Aphid Parasitism Research Articles

The influence of genetic variation on pre‐oviposition processes for host‐parasitoid co‐evolution

Abstract Despite the importance of parasitoid wasps as biological control agents and the vast literature available on different aspects of their natural history and ecology, it is only recently that an interest in integrating genetics into aphid‐parasitoid studies has emerged. Some studies have been completed on the effect of genetic variation on aphid parasitism outcomes, especially after the description of aphid physiological resistance to parasitoids and its role in their co‐evolution. The interaction between aphids and parasitoids goes beyond the physiological conflict between the parasitoid egg and the aphid internal defences. A series of aphid and parasitoid attributes, that can be influenced by biotic and abiotic factors, precedes that last step in the oviposition process. The understanding of how genetic variation can play a crucial role in influencing the pre‐egg‐laying stages of the aphid‐parasitoid interaction remains relatively unexplored. Here, we review currently available information on this topic. We contextualise the aphid‐parasitoid co‐evolution process exemplified by the post‐oviposition approach. Knowledge gaps are also discussed and the significance of fulfilling them is addressed. An ecology‐evolutionary perspective on aphid‐parasitoid research is advocated, by incorporating genetic variation into the study of aphid‐parasitoid co‐evolution. This will increase the understanding of the adaptation and evolution of both organism's characteristics in response to each other and abiotic pressures, and also the implications for pest management.

Aphid parasitism in winter wheat fields in a heterogeneous agricultural landscape.

The number, timing, and fitness of colonizing parasitoids in fields of ephemeral crops often depend on factors external to the fields. We investigated cereal aphid parasitism in 23 winter wheat fields using sentinel plants infested with bird cherry-oat aphids, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), and we investigated the effect of parasitoids on cereal aphid population growth using exclusion and parasitoid-accessible cages infested with bird cherry-oat aphids. Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae), Aphelinus nigritus (Howard) (Hymenoptera: Aphelinidae),and Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae), in decreasing order of abundance, parasitized R. padi on sentinel plants. The mean percent parasitism in parasitoid-accessible cages was 5.2% in autumn and 35.0% in spring. Aphid population intensity was greater in complete exclusion than in parasitoid-accessible cages. Measures of landscape composition and configuration were quantified, and aphid parasitism in autumn by L. testaceipes and A. nigritus was positively associated with % landcover by summer crops and patch density. Parasitism by both species was negatively associated with contagion and % woodlands. Parasitism during spring was positively associated with % grassland and fractal dimension and negatively associated with % canola. The number of braconid mummies per sentinel plant was positively correlated to the number of braconid mummies on wheat stems from parasitoid-accessible cages. Results indicate that cereal aphid mortality caused by parasitoids and their ability to exert effective biological control is related to landscape structure. Comparing this study to an earlier study in the same agroecosystem demonstrated temporal stability of the landscape influence on aphid parasitism by L. testaceipes in winter wheat.

Assessing the sub‐lethal impacts of insecticides on aphid parasitoids through laboratory‐based studies

AbstractAphids are a major pest of cropping systems throughout the world. In most cases, crop aphids are controlled with broad‐spectrum insecticides; although generally very effective at preventing yield loss, this approach risks non‐target damage to beneficial organisms. In the last 20 years, a number of selective insecticides have become available to control aphids while minimising harm to other arthropods. Previous studies have found that two such insecticides, flonicamid and afidopyropen, cause only low‐level acute mortality impacts on aphid parasitoids in Australian grain crops. However, little research has examined the sub‐lethal effects of these chemicals, which could induce various physiological changes that impact pest control. We hypothesised that both flonicamid and afidopyropen have negative effects that extend beyond the immediate acute mortality previously published. To test this hypothesis, we undertook a series of experiments to determine the effects of flonicamid and afidopyropen, along with the synthetic pyrethroid gamma‐cyhalothrin, on aphid parasitism (mummification) rate, emergence rate of the next generation and the next generation sex ratio in three important aphid parasitoids, Aphidius colemani (Viereck), Diaeretiella rapae (M'Intosh) and Aphelinus abdominalis (Dalman). Analogous with previous research, our acute toxicity bioassays showed that all three insecticides had low (<30%) mortality impacts. Although sub‐lethal impacts could not be assessed for D. rapae due to the low level of aphid parasitism by that species, our findings showed negative impacts on fecundity in surviving A. abdominalis and A. colemani. Of particular note is the increase in International Organisation for Biological Control ratings to moderate (30%–80% mortality and/or reproductive reduction) when mortality and reduced fecundity effects were combined to determine overall fitness impacts. Gamma‐cyhalothrin typically resulted in higher negative impacts on A. abdominalis and A. colemani (compared with flonicamid and afidopyropen); however, quite surprisingly, these impacts were not rated as highly toxic. Taken together, our results suggest that, even when sub‐lethal impacts are considered, flonicamid and afidopyropen are useful tools for farmers targeting aphid populations while minimising the non‐target impacts on parasitoids. We recommend semi‐field and/or field trials to further assess the impacts of these insecticides on aphid parasitoid populations.

