Toxicity, and biological and biochemical effects of hexaflumuron on the elm leaf beetle, Xanthogaleruca luteola (Col.: Chrysomelidae)

The elm leaf beetle, Xanthogaleruca luteola Müll., is the most important pest of elm trees in Iranian cities. Insect growth regulators (IGRs) such as hexaflumuron are recommended to use in urban areas for their low toxicity to human and environment. In this study, the impact of the chitin synthesis inhibitor, hexaflumuron, was evaluated on some biochemical and biological characteristics of the elm leaf beetle under laboratory conditions. The toxicity of this insecticide investigated on the last instar larvae of X. luteola using leaf dip method (25 ± 2 ºC, 75 ± 10% relative humidity, 16 h (light): 8 h (dark)). LC30 and LC50 values were calculated at 53.45 and 122.02 ppm, 72 h post treatment, respectively. Biological and biochemical characteristics were evaluated for 3rd instar larvae, following 72 h feeding on the elm leaves treated with LC50 and LC30 concentrations of hexaflumuron. The LC30 and LC50 concentrations of hexaflumuron increased the duration of larval stage, 10.04 ± 0.24 and 9.27 ± 0.43 days, respectively, compared with the control, 7.07 ± 0.413 days. There were no significant differences in the duration of pupal stage for LC30 and LC50 concentrations and control group. Hexaflumuron significantly decreased adult longevity compared with the control. Several morphological abnormalities were also observed in treated larvae and pupae. The results showed significant reductions of carbohydrate, protein, glycogen and lipid contents at the LC30 and LC50 concentrations of hexaflumuron. The activities of the detoxifying enzyme glutathione S-transferase, general esterases (α-esterases and β-esterases) and the immunological enzyme phenoloxidase were significantly affected by hexaflumuron. Although the results are clearly indicative of the adverse effects of sublethal concentrations of hexaflumuron on the beetle pest, further investigations are required to improve the efficiency of the chemical for being viably used in integrated pest management programs against the elm leaf beetle.