Biological Control Strategies Research Articles

Backward bifurcation of a plant virus dynamics model with nonlinear continuous and impulsive control.

Roguing and elimination of vectors are the most commonly seen biological control strategies regarding the spread of plant viruses. It is practically significant to establish the mathematical models of plant virus transmission and regard the effect of removing infected plants as well as eliminating vector strategies on plant virus eradication. We proposed the mathematical models of plant virus transmission with nonlinear continuous and pulse removal of infected plants and vectors. In terms of the nonlinear continuous control strategy, the threshold values of the existence and stability of multiple equilibria have been provided. Moreover, the conditions for the occurrence of backward bifurcation were also provided. Regarding the nonlinear impulsive control strategy, the stability of the disease-free periodic solution and the threshold of the persistence of the disease were given. With the application of the fixed point theory, the conditions for the existence of forward and backward bifurcations of the model were presented. Our results demonstrated that there was a backward bifurcation phenomenon in continuous systems, and there was also a backward bifurcation phenomenon in impulsive control systems. Moreover, we found that removing healthy plants increased the threshold $ R_{1}. $ Finally, numerical simulation was employed to verify our conclusions.

Oviposition behavior of the quasi-gregarious parasitoid, Ooencyrtus kuvanae (Hymenoptera: Encyrtidae).

The parasitoid wasp, Ooencyrtus kuvanae (Howard) (Hymenoptera: Encyrtidae), is a natural enemy of the spongy moth, a significant forest pest in North America. We investigated the oviposition behavior of O. kuvanae females on spongy moth egg masses by (i) presenting female parasitoids with a single spongy moth egg mass that was replaced every day, 2nd day, 4th day, 8th day, or 16th day (which is the total length of the oviposition period) and (ii) presenting female parasitoids with 1, 2, 4, or 8 egg masses at a time. Offspring developmental length ranged from 18 to 24 days. On average, male offspring exhibited faster developmental times, emerging approximately 1 day ahead of females. The amount of time that adult females spent on an egg mass affected the number of parasitized eggs. Specifically, more offspring emerged in the 4-, 8-, and 16-day treatments than in scenarios involving daily or every second-day egg mass replacement. The percentage of male offspring decreased as the number of egg masses presented to females increased. Interestingly, the total number of female offspring remained constant, but the number of male offspring decreased with an increase in the number of egg masses and time spent by the parent within a patch. The observed sexual dimorphism in development time, the influence of resource availability on offspring sex ratios, and flexible oviposition patterns illustrate the adaptability of O. kuvanae in response to varying conditions. These insights have implications for our understanding of parasitoid-host interactions and their potential role in biological control strategies.

Capnodis tenebrionis (Coleoptera: Buprestidae), an important pest of stone fruits in the Mediterranean basin: current management strategies and prospects for integrated pest management

Abstract Capnodis tenebrionis (Linné) is a devastating pest of stone fruits (Prunus spp.) in the Mediterranean region. The endophytic root-boring larvae cause the main damage and can kill a large tree within 2 years. For several decades, with the absence of an effective biological control strategy, the management of this pest has mainly relied on the use of nonselective insecticides. These insecticides are applied either as a foliar spray targeting adults or as a soil treatment targeting neonate larvae. The search for alternative management options has increased since 2000 as a result of reduced efficacy of chemical control, decreased number of available insecticides, and the need for control measures suitable for organic stone fruit production. The main focus was on entomopathogenic nematodes and fungi. Several isolates/strains of these pathogens were found to be effective against larvae and adults of C. tenebrionis under laboratory and semi-field conditions. In this article, we review the current management options of C. tenebrionis, including chemical, biological, resilient rootstock, and cultural options. The prospects for developing an integrated management approach for this pest are also discussed.

Parasitic efficiency of different egg parasitoids against invasive fall armyworm, <i>Spodoptera frugiperda</i> (J. E. Smith)

A study was conducted to examine the parasitic efficiency of different egg parasitoids viz., Trichogramma chilonis Ishii, Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) and Telenomus remus Nixon (Hymenoptera: Scelionadae) of Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae) and Corcyra cephalonica Stainton (Lepidoptera: Pyralidae), respectively under the laboratory condition at 28 ± 3°C. The investigation showed that T. chilonis displayed a parasitic efficiency ranging from 85 to 87 per cent, T. pretiosum from 80 to 89 per cent, and T. remus from 7 to 90 per cent. Both host species were accepted for parasitization, but C. cephalonica was identified as more suitable for the development of T. chilonis and T. pretiosum, while S. frugiperda was deemed the most suitable host for rearing T. remus. These findings contribute valuable insights into the host preferences and parasitic efficiencies of these parasitoids, essential information for potential applications in biological control strategies against agricultural pests.

