Aedes aegypti, is a major vector of several human diseases such as dengue, yellow fever, chikungunya and Zika virus. Multiple strategies are adopted for its control including eradication of mosquito ...breeding sites by improving water storage and solid waste disposal as well as treating breeding sites with chemical insecticides. However, continuous use of insecticides has resulted in development of insecticide resistance in Ae. aegypti. This study explores the potential biocontrol of Ae. aegypti by the use of commercial entomopathogenic nematodes, namely Heterorhabditis bacteriophora, H. downesi, H. megidis, Steinernema carpocapsae, S. feltiae and S. kraussei. The pathogenic effect of nematodes (concentrations 10, 250, 500 and 1,000 infective juveniles (IJs)) was assessed against third instar Ae. aegypti in multi-well culture plates for 3 days. The evaluated nematode species were pathogenic to Ae. aegypti, however, their virulence varied significantly. Heterorhabditis bacteriophora and S. carpocapsae were most virulent causing 90-100% mortality at 100 IJs per larva, whereas H. megidis and S. kraussei showed least virulence causing 40-60% mortality. Heterorhabditis downesi and S. feltiae had intermediate virulence. Third instar Ae. aegypti indiscriminately overfeed nematodes triggering melanisation but ingested nematodes overcome the defence system resulting in killing the larvae and reproduced within them. Some of the nematodes were melanised, suggesting a strong humoral defence response by Aedes, nevertheless, with variable degree of melanisation. The melanisation did not stop nematode from multiplying and killing Aedes larvae and thus, they have potential to be developed into a novel strategy for Ae. aegypti control.
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•Bacterial metabolites of Xenorhabdus enter Tetranychus urticae adults through cuticle.•Predatory mites were less affected by the bacterial metabolites than T. urticae.•Eggs of ...predatory mites were resistant to X. szentirmaii or X. nematophila supernatant.•Bacterial supernatants killed 18.5%-39.2% of mobile stages of predatory mites.•Long legs and thick cuticle of predatory mites reduce their contact with metabolites.
The bacterial metabolites in supernatants of Xenorhabdus species have acaricidal activity, but this mode of entry into mites has not yet been elucidated. Herein, we report on the possible mode of entry of Xenorhabdus szentirmaii and Xenorhabdus nematophila supernatants into Tetranychus urticae (Acari: Tetranychidae) adult females. We also assessed the toxicity of the supernatants against the developmental stages of the predatory mites, Phytoseiulus persimilis and Neoseiulus californicus (Acari: Phytoseiidae). Experiments were conducted at 25 ± 1 °C, 70 ± 5% relative humidity, and 16:8h light:dark conditions. Our data showed that the bioactive acaricidal compound is most effective (86.5 to 89% mortality) when the entire integument of T. urticae comes in contact with it compared to contact of the ventral side only (26.5–34%). Against P. persimilis and N. californicus at 6 days post-application (dpa), the eggs were not affected by the X. szentirmaii or X. nematophila supernatant, whereas mortality of the mobile stages (larva, protonymph, deutonymph, adult) was 18.5% to 39.2%. Overall, the predatory mites were less affected by the bacterial metabolites than T. urticae. We hypothesize that the differences in morphology such as longer legs and thicker cuticle, as well as the diet of the predatory mites, reduce the contact of the body parts to the supernatant-treated surfaces. We need to isolate, identify, and characterize the X. szentirmaii and X. nematophila metabolite(s) and demonstrate efficacy to pestiferous mites and safety to plants, non-target organisms and the environment before it can be used as an acaricide.
The gastropod Pseudosuccinea columella participates in the dissemination of Fasciola hepatica in the environment, acting as the main intermediate host of this parasite in Brazil. The present study ...sought to elucidate the possible pathogenic effects of the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora on P. columella, by evaluating the influence of infection on alanine aminotransferase (ALT) and aspartate aminotransferase (AST), as well as the concentrations of total protein, uric acid, and urea in the snail's hemolymph. For this, the snails were exposed to EPNs for 24 and 48 h, and for each exposure time, 20 snails were dissected after 7, 14 and 21 days for hemolymph collection. The primary findings suggest a significant proteolysis alongside elevated levels of uric acid and urea in P. columella infected individuals. These findings reveal that H. bacteriophora HP88 infection induced serious changes in the snail's metabolism, triggering important deleterious effects.
