Aphid Brevicoryne Brassicae Research Articles

Benefit-cost ratio evaluation for management of Brevicoryne brassicae L. in canola (Brassica napus L.) crop production

Canola is an important oilseed crop. It is attacked by different insect pests. Cabbage aphid (Brevicoryne brassicae L.) is one the most destructive sucking insect pests of this crop. Its infestation affects the yield and quality of seed. Three different levels of nitrogen fertilizers, i.e., 120, 60 and 30 kg/hac, two environmentally safe insecticides i.e., emamectin benzoate and imidacloprid at three different application intervals i.e., 4, 8 and 12 days after first application (DAFA) were tested for management of cabbage aphid in canola. The experiment was laid out in a sub-sub plot design keeping nitrogen fertilizer levels as main plot, insecticides as sub plot and insecticide application intervals as sub-sub plots. Number of aphids per plant and canola seed yield for each combination was recorded. Total expenses from crop production till harvest were calculated on market rates of 2019. Benefit-cost ratio for each treatment combination was calculated. Lowest aphid infestation was fond for 4DAFA. Highest benefit-cost ratio (2.57) was recorded for imidacloprid applied at 4DAFA with 120 kg/ha nitrogen fertilizer. But for the management of cabbage aphid in environment friendly manner we recommend emamectin benzoate at 8DAFA with nitrogen level of 60 kg/hac giving slightly lower BCR (2.37).

Action threshold development in cabbage pest management using synthetic and botanical insecticides

As synthetic insecticides can have environmentally detrimental side effects, it is desirable to limit their use while still achieving good marketable yield. One approach is to apply pesticides only when needed, as determined by an action threshold (AT), defined as the number of pests per crop plant or damage intensity at which application is recommended. Another approach is to adopt alternative pesticides, such as botanical biopesticides, which can also be applied according to ATs. Here, ATs are developed in cabbage pest management using both approaches against the moths Plutella xylostella (L.), Helicoverpa armigera (Hubner) and Spodoptera litura (F.) and the aphid Brevicoryne brassicae (L.). Action thresholds were derived using fixed spraying regimes for the synthetic insecticides (imidacloprid and Voliam Flexi) and for azadirachtin, a neem-derived botanical. For synthetics, derived ATs are 40 individuals per plant for B. brassicae, 0.3 larvae for P. xylostella and 0.2 medium-sized larvae for H. armigera and for S. litura. For H. armigera and S. litura, negative relationships between marketable yield and pest were found when larvae were medium or large sized, but not when larvae were small. Compared to synthetics, benefits of using neem formulations include higher action thresholds against P. xylostella (0.6/plant) and H. armigera (0.4/plant) and an oviposition deterrent effect against S. litura. Overall, botanical insecticides were effective alternatives to synthetic pesticides. Although regional limits may apply to the accuracy of any ATs derived, the approach used towards their establishment is simple and transferable to other agricultural regions and crops.

Plant ontogeny determines strength and associated plant fitness consequences of plant-mediated interactions between herbivores and flower visitors.

Plants show ontogenetic variation in growth–defence strategies to maximize reproductive output within a community context. Most work on plant ontogenetic variation in growth–defence trade‐offs has focussed on interactions with antagonistic insect herbivores. Plants respond to herbivore attack with phenotypic changes. Despite the knowledge that plant responses to herbivory affect plant mutualistic interactions with pollinators required for reproduction, indirect interactions between herbivores and pollinators have not been included in the evaluation of how ontogenetic growth–defence trajectories affect plant fitness.In a common garden experiment with the annual Brassica nigra, we investigated whether exposure to various herbivore species on different plant ontogenetic stages (vegetative, bud or flowering stage) affects plant flowering traits, interactions with flower visitors and results in fitness consequences for the plant.Effects of herbivory on flowering plant traits and interactions with flower visitors depended on plant ontogeny. Plant exposure in the vegetative stage to the caterpillar Pieris brassicae and aphid Brevicoryne brassicae led to reduced flowering time and flower production, and resulted in reduced pollinator attraction, pollen beetle colonization, total seed production and seed weight. When plants had buds, infestation by most herbivore species tested reduced flower production and pollen beetle colonization. Pollinator attraction was either increased or reduced. Plants infested in the flowering stage with P. brassicae or Lipaphis erysimi flowered longer, while infestation by any of the herbivore species tested increased the number of flower visits by pollinators.Our results show that the outcome of herbivore–flower visitor interactions in B. nigra is specific for the combination of herbivore species and plant ontogenetic stage. Consequences of herbivory for flowering traits and reproductive output were strongest when plants were attacked early in life. Such differences in selection pressures imposed by herbivores to specific plant ontogenetic stages may drive the evolution of distinct ontogenetic trajectories in growth–defence–reproduction strategies and include indirect interactions between herbivores and flower visitors. Synthesis. Plant ontogeny can define the direct and indirect consequences of herbivory. Our study shows that the ontogenetic stage of plant individuals determined the effects of herbivory on plant flowering traits, interactions with flower visitors and plant fitness.

