International audience | Biocontrol solutions (macroorganisms, microorganisms, natural substances, semiochemicals) are presented as potential alternatives to conventional plant protection products (PPPs) because they are supposed to have lower impacts on ecosystems and human health. However, to ensure the sustainability of biocontrol solutions, it is necessary to document the unintended effects of their use. Thus, the objectives of this work were to review (1) the available biocontrol solutions and their regulation, (2) the contamination of the environment (soil, water, air) by biocontrol solutions, (3) the fate of biocontrol solutions in the environment, (4) their ecotoxicological impacts on biodiversity, and (5) the impacts of biocontrol solutions compared to those of conventional PPPs. Very few studies concern the presence of biocontrol solutions in the environment, their fate, and their impacts on biodiversity. The most important number of results were found for the organisms that have been used the longest, and most often from the angle of their interactions with other biocontrol agents. However, the use of living organisms (micro and macroorganisms) in biocontrol brings a specific dimension compared to conventional PPPs because they can survive, multiply, move and colonize other environments. The questioning of regulation stems from this specific dimension of the use of living organisms. Concerning natural substances, the few existing results indicate that while most of them have low ecotoxicity, others have a toxicity equivalent to or greater than that of the conventional PPPs. There are almost no result regarding semiochemicals. Knowledge of the unintended effects of biocontrol solutions has proved to be very incomplete. Research remains necessary to ensure their sustainability.

Under intensive human activity, sewage discharge causes eutrophication-driven cyanobacteria blooms as well as nanomaterial pollution. In biological control of harmful cyanobacteria, top-down effect of protozoan has great potentials for removing cyanobacterial populations, degrading cyanotoxins, and improving phytoplankton community. ZnO nanoparticles as a kind of emerging contaminants have attracted increasing attention because of wide application and their high bio-toxicity effects on reducing the ingestion of aquatic animals including Paramecium, thereby possibly disturbing top-down control of cyanobacteria. Therefore, this study investigated the effects of ZnO nanoparticles at environmental-relevant concentrations on the protozoan Paramecium removing toxic Microcystis. Results showed Paramecium effectively eliminated all the Microcystis, despite exposure to ZnO nanoparticles. However, their ingestion rate was significantly reduced at more than 0.1 mg L⁻¹ ZnO nanoparticles, thereby delaying Microcystis removal. Nevertheless, at 0.1 mg L⁻¹ ZnO nanoparticles, the time to Microcystis extinction decreased compared to the group without ZnO nanoparticles, because Microcystis populations were reduced under this circumstance, while ingestion rate of Paramecium was unaffected. Furthermore, ZnO nanoparticles obviously accumulated in food vacuoles of Paramecium, and the size of nanoparticles aggregates and zinc concentrations in Paramecium were increased with ZnO nanoparticles concentrations. At the end of experiment, these food vacuoles were not dissipated. Overall, these findings suggest that ZnO nanoparticles impair protozoan top-down effects through reducing Microcystis and ingestion rate as well as disturbing functions of their digestive organelles, and highlight the need to consider the interfering effects of environmental pollutants on cyanobacterial removal efficiency by protozoans in natural waters.

In recent years, pollution of antibiotics and heavy metal has often been reported in organic wastes. Saprophytic insects have been recorded as biological control agents in organic waste management. During organic waste conversion, the intestinal bacteria of the saprophytic insects play an important role in digestion, physiology, immunity and prevention of pathogen colonization. Black soldier fly (BSF) Hermetia illucens has been widely used as saprophytic insects and showed tolerance to sulfonamides (SAs) and cadmium (Cd). Diversity and changes in gut microbiota of black soldier fly larvae (BSFL) were evaluated through 16S rRNA high-throughput sequencing, and a decrease in diversity of gut microbiota along with an increase in SAs stress was recorded. Major members identified were Actinomycetaceae, Enterobacteriaceae, and Enterococcaceae. And fourteen multi-resistance Klebsiella pneumoniae strains were isolated. Two strains BSFL7-B-5 (from middle midgut of 7-day BSFL) and BSFL11-C-1 (from posterior midgut of 11-day BSFL) were found to be low-toxic and multi-resistance. The adsorption rate of SAs in 5 mg/kg solutions by these two strains reached 65.2% and 61.6%, respectively. Adsorption rate of Cd in 20 mg/L solutions was 77.2% for BSFL7-B-5. The strain BSFL11-C-1 showed higher than 70% adsorption rates of Cd in 20, 30 and 40 mg/L solutions. This study revealed that the presence of multi-resistance bacterial strains in the gut of BSFL helped the larvae against SAs or Cd stress. After determining how and where they are used, selected BSFL gut bacterial strains might be utilized in managing SAs or Cd contamination at suitable concentrations in the future.