The infective juveniles (IJs) of entomopathogenic nematode (EPN)
find and infect their host insects in heterogeneous soil ecosystems by sensing a universal host cue (CO
) or insect/plant-derived ...odorants, which bind to various sensory receptors, including G protein-coupled receptors (GPCRs). Nematode chemosensory GPCRs (NemChRs) bind to a diverse set of ligands, including odor molecules. However, there is a lack of information on the NemChRs in EPNs. Here we identified 21 GPCRs in the
genome sequence in a triphasic manner, combining various transmembrane detectors and GPCR predictors based on different algorithms, and considering inherent properties of GPCRs. The pipeline was validated by reciprocal BLAST, InterProscan, GPCR-CA, and NCBI CDD search. Functional classification of predicted GPCRs using Pfam revealed the presence of four NemChRs. Additionally, GPCRs were classified into various families based on the reciprocal BLAST approach into a frizzled type, a secretin type, and 19 rhodopsin types of GPCRs. Gi/o is the most abundant kind of G-protein, having a coupling specificity to all the fetched GPCRs. As the 21 GPCRs identified are expected to play a crucial role in the host-seeking behavior, these might be targeted to develop novel insect-pest management strategies by tweaking EPN IJ behavior, or to design novel anthelminthic drugs. Our new and stringent GPCR detection pipeline may also be used to identify GPCRs from the genome sequence of other organisms.
Odontotermes obesus (Blattodea: Termitidae) is a prevalent subterranean wood-eating termite species that causes damage to mature trees, saplings and seedlings. The efficacy of most synthetic ...insecticides against this notorious pest has been compromised primarily because of its enigmatic feeding behavior and development of resistance to a number of insecticides. It has therefore become necessary to explore other alternative biologically sound and low-impact termite control methods, particularly for use in forests. Hence, this study was designed to verify the efficacy of different indigenous EPN isolates (Steinernema carpocapsae, Heterorhabditis bacteriophora and Heterorhabditis indica) against workers of Odontotermes obesus. The pathogenicity of each nematode isolate was assessed in laboratory conditions using filter paper and sawdust bioassay at two different temperatures (16 ± 1 and 26 ± 1 °C). Additionally, the efficacy of the nematode species was also assessed in field conditions. The results of the experiments revealed that the mortality of termite workers was more pronounced in sawdust bioassay in comparison with filter paper bioassay at both the tested temperatures. The mortality response in both bioassays was more pronounced at the higher temperature. A significantly higher mortality was recorded at both tested temperatures for S. carpocapsae followed by H. bacteriophora and H. indica. A dose-dependent positive mortality response was also recorded at both tested temperatures. Similar to the laboratory trials, the field applications of the three tested nematode species showed that maximum mortality was recorded for S. carpocapsae followed by H. bacteriophora and H. indica. It was therefore concluded that indigenous EPNs can provide more effective control of termites, possibly because of their direct interaction with pest species in the soil and the possibility of causing secondary infection through infected cadavers.
•The polyphenol oxidase of G. mellonella is resistant to H. beicherriana.•Use thiourea as an adjuvant for biopesticide to enhance the effectiveness of EPN.•Suppressing host immunity combined with EPN ...can accelerate host death.
