Background: The biological diversity on planet earth is declining day by day, due to different factors such as excessive applications of pesticides. The utilization of chemical pesticides affected environment as well as microorganisms. The awareness among the peoples towards the hazards by the residual toxicity of chemical pesticides should be developed for agro-environmental sustainability. Main body: Entomopathogenic nematodes (EPNs) are the bacto-helminth parasites which show classical mutualism with the genera Xenorhabdus and Photorhabdus. The nematodes along with its endosymbiotic bacteria have a biocontrol potential which could be used to reduce chemical pesticides. Applications of bioagents have been reported and resulted in considerable reduction in pathogens. Furthermore, these bioagents are biodegradable, eco-friendly and easy to apply for protection of crops against diverse pathogenic organism. The nematode-bacterium complexes are effective against huge range of bacteria, fungi, nematodes and insects that are harmful to the crops. Along with biocontrol potential, the endosymbionts produce diverse secondary metabolic compounds, exoenzymes and toxic compounds that show antibiotic, antimycotic, nematicidal, miticidal and anticancerous properties. Conclusion: The present review deals with the diversity of endosymbiotic microbes from EPNs and their role in biocontrol for the agro-environmental sustainability.

The cabbage butterfly, Pieris brassicae Linnaeus (Lepidoptera: Pieridae), is an oligophagous and invasive insect pest of various economically important cole crops. Recently, there have been reports about an increase in the incidence and damaging activities of cabbage butterflies, signifying that the existing control methods fail to meet the grower’s expectations. Entomopathogenic nematodes (EPNs) and their endosymbiotic bacteria have immense potential for the control of a wide range of insect pests. In this investigation, the EPN species Steinernema carpocapsae and its associated bacterial species, Xenorhabdus nematophila, were isolated and identified through morphological and molecular techniques. The laboratory bioassay experiment was performed using S. carpocapsae and X. nematophila against the 3rd instar larvae of P. brassicae (25 ± 1 °C; RH = 60%). The efficacy of EPN suspension (30, 60, 90, 120, 150 IJs/mL) and bacterial suspension (1 × 10⁴, 2 × 10⁴, 3 × 10⁴, 4 × 10⁴, and 5 × 10⁴ CFU/mL) via contact and oral routes showed significant mortality among the larvae. Surprisingly, 100% insect mortality within 48 h was recorded in the bacterial inoculum 5 × 10⁴ CFU/mL. However, in the case of EPNs (S. carpocapsae), 150 IJs/mL caused the highest, 92%, larval mortality rate after 96 h. The results signify that both indigenous EPNs and their associated bacteria can provide efficient control against P. brassicae larvae and could effectively contribute to IPM programs. However, further analyses are required to authenticate their effectiveness in field conditions.

Background: Entomopathogenic nematodes (EPNs) have been regarded as the most convenient strategy for insect pest management. The native strains of EPNs: Heterorhabditis bacteriophora EUPT-SD, H. bacteriophora EUPT-R, H. bacteriophora EUPT-KN, H. bacteriophora EUPT-K and H. bacteriophora EUPT-H isolated from mid-Himalayan region of Himachal Pradesh were tested in laboratory for their multiplication and virulence against 3rd and 4th larval instars of the tobacco cutworm, Spodoptera litura Fabricius (Lepidoptera: Noctuidae), the serious polyphagous pest affecting a wide range of agricultural crops worldwide. Results: All the EPN strains were effective against 3rd and 4th larval instars of S. litura. Insect mortality reached 90–96% after 96 h at nematode concentrations of 150 infective juveniles (IJs)/ml. The insect mortality was also recorded at low concentrations of IJs, but the most exposure period was required. High virulence was shown by H. bacteriophora EUPT-SD 96 and 94%, followed by H. bacteriophora EUPT-R 92 and 90%, H. bacteriophora EUPT-KN 92 and 90%, H. bacteriophora EUPT-K 92 and 90% and H. bacteriophora EUPT-H 92 and 90%, respectively, against 3rd and 4th larval instars in terms of reproductive potential and killing. All the insects were alive in the absolute control. Conclusion: Utilization of EPNs for the management of S. litura may be the best method to overcome the insect resistance problems and to manage the population of this insect pest. It may be an effective method and may be a partial substitute of synthetic insecticides, thus minimizing the excessive use of synthetic chemicals. The results demonstrated the potential of indigenous EPNs isolates against S. litura, but before further recommendation, multiplication field trials need to be conducted to confirm their efficacy at farm level.

