with the classical logistic model to describe the changes in seasonal population abundance from colonization to extinction in the field. Then, the increasing and decreasing phases of the population fluctuation were divided by calculating the inflection points of the models, which exhibited distinct seasonal trends of the soybean aphid populations in each year. In addition, multifactor logistic models were then established for the first time, in which the abundance of soybean aphids in the field changed with time and relevant environmental conditions. This model enabled the prediction of instantaneous aphid abundance at a given time based on relevant meteorological data. Taken as a whole, the successful approaches implemented in this study could be used to build a theoretical framework for practical IPM strategies for controlling soybean aphids.

Differential effects of weather, plant phenology and predators on the seasonal variation of aphids on cabbage.

The aphids Lipaphis erysimi pseudobrassicae (Davis) and Myzus persicae (Sulzer) pose serious threats to the production of cruciferous crops in the tropics. Understanding their population dynamics is important for developing integrated pest management programmes to minimize their damage to crops. This study investigated the effects of climatic factors, natural enemies and plant age on the population dynamics of these pests. The population density of aphids and their natural enemies in 20 cabbage plants, and weather conditions were monitored for five cropping seasons from 2019 to 2021 in two agroecological zones of Ghana (Coastal Savannah and Deciduous Forest zones). The highest population density of L.e pseudobrassicae was recorded in January (dry season) in both agroecological zones, while the highest population density for M.persicae occurred in September (minor rainy season) and August (dry spell) in the Coastal Savannah and Deciduous Forest zones, respectively. The highest aphid densities were noted to occur during periods with low relative humidity and low rainfall. The population density of L.e.pseudobrassicae was significantly negatively related to plant age, air temperature and relative humidity, and positively related to syrphids (Paragus borbonicus) and spiders in the Coastal Savannah zone, while in the Deciduous Forest zone, it was significantly positively related to coccinellids. On the other hand, M.persicae population density was significantly positively related to syrphids and coccinellids in the Deciduous Forest zone. Rainfall negatively affected syrphids in the Coastal Savannah zone, while air temperature positively affected syrphids and negatively affected spiders in the Deciduous Forest zone. Coccinellids had a significant positive relationship with relative humidity in the Deciduous Forest zone. This study provides important insights into the key factors that regulate aphid population densities on cabbage and will support development of timely interventions to manage these pests.

Phenotypic specialization of the pea aphid in its southern limit of distribution

The success of biological invasions ultimately relies on phenotypic traits of the invasive species. Aphids, which include many important pests worldwide, may have been successful invading new environments partly because they can maximize reproductive output by becoming parthenogenetic and losing the sexual phase of their reproductive cycle. However, invasive populations of aphids invading wide ranges can face contrasting environmental conditions and requiring different phenotypic strategies. Besides transitions in their reproductive cycle, it is only partially known which phenotypic traits might be associated to the invasion success of aphid populations in extended novel ranges. Here, we used four genotypes of the pea aphid Acyrthosiphon pisum from two localities in Chile to test for phenotypic specialization that might explain their establishment and spread in habitats exhibiting contrasting environmental conditions. We show that lineages living at a higher latitude with low temperatures show, in addition to facultative sexual reproduction, smaller body sizes, lower metabolic rates and a higher tolerance to the cold than the obligate asexual lineages living in a mild weather, at the expense of fecundity. Conversely, at higher temperatures only asexual lineages were found, which exhibit larger body sizes, higher reproductive outputs and consequently enhanced demographic ability. As a result, in conjunction with the reproductive mode, lineage specialization in physiological and life-history traits could be taken into account as an important strategy for populations of pea aphid to effectively invade extended novel ranges comprising different climatic conditions.