Entomopathogenic nematodes (EPN) are potent microbial biocontrol agents applied commercially against various economically important insect pests. The efficacy of EPN in the field may be partially reduced when compared to chemical insecticides due to its sensitivity to environmental stressors like temperature, desiccation, and UV light. Thus, researchers have developed methods to enhance the effectiveness of EPN, such as screening or breeding stress-resistant strains and creating adjuvants for EPN protection in the field. This study used another strategy to lower the host’s immunity so that the anti-infection ability of the pest wanes, and the virulence of EPN waxes accordingly. In addition to its use as a plant growth regulator, thiourea also functions as an inhibitor of polyphenol oxidase (PO) in insects. Thiourea can inhibit a key interaction in the humoral immunity of insects, so we utilized it to enhance the efficacy of EPN. To investigate the effects of thiourea on PO activity inhibition and EPN pathogenesis, we studied the effects of thiourea on survival, infectivity, reproduction, and host searching ability of the EPN, Heterorhabditis beicherriana, and monitored in vivo and in vitro polyphenol oxidase activity of the model insect host, Galleria mellonella. The survival of H. beicherriana infective juveniles (IJs) was barely affected after exposure to 0.5 mM and 1 mM thiourea solution, and the reproductive output of H. beicherriana IJs (after applying 50, 100 and 200 IJs per host) in 0.5 mM and 1 mM thiourea was not different compared to the control. However, the LD50 of G. mellonella larvae caused by H. beicherriana without thiourea was significantly higher than H. beicherriana IJs in thiourea. Moreover, thiourea inhibited in vivo and in vitro polyphenol oxidase activity of G. mellonella infected by EPNs at different concentrations. Thus, thiourea can improve the biological control efficacy of EPNs, and the enhanced environmentally friendly approach may apply to diverse cropping systems.
Plants defend themselves against herbivores through the production of toxic and deterrent metabolites. Adapted herbivores can tolerate and sometimes sequester these metabolites, allowing them to feed ...on defended plants and become toxic to their own enemies. Can herbivore natural enemies overcome sequestered plant defense metabolites to prey on adapted herbivores? To address this question, we studied howentomopathogenic nematodes cope with benzoxazinoid defense metabolites that are produced by grasses and sequestered by a specialist maize herbivore, the western corn rootworm. We find that nematodes from US maize fields in regions in which the western corn rootworm was present over the last 50 y are behaviorally and metabolically resistant to sequestered benzoxazinoids and more infective toward thewestern corn rootworm than nematodes from other parts of the world. Exposure of a benzoxazinoid-susceptible nematode strain to the western corn rootworm for 5 generations results in higher behavioral and metabolic resistance and benzoxazinoid-dependent infectivity toward the western corn rootworm. Thus, herbivores that are exposed to a plant defense sequestering herbivore can evolve both behavioral and metabolic resistance to plant defense metabolites, and these traits are associated with higher infectivity toward a defense sequestering herbivore. We conclude that plant defense metabolites that are transferred through adapted herbivores may result in the evolution of resistance in herbivore natural enemies. Our study also identifies plant defense resistance as a potential target for the improvement of biological control agents.
•Wireworms, Limonius californicus are significant pests of wheat in Montana.•No effective control measures are available for wireworms.•Seed treatment with neonicotinoids can only repel the wireworms ...temporarily.•Entomopathogenic nematodes might help control wireworms.•Steinernema carpocapsae and Steinernema riobrave worked against wireworms in laboratory and indoor conditions.
Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), are economically important soil-dwelling pests that attack many field crops worldwide. Wireworms have become a serious threat to spring wheat in the Northern Great Plains because of lack of effective control measures, creating a need for alternative control methods such as biological control with entomopathogenic nematodes (EPNs). A laboratory bioassay was used to test ten EPN strains and identify infective EPN strains against the sugarbeet wireworm, Limonius californicus (Mannerheim) (Coleoptera: Elateridae). Steinernema carpocapsae (Weiser) (All and Cxrd strains) and S. riobrave Cabanillas, Poinar, and Raulston (355 and 7–12 strains) killed 60–70% of L. californicus larvae in four weeks when applied at 700 Infective juveniles (IJs) (25 IJs/cm2), 1400 IJs (50 IJs/cm2), 2800 IJs (100 IJs/cm2), and 5600 IJs (200 IJs/cm2) per larva in the laboratory. Also, Heterorhabditis bacteriophora (Poinar) VS strain and Steinernema rarum (Doucet) 17c + e strain caused 50–60% mortality to L. californicus larvae after four weeks when applied at 5600 IJs/larva. However, regardless of the concentration applied, the penetration rate of infective juveniles into the host did not exceed 33%. In shade house trials, S. riobrave and S. carpocapsae strains caused 34–56% L. californicus mortality after four weeks with 50 and 56% mortality caused by S. carpocapsae All and S. riobrave 355 strain, respectively when applied at the rate of 80,000 IJs/pot. These results suggest that S. carpocapsae and S. riobrave may have significant potential for protecting spring wheat crops from L. californicus.