Susceptibility of Myzus persicae, Brevicoryne brassicae and Nasonovia ribisnigri to Fungal Biopesticides in Laboratory and Field Experiments.

The aim of this study was to evaluate the potential of entomopathogenic fungi (EPF) for the control of aphid pests of field vegetable crops. Four biopesticides based on the EPF Beauveria bassiana (Botanigard ES and Naturalis L), Cordyceps fumosorosea s.l. (Preferal WG), and Akanthomyces dipterigenus (Vertalec) were evaluated in a laboratory bioassay against peach-potato aphid Myzus persicae, cabbage aphid Brevicoryne brassicae, and currant-lettuce aphid Nasonovia ribisnigri. There was significant variation in the spore dose provided by the products, with Botanigard ES producing the highest dose (639 viable spores per mm2). Botanigard ES also caused more mortality than the other products. Combining Vertalec with the vegetable oil-based adjuvant Addit had an additive effect on the mortality of B. brassicae. All fungal products reduced the number of progeny produced by M. persicae but there was no effect with B. brassicae or N. ribisnigri. When aphid nymphs were treated with Botanigard ES and Preferal WG, both products reduced population development, with up to 86% reduction occurring for Botanigard ES against M. persicae. In a field experiment, Botanigard ES sprayed twice, at seven-day intervals, against B. brassicae on cabbage plants, reduced aphid numbers by 73%. In a second field experiment with B. brassicae, M. persicae, and N. ribisnigri, Botanigard ES reduced populations of B. brassicae and N. ribisnigri but there was no significant effect on M. persicae.

Foliar herbivory by caterpillars and aphids differentially affects phytohormonal signalling in roots and plant defence to a root herbivore.

Plant‐mediated interactions are an important force in insect ecology. Through such interactions, herbivores feeding on leaves can affect root feeders. However, the mechanisms regulating the effects of above‐ground herbivory on below‐ground herbivores are poorly understood. Here, we investigated the performance of cabbage root fly larvae (Delia radicum) on cabbage plants (Brassica oleracea) previously exposed to above ground herbivores belonging to two feeding guilds: leaf chewing diamondback moth caterpillars (Plutella xylostella) or phloem‐feeding cabbage aphids (Brevicoryne brassicae). Our study focusses on root‐herbivore performance and defence signalling in primary roots by quantifying phytohormones and gene expression. We show that leaf herbivory by caterpillars, but not by aphids, strongly attenuates root herbivore performance. Above‐ground herbivory causes changes in primary roots in terms of gene transcripts and metabolites involved in plant defence. Feeding by below‐ground herbivores strongly induces the jasmonate pathway in primary roots. Caterpillars feeding on leaves cause a slight induction of the primary root jasmonate pathway and interact with plant defence signalling in response to root herbivores. In conclusion, feeding by a leaf chewer and a phloem feeder differentially affects root‐herbivore performance, root‐herbivore‐induced phytohormonal signalling, and secondary metabolites.

Ekonomski značajne štetočine povrtarskih useva u Smederevskoj Palanci

The aim of this research was to determine insect pests on vegetable crops in Smederevska Palanka area. By using standard methods, equipment and tools, insect pests that caused significant and less significant damages have been determined on vegetable crops: pepper, tomato, cucumber, melon, zucchini, cabbage, pea, bean, spinach and beet at the arable area at the Institute for Vegetable Crops. The most significant insect pests, causing the most damages were Frankliniella occidentalis and Tuta absoluta, and also several species of aphids (Brevicoryne brassicae, Myzus persicae, Aphis gossypii, Aphis fabae and Macrosiphum euphorbiae), stink bugs (Nezara viridula, Eurydema spp.) and flea beetle (Phyllotreta spp.). These insects caused direct and indirect damages. The most significant damages have been noted in green houses due to favourable conditions for insect reproduction and sufficient food supplies.