Population Dynamics of Aphid Pests of Wheat and Their Natural Enemies

Four aphid species (Schizaphis graminum, Sitobion avenae, Rhopalosiphum padi and Diuraphis noxia) were observed when the population dynamics of aphids in four wheat varieties were analysed. Maximum population abundance (104± 1.79 aphids/ plant) was observed during middle of March. Rhopalosiphum padi and D. noxia were predominant throughout (52.86.1± 0.21 and 56.10± 0.24 aphids/ plant, respectively). The variety ANAJ-2017 showed the least incidence (26.28± 0.27 aphids/ plant) being more resistant. Aphid parasitism was also more in ANAJ-2017 with the parasites Aphidius ervi (15.35± 0.13) and Praon volucre (12.45± 0.12). Abundance of predators (ladybird beetle, green lace wing, syrphid fly and spiders) was observed with the highly infested varieties UJALA-2016 and FSD-2008. With incidence of aphids, temperature showed positive correlation while relative humidity (RH) and rainfall did not show any significant effect. The yield varied significantly among the tested varieties and it was found positively correlated with aphid incidence with ANAJ-2017 exhibiting the maximum 1000 grain weight (55 g).

Complex Effects of a Land-Use Gradient on Pollinators and Natural Enemies: Natural Habitats Mitigate the Effects of Aphid Infestation on Pollination Services.

Pollinators and natural enemies are essential ecosystem service providers influenced by land-use and by interactions between them. However, the understanding of the combined impacts of these factors on pollinator and natural enemy activities and their ultimate effects on plant productivity remains limited. We investigated the effects of local and landscape vegetation characteristics and the presence of herbivorous pests on pollination and biological control services and their combined influence on phytometer seed set. The study was conducted in a Mediterranean agro-ecosystem, encompassing ten shrubland plots spanning a land-use gradient. Within each plot, we placed caged and uncaged potted phytometer plants that were either aphid-infested or aphid-free. We quantified insect flower visitation, aphid predation and parasitism rates, and fruit and seed set. We found scale-dependent responses of pollinators and natural enemies to land-use characteristics. Flower species richness had a positive impact on aphid parasitism rates but a negative effect on pollinator activity. Notably, we found a more pronounced positive effect of natural areas on pollinator activity in aphid-infested compared to aphid-free plants, indicating a potentially critical role of natural habitats in mitigating the adverse effects of aphid infestation on pollination services. These results highlight the complex and interactive effects of land-use on pollinators and natural enemies, with significant implications for plant productivity.

Aphid biological control in arable crops via flower strips: The predominant role of food resources over diversity effects

Abstract Plant taxonomic and functional diversity promotes interactions at higher trophic levels, but the contribution of functional diversity effects to multitrophic interactions and ecosystem functioning remains unclear. In agroecosystems, flower strips can be sown to promote biodiversity and associated services, but their plant composition is poorly considered from a functional diversity perspective so as to promote multitrophic interactions. In a field experiment, aphid biological control was compared across contrasting flower strip mixtures, over a 4‐year arable crop rotation. The effects of plants providing food resources, that is nectar and legumes supporting alternative hosts and prey, and the effects of plant species richness and functional dispersion were investigated on the biological control of aphid populations. In general, increases in the percentage of plant cover providing nectar and alternative prey (Fabaceae) to natural enemies increased predator–prey ratios and aphid parasitism and decreased aphid population growth rates. These effects however depended on the crop species. Species richness and the functional dispersion of traits involved in plant–arthropod interactions were of lesser importance, and the directions of their effects were crop‐specific. Synthesis and applications. These findings provide useful insight for designing perennial plant mixtures for creating or restoring habitats supporting aphid regulation. It is not adequate to sow any mixture containing simply flowering plants. Plant mixtures should comprise a large proportion of plant species supporting alternative prey, like legumes, and species producing nectar being easily accessible to natural enemies (corollas with nondeep nectar). To be efficient over a crop rotation, with aphids being present at different seasons, these nectar resources should be provided throughout the year thanks to a diversity of plant flowering periods.

