In this study, pyridaben LC values, resistance ratios, detoxification enzyme activities, synergism tests, and the H92R target-site mutation were investigated in T. urticae populations collected from apple orchards, providing important insights into the biochemical and molecular mechanisms underlying pyridaben resistance and the genetic basis of resistance evolution.
The two-spotted spider mite, Tetranychus urticae Koch, is a highly polyphagous and economically important pest affecting a wide range of crops worldwide. This study evaluated the potential of four rhizobacterial isolates—Leucobacter aridicollis (IQR1), Paenochrobactrum sp. (IQR2), uncultured bacterium IQR3, and marine bacterium AK6_052 (IQR5)—as candidate biological control agents against T. urticae. The rhizobacterial isolates were obtained from the tomato rhizosphere at the INRA experimental farm (Agadir, Morocco) and evaluated for their acaricidal and repellent activities against T. urticae. Corrected mortality and repellency index were assessed after 24, 48, and 72 h of exposure. All four isolates exhibited acaricidal activity, with IQR3 and IQR5 showing the greatest efficacy. Corrected mortality reached 69.9% with IQR3 at the highest concentration after 72 h of exposure. The isolates showed no statistically significant repellent activity. Under greenhouse conditions (108 CFU mL−1), IQR3 was associated with the lowest infestation incidence (64%), the lowest infestation severity (13.3%) and the lowest adult density (1.8 adults leaf−1); IQR5 showed a comparable trend. Overall, IQR3 and IQR5 represent promising rhizobacterial candidates for the sustainable management of T. urticae in tomato production. Further studies are needed to optimize their formulation, elucidate their mechanisms of action, and validate their efficacy under field conditions.
Said Bahoch, S. Chafiki, Soumaya El Assri et al.· International Journal of Pla...· 0 citations
The two-spotted spider mite, Tetranychus urticae Koch, is a major agricultural pest with a rapid propensity for developing acaricide resistance. Bifenazate targets mitochondrial cytochrome b (CYTB). While the G126S mutation is associated with resistance, its independent role remains unclear, as it often occurs with other SNPs. This study explores the molecular basis of bifenazate resistance in a Russian laboratory strain derived from a St. Petersburg greenhouse population. Disruptive selection with increasing bifenazate concentrations generated resistant and susceptible isofemale lines. AlphaFold2 structural modeling of CYTB indicated that G126S causes a steric clash, leading to conformational destabilization, whereas other reported mutations primarily affect the ligand-binding pocket. Oxford Nanopore sequencing revealed a low initial frequency of the G126S allele (<1%; 226/35,895 reads) in the unselected population. After one year of stepwise selection (0.00005–0.031% a.i.), the mutant allele frequency surged to 90% (7272/8056 reads). No other resistance-associated mutations were found in the analyzed cytb fragment. We report the first identification of the G126S mutation in a Russian T. urticae population and demonstrate rapid fixation under bifenazate selection. Within this genetic background, G126S alone appears sufficient to confer high-level resistance, emphasizing the population-specific nature of resistance evolution and the critical need for local monitoring.
E. S. Okulova, Dmitrij D. Skrypka, Olesja D. Bogomaz et al.· Horticulturae· 0 citations
The potential of synergists to improve insecticide efficacy and strengthen insecticide resistance management (IRM) strategies is highlighted and Cytochrome P450 monooxygenases and carboxyl esterases appear more influential in BBPL while glutathione S-transferases are more significant in BPPL.
Q. Sajiya, K. Manoj, S. Arundhati et al.· Plant Science Today· 0 citations
Brown rot, caused by Monilinia fructicola, is the most destructive pre- and postharvest fruit rot of peach worldwide. In 2024, a disease outbreak occurred in a South Carolina orchard despite a rigorous chemical management program consisting of preharvest applications of SDHI, QoI, and DMI fungicides. Isolates from affected orchards carried the Mona element upstream of the MfCYP51 gene, associated with reduced DMI fungicide sensitivity in the southeastern region. They displayed low, moderate, or high levels of resistance to boscalid, isofetamid, fluopyram, and fluxapyroxad based on EC50 values ranging from 0.33 to >300, 0.22 to 1.95, 0.28 to 7.41 and 0.30 to 115.11 µg/ml, respectively. In contrast, EC50 values obtained for historic isolates were ≤ 0.05 µg/ml for all SDHI fungicides. Whole-genome sequencing identified five SDH genotypes: wild type (WT; no aa substitutions); G1 (N226H in SDHB); G2 (P80H in SDHC); G3 (N226H in SDHB + V26I in SDHD); and G4 (N226H in SDHB, P80H in SDHC, and T24A in SDHD). Isolates harboring aa changes in multiple SDH subunits had the highest EC50 values and were resistant to all SDHIs tested. Detached fruit assays confirmed that label rates of SDHI fungicides failed to control isolates carrying multiple aa changes. To the best of our knowledge, this study provides the first report worldwide of SDHI resistance in Monilinia species field isolates linked to aa changes in the SDH subunits and combined SDHI and DMI resistance in peach orchards, highlighting the need for resistance monitoring and management.
J. Gelain, Johanna Wesche, E. Trotter et al.· Phytopathology· 0 citations