Evaluation of cow urine + plant extracts against the cabbage aphid Brevicoryne brassicae

Field experiments were conducted during rabi 2017 and 2018 at the Vegetable Research Farm, College of Agriculture, Central Agricultural University, Imphal to evaluate the efficacy of cow-urine + indigenous plant extracts against cabbage aphid Brevicoryne brassicae. The results revealed that three sprays of Neemazal T/S (azadirachtin 1500 ppm) @ 1500 ml/ha was the most effective with minimum aphid counts of 28.92 aphids/plant (2017) and 28.94/plant (2018), respectively. The yield (21.88 t/ha and 22.50 t/ha) was also maximum with this treatment.

Effect of nitrogen fertilizer on Brassica carinata and its effect on cabbage aphid Brevicoryne brassicae L.

Effect of nitrogen fertilizers on total glucosinolate concentration of Ethiopian mustard Brassica carinata plants and cabbage aphid Brevicoryne brassicae L. was studied under greenhouse condition. Nitrogenous fertilizers’ application was observed positively correlated with total nitrogen, protein and sugar content of B. carinata but negatively with leaf phosphorus and total glucosinolate contents. Aphids that fed on plants treated with highest nitrogen rate (150%) had shorter prereproduction, and longer reproduction periods with more longevity. Thus, increase in nitrogen led to intrinsic rate of increase, with a greater number of nymphs, apterous and alate adults.

Combined effects of soil silicon and drought stress on host plant chemical and ultrastructural quality for leaf‐chewing and sap‐sucking insects

AbstractIt was postulated that Si‐mediated plant resistance to herbivory changes with soil water status, increasing when plants are under drought stress. We subjected collard (Brassica oleracea) to such soil variables and assessed plant responses and effects on the leaf‐chewing larvae of Plutella xylostella and the sap‐sucking aphid Brevicoryne brassicae. Silicon accumulated in collard leaves independently of soil water conditions, but it influenced mainly drought‐stressed plants. Silicon suppressed harmful effects of drought on leaf and root length and raised leaf water content and stomatal size to the same conditions of well‐watered plants. Drought stress reduced hemicellulose and cellulose, but Si did not influence them or lignin. Combination of drought and Si increased total and soluble leaf nitrogen. Drought decreased total glucosinolates, but Si increased such defence metabolites to similar concentrations that were found in well‐watered plants. Nutritional changes mediated by drought and Si in fibre, leaf water content, soluble nitrogen and glucosinolates did not increase insect performance in any feeding guild. Instead, caterpillars performed worse in drought‐stressed or Si‐treated collards, mainly in plants under combined conditions. Silicon improved plant resistance to drought and herbivore stresses.

Estimating population dynamics parameters of cabbage pests in temperate mixed apple tree-cabbage plots compared to control vegetable plots

Mixed fruit tree-vegetable systems, a particular type of agroforestry, simultaneously combine the production of vegetables at the ground level with that of fruits in tree canopies. Crop diversification generally promotes pest natural enemies but its impact on pest abundance is more ambivalent, possibly because the presence of trees also directly impacts pest reproduction, survival and movements. The purpose of this study was thus to estimate population dynamics parameters of vegetable pests (predation, immigration and survival) and compare them between mixed fruit tree-vegetable plots and vegetable control plots. For this purpose, seven pest stages were monitored in an experiment with exclusion cages set up in mixed fruit tree-vegetable plots, combining apple and cabbage, and two control plots grown with cabbage only, over one growing season. The data were then fed into a mechanistic-statistical model to estimate these parameters. Most significant results concerned the aphid Myzus persicae that had higher intrinsic growth rate, less immigration and suffered less predation in mixed fruit tree-vegetable plots. Egg laying also appeared larger for Lepidoptera species in these plots but egg survival was lower. Predation of caterpillars was also lower. Lastly predation of the aphid Brevicoryne brassicae, in contrast to M. persicae, was higher in mixed fruit tree-vegetable plots. Either no difference was noted between plot types for other parameters or the pest biology made it difficult to relate the model parameters to population dynamics process. We thus provide evidence that reproduction or survival of some pests may increase in mixed fruit tree-vegetable plots and their predation level may be similar or lower than in control plots which could explain the diversity of results concerning the effects of agroforestry on pest control. We also found no strong evidence that trees were a barrier to immigration in our simple mixed fruit tree-vegetable plots.