Aggregation of organically managed fields promotes aphid parasitism in cereal crops under Mediterranean conditions

ContextMaintaining a balance between semi-natural habitats and arable land is not always feasible for farmers. The promotion of biological control agents can be addressed through management at farm or field level, and/or by deploying lower intensity, biodiversity-friendly practices which can act either directly or indirectly through their effect of the plant community.ObjectivesWe studied the effects on cereal aphids and their parasitoids of agricultural management at field and landscape levels. We tested the effect of organic and conventional farming, and of the within field characteristics, on the cereal aphid-parasitoid community, across a gradient of organic farming aggregation and of percentage of arable land.MethodsIn spring 2015, we sampled aphid populations in 30 cereal fields in five agricultural areas in Catalonia (Spain) with contrasting levels of organic farming aggregation. In each field, we also assessed weed and crop cover. As landscape variables, we calculated the Percentage of Agricultural Land (PAL) and the Percentage of Organically Managed Land (POML) in a 500-m buffer around each field. We sampled cereal tillers 3 m from the field edges and collected all aphids detected. In addition, we reared mummies (parasitized aphids) until they hatched.ResultsOur results show that management at landscape level has significant effects on parasitism rates: a higher proportion of surrounding fields under organic management increased the amount of parasitism, as did less agricultural land cover. On the other hand, aphid populations were mainly affected by two in-field factors, namely, crop density and crop variety. Differences in weed communities did not seem to have any effects on either aphids or parasitoids.ConclusionsRather than concentrating on the individual management of fields, a coordinated implementation of organic farming at landscape level would seem to be a much better strategy for improving the biological control of aphids.

Role of parasitoids and landscape structure in aphid population dynamics in winter canola

Three aphid species infest winter canola, Brassica napus L. fields in central Oklahoma and are serious pests: the cabbage aphid, Brevicoryne brassicae L., green peach aphid, Myzus persicae (Sulzer), and turnip aphid, Lipaphis pseudobrassicae (Davis). Mortality caused by parasitoids may be an important component of biological control of aphids in Oklahoma canola fields. Therefore, it is important to determine the effect of parasitoids on aphids in canola and the factors that affect it. We undertook a study during three consecutive growing seasons to: 1) estimate aphid suppression by parasitoids in each of 23 canola fields using cages that excluded natural enemies and cages that permitted access by parasitoids; and 2) evaluate how aphid parasitism in canola is related to the composition and configuration of the landscape surrounding each canola field. Parasitism was estimated using turnip aphid infested sentinel canola plants stationed in each field in autumn and in spring of each growing season. Two parasitoids with broad host ranges, Diaeretiella rapae (M’Intosh) and Aphelinus nigritus (Howard), parasitized turnip aphids in canola. There were fewer aphids and more parasitoids in cages that permitted access to parasitoids than in cages that excluded natural enemies. Partial redundancy analysis demonstrated that parasitism rate by D. rapae was positively related to landcover of wetlands and negatively related to contagion of patches. Parasitism by A. nigritus was positively but weakly associated with landcover of summer crops, but not with any other measured landscape variable. Wetlands in central Oklahoma agricultural landscapes apparently are habitat for aphid parasitoids from which they disperse to canola fields and parasitize aphids. Partial redundancy analysis showed that relative aphid density in fields was negatively related to parasitism by D. rapae. Results indicate that parasitoids suppress aphid infestations in canola fields and demonstrate potential for habitat management to improve biological control of aphids in canola.