Efficacy of rhizobacteria Paenibacillus polymyxa SY42 for the biological control of Atractylodes chinensis root rot

Atractylodes chinensis is one of the most commonly used bulk herbs in East Asia; however, root rot can seriously affect its quality and yields. In contrast to chemical pesticides, biological control strategies are environmentally compatible and safe. For this study, 68 antagonistic bacterial strains were isolated from the rhizospheres of healthy Atractylodes chinensis. Strain SY42 exhibited the most potent fungicidal activities, with inhibition rates against F. oxysporum, F. solani, and F. redolens of 67.07 %, 63.40 % and 68.45 %, respectively. Through morphological observation and molecular characterization, strain SY42 was identified as Paenibacillus polymyxa. The volatile organic components (VOCs) produced by SY42 effectively inhibited the mycelial growth of pathogenic fungi through diffusion. SY42 significantly inhibited the germination of pathogenic fungal spores. Following co-culturing with SY42, the mycelium of the pathogenic fungus was deformed, folded, and even ruptured. SY42 could produce cellulases and proteases to degrade fungal cell walls. Pot experiments demonstrated the excellent biocontrol efficacy of SY42. This study revealed that P. polymyxa SY42 inhibited pathogenic fungi through multiple mechanisms, which verified its utility as a biocontrol agent for the control of A. chinensis root rot.

Parasitoid-induced changes in metabolic rate and feeding activity of the emerald ash borer (Coleoptera: Buprestidae): implications for biological control

Parasitoid-host interactions form the foundation of biological control strategies against many agriculture and forest insect pests. The emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), is a serious invasive pest of ash (Fraxinus spp.) trees in North America. Tetrastichus planipennisi (Hymenoptera: Eulophidae) is a gregarious, koinobiont endoparasitoid, attacking late (3rd to 4th) instars of EAB larvae, which feed in the live phloem of ash trunks or branches, making serpentine-like galleries filled with larval frass. In the present study, we tested the hypothesis that T. planipennisi regulates the host metabolism and feeding activity to optimize its offspring development and fitness. We first compared the respiration rate of parasitized and unparasitized host larvae at different times after parasitism, and then measured feeding activity of both parasitized and unparasitized host larvae inside their feeding galleries. Although parasitized host larvae increased metabolic rate and feeding activity in the first few days of parasitism, T. planipennisi parasitism induced an overall reduction of the metabolic rate and decrease in feeding activity of parasitized host larvae over their development period. In addition, there was a negative relationship between feeding activity of parasitized hosts and brood sizes of the parasitoid progeny—i.e., the more parasitoid progeny a host larva received, the less feeding activity the host had. These findings suggest that T. planipennisi has limited ability to optimize its offspring development and fitness through regulations of the host metabolism and feeding activity and its parasitism reduces feeding damage of parasitized EAB larvae to infested ash trees.

Predation evaluation of the green lacewing, Chrysopa pallens on the pink tea mite pest, Acaphylla theae (Watt) (Acarina: Eriophyidae).

A better understanding of predator-prey interactions is crucial for the development of biological control strategies. The green lacewing, Chrysopa pallens, is a well-known generalist predator and reportedly functions as one of the most important biological control agents of insect pests. However, information regarding C. pallens' predation on tea plant pests, particularly notorious tea mites, remains largely unknown. In this study, we focused on the predator-prey relationship between C. pallens and an important tea mite pest, Acaphylla theae. We designed species-specific primers for the detection of A. theae DNA and established a PCR-based DNA gut content analysis assay. These results demonstrated that the primers were A. theae-specific and suitable for its molecular identification. The laboratory feeding experiment showed that the detectability success (DS50) of A. theae DNA remaining in C. pallens' guts was 2.9h. We then performed a molecular detection of field predation, and achieved a 23.53% positive detection rate of A. theae DNA in the guts of field-collected C. pallens. This, for the first time, provides direct evidence that C. pallens can prey on A. theae in tea plantations. Finally, we tested the prey preference and estimated the predation ability of C. pallens on different developmental stages of A. theae. The results revealed that C. pallens had no significant preference for different developmental stages of A. theae. The functional responses of C. pallens' predation on different densities of A. theae at different developmental stages followed a Type II Holling model. The initial attack rate (a') ranged from 0.735 to 0.858 and the handling time (Th) was approximately 0.01. This study is the first to demonstrate the trophic interactions between C. pallens and A. theae and provides evidence for the development of biological control strategies against A. theae using C. pallens as a candidate predator.