<i>Anthocoris nemorum</i> (Heteroptera: Anthocoridae) as predator of cabbage pests – voracity and prey preference

Laboratory experimentswere performed with adult female Anthocoris nemorum (Linnaeus) (Heteroptera: Anthocoridae) at 20°C ± 1°C, L16:D8, 60–70% RH to determine voracity and preference on cabbage aphids (Brevicoryne brassicae L.) (Hemiptera: Aphididae), diamondback moth larvae (Plutella xylostella L.) (Lepidoptera: Plutellidae) and Western flower thrips (Frankliniella occidentalis Pergande) (Thysanoptera: Thripidae) (model species for cabbage thrips (Thrips angusticeps Uzel) (Thysanoptera: Thripidae)). When offered individually, A. nemorum readily accepted all three species with no significant differences in consumption. When aphids and moth larvae were offered simultaneously, A. nemorum showed preference for the latter (numbers eaten and biomass consumed). When aphids and thrips were offered together, A. nemorum preferred thrips in terms of numbers eaten but preferred aphids in terms of biomass consumed. The results showed that A. nemorum is a voracious predator of B. brassicae, P. xylostella and F. occidentalis and can therefore be considered as a potential candidate for biological control in cabbage.

Natural Entomophages of Brevicoryne Brassicae (L.) (Hemiptera: Aphididae) in Uzbekistan

In our studies phenological phases of cabbage aphids Brevicoryne brassicae (L.) were studied. The influence of external factors (humidity and temperature) was studied under laboratory conditions. The maximum reproductive ability of cabbage aphids was noted in spring and autumn. Some of the parthenogenetic aphids gave about 82 larvae. The daily reproductive ability of aphids was 3-5, and the maximum 5-11. When studying the reproductive ability of parthenogenetic aphids, this indicator was slightly lower than that of the wingless aphids (average 28, maximum 51). The overall development of cabbage aphid seeds averaged 7–9 days in summer and 12–21 days in early spring and autumn. The importance and bioecological features of Metamorphus corollae (F.), Episyrphus balteatus (De Geer, 1776), Syrphus vitripennis (Meigen, 1822), Scaeva pyrastri (L.) Coccinella septempunctata (L.) and Adonia variegata (G.), Chrysopa carnea Steph. with natural control of the cabbage aphid were studied.
 
 Studying the biological effectiveness of a simple golden-eyed fly in relation to the cabbage bug, efficiencies were observed at a ratio of II-year-old larvae of simple golden-eyed and cabbage bug in a ratio of 1:5 and 1:10. For 4 day old gold-eyed eggs, this efficiency was observed when the ratio with cabbage bug was 1:1 on the 17th day of the experiment.

Biotic Factors Responsible for Management the Population Trend of Cabbage Aphid Brevicoryne brassicae L, Inhabiting Canola Plants

The present study was conducted to determine the species composition and seasonal abundance of the prevalent arthropod pests and natural enemies inhabiting canola plantations during 2017 and 2018, growing seasons in Assiut, Upper Egypt. Plant relative susceptibility to cabbage aphid Brevicoryne brassicae L.and effect of the naturally occurring parasitoid species to manage the population trend of this insect pest was evaluated. Data revealed the presence of 14 species belonging to 14 genera, 10 families and 5 orders. Predatory species (Campylomma impicta Wagner and Coccinella undecimpunctata L) were constituted the highest proportion of entomophagous species, while parasitoids were presented by one species only [Diaeretiella rapae (McIntosh)]. The predatory species showed less than 6% dominance and 40% abundance. However, the aphid parasitoid was presented by more than 90% dominance and 60% abundance. Thrips tabaci Lindeman was the highest prevalent phytophagous species, while cabbage aphid B. brassicae ranked the second by less dominance and abundance percentages. Cabbage aphid B. brassicae was found to be active on canola plantations all over both growing seasons. A gradual increase in B. brassicae populations was recorded until the appearance of its peak in March, 5. A gradual decrease in the pest populations was recorded until the end of the season. Bactol cultivar harbored the highest aphid mean numbers (132.47individuals/plant) throughout both seasons of study and classified as susceptible (S) cultivar. Serw 4 and Serw 6 cultivars harbored fewer numbers (98.05 and 85.08 individuals/plant) and classified as low resistant (LR) and moderately resistant (MR) cultivars, respectively. The mean percentage of B. brassicae parasitized by D. rapae during both growing seasons was estimated. Although, the pest populations decreased at mid-March, the parasitism percentages increased until the end of both seasons. The seasonal mean of parasitism percentage recorded 34.76%. Simultaneous decrease of the pest numbers with the increase of its parasitoid confirms the responsibility of D. rapae as a good biological control agent against B. brassicae populations