Perennial woodlands benefit parasitoid diversity, but annual flowering fallows enhance parasitism of wheat aphids in an agricultural landscape

Agriculture intensification poses serious threats to natural enemy biodiversity and associated ecological services. The conservation or reestablishment of semi-natural habitats is used to counteract negative effects of agriculture intensification on natural enemies. Understanding specific functions of different habitats for natural enemies from a landscape perspective is an important step needed for the development of sustainable agriculture. Here, focusing on parasitoids of wheat aphids, we examined effects of the proportion and connectivity of two main semi-natural habitats (woodlands and fallows) present in landscapes, measured within circular buffer radii of 0.5, 1.0, 1.5, and 2.0 km around sampling sites, on parasitoid (mummy) density, biodiversity (Shannon diversity) and associated services (parasitism rate) in 35 wheat fields. We also compared local vegetation communities of these two semi-natural habitats to test whether plant characteristics can shed light on the potential mechanisms driving parasitoids responses to different landscape habitats. We found that the parasitoid diversity was much higher in landscapes dominated by woodlands, while fallows in the landscape promoted parasitoid density and parasitism. Woodlands connectivity at larger scales (such as 1.5 or 2.0 km) displayed positive effects on parasitoid activities, fallows connectivity at the smaller scale (0.5 km) had a positive effect on the hyperparasitism rate. In terms of vegetation characteristics, fallows provided more flowering plants and floral resources, while woodlands suffered less disturbance across years. Local vegetation composition of the semi-natural habitats indeed help explain their different effects on parasitoids at larger landscape scales. We suggested that future research should investigate the role of different types of semi-natural habitats. Conservation management should combine different habitats, such as perennial and annual habitats, to promote the functional complementarity for beneficial organisms. Based on results from local vegetation survey, we also suggested native flowering plants such as Capsella bursa-pastoris L., Lagopsis supina Steph., and Calystegia hederacea Wall. in fallows could be used as functional plants to conserve wheat aphid parasitoids.

Defense against Feeding by Spring Aphid Parasitism in the Upper Leaf Parts of Host Plants

In a symbiosis, each participant gains more fitness benefits than is paid in maintenance costs for the symbiosis. The mugwort aphid, Macrosiphoniella yomogicola, is ant-associated, and the host mugwort Artemisia montana is a genet-producing plant that has clonal aboveground shoots. M. yomogicola infests most A. montana shoots from spring to midsummer, and attending ants also repel leaf-eaters of the host plant. However, most aphid colonies become extinct after budding of A. montana inflorescence after early August. A few surviving aphid colonies (1∼3 per genet) produce sexuparae in mid-October. The shoots on which the sexuparae emerged lost most of their fitness because the aphids strongly suppress budding and growth of inflorescence. However, as the shoots are genetic clones of each other, the appearance of stem mothers in the next spring may result in early spreading of the aphids and attending ants to clonal shoots, which would protect the host from leaf-eaters. Here, we show that all shoots on a genet with stem mothers are occupied by aphids and ants much faster than those on a genet without stem mothers. The attending ants repel leaf-eaters to unimportant leaves for the host. Our results suggest that, as the shoots of a genet are all clones, sustaining the aphids on a few shoots may be beneficial to a genet as a whole through kin selection.

Biological Control Services from Parasitic Hymenoptera in Urban Agriculture.

Simple SummaryOur findings support the enemies hypothesis in urban agroecosystems. Local factors, including increased mulch coverage, crop richness, and percent of non-crop areas, are predictors of increased PH abundance and aphid parasitism rates. Our findings support and strengthen previous findings in UA research. Urban farmers should be encouraged to diversify urban agroecosystem spatial composition and implement APM practices to reduce pest impacts.Urban agriculture is practiced in spatially fragmented landscapes with unique characteristics that can impact species occurrence in time and space. As a result, biological control services, an ecosystem service from naturally occurring arthropod natural enemies, can be negatively impacted. Many urban farms forgo pesticides and utilize agroecological pest-management strategies that rely on natural enemies to help regulate pest populations. Understanding how these enemies are affected by landscape composition and on-farm management practices is critical to understanding agroecological pest management in UA and furthering our understanding of landscape-mediated population dynamics. Over two growing seasons, we sampled brassica crops in urban agriculture sites occurring on a spectrum of surrounding landscape imperviousness, spatial composition, size, and management practices to better understand parasitic Hymenoptera abundance, richness, and parasitism rates on the common cabbage aphid (Brevicoryne brassicae). We found that on-farm agroecological pest-management practices such as mulch coverage, floral richness, and overall crop-plant richness impacted parasitic Hymenoptera abundance. Larger proportions of on-farm noncrop area increased parasitoid abundance on urban farms. Aphid parasitism increased in relation to on-farm management practices, including increased crop-plant richness. These findings add to a growing understanding of urban agroecosystem function and support the enemies hypothesis in urban agroecosystems.