The flatheaded root-borer Capnodis tenebrionis (Linné) (Coleoptera: Buprestidae) causes serious damage to stone fruit trees in Mediterranean countries. The use of entomopathogenic nematodes (EPNs) is ...an eco-friendly tool that can efficiently control C. tenebrionis. In this study, the efficacy of five EPN isolates native to Morocco was assessed against different developmental stages of C. tenebrionis in laboratory and greenhouse experiments. In Bioassay 1, the susceptibility of neonate larvae of C. tenebrionis to EPNs was evaluated according to temperature (25 and 32 °C) and soil moisture (5 and 10%). The greatest mortality rates were observed for Heterorhabditis bacteriophora HB-MOR7 (97.5%) and Steinernema feltiae SF-MOR9 (95%) with the 10% soil moisture-25 °C combination. S. feltiae SF-MOR9 and Heterorhabditis sp. HJo-MOR14 induced moderate to high mortality regardless of the temperature-soil moisture combination. In Bioassay 2, Heterorhabditis sp. HJo-MOR14 performed better against adults of C. tenebrionis than the other isolates. In addition, no difference in susceptibility between females and males was recorded for each EPN isolate. In pot experiment, more live larvae of C. tenebrionis were found in roots and collar of almond trees for HJo-MOR14 (0.93) than HB-MOR7 (0.47) and SF-MOR9 (0.43). Furthermore, treatments by SF-MOR9 and HB-MOR7 ensured low infestations of trees by larvae of C. tenebrionis than the treatment by HJo-MOR14 (36.7, 43.3 and 66.7% respectively). Our results show that Moroccan EPN isolates have potential as alternative methods for the control of C. tenebrionis.
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•The susceptibility of different developmental stages of C. tenebrionis to Moroccan entomopathogenic nematodes was evaluated.•The efficacy of Moroccan EPN depends on EPN species/strains and the different developmental stages of the pest.•EPN strains from area infested by C. tenebrionis or from desert area, were the most effective in C. tenebrionis.•The simultaneous use of the strains SF-MOR9 and HJo-MOR14 in the same orchards, is possible for a broad control of C. tenebrionis.
•Adults and larvae of L. cinnamomeus were susceptible to entomopathogenic nematodes.•S. carpocapsae caused high mortality of adults at 10 °C with 6 h a day at 15 °C.•Some populations of S. feltiae ...were virulent against mycophagous larvae at 10 °C.•Larvae in summer diapause are susceptible to H. bacteriophora at 25 °C.•There are short periods with optimal temperatures for EPN applications in autumn.
The European truffle beetle Leiodes cinnamomeus (Panzer) (Coleoptera: Leiodidae) is the most important pest in black truffle (Tuber melanosporum) plantations. Adults and larvae feed on truffles during the cold months of autumn and winter, while during spring and summer larvae are in diapause. This study aims to test the susceptibility of L. cinnamomeus adults and larvae to different entomopathogenic nematode (EPN) species at various temperatures under laboratory conditions. Different populations of Steinernema carpocapsae and Steinernema feltiae were applied against adults and mycophagous larvae at 20 °C, 10 °C and 10–15 °C (10 °C during 18 h and 15 °C during 6 h a day), while Heterorhabditis bacteriophora was only applied against diapause larvae at 25 °C. S. carpocapsae caused 100% mortality of adults three days after application at 20 °C. At 10 °C, adults were not susceptible to any EPN species seven days after treatment, while at 10–15 °C S. carpocapsae was the most virulent species (76.6–96.6% mortality). In the case of larvae, all EPN species were infective at 20 °C (43.3–83.3% mortality), despite differences among some populations. At 10 °C, only two populations of S. feltiae caused higher mortality of larvae (50–53.3%) than control seven days after treatment. H. bacteriophora caused 100% mortality against diapause larvae five days after application at 25 °C. Soil temperature was measured in a truffle plantation for each hour every day from September 2021 to April 2022 at 20 cm depth. From September to mid-October it was registered a temperature above 15 °C for more than 20 h a day. Temperatures were generally below 10 °C from November to March. An appropriate timing of field applications should be considered due to the short periods of time when temperature is optimal for each EPN species tested.
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