Formulation of plant based insecticides, their bio-efficacy evaluation and chemical characterization

The aim of this study was to develop Emulsifiable Concentrate (EC) formulations from seed oils of Pongamia pinnata L., Pachyrhizus erosus L. and Annona squamosa L. Insecticidal efficacy of developed formulations was tested in-vitro against cabbage aphid (Brevicoryne brassicae L.) and in-vivo against aubergine aphid (Aphis gossypii G.) and whitefly (Bemisia tabaci G.). EC formulations comprising of seeds extract (40%) were prepared using bio-degradable solvents (50%) and emulsifier blends (10%) with hydrophilic-lypophilic balance (HLB) value (12.54) suitable for the seed oils formulation. Among nine EC formulations prepared from seed oils of each plant, EC-1 type performed well in terms of emulsion stability, cold test, accelerated storage and flash point test indicating feasibility for their commercial production. In-vitro study of A. squamosa 40 EC at 1% dose caused the maximum mortality of 80.7% (LC50 = 0.08%) against B. brassicae at 72 h after the treatment. The bio-efficacy was comparable with the synthetic insecticide dimethoate 30 EC at 0.1% dose. Besides A. squamosa, the 40 EC formulation of P. pinnata at 1% dose having 70.6% mortality at 72 h after treatment (LC50 = 0.19%) was also found promising. In-vivo studies in brinjal also indicated the maximum reduction of aphids (67.3–72.3%) and whiteflies (67.5–75.6%) within 5–14 days after application of A. squamosa 40 EC formulation at 1.0% dose followed by P. pinnata 40 EC. The total flavonoids and phenolic content in all the crude seed extracts varied from 20.9 to 53.9 mg QE/g and 5.8–9.5 mg GAE/g, respectively. Further analysis of the extracts by GC-MS revealed some bioactive constituents belonging to fatty acids, esters, aldehyde, phenols, etc. The study unveiled its significance in developing herbal insecticidal formulations as an alternative to harmful synthetic chemical insecticides and a step forward towards development of a promising eco-friendly technology in crop protection.

The plastidial metabolite 2-C-methyl-D-erythritol-2,4-cyclodiphosphate modulates defence responses against aphids.

Feeding by insect herbivores such as caterpillars and aphids induces plant resistance mechanisms that are mediated by the phytohormones jasmonic acid (JA) and salicylic acid (SA). These phytohormonal pathways often crosstalk. Besides phytohormones, methyl‐D‐erythriol‐2,4‐cyclodiphosphate (MEcPP), the penultimate metabolite in the methyl‐D‐erythritol‐4‐phosphate pathway, has been speculated to regulate transcription of nuclear genes in response to biotic stressors such as aphids. Here, we show that MEcPP uniquely enhances the SA pathway without attenuating the JA pathway. Arabidopsis mutant plants that accumulate high levels of MEcPP (hds3) are highly resistant to the cabbage aphid (Brevicoryne brassicae), whereas resistance to the large cabbage white caterpillar (Pieris brassicae) remains unaltered. Thus, MEcPP is a distinct signalling molecule that acts beyond phytohormonal crosstalk to induce resistance against the cabbage aphid in Arabidopsis. We dissect the molecular mechanisms of MEcPP mediating plant resistance against the aphid B. brassicae. This shows that MEcPP induces the expression of genes encoding enzymes involved in the biosynthesis of several primary and secondary metabolic pathways contributing to enhanced resistance against this aphid species. A unique ability to regulate multifaceted molecular mechanisms makes MEcPP an attractive target for metabolic engineering in Brassica crop plants to increase resistance to cabbage aphids.

Corrigendum.

[This corrects the article DOI: 10.1002/ece3.4639.].