Diversity of endosymbiotic bacteria in the pea aphid (Acyrthosiphon pisum) on alfalfa in Chile

Facultative bacterial endosymbionts are prevalent in aphid pest species and key organisms for the rapid adaptation to changing environment conditions under agricultural management. Facultative endosymbiont interactions allow beneficial phenotypes of insect hosts, providing resistance against natural enemies, fungal infections as well as enhanced resistance to thermal conditions, among others. These interactions have been highlighted as important modulators in the evolution of aphid defenses, being a key aspect for the invasive potential of aphids as pests. In this study, we have examined the bacterial community diversity associated to the pea aphid Acyrthosiphon pisum on alfalfa (Medicago sativa L.) crops in Central Chile by determining the presence and abundance of the seven most common facultative endosymbionts reported for aphid species, including: Hamiltonella defensa, Regiella insecticola, Serratia symbiotica, Spiroplasma sp., Rickettsia sp., Rickettsiella viridis and Fukatsuia symbiotica (or pea aphid X-type symbiont’ PAXS), using a PCR-based approach across species-specific primers, in 16 alfalfa fields during the Chilean spring in the Maule Region. We reported six of the seven endosymbiont species studied, observing a high frequency of infected aphids being the endosymbiont H. defensa, the most predominant among the aphid populations in the different alfalfa fields studied. As H. defensa has been extensively studied in its defensive role to parasitoids, we discuss implications for biological control of this aphid pests. We also discuss the absence of a relevant defensive endosymbiont such as F. symbiotica in the Chilean pea aphid populations and potential implications for the success of the pea aphid biological control program.

Predicting the incidence and severity of wheat aphids and development of a web-enabled forewarning system in India

Aim: Forecasting the incidence and severity of aphids, the major insect pest of wheat, is expected to significantly help in their management. In the present study, a set of weather-based models were developed to predict the timing and severity of Rhopalosiphum maidis infestation at Ludhiana falling under the North Western Plain Zone and R. padi at Niphad in the Peninsular Zone of India. Methodology: The weather indices-based regression models for two locations, Ludhiana and Niphad, were developed using the aphid population and weather data gathered over eight years (2006–14), and the models' predictive accuracy was successfully tested over four additional years (2014-18). The developed statistical models were transformed into three-tier architecture, web-based system, i.e. Presentation, application and data tier for dissemination of information. Results: The developed models can predict the crop’s age - when aphids first colonize the plants, when the aphid population attains the peak and the information about the peak intensity of the aphid population. For predicting the crop’s age at which population peaked at Ludhiana, the weighted interaction of the relative humidity (RH) in the evening and the number of hours of sunshine (NHS) along with the weighted interaction of minimum temperature and RH (morning) were important parameters while, at Niphad, the weighted NHS and the interaction of RH (morning and evening) were important. Likewise, for predicting the maximum aphid population at Ludhiana, the weighted interaction of minimum temperature and RH (morning) were important, while at Niphad, the key parameters were the weighted interaction of RH (evening) with the NHS. Interpretation: A prototype system developed to forecast the location-specific (Ludhiana and Niphad) infestation of wheat crops by aphids is expected to facilitate aphid management through an accurate forewarning at the locations.

Volatile interactions between specific undamaged barley cultivars affect aphid feeding behavior and performance

Recent studies have demonstrated that cultivar mixtures can reduce aphid plant acceptance and population development. It is still unknown as to which underlying mechanisms may contribute to this phenomenon. We investigated the effects of volatile interactions between undamaged barley cultivars on aphid feeding behavior and performance in the laboratory. Spring barley (Hordeum vulgare L.) cultivar Salome was exposed to volatiles from Fairytale (SeF), Anakin (SeA), or clean air (Se0). We used an electrical penetration graph to test the effect of exposure to neighbor volatiles on the feeding behavior and performance of bird cherry-oat aphids (Rhopalosiphum padi L.). We also assessed aphid relative growth rate, intrinsic rate of increase, and development time on exposed and unexposed Salome plants. Aphids spent significantly longer time on epidermis and mesophyll plant tissues on SeF than Se0, and no difference was observed between SeA and Se0. Significant decreases in the duration of phloem ingestion and phloem sustained ingestion were recorded in SeF showing that volatile-induced effects cause difficulty for aphids to feed. However, no differences in these variables were detected between SeA and Se0. We also observed reduced aphid relative growth rate and intrinsic rate of increase on SeF compared to Se0 and SeA. Our study demonstrated that, in a specific combination, exposure of one barley cultivar to volatiles from another one can change aphid feeding behavior and performance, probably due to changes in host plant properties/quality. Our results provide an insightful explanation of mechanisms responsible for the reduced aphid population development previously observed in the field.