A multi-site experiment to test biocontrol effects of wildflower strips in different French climate zones

Sowing of wildflower strips has been integrated in agri-environment schemes of several European countries. Their beneficial effects on natural enemies of pest insects are well documented but (1) the desired spill-over into crop fields has not always been demonstrated, and (2) the need to adapt sown mixtures to regional climatic differences has been rarely addressed.We set up a multi-site experiment in different French climatic regions to compare effects of a wildflower strip with a grass mixture and spontaneous vegetation. The design included five regions, three to five fields per region and the three strip treatments being repeated in each field. We tested strip treatment effects on vegetation (plant species richness, plant and flower cover) and on natural enemies (hoverflies, ladybirds, aphid predation). In a subset, we further analysed the spill-over into winter wheat fields including natural enemies and pest insects (cereal aphids, leaf beetles).The wildflower strip mixture developed well in all regions and increased plant species richness and flower cover compared with grass strips and spontaneous vegetation. We found a corresponding higher hoverfly abundance and aphid predation in wildflower strips that were consistent in all regions, whereas ladybird abundance was not affected. A significantly higher hoverfly abundance, aphid predation and aphid parasitism in wheat fields close to wildflower strips indicated a spill-over. No corresponding margin treatment effects were observed for aphid and leaf beetle abundance in the field. A multivariate analysis comparing the influence of climate and vegetation parameters showed that floral cover better explained variation in natural enemy abundance and predation than climate. Our results demonstrated that similar mixtures of native plants can be used over large climatic gradients to improve biocontrol. Further research is needed to improve spill-over into crop fields and to obtain consistently strong effects in different climate zones.

Strip intercropping of wheat and oilseed rape enhances biodiversity and biological pest control in a conventionally managed farm scenario

Abstract Conventional agriculture in the global north is typically characterized by large monocultures, commonly managed with high levels of pesticide or fertilizer input and mechanization. Strip intercropping, that is, diversifying cropland by growing strips of different crops using conventional machinery, may be a viable strategy to promote natural predator diversity and associated biological pest control in such conventional farming systems. We tested the influence of strip intercropping of conventionally managed winter wheat with oilseed rape, using common machinery with 27–36 m broad strips, on arthropod predator diversity and biological pest control. We characterized spider and carabid beetle communities, calculated pest aphid and pollen beetle densities and recorded parasitism rates for both crops (number of mummified aphids on wheat and number of parasitized pollen beetle larvae on oilseed rape). We observed a significant reduction in the densities of wheat aphids (50% decrease) and pollen beetle larvae (20% decrease) in strip intercropping areas compared to monocultures. Parasitism rates of wheat aphids increased significantly from 10% in monocultures to 25% in strip intercropping areas. The number of parasitized pollen beetle larvae did not show the same pattern but was higher towards the centre of the oilseed rape strip. Overall, the composition of predator communities benefited from the close neighbourhood of the two crop species in the strips, as carabid beetles were more abundant in oilseed rape and spiders were more abundant in wheat fields. Overall, strip intercropping reduced the dominance of one predator group and allowed for an equal representation of both spiders and carabid beetles in the mixture. Synthesis and applications. Our study presents evidence of the benefits of adopting strip intercropping with relatively large strips (adapted to existing machinery) for natural predator diversity and biological pest control in a large‐scale conventionally managed farm scenario. Wheat–oilseed rape strip intercropping reduced pest densities, increased parasitism of wheat aphids and promoted equal representation of natural predator groups well beyond the areas of monoculture. Overall, by reducing the area dedicated to only one crop, the implementation of strip intercropping adapted to mechanized agricultural scenarios can be used to increase crop heterogeneity at regional scales and enhance biodiversity and biological control, even in simplified landscapes dominated by large‐scale conventional agriculture.