Role of Mermithid Nematodes in the Management of Agricultural and Household Insect Pests: A review

The increasing challenges associated with using chemicals in managing agricultural and household insect pests has prompted a re-evaluation of previous approaches and the search for new ones as alternatives or supplements to the present management programmes. The introduction and release of bio-agents, like fungi, bacteria, viruses, nematodes, and insects for the control of pests is a novel biological control strategy. Among bio-agents, the role of mermithid nematodes in insect-pest management has been considered. Mermithids are prime candidates for biocontrol of insects due to their adaptability to the life cycle of the host, a high degree of host specificity often limited to one or more species of insects, high reproductive potential, free swimming behavior making dissemination of pre-parasitic stage easy, pathogenic ability and high levels of parasitism. Another useful trait favoring their employability is their non-feeding habit soon after emerging from the host body, making their handling simple. The morphological, physiological, and behavioral responses of host insects are significantly disrupted by mermithid infective juveniles often the J2 stage. Many mermithid infections cause abdominal distortion, discolored cuticle/integument, and a decrease in total fat body content of the host. The parasitism by these nematodes can lead to formation of intersexual conditions in the host insects which also create distortion to endocrine system. Owing to such mechanism of parasitism of mermithids, these nematodes are one the best considerations as bio-control agents.

Morphological and molecular identification of the root and stem base rot pathogen on broad bean crop and control it using some Trichoderma biological agents

This study looked at the effects of biological control strategies for root and stem rot disease caused by Rhizoctonia solani using soil organisms as biocontrol agents. The results of the field survey showed the spread of root and stem rot disease on broad bean plants in some areas of Najaf Governorate, where the infection rate ranged from 32- to 89.5%. The Isolation process showed that five fungal isolates of Rhizoctonia solani were associated with the disease, which differed in some phenotypic characteristics in terms of growth speed and color difference. The results of the molecular diagnosis using the ITS marker sequencing for the three most pathogenic isolates showed that they were belonging to Rhizoctonia solani, thus were named Ahmed 1, 3, 4 and registered in the GenBank under accession numbers; ON 394595.1, ON 394597.1, and ON 394599.1, respectively. In the pathogenicity test, R. solani isolates displayed a difference in their virulence on broad bean plants, where R. solani 1 (Al-Mashkhab isolate) was the most virulent among the isolates and was selected for subsequent studies. Isolate T. longibrachiatum (T3) showed high antagonistic efficiency against isolate of the pathogenic fungus R. solani on P.D.A culture media, gave the highest inhibitory percentage 75.06% compared to isolates T1 and T2 of Trichoderma harzianum, which led to inhibition of the pathogen to 68.71% and 68.94%, respectively. In the culture filtrate test of isolates of the living fungi, isolate T3 had the highest inhibition in the growth of pathogenic R. solani, which was 5.20 cm compared to the two live fungi T1 and T2, which led to 6.20 and 5.95 cm, respectively. As for the pots experiment, the results revealed that the isolate of T. longibrachiatum (T3) protected the broad beans plants from root and stem rot pathogen, where the disease was not seen compared to the treatment of the pathogenic fungus R. solani, only in which the infection severity was 80%.

Diversity of Platygastroidea Species in Coffee Ecosystem at Thadiyankudisai, Tamil Nadu

During a one-year study from January, 2018 to January, 2019 at the Horticultural Research Station, Thadiyankudisai, Tamil Nadu, a combined count of 550 individuals of Platygastroidea species were documented under two family platygastridae (1 species) and scelionidae (9 species). Among the species diversity comprised of Telenomus sp. (52.0%) followed by Scelio sp. (11.4%), Calliscelio sp. (9.1%), Sparasion sp. (6.9%), Idris sp. (5.8%) and Baryconus sp. (4.0%). The least population was recorded in Tritelia sp. (2.2%). Researches on seasonal abundance exposed that the winter season exhibited the highest species population at 32.55%, with the South West Monsoon (SWM) following closely at 30.36%, while the North East Monsoon (NEM) period recorded the lowest species count at 16.54%. The prevalence of insect pests poses a significant challenge to achieving optimal yields in horticultural crops. Consequently, the examination of Platygastroidea species diversity assumes a pivotal role in the success of biological control strategies.