Seed coating (‘seed treatment’) is the leading delivery method of neonicotinoid insecticides in major crops such as soybean, wheat, cotton and maize. However, this prophylactic use of neonicotinoids is widely discussed from the standpoint of environmental costs. Growing soybean plants from neonicotinoid-coated seeds in field, we demonstrate that soybean aphids (Aphis glycines) survived the treatment, and excreted honeydew containing neonicotinoids. Biochemical analyses demonstrated that honeydew excreted by the soybean aphid contained substantial concentrations of neonicotinoids even one month after sowing of the crop. Consuming this honeydew reduced the longevity of two biological control agents of the soybean aphid, the predatory midge Aphidoletes aphidimyza and the parasitic wasp Aphelinus certus. These results have important environmental and economic implications because honeydew is the main carbohydrate source for many beneficial insects in agricultural landscapes.

The use of some systemic insecticides has been banned in Europe because they are toxic to beneficial insects when these feed on nectar. A recent study shows that systemic insecticides can also kill beneficial insects when they feed on honeydew. Honeydew is the sugar-rich excretion of hemipterans and is the most abundant carbohydrate source for beneficial insects such as pollinators and biological control agents in agroecosystems. Here, we investigated whether the toxicity of contaminated honeydew depends on i) the hemipteran species that excretes the honeydew; ii) the active ingredient, and iii) the beneficial insect that feeds on it. HPLC-MS/MS analyses demonstrated that the systemic insecticides pymetrozine and flonicamid, which are commonly used in Integrated Pest Management programs, were present in honeydew excreted by the mealybug Planococcus citri. However, only pymetrozine was detected in honeydew excreted by the whitefly Aleurothixus floccosus. Toxicological studies demonstrated that honeydew excreted by mealybugs feeding on trees treated either with flonicamid or pymetrozine increased the mortality of the hoverfly Sphaerophoria rueppellii, but did not affect the parasitic wasp Anagyrus vladimiri. Honeydew contaminated with flonicamid was more toxic for the hoverfly than that contaminated with pymetrozine. Collectively, our data demonstrate that systemic insecticides commonly used in IPM programs can contaminate honeydew and kill beneficial insects that feed on it, with their toxicity being dependent on the active ingredient and hemipteran species that excretes the honeydew. Insecticides recommended in Integrated Pest Management programs reach honeydew and kill beneficial insects that feed on it.

Common varieties of genetically modified (GM) cotton increasingly display insect-resistant properties via expression of bacterial-derived toxins from Bacillus thuringiensis (Bt). This necessitates a deeper understanding of the possible effects of these crops on non-target insects. The mirid bug Apolygus lucorum is a major pest in cotton production in China, however, the effect of GM cotton on this non-target species is currently virtually unknown. This insect is exposed to these transgenic plants by consuming genetically modified (GM) leaves. In this study, laboratory experiments were conducted to assess the toxicity of CCRI41 and CCRI45, (genetically modified cotton varieties which express the toxins Cry1Ac and CpTI (Cowpea Trypsin Inhibitor)) on nymphs and adults of A. lucorum. There was no detectable increase in mortality after A. lucorum fed on GM cotton leaves for 20 days. While we detected trace amounts of Cry1Ac proteins in both A. lucorum nymphs and adults (<10 ng/g fresh weight), the expression of genes related to detoxification did not detectably differ from those feeding on non-GM cotton. Our binding assays did not show Cry1Ac binding to receptors on the midgut brush border membrane from either A. lucorum nymphs or adults. Our findings collectively indicate that feeding on leaves of the GM cotton varieties CCRI41 and CCRI45 have few toxic effects on A. lucorum.

Sclerotinia stem rot (SSR), a soil-borne plant disease, cause the yield loss of oilseed rape. Selenium (Se), a beneficial element of plant, improves plant resistance to pathogens, and regulates microbial communities in soil. Soil microbial communities has been identified to play an important role in plant health. We studied whether the changes in soil microbiome under influence of Se associated with oilseed rape health. SSR disease incidence of oilseed rape and soil biochemical properties were investigated in Enshi district, “The World Capital of Selenium”, and soil bacterial and fungal communities were analyzed by 16S rRNA and ITS sequencing, respectively. Results showed that Se had a strong effect on SSR incidence, and disease incidence inversely related with plant Se concentration. Besides, soil Se enhanced the microbiome diversities and the relative abundance of PGPR (plant growth promoting rhizobacteria), such as Bryobacter, Nitrospirae, Rhizobiales, Xanthobacteraceae, Nitrosomonadaceae and Basidiomycota. Furthermore, Soil Se decreased the relative abundance of pathogenic fungi, such as Olpidium, Armillaria, Coniosporium, Microbotryomycetes and Chytridiomycetes. Additionally, Se increased nitrogen metabolism, carbohydrate metabolism and cell processes related functional profiles in soil. The enrichment of Se in plants and improvement of soil microbial community were related to increased plant resistance to pathogen infection. These findings suggested that Se has potential to be developed as an ecological fungicide for biological control of SSR.