Translocation of Loline Alkaloids in Epichloë-Infected Cereal and Pasture Grasses: What the Insects Tell Us.

Aphids are major pests of cereal and pasture grasses throughout the world, vectoring disease and reducing plant production. There are few control options other than insecticides. Epichloë endophytes that produce loline alkaloids in their hosts provide a possible mechanism of control, with both meadow fescue and tall fescue naturally infected with loline-producing endophytes showing a resistance to Rhopalosiphum padi. We screened Elymus spp. naturally infected with endophytes that produced loline alkaloids at concentrations known to affect aphids on fescue but found no effect on these insects infesting Elymus. A synthetic loline-producing endophyte association with rye also had no effect on the aphids. After hypothesizing that the lolines were being translocated in the xylem in Elymus and rye rather than the phloem, we tested the rye and meadow fescue infected with loline-producing endophytes against a xylem feeding spittlebug. The endophyte in rye inhibited the feeding of the insect and reduced its survival, whereas the endophyte-infected meadow fescue had no effect on the spittlebug but reduced the number of aphids. Lolines applied to the potting medium of endophyte-free and endophyte-infected rye, ryegrass, and tall fescue resulted in a decrease in the aphid populations on the endophyte-free pasture grasses relative to the untreated controls but had no effect on aphid numbers on the rye. We tentatively conclude that lolines, produced in both natural and synthetic association with Elymus and rye, are partitioned in the xylem rather than the phloem, where they are inaccessible to aphids.

Analysis of the Genetic Diversity of Two Rhopalosiphum Species from China and Europe Based on Nuclear and Mitochondrial Genes.

Population genetic studies can reveal clues about the evolution of adaptive strategies of aphid species in agroecosystems and demonstrate the influence of environmental factors on the genetic diversity and gene flow among aphid populations. To investigate the genetic diversity of two Rhopalosiphum aphid species from different geographical regions, 32 populations (n = 535) of the bird cherry-oat aphid (Rhopalosiphum padi Linnaeus) and 38 populations (n = 808) of the corn leaf aphid (Rhopalosiphum maidis Fitch) from China and Europe were analyzed using one nuclear (elongation factor-1 alpha) and two mitochondrial (cytochrome oxidase I and II) genes. Based on the COI-COII sequencing, two obvious clades between Chinese and European populations and a low level of gene flow (Nm = 0.15) were detected in R. padi, while no geographical-associated genetic variation was found for EF-1α in this species. All genes in R. maidis had low genetic variation, indicating a high level of gene flow (Nm = 5.31 of COI-COII and Nm = 2.89 of EF-1α). Based on the mitochondrial result of R. padi, we concluded that the long distance between China and Europe may be interrupting the gene flow. The discordant results of nuclear gene analyses in R. padi may be due to the slower evolution of nuclear genes compared to mitochondrial genes. The gene exchange may occur gradually with the potential for continuous migration of the aphid. This study facilitates the design of control strategies for these pests.

MANAGEMENT OF APHID, LIPAPHIS ERYSIMI (KALTENBACH) (HOMOPTERA: APHIDIDAE) IN CANOLA (BRASSICA NAPUS L.) CROP USING NITROGENOUS FERTILIZERS AND SYNTHETIC INSECTICIDES

Field experiment was conducted at the farm of Faculty of Agriculture, GomalUniversity, Dera Ismail Khan to determine integrated effect of nitrogenous fertilizer and syntheticinsecticides on aphid, Lipaphis erysimi (Kaltenbach) (Homoptera: Aphididae) population in canolacrop during 2010-11. Results showed that tested insecticides significantly reduced aphid populationcompared to control. Minimum (8.67aphids) were recorded after 3rd week of treatment with karate 2.5EC (625ml.ha-1) using medium dose (58kg.ha-1) of nitrogen fertilizer. The same treatment also provided maximum (1246.91kg.ha1) grains yield. It was concluded from the present studies that testedlevels of nitrogen fertilizer had no effect on aphid population, while synthetic insecticides significantlyreduced pest infestation.