Control of two-spotted spider mite, Tetranychus urticae, on strawberry by integrating with cyetpyrafen and Phytoseiulus persimilis

The two-spotted spider mite (TSSM, Tetranychus urticae Koch) is a significant agricultural pest, particularly in strawberries. Management of TSSM has traditionally relied on synthetic acaricides, but to mitigate dependency on these chemicals, the control of TSSM on strawberry is often combined with biological control measures and chemical control strategies. The predatory mite, Phytoseiulus persimilis, is a promising biological control agent, preying on all TSSM developmental stages. In this study, we examined the toxicity of six common acaricides on TSSM and P. persimilis, and cyetpyrafen was selected due to its highest relative toxicity value. Then, we examined the compatibility of cyetpyrafen with P. persimilis for TSSM management on strawberries. The results suggested that cyetpyrafen revealed no substantial differences in prey consumption or longevity when compared to the control, though minor effects on the development durations of protonymphs and deutonymphs were noted in the subsequent generation. Additionally, cyetpyrafen's toxicity on key pollinators, such as Apis mellifera and Bombus terrestris, was found to be low. Thus, an integrated strategy combining cyetpyrafen (0.83 mg/L) with P. persimilis (predator–prey ratio of 1:30) was examined under laboratory and field conditions. Laboratory trials demonstrated a reduction in mites per leaf from 32.72 to 14.50 within 3 days, correlating to a 70.23% control efficiency. This efficacy increased to 96.04% by day 9 and was sustained until the experiment concluded on day 27. Field trials similarly showed a reduction in TSSM from 53.93 to 9.63 mites/leaf by day 6, achieving an 83.64% control efficiency, and culminated in a 98.46% reduction by day 10. These findings suggested that an integrated approach utilizing cyetpyrafen in conjunction with P. persimilis can be an effective alternative for TSSM management on strawberry plants.

Detection of citrus diseases in complex backgrounds based on image–text multimodal fusion and knowledge assistance

Diseases pose a significant threat to the citrus industry, and the accurate detection of these diseases represent key factors for their early diagnosis and precise control. Existing diagnostic methods primarily rely on image models trained on vast datasets and limited their applicability due to singular backgrounds. To devise a more accurate, robust, and versatile model for citrus disease classification, this study focused on data diversity, knowledge assistance, and modal fusion. Leaves from healthy plants and plants infected with 10 prevalent diseases (citrus greening, citrus canker, anthracnose, scab, greasy spot, melanose, sooty mold, nitrogen deficiency, magnesium deficiency, and iron deficiency) were used as materials. Initially, three datasets with white, natural, and mixed backgrounds were constructed to analyze their effects on the training accuracy, test generalization ability, and classification balance. This diversification of data significantly improved the model’s adaptability to natural settings. Subsequently, by leveraging agricultural domain knowledge, a structured citrus disease features glossary was developed to enhance the efficiency of data preparation and the credibility of identification results. To address the underutilization of multimodal data in existing models, this study explored semantic embedding methods for disease images and structured descriptive texts. Convolutional networks with different depths (VGG16, ResNet50, MobileNetV2, and ShuffleNetV2) were used to extract the visual features of leaves. Concurrently, TextCNN and fastText were used to extract textual features and semantic relationships. By integrating the complementary nature of the image and text information, a joint learning model for citrus disease features was achieved. ShuffleNetV2 + TextCNN, the optimal multimodal model, achieved a classification accuracy of 98.33% on the mixed dataset, which represented improvements of 9.78% and 21.11% over the single-image and single-text models, respectively. This model also exhibited faster convergence, superior classification balance, and enhanced generalization capability, compared with the other methods. The image-text multimodal feature fusion network proposed in this study, which integrates text and image features with domain knowledge, can identify and classify citrus diseases in scenarios with limited samples and multiple background noise. The proposed model provides a more reliable decision-making basis for the precise application of biological and chemical control strategies for citrus production.