Predicting the abundances of aphids and their natural enemies in cereal crops: Machine-learning versus linear models

Predicting the effects of crop management and landscape structure on biological pest control is a key challenge for implementing innovative pest management systems. Here, we compare the performances of two machine-learning methods (regression trees and random forests) with those of linear models in predicting cereal aphid abundance, parasitism, and natural enemies.We trained models using data describing the landscapes, cropping systems, and margins of 88 cereal fields in France. To assess the predictive performances of our models, we measured pseudo-R2 and root-mean-square error using cross-validation.The two machine-learning methods performed reasonably well in comparison with linear models. Aphid abundance, parasitism, and natural enemies were predicted by both biological (abundances of functional groups) and environmental variables (describing fields, crop management and landscape structure). Parasitoids and hoverfly larvae, unlike coccinellid and lacewing larvae, presented a density-dependent numerical response to aphid populations. At the landscapes scale, linear elements (both grassy strips and hedgerows) were the most important predictors of aphid abundance and parasitism. In contrast, hoverfly larvae were more influenced by the proportion of cultivated areas and woodlands. At the field scale, our models ranked factors related to field size, margins, and soil type as the most important predictors of aphids and their natural enemies.Our analysis shows that machine-learning models outperform classical statistical ones, and therefore provide useful tools for predicting highly variable ecosystem services such as biological pest control.

Aphid seasonality and host plant relationship: A Review

Aphids are harmful agricultural insect pests that feed on the phloem sap of their hosts, infecting them with diseases. Plant-aphid interaction is a dynamic system that is always changing and varying. During their life cycle, several aphid species change their host plant. They travel between main and secondary host plant species in the spring and fall. This host shift has happened due to the phloem sap's nutritional importance and necessity for reproduction. According to certain experiments, the aphid parasitism impact reduces the number of inflorescences and the average weight of floral buds. With the aid of enzymatic adaptability and sequestering secondary metabolites, the host plant possesses biochemical and physical defence mechanisms. Aphids circumvent this by secreting Mixed Function Oxidase (MFO), which catalyses oxidative reactions, allowing them to eat, develop, and breed on their host plant.

Aphididae Species, Their Natural Enemies and Rates of Parasitism on Rumex crispus L. in Northeast Turkey and First Report of Acyrthosiphon rubi Narzikulov damaging Rumex crispus L.

Aphid species, their parasitoids and predators on Curled dock (Rumex crispus L.) naturally grown in Erzincan and Erzurum provinces, Turkey were determined. Surveys were conducted at two week intervals from the seedling period until the end of the harvest period in 2017 and 2018. In the surveys, 30-40 plants were randomly selected and all parts of these plants were investigated with a magnifier. Four aphid species, thirteen predator and two parasitoid species were found. Rumex crispus was recorded for the first time as a host of Acyrthosiphon rubi Narzikulov (Hemiptera: Aphididae). In addition, parasitism rates of aphids were also established. The mean parasitism rate changed between 23.2% in 2017 and 23% in 2018. The relationship between total aphid number, total parasitized (mummified) aphid number and parasitism rate was measured. There was a high positive correlation (r = 0.838-0.861) between total aphid number and total parasitized aphid number, and a weak or intermediate correlation (r = 0.180-0.412) between total aphid number and parasitism rate during both growing seasons.

Plant silicon application alters leaf alkaloid concentrations and impacts parasitoids more adversely than their aphid hosts.

Grasses accumulate large amounts of silicon (Si) which acts as a highly effective physical defence against insect herbivory, however recent evidence shows that Si supplementation also modifies plant secondary metabolite concetrations. Changes in plant secondary metabolites concentrations can have cascading effects on higher trophic levels, such as parasitoids, as they are dependent on the host herbivore for growth and development. However, relatively little is known about how Si application affects higher trophic levels. We examined the effects of Si addition on alkaloid content in leaves of Phalaris aquatica (Poaceae) and the effect on interactions between an aphid (Rhopalosiphum padi) and its parasitoid (Aphidius colemani). Si supplementation had no effect on aphid abundance or parasitism rate. Adult aphids, aphid mummies (parasitised aphids) and the emergent parasitoids were, however, significantly smaller on Si+ plants. Parasitoid traits (size and emergence) were correlated with aphid mummy size. Si addition reduced parasitoid emergence rate and size due to reduced host mummy size, in addition, significantly fewer females emerged from mummies on Si+ plants. Aphid infestation significantly altered alkaloids concentrations, reducing gramine by 80% while increasing tryptamine by 91% in Si- plants. Si addition reduced aphid-induced tryptamine concentrations by 64% and increased 5-MeO-tryptamine by over 800% in control and 142% in aphid infested plants. Our results show that while Si addition has modest impacts on the herbivore, it significantly alters secondary metabolites and has stronger effects on the higher trophic level through changes in the quality of the parasitised host.