Cotton Aphid (Hemiptera: Aphididae) Resistance to Afidopyropen in Xinjiang Region, China

Abstract Concentration-mortality response bioassays were conducted in 2021 to define the toxicity of afidopyropen to field populations of cotton aphids, Aphis gossypii Glover (Hemiptera: Aphididae), in Xinjiang region, China. Levels of activity of selected enzymes also were measured. Varying levels of resistance to afidopyropen were detected among aphids from nine major cotton-growing areas in the region. Higher resistance levels were detected in aphids collected from Tumshuk, Alar, and Kurle, with resistance ratios of 4.570, 2.058, and 1.565, respectively. Lower resistance ratios of 0.506, 0.632, and 0.775 were detected in aphids collected from Yinli, Wujiaqu, and Hami, respectively. Biochemical assays showed a highly significant positive correlation of the detoxifying enzymes carboxylesterase and multifunctional oxidase with the level of tolerance, with enzyme activity increasing with the level of tolerance. Glutathione S-transferases and acetylcholinesterase activity in field-collected aphids differed significantly from laboratory colony populations, but their activity did not differ among the field populations. We concluded that cotton aphids in major cotton areas of Xinjiang have not yet developed resistance to afidopyropen and remain sensitive to afidopyropen as indicated by resistance ratios of <5; however, resistance of cotton aphids to afidopyropen in southern Xinjiang is higher than that detected in cotton aphid populations in northern Xinjiang.

Bioefficacy of different insecticides against pomegranate insect pests and their impact on natural enemies

A field experiment was conducted during rabi 2021-22 and 2022-23 at Horticulture Research and Extension Centre, Vijayapur, Karnataka, India, to evaluate the bioefficacy of different insecticides against pomegranate insect pests and their impact on natural enemies. During 2021-22, Cyantraniliprole 10.26% OD @ 70 g.a.i/ha recorded significantly lowest population of aphids (10.42 and 1.91 per 5cm twig), and thrips (6.33 and 1.22 per 5cm twig) at 7 days after imposition of treatment during first and second spray, respectively. Further, Cyantraniliprole 10.26% OD @ 70g.a.i/ha recorded the lowest fruit damage (6.67%) by pomegranate fruit borer and the highest damage reduction over control (84.53%) on fruits. Imidacloprid 17.8 % SL @ 71.8 g.a.i/ha was next best with higher population reduction over control in different pests viz., aphids (91.89%), thrips (91.24%). However, Emamectin benzoate 5% SG @ 220g.a.i/ha recorded lower fruit damage (7.11%) and higher reduction over control (83.51%). Cyantraniliprole 10.26% OD @ 70 g.a.i/ha was also found to be safer for natural enemies. At harvest, Cyantraniliprole 10.26% OD @ 70 g.a.i/ha recorded the highest yield (13.21 t/ha), followed by, Imidacloprid 17.8 % SL @ 71.8 g.a.i/ha (12.97 t/ha). A similar trend was observed during 2022-23 for pest control and the impact of different insecticides on natural enemies.

Prediction Dynamics in Cotton Aphid Using Unmanned Aerial Vehicle Multispectral Images and Vegetation Indices

Cotton harvest can be increased by having real-time information on the state of cotton aphid populations. However, traditional cotton aphid monitoring relies on ground sample methods supported by models such as linear regression, resulting in low forecast accuracy. Therefore, this paper purposes to enhance the precision of the remote sensing prediction model by investigating the cotton aphid prediction model construction approach. We explored the effectiveness of the XGBoost algorithm combined with the GWO algorithm and SVR method for cotton aphid prediction relying on vegetation indices derived from UAV multispectral photography. Originally, 12 indices related to cotton aphids were calculated by UAV multispectral reflectance. Additionally, the optimal index combination for pest prediction was determined utilizing analysis of correction and two-way ANOVA, combined with the XGBoost algorithm. Furthermore, a pest prevalence prediction model for cotton aphids was constructed via the SVR methodology associated with the optimal catalog combination, and the model was optimized using the GWO algorithm. Compared with the seven algorithms, experimental results demonstrate that the MSE and MAE of the XGBoost-GWO-SVR model are reduced by 90.20% and 70.36% (SVR), 90.14% and 70.26% (XGBoost-SVR), 7.47% and 0.14% (XGBoost-GA-SVR), 5.80% and 0.11% (XGBoost-PSO-SVR), 12.06% and 58.95% (LR), and 84.77% and 89.22% (BPNN), whereas the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> is increased by 22.5% (SVR and XGBoost-SVR), 0.3% (LR), and 12.51% (BPNN). The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> of the prediction model of XGBoost-SVR combined with GWO, PSO, and GA is not significantly different. Among these models, the XGBoost-GWO-SVR obtained the highest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> of 0.980 and the lowest MAE of 2.838.