Plant essential oils are regarded as interesting alternative tools to be integrated into the management of pest insects. However, as they generally consist of mixtures of numerous molecules, the physiological basis for their action is unresolved. Here, we evaluated the effects of essential oil of the Neotropical plant Siparuna guianensis Aubl., commonly known as Negramina, against an important pest insect: the green peach aphid Myzus persicae (Sulzer), and also in two non-target natural enemies: the ladybeetle predators Coleomegilla maculata (DeGeer) and Eriopis connexa (Germar). In addition, we conducted a computational docking analysis for predicting the physical interactions between the two Negramina essential oil major constituents: β-myrcene and 2-undocanone, and the transient receptor potential (TRP) channels as potential binding receptors in the aphid and ladybeetles. As the most important results, Negramina essential oil caused mortality in M. persicae aphids with an LC95 = 1.08 mg/cm2, and also significantly repelled the aphids at concentrations as low as 0.14 mg/cm2. Our computational docking analysis reinforced such selectivity actions as the Negramina essential oil major compounds (i.e., β-myrcene and 2-undocanone) bound to the TRP channels of M. persicae but not to ladybeetle-related TRP channels. Interestingly, the exposure to the Negramina essential oil did not affect the predatory abilities of C. maculata but increased the abilities of E. connexa to prey upon M. persicae. Collectively, our findings provided a physiological basis for the insecticidal and selectivity potential of Negramina essential oil, reinforcing its potential as a tool to be used in integrated pest control programs.

Hydroponic greenhouse studies were used to investigate the effect of four anthropogenic pollutants (perchlorate (ClO4-), selenium (Se), manganese (Mn), and hexavalent chromium (Cr (VI))) on the biological control agent Diorhabda elongata Brullé. Contaminant concentrations were quantified for experimental Tamarix ramosissima Ledab. plants and D. elongata beetles. Growth of larvae was significantly reduced by Se contamination, but was not affected by the presence of perchlorate, Mn, or Cr (VI). All of the contaminants were transferred from plants to D. elongata beetles. Only Cr (VI) was accumulated at greater levels in beetles than in their food. Because T. ramosissima grows in disturbed areas, acquires salts readily, and utilizes groundwater, this plant is likely to accumulate anthropogenic pollutants in contaminated areas. This study is one of the first to investigate the potential of an anthropogenic pollutant to influence a weed biological control system.

The use of some systemic insecticides has been banned in Europe because they are toxic to beneficial insects when these feed on nectar. A recent study shows that systemic insecticides can also kill beneficial insects when they feed on honeydew. Honeydew is the sugar-rich excretion of hemipterans and is the most abundant carbohydrate source for beneficial insects such as pollinators and biological control agents in agroecosystems. Here, we investigated whether the toxicity of contaminated honeydew depends on i) the hemipteran species that excretes the honeydew; ii) the active ingredient, and iii) the beneficial insect that feeds on it. HPLC-MS/MS analyses demonstrated that the systemic insecticides pymetrozine and flonicamid, which are commonly used in Integrated Pest Management programs, were present in honeydew excreted by the mealybug Planococcus citri. However, only pymetrozine was detected in honeydew excreted by the whitefly Aleurothixus floccosus. Toxicological studies demonstrated that honeydew excreted by mealybugs feeding on trees treated either with flonicamid or pymetrozine increased the mortality of the hoverfly Sphaerophoria rueppellii, but did not affect the parasitic wasp Anagyrus vladimiri. Honeydew contaminated with flonicamid was more toxic for the hoverfly than that contaminated with pymetrozine. Collectively, our data demonstrate that systemic insecticides commonly used in IPM programs can contaminate honeydew and kill beneficial insects that feed on it, with their toxicity being dependent on the active ingredient and hemipteran species that excretes the honeydew. Insecticides recommended in Integrated Pest Management programs reach honeydew and kill beneficial insects that feed on it.