Fecundity of diamondback moth females when offered honey with pyridalyl, a selective insecticide

AbstractWe previously reported that the presence of pyridalyl, a selective insecticide, in aqueous honey (50% v/v) negatively affects the survival of diamondback moth (Plutella xylostella: DBM) adults. However, it remains unclear whether toxicity of pyridalyl in aqueous honey affects the fecundity of adult female DBMs. We analysed the survival and fecundity of adult DBM under the water, honey or honey + pyridalyl conditions in glass tubes containing Japanese mustard spinach (Brassica rapa: Komatsuna) leaves for 10 days. The survival of adults under the honey (50% v/v) and honey + pyridalyl (100‐fold dilution) conditions was significantly higher and lower, respectively, than under the water condition during the experimental period. The number of eggs laid by DBM females each day (fecundity) under the water condition was significantly lower than that under the honey condition throughout the experimental period, except on day 1. In contrast, the numbers under the water and honey + pyridalyl conditions were not significantly different, except on day 2 (the honey + pyridalyl condition was significantly lower). To study the effects of plants grown in pots on the survival and fecundity of DBM females, we conducted experiments using acrylic cages containing potted komatsuna plants. The survival trends under the honey, and honey + pyridalyl conditions in the cages were similar to those in the glass tubes. Fecundity was evaluated based on the total number of subsequent generations (DBM larvae and pupae) on day 10. The numbers were significantly higher in the honey condition than in the water condition. In contrast, the number in the honey + pyridalyl condition was not significantly different from that in the water condition. Given our previous findings that the longevity and fecundity of Cotesia vestalis, an effective natural enemy of DBM larvae, remained unaffected by the presence of pyridalyl in honey as a food supply, our research suggests that introducing devices providing honey infused with pyridalyl in greenhouses as a nutritional source for C. vestalis could be an effective biological control strategy for managing DBM populations within greenhouse environments.

Earwig Releases Provide Accumulative Biological Control of the Woolly Apple Aphid over the Years.

Nature-based solutions, such as biological control, can strongly contribute to reducing the use of plant protection products. In our study, we assessed the effect of augmentative releases of the European earwig (Forficula auricularia) to control the woolly apple aphid (Eriosoma lanigerum), a worldwide pest that causes serious damage to apple trees. The trials were carried out in two organic apple orchards located in Catalonia (NE Spain) from 2017 to 2020. Two treatments were compared: with vs. without earwig release. For the treatment, 30 earwigs per tree were released by means of a corrugated cardboard shelter. These releases were performed once per season and were repeated every year. We periodically assessed the length of the woolly apple aphid colonies, the number of colonies per tree, the percentage of aphids parasitized by Aphelinus mali, and the number of earwigs per shelter. Our results showed that earwig releases reduced the length of the colonies, but this effect was noticeable only for the second year onwards. Moreover, we found that those releases were compatible with A. mali. Overall, we demonstrated the positive impact of earwig releases on the woolly apple aphid control and the importance of considering time on augmentative biological control strategies.

Chemical Ecology of Rathayibacter toxicus and Associated Bacteria: Profiling Volatile Compounds for Insights into Annual Ryegrass Toxicity Causative Agent

The study involved the isolation of bacteria from the surface of Rathayibacter toxicus infested ryegrass seeds, followed by an analysis of volatile organic compounds (VOCs) to identify biomarkers associated with each bacterial species. Among the four isolated bacteria (a species of Pantoea, two species of Pseudomonas and R. toxicus), three were evaluated for their antibiosis potential against R. toxicus. The main objective of this research was to characterize the volatile compounds produced by R. toxicus and to assess the capability of the other three bacteria to serve as biological control agents. The volatile chemicals were identified by using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC–MS) in the aforementioned bacterial species. The identified compounds such as 1-nonanol, geraniol, decanoic acid and 2-decanone may serve as biomarkers for R. toxicus. Additionally, obtained information on VOCs may facilitate chemical communication between bacteria and the nematode which is responsible to carry it to the ryegrass plant. During the antibiosis assay, Pantoea agglomerans and Pseudomonas cedrina, among the endophytic/epiphytic bacterial species, produced compounds that significantly inhibited R. toxicus growth in vitro, with capacity values 22.7 ± 2.3 and 20.0 ± 2.0, respectively. In conclusion, this study's findings have significant implications for the management of annual ryegrass toxicity (ARGT), as they highlight the promising potential of P. agglomerans and Ps. cedrina as viable candidates for biological control strategies in ARGT management.

Pilot Testing of an Area-Wide Biological Control Strategy against the Coffee Berry Borer in Colombia Using African Parasitoids.