Population dynamics of walnut aphid, Chromaphis juglandicola Kaltenbach, 1843 (Hemiptera: Aphididae) on Juglans regia (Walnut) in Kashmir

Regarded as one of the economically important crops of Kashmir, walnut trees are vulnerable to insect pests and diseases leading to great economic losses every year, thus to have knowledge about various factors that leads to it, is indispensable. The objective of the present study was to evaluate the population dynamics in terms of abundance and distribution of Chromaphis juglandicola in response to biotic and abiotic factors. Sites were monitored for two years from January 2017 to December 2018, in which five trees were randomly selected from two sites and each site was visited fortnightly. The counted collected specimens were identified and sampling protocol was established by seasonal richness peaks. The data depicted that C. juglandicola showed definite seasonal trend with highest population in summer and lowest in autumn with peak population in the month of June. Further, it was observed aphidophagous coccinellids also played a significant role in controlling aphid population. Six beetles were reported during two years of study out of which Calvia punctata and Harmonia diamadata were most abundant.

Aphids and Citrus responses to excessive nitrogen fertilization

The aim of this study was to assess the effect of an excessive nitrogen mineral fertilizer on the vegetative growth of Citrus as well as on the densities and population dynamics of the main aphid species Aphis spiraecola Patch (Hemiptera, Aphididae). Two trials were conducted on clementine trees, Citrus clementine Hort. ex Tan. in 2016 and 2017. The quantities of nitrogen delivered varied from no nitrogen (control) to the triple recommended dose of nitrogen (3ARD) in a complete randomized block design. Results showed that all vegetative growth parameters evaluated for the clementine trees responded positively to the amount of nitrogen supplied. The highest values were obtained with the highest N doses in both years. A positive response also was observed for aphids for all doses of N even the lowest, with densities increasing proportionally to N inputs. The highest dose (3ARD) increased aphid populations by 3 times compared to the control. The aphid dynamics differed between the two years, probably under the influence of other factors such as rainfall. Thus, too much nitrogen should be avoided in Citrus orchards. Aphid management cannot be separated from the management of fertilization, as this agronomic practice would maintain aphid densities at acceptable levels without the need for repeated insecticide applications.

Seasonal incidence and effect of abiotic factors on population dynamics of major insect pests on Brinjal crop

Experiment was carried out on Seasonal incidence and effect of abiotic factors on population dynamics of major insect pests on Brinjal (Solanum melongena L.) at College Farm, N. M. College of Agriculture, Navsari Agricultural University, Navsari during summer-2020. The results revealed that incidence of shoot borer infestation on shoot was commenced from second week of March (11th SMW) to third week of May (21st SMW) while, infestation of fruit damage was noticed at first picking of the brinjal fruit in the first week of April (14th SMW) with maximum in fourth week of May (21st SMW). Shoot and fruit borer infestation exhibited significant and positive correlation with maximum temperature (r= 0.8129) and minimum temperature (r= 0.8444) and wind velocity (r= 0.5871), respectively. Whitefly population was started from second week of February (9th SMW) with 0.93 whitefly per leaf, increased gradually to reach its peak in the last week of April, i.e.17th SMW (15.95 whiteflies/leaf) and positively and significantly correlated with and maximum temperature (r= 0.8062). The jassid infestation started from first week of March, i.e. 10th SMW (0.34 jassids/ leaf), initially increased slowly and reached to its peak level (11.89 jassids/leaf) at last week of April (17th SMW) and positively and significantly correlated with maximum (r= 0.7202) and minimum (r= 0.5712) temperatures. Aphid population started from the first week of March (10th SMW) with a minimum level of 0.60 aphids/leaf, increased slowly and reached to its peak level (5.04 aphids/leaf) at third week of April (16th SMW) and exhibited positive and significant correlation with maximum temperature (r= 0.7849).