English

Host preference and performance of cabbage aphid Brevicoryne brassicae were studied on seven brassica varieties under Greenhouse. Nymphs, apterous and alate aphids were significantly different on day three and day 15 among tested varieties. Higher total number of aphids per plant was recorded on Brassica carinata and lower on Brassica oleracea. Alates of B. brassicae preferred more to feed and reproduce on B. carinata varieties than the other tested varieties. Developmental and reproduction periods, fecundity and longevity of B. brassicae were significantly different among tested varieties. Shortest and longest developmental period were recorded on Holeta-1 (6.4 days) and Kale (8.9 days), respectively. The aphid had the highest fecundity on B. niger (79.5 nymphs/adult) and the lowest on cabbage (62.4 nymphs/adult).The reproductive rate, intrinsic rate of increase, generation time, doubling time of B. brassicae were significantly different among tested varieties. The intrinsic rate of increase of B. brassicae was 0.337, 0.310, 0.286, 0.276, 0.262, 0.250 and 0.239 days-1 on Holeta-1, Yellow Dodola, Axana, Blinda, B. niger, Cabbage, and kale respectively. Varieties of B. carinata were more suitable for cabbage aphid feeding and reproduction than the other tested varieties. Key words: B. brassicae, reproduction, development, intrinsic rate of increase, fecundity, Ethiopian mustard.

Control of Brevicoryne brassicae (Hemiptera: Aphididae) with extracts of Agave americana var. Marginata Trel. in Brassica oleracea crops

Alternative methods of pest control can and should be encouraged, especially those that consider the reality of smallholder family farmers. Here, we evaluated the potential of Agave americana (agave) extracts for the control of the aphid Brevicoryne brassicae in cabbage (Brassica oleracea L. var acephala) in the field and laboratory. The field experiments consisted of the evaluation of the proportion of dead aphids on cabbage plants after application of agave extracts. In the field, agave mixed with cow milk caused mortality above 80% and was the most effective extract. Agave mixed with water and agave mixed with ethanol elicited mortality above 60%. In the laboratory, we evaluated the mortality of aphids after the application of different concentrations of aqueous agave extracts; the commercial insecticide deltamethrin was included as positive control. Evaluation took place at 3, 6, 12, 24, 48 and 72 hr after applying the treatment. As expected, deltamethrin was the most effective treatment. However, agave extract at concentrations of 0.750 and 0.500 g/mL caused >70% mortality 3 hr after application. We conclude that A. americana extracts decreased aphid populations and is a promising alternative to the commercial insecticide against aphids in cabbage.

Influence of Brevicoryne brassicae L. incidence on the yield of marketable cabbage heads under different insecticide spray regimes in highlands of Himachal Pradesh (India)

Strong and negative correlation was observed between the yield of marketable cabbage heads and populations of/plant infestations by cabbage aphid (Brevicoryne brassicae L.) 14 days after first and second spray. Weak correlation existed between yield of marketable cabbage heads and aphid populations/plant infestations at pre-treatment. Therefore, insecticide sprays should be done to control late aphid infestations and avoided against early aphid infestations.

Bacteria and Competing Herbivores Weaken Top-Down and Bottom-Up Aphid Suppression.

Herbivore suppression is mediated by both plant defenses and predators. In turn, plant defenses are impacted by soil fertility and interactions with soil bacteria. Measuring the relative importance of nutritional and microbial drivers of herbivore resistance has proven problematic, in part because it is difficult to manipulate soil-bacterial community composition. Here, we exploit variation in soil fertility and microbial biodiversity across 20 farms to untangle suppression of aphids (Brevicoryne brassicae) through bottom–up and top–down channels. We planted Brassica oleracea plants in soil from each farm, manipulated single and dual infestations of aphids alone or with caterpillars (Pieris rapae), and exposed aphids to parasitoid wasps (Diaeretiella rapae) in the open field. We then used multi-model inference to identify the strongest soil-based predictors of herbivore growth and parasitism. We found that densities of Bacillus spp., a genus known to include plant-growth-promoting rhizobacteria, negatively correlated with aphid suppression by specialist parasitoids. Aphid parasitism also was disrupted on plants that had caterpillar damage, compared to plants attacked only by aphids. Relative abundance of Pseudomonas spp. bacteria correlated with higher aphid growth, although this appeared to be a direct effect, as aphid parasitism was not associated with this group of bacteria. Non-pathogenic soil bacteria are often shown to deliver benefits to plants, improving plant nutrition and the deployment of anti-herbivore defenses. However, our results suggest that these plant growth-promoting bacteria may also indirectly weaken top–down aphid suppression by parasitoids and directly improve aphid performance. Against a background of varying soil fertility, microbial biodiversity, competing herbivores, and natural enemies, we found that effects of non-pathogenic soil microbes on aphid growth outweighed those of nutritional factors. Therefore, predictions about the strength of plant defenses along resource gradients must be expanded to include microbial associates.