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Background Entomopathogenic nematodes (EPNs) (Steinernematidae and Heterorhabditidae) and their symbiotic bacteria are pathogenic for a wide range of insect pests and have been used successfully as a biological control agent. Although EPNs are well studied against many agricultural insect pests, the efficacy of their symbiotic bacteria still remains unclear for many insect pests of agricultural importance. In the present study, the virulence of native EPN isolates and their cell-free supernatants of symbiotic bacteria were tested against the 3rd and 4th larval instars of Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae) under laboratory conditions (25 ± 1 °C and R.H. 60%). Results The 4th instar larvae were more susceptible to infective juveniles (IJs) and mortalities over (95%) were achieved by all tested EPN isolates at the concentration of 100 IJs/cm2 after 72 hrs of exposure. The cell-free supernatants were more effective against the 3rd instar larvae and the highest mortalities were recorded as 42 and 60% in the contact and leaf disc bioassays, respectively. Conclusion The results indicated that the cell-free supernatants can be an ideal application for young larval stages of A. segetum. However, further studies are required to test the effectiveness of both EPNs and the cell-free supernatants of their symbiotic bacteria in field conditions.

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BACKGROUND Tuta absoluta is a devastating pest in tomato production areas worldwide. After its first introduction to Turkey in 2009, it quickly became the major pest of tomato‐growing areas. Although some biocontrol agents have been used, especially in greenhouses, the main control of T. absoluta relies heavily on chemical insecticides. However, failure in chemical control has often been reported due to resistance development. In this study, we investigated (i) the population structure of 22 T. absoluta populations across Turkey by analysing haplotypes, based on the cytochrome oxidase subunit I gene; (ii) the efficacy of three registered insecticides from different classes (metaflumizone, chlorantraniliprole and spinosad) in real field‐greenhouse conditions; and (iii) the geographic distribution of target‐site mutations associated with insecticide resistance. RESULTS The efficacy of spinosad was higher than that of chlorantraniliprole and metaflumizone in the greenhouse trials, as documented by the mortality rates obtained, up to 14 days post application. Known resistance mutations in ryanodine receptors (RyR) (i.e. the I4790M/K and G4946E), nicotinic acetylcholine receptors (G275E), acetylcholinesterases (A201S) and voltage‐gated sodium channels (F1845Y and V1848I) were found at various frequencies across the populations genotyped. The I4790K diamide resistance mutation in the RyR has been reported for the first time in T. absoluta populations. Although a total of eight haplotypes were found, the overall mean genetic distance was lower than 0.001, indicating the high genetic homogeneity among Turkish T. absoluta populations. CONCLUSION The results will contribute to design area‐wide resistance management programs in T. absoluta control in Turkey. However, more monitoring studies are needed to implement evidence‐based insecticide resistance management strategies in the frame of integrated pest management. © 2021 Society of Chemical Industry.