Genome-wide studies of PAL genes in sorghum and their responses to aphid infestation

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.25) plays a crucial role in plant adaptation to biotic and abiotic stresses. However, the current knowledge about PAL proteins in sorghum is essentially lacking. Thus, in this study we aimed to analyze the PAL family genes in sorghum using a genome-wide approach and to explore the role of PAL genes in host plant resistance to aphids via SA-mediated defense signaling. Here, we report gene structural features of 8 PAL (SbPAL) genes in sorghum (Sorghum bicolor), their phylogeny, protein motifs and promoter analysis. Furthermore, we demonstrated that the SbPAL genes were induced by sugarcane aphid (SCA) infestation and SbPAL exhibited differential gene expression in susceptible and resistant genotypes. PAL activity assays further validated upregulated expression of the SbPAL genes in a resistant genotype. In addition, exogenous application of SA reduced plant damage and suppressed aphid population growth and fecundity in susceptible genotype, suggesting that those SbPAL genes act as positive regulator of the SA-mediated defense signaling pathway to combat aphid pests in sorghum. This study provides insights for further examination of the defense role of PAL in sorghum against other pests and pathogens.

Lethal impacts of insecticides and miticides on three agriculturally important aphid parasitoids

Globally, agricultural industries are contending with escalating insecticide resistance evolution among a number of arthropod pests. The Australian grains industry is no exception, with the indiscriminate use of broad-spectrum insecticides contributing to the rise of resistant aphid populations. As such, there is a growing appreciation for the need to harness the full potential of biological control offered by aphid parasitoid wasps, yet few studies have quantified the non-target effects of pesticide use on these taxa using Australian populations and rates relevant to the grains industry. With this in mind, we followed IOBC protocols and tested the acute toxicity of 20 insecticides and miticides against three important aphid parasitoids: Diaeretiella rapae (M’Intosh), Aphidius colemani Viereck, and Aphelinus abdominalis (Dalman). We found toxicities across the three species were generally consistent for many of the active ingredients tested, however notable differences for paraffinic oil, diafenthiuron, indoxacarb, and thiodicarb were observed. Overall, the aphelinid, A. abdominalis, showed greater tolerance to several active ingredients, with lower IOBC toxicity rating categories compared with the two braconid species, D. rapae and A. colemani. Of the eight active ingredients tested that are currently registered to control aphids in Australian grain crops, only two (flonicamid and afidopyropen) had low toxicity across all three parasitoid species, with four active ingredients resulting in very high toxicity for one or more species. We additionally found that the toxicity of synthetic pyrethroids differed between chemical types, with type I pyrethroids (bifenthrin) found to be more toxic than type II (gamma-cyhalothrin and lambda-cyhalothrin) pyrethroids. Taken together, these results highlight the risks of making generalised toxicity inferences across active ingredients and species. We recommend further toxicity testing be undertaken in the field, in addition to quantifying the sub-lethal effects of insecticides and miticides on aphid parasitoids.

The Efficacy of Biological Control for the Suppression of the Pea Aphid (Acyrthosiphon Pisum): Does the Resistance of Alfalfa Cultivars Matter?

The pea aphid, Acyrthosiphon pisum Harris, is a major pest of alfalfa in northwestern China. However, the roles of different groups of natural enemies in combination with aphid-resistant cultivars in the suppression of the pea aphid have not been clarified under field conditions. In this study, we used experimental cages to better understand the top-down (natural enemies) and bottom-up (nine alfalfa cultivars) biological processes, as well as the individual roles of the two processes, in the control of the pea aphid. There was a significant difference in resistance among cultivar classes revealed when natural enemies were excluded. The functional contribution of top-down suppression was higher than the bottom-up process, with natural enemies significantly suppressing aphid populations, regardless of the resistance level of different alfalfa cultivars. The mean biological efficacies of predators, parasitoids, and mixed populations of natural enemies were 85%, 42%, and 88%, respectively. Overall, our study indicated that natural enemies play a critical role in suppressing aphid populations, especially in the summer, whereas cultivar resistance did not combine effectively with natural enemies to inhibit the growth of aphids. Conservation biological control (CBC) can be implemented in the alfalfa production regions in northwestern China to reduce the overreliance on insecticides for the control of pests and mitigate their harmful effects on humans, ecosystems, and biodiversity.