Organic fertilizer amendment promotes wheat resistance to herbivory and biocontrol services via bottom-up effects in agroecosystems

Excessive mineral fertilizer input results in little extra yield but exacerbates insect herbivory and affects environmental health and ecosystem services. The use of organic fertilizer is considered to have promise for mitigating those impacts. How organic fertilizer amendment modifies crop resistance to insect herbivory and modulates biocontrol services on a landscape scale has not been well studied. We conducted a series of field experiments on a large spatial scale with three fertilization regimes (mineral fertilizer, mineral fertilizer amended with organic matter, and no fertilizer control) in Shandong Province, northern China. Soil nutrient content, wheat plant metabolism, cereal aphid abundance, parasitism rate, and wheat yield were quantified. Maize straw amendment combined with mineral fertilization significantly reduced cereal aphid abundance and promoted parasitism during the peak aphid period, compared with mineral fertilizer alone and the no fertilizer control. Modeling simulations showed increased biological pest control when a larger proportion of fields were additionally treated with maize straw amendment. Foliar chemical analyses revealed that the types and content of plant free amino acids, rather than plant defensive compounds, most likely accounted for the variation in aphid abundance and biological control efficiency. A mineral fertilization regime plus plant straw amendment may promote wheat resistance to herbivory and benefit biocontrol via bottom-up effects. Heterogeneity in fertilizer regimes between fields may be the key ecological force shaping pest control at a landscape scale.

Spatial and Temporal Variation in the Aphid–Parasitoid Interaction under Different Climates

Global warming will increase pest insect population sizes and diminish the effectiveness of biological control. This biological control failure scenario appears to be of particular concern for areas with a significant increase in maximum temperatures, such as the increase experienced in the Central Valley of Chile over the last 40 years. We assessed the impact of different climatic zones and maximum temperatures along the coast and the Chilean Central Valley on the grain aphid (Sitobion avenae) density, parasitism rate, and facultative endosymbionts in wheat fields during the growing season in the springs of 2017 and 2018. A significant effect on aphid density due to zones and maximum temperatures was detected; however, this depended on the zone and year analyzed. Changes between zones and seasons were observed for parasitism rates, while maximum temperatures only significantly affected the parasitism rate in 2017. The main parasitoid wasp found was Aphidius ervi in both zones and seasons. Regiella insecticola infected 95% of the samples in both zones, although it does not seem to have a protective role at the field level. Our findings suggest that, at present, global warming does not significantly affect the grain aphid outbreaks and their biological control in Chile. However, this study points out the importance of pre-emptive monitoring to detect aphids and the synchrony loss of their parasitoid wasps.

Наездники (Hymenoptera, Aphelinidae, Aphidiidae) - паразиты тлей (Hemiptera, Aphidoidea) Азербайджана

As a result of many years of research, 30 species of parasites derived from aphids have been identified for the fauna of Azerbaijan. For the first time an annotated list of aphelinids and aphidiids (Hymenoptera: Aphelinidae, Aphidiidae), parasites of aphids of Azerbaijan is given. Of these parasites, there are 14 species of aphelinids (Hymenoptera, Aphelinidae) and 16 species of aphidiids (Hymenoptera, Aphidiidae). Of aphelinids two species are recorded for the first time for the fauna of the South Caucasus, and 4 species for the fauna of Azerbaijan. All the 16 known species of the aphidiids are new for the fauna of Azerbaijan. Aphidiids Adialytus salicaphis, Lysiphlebus fabarum, Aphidius rosae are recorded for the first time for the fauna of the South Caucasus.