The widespread applications of ZnO NPs in the different areas of science, technology, medicine, agriculture, and commercial products have led to increased chances of their release into the environment. This created a growing public concern about the toxicological and environmental effects of the nanoparticles. The impact of these NPs on the genetic materials of living organisms is documented in some cultured cells and plants, but there are only a few studies regarding this aspect in animals. In view of this, the present work regarding the assessment of the genotoxicity of zinc oxide nanoparticles using the mosquito Culex quinquefaciatus has been taken up. Statistically significant chromosomal aberrations over the control are recorded after the exposure of the fourth instar larvae to a dose of less than LD₂₀ for 24 h. In order to select this dose, LD₂₀ of ZnO NPs for the mosquito is determined by Probit analysis. Lacto-aceto-orcein stained chromosomal preparations are made from gonads of adult treated and control mosquitoes. Both structural aberrations, such as chromosomal breaks, fragments, translocations, and terminal fusions, resulting in the formation of rings and clumped chromosomes, and numerical ones, including hypo- and hyper-aneuploidy at metaphases, bridges, and laggards at the anaphase stage are observed. The percentage frequency of abnormalities in the shape of sperm heads is also found to be statistically significant over the controls. Besides this, zinc oxide nanoparticles are also found to affect the reproductive potential and embryo development as egg rafts obtained from the genetic crosses of ZnO nanoparticle-treated virgin females and normal males are small in size with a far smaller number of eggs per raft. The percentage frequencies of dominant lethal mutations indicated by the frequency of unhatched eggs are also statistically significant (p < 0.05) over the control. The induction of abnormalities in all of the three short-term assays studied during the present piece of work indicates the genotoxic potential of ZnO NPs, which cannot be labeled absolutely safe, and this study pinpoints the need to develop strategies for the protection of the environment and living organisms thriving in it.

Excessive use of insecticides are responsible to contaminate the environment, soil health, developing resistance in the insect pests, introduces new species, toxic to human and eliminates non-target organisms and affects the eco-balance and biodiversity adversely. Application of microbial bio-agents with the chemical insecticides is an assertive way to manage the population of pests, in an addition to dropping down the chemical residues risk to the eco-system. Larval stages of Spodoptera litura are prolific eater, caused huge losses globally. Individual and combined effect of chemical insecticides Barazide (Novaluron 5.25 %+Emamectin benzoate 0.9 % SC), entomopathogenic bacterial (Bacillus thuringiensis var. kurstaki), and entomopathogenic fungus (Beauveria bassiana and Metarhizium anisopliae) is assessed against the larvae of S. litura in bio-assay experiment. The decreasing trend in the observed mortality among insecticides alone is Barazide (95.80 ± 1.16, 85.30 ± 1.85 and 82.00 ± 1.72) > B. thuringiensis var. kurstaki (88.70 ± 1.01, 79.90 ± 2.01 and 78.00 ± 2.91) > B. bassiana (82.60 ± 2.46, 73.90 ± 2.46 and 73.00 ± 4.16) > M. anisopliae (78.60 ± 1.46, 68.90 ± 2.96 and 69.00 ± 3.46) after 96 h at its highest inoculation level against 3rd, 4th and 5th instar larvae. The combined application of Barazide @0.1 % with B. thuringiensis @1.5%induced mortality cent percent after 72 and 96 h against 3rd and 4th instar. Chi-squared test indicated a significant level of mortality at p < 0.05 level at highest dose and the probit analysis showed lowest LC₅₀ value at dose 5.15 and 7.63 % with 95 % FL:1.38-19.22 and 2.85-20.39 after 72 and 96 h of exposure against 3rd and 4th instar. The increasing trend in the observed mortality among insecticides used in combination is Barazide + B. thuringiensis < Barazide + B. bassiana < Barazide + M. anisopliae. Insecticides used in combination induced synergism that providing valuable practice to manage insect pests. These results suggested that the combined treatments could be a successful method for controlling the population of S. litura and at the same time farmers will decrease the inappropriate misuse and overuse of harmful chemical insecticides.