The coffee berry borer (CBB), Hypothenemus hampei (Ferrari, 1867) (Coleoptera: Curculionidae: Scolytinae), native to Africa, is a major global insect pest of coffee. It has invaded many coffee production areas around the world that do not have natural enemies. In this study, two African parasitoids, Prorops nasuta Waterston (Hymenoptera: Bethylidae) and Phymastichus coffea Waterston (Hymenoptera: Eulophidae), were mass-reared for field release against H. hampei in Chinchiná, Colombia. More than 1.5 million wasps of each species were released on a 61-hectare coffee farm in replicated plots, resulting in parasitism rates of up to 7.7% for P. nasuta and 56.3% for P. coffea. This led to a maximum reduction in H. hampei field populations of 81% from dispersal coffee plots (old coffee crops before plant stumping) and 64.3% in colonization coffee plots (new coffee crops with active growing and fruiting plants) within the farm. As a result of this area-wide strategy, the percentage of CBB-infested coffee berries in colonization coffee plots decreased from 51.1 to 77.5% compared to coffee plots without parasitoid releases. This approach offers a promising alternative to the use of chemical insecticides and could be integrated into current pest management programs to control H. hampei.

Using Biological Control as a Tool for Sustainability

The basic premise of biological control is to control agricultural pests and disease-transmitting insects using their natural enemies, which can be other beneficial insects, predators, parasitoids, and microorganisms such as fungi, viruses, and bacteria. Biological control has been growing exponentially in recent years, and the main reason for some countries is the demand for chemical-free food. Biological control of harmful insects is an environmentally correct technique and should be considered as a tool in Integrated Pest Management or organic farming systems. The objective of this practice is to control and even eliminate agricultural pests without leaving residues or causing damage to plants and the environment. Biological control is also essential when conventional methods do not work properly. This review aims to verify the biological control strategies of pests and diseases in agriculture, given the need for more efficient, sustainable, and profitable methods for their control. To achieve the main objective, we used the qualitative method based on research and analysis of theoretical books, theses banks, university dissertations, national and international scientific articles, scientific journals, documents, and digital platforms.

A Modular Endoscopic Tool and Laser Ablation Test-Bed for Studying Biological Tissue Ablation Control Strategies

A Modular Endoscopic Tool and Laser Ablation Test-Bed for Studying Biological Tissue Ablation Control Strategies

Implications of mosquito metabolism on vector competence.

Mosquito-borne diseases (MBDs) annually kill nearly half a million people. Due to the lack of effective vaccines and drugs on most MBDs, disease prevention relies primarily on controlling mosquitoes. Despite huge efforts having been put into mosquito control, eco-friendly and sustainable mosquito-control strategies are still lacking and urgently demanded. Most mosquito-transmitted pathogens have lost the capacity of de novo nutrition biosynthesis, and rely on their vertebrate and invertebrate hosts for sustenance during the long-term obligate parasitism process. Therefore, a better understanding of the metabolic interactions between mosquitoes and pathogens will contribute to the discovery of novel metabolic targets or regulators that lead to reduced mosquito populations or vector competence. This review summarizes the current knowledge about the effects of mosquito metabolism on the transmission of multiple pathogens. We also discuss that research in this area remains to be explored to develop multiple biological prevention and control strategies for MBDs.

Synergistic effects of grass competition and insect herbivory on the weed Rumex obtusifolius in an inundative biocontrol approach

Outcomes of weed biological control projects are highly variable, but a mechanistic understanding of how top-down and bottom-up factors influence the success of weed biological control is often lacking. We grew Rumex obtusifolius, the most prominent native weed in European grasslands, in the presence and absence of competition from the grass Lolium perenne and subjected it to herbivory through targeted inoculation with root-boring Pyropteron spp. To explore whether the interactive effects of competition and inundative biological control were size-dependent, R. obtusifolius was planted covering a large range of plant sizes found in managed grasslands. Overall, competition from the grass sward reduced aboveground biomass and final root mass of R. obtusifolius about 62- and 7.5-fold, respectively, and increased root decay of R. obtusifolius from 14 to 58%. Herbivory alone increased only root decay. However, grass competition significantly enhanced infestation by Pyropteron spp. and, as a consequence, enhanced the impact of herbivory on aboveground biomass and final root mass. The synergistic effect was so strong that R. obtusifolius plants grown from initially smaller roots did no longer develop. Inoculating R. obtusifolius with Pyropteron species in grasslands should be further pursued as a promising inundative biological control strategy in the weed’s native range.