Leaf UV-B Irradiation and Mycorrhizal Symbionts Affect Lettuce VOC Emissions and Defence Mechanisms, but Not Aphid Feeding Preferences

Arbuscular mycorrhizal fungi (AMF) and ultraviolet-B radiation (UV-B) play important roles in plant-insect interactions by altering plant physiology and histology. We hypothesized that UV-B-induced oxidative stress was mitigated by AMF symbiosis. In this study, we conducted a multifactorial experiment to explore lettuce plant response to AMF inoculation and UV-B exposure (0.4 W m-2; 16 h d-1; 2 weeks), either together or individually, as well as the interaction with the polyphagous insect pest Myzus persicae (Sulzer). Lettuce plants subjected to UV-B radiation showed an increase in callose and oxidative stress indicators, as well as a decrease in stomatal density. Mycorrhizal colonization cancelled out the effect of UV-B on stomatal density, while the symbiosis was not affected by UV-B treatment. The plant volatile emission was significantly altered by UV-B treatment. Specifically, the non-terpene 1-undecene abundance (+M/+UVB: 48.0 ± 7.78%; -M/+UVB: 56.6 ± 14.90%) was increased, whereas the content of the non-terpene aldehydes decanal (+M/+UVB: 8.50 ± 3.90%; -M/+UVB: 8.0 ± 4.87%) and undecanal (+M/+UVB: 2.1 ± 0.65%; -M/+UVB: 1.20 ± 1.18%) and the sesquiterpene hydrocarbons (+M/+UVB: 18.0 ± 9.62 %; -M/+UVB: 19.2 ± 5.90%) was decreased. Mycorrhization, on the other hand, had no significant effect on the plant volatilome, regardless of UV-B treatment. Aphid population was unaffected by any of the treatments, implying a neutral plant response. Overall, this study provides new insights about the interactions among plants, UV-B, and AMF, outlining their limited impact on a polyphagous insect pest.

Ingenious characterization and assessment of lentil germplasm collection to aphid Acyrthosiphon pisum stress unveils distinct responses.

Lentil cultivation is often hampered by aphid population outspreads with detrimental impacts to crop development and production, challenging food safety and agriculture sustainability. The pea aphid (Acyrthosiphon pisum) is a significant threat to lentil in the temperate zone rainfed systems. A set of management practices including resilient cultivars and application of insecticides have effectively controlled aphid infestation. However, the plant defense against insect pests is scantily dissected and limited to the individual components including antibiosis, antixenosis and tolerance that constitute a combination of plant stress responses. Utilizing a lentil germplasm collection, we assessed the antixenosis and aphid tolerance mechanisms in association to important morphological parameters. Physiological parameters including relative water content (RWC) measured at 24h and 48h post-aphid infestation revealed genotype-specific responses. The contents of key plant hormones including salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA) and indoleacetic acid (IAA) implicated in defense signal-transduction pathways were also determined in lentil accessions after aphid herbivory infestation. In parallel, the expression of hallmark defense genes governed by SA- and JA-signaling pathways at 24h and 48h post aphid herbivory revealed significant differentiation patterns among the accessions. An interplay of hormone crosstalk is unveiled that possibly governs defense responses and aphid resistance. Besides the metabolomic profiling of accessions under aphid herbivory indicated the indispensable role of key secondary metabolites accumulation such as flavonoids, alkaloids, phenolics and fatty acids as a front line of plant defense and a potential integration of hormone signaling pathways in metabolome reprogramming. Overall, the study presents a panorama of distinct lentil responses to aphids and a critical view of the molecular mechanisms implicated in lentil insect defense to further our insight and advance crop protection and breeding approaches in a climate changing environment.