Ovicidal and Physiological Effects of Essential Oils Extracted from Six Medicinal Plants on the Elm Leaf Beetle, Xanthogaleru-Ca Luteola (Mull.)

Plant essential oils may serve as safe alternatives to detrimental synthetic pesticides due to relatively lower side effects on the environment and non-targeted organisms. The current study was conducted to investigate the ovicidal toxicity and physiological disruptions of six medicinal plant essential oils, including Artemisia annua L., Lavandula angustifolia Mill., Origanum vulgare L., Rosmarinus officinalis Spenn., Satureja hortensis L., and Thymus vulgaris L., on elm leaf beetle Xanthogaleruca luteola (Mull.). The LC50 (Lethal Concentration to kill 50% of tested insects) values of 122.8, 287.5, 152.8, 180.6, 315.9, and 1366.2 ppm were recorded for T. vulgaris, L. angustifolia, A. annua, S. hortensis, R. officinalis, and O. vulgare, respectively, 72 h after treatment of 3-day-old eggs of the pest. Significant decreases in the amounts of glucose, protein, and triglyceride macromolecules were also observed after treatment. The application of essential oils derived from T. vulgaris, A. annua, and S. hortensis at 400 ppm revealed 100% ovicidal activity. Accordingly, tested essential oils, particularly the essential oil of T. vulgaris, have been promising potential as biorational insecticides in the management of X. luteola.

Pyrrhalta luteola (elm leaf beetle).

The elm leaf beetle P. luteola is a serious pest of ornamental elms in most areas where they are grown. This insect is native to southern Europe and was introduced to the USA in the 1800s, but has also reached Central Asia, the Middle East, North Africa and South America and was recently detected in Australia. It feeds on all species of native and introduced elms, including American (Ulmus americana), English (U. procera), Chinese (U. parvifolia) and Siberian elm (U. pumila). Wu et al. (1991) identified elm leaf beetle as the second most important urban tree pest in the western United States and third most important nationally.

Pathogenicity of two fungal pathogens on larvae of the elm leaf beetle, Xanthogaleruca luteola Muller (Coleoptera: Chrysomelidae)

Background The elm leaf beetle (ELB), Xanthogaleruca luteola Muller (Coleoptera: Chrysomelidae), is one of the most important insect pests that cause damage and physiological stress for the trees. In the present research, pathogenicity of both entomopathogenic fungi (EPF), Beauveria bassiana and Metarhizium anisopliae on the 1st, 2nd, and 3rd instar larval of ELB at the concentrations of 105, 106, 107, and 108 conidia per ml, using immersion and spray methods and were evaluated. Results The results showed that LC50 of B. bassiana in immersion and spray methods were 3.88 × 102 and 7.52 × 102 conidia/ml, while LC50 of M. anisopliae in mentioned methods were 7.05 × 102 and 11.85 × 102 conidia/ml, respectively. The highest mortality rate in both EPF was observed in the 1st instar larvae that were significantly different than the control treatment. Moreover, the highest and lowest mortality in both EPF, using immersion and spray methods, were observed at the concentrations of 108 and 105 conidia/ml, respectively. Therefore, susceptibility of 1st and 2nd larval instars was more than 1st instar larvae. Based on the findings of the present study, there was no mortality during the first 24 h, while after 2 days, the mortality was recorded and increased over time in case of both pathogens. Accordingly, B. bassiana and M. anisopliae were pathogenic on larvae of ELB. Conclusions The outputs of the study demonstrated that applications of these eco-friendly fungal pathogens with other non-chemical methods are recommended. Of course, under natural conditions, their efficiency may change; thus, more comprehensive studies are necessary.

Laboratory assay of entomopathogenic nematodes against the elm leaf beetle, Xanthogaleruca luteola Müller (Col.: Chrysomelidae)

The susceptibility of the elm leaf beetle, Xanthogaleruca luteola Müller (Col.: Chrysomelidae), 3<sup style="text-align: justify;">rd</sup> instar larvae and adults to the entomopathogenic nematodes Steinernema feltiae, S. carpocapsae, and Heterorhabditis bacteriophora was determined in laboratory assays. Larval mortality was assessed at 0, 16, 32, 48, 64, 80, 96, and 112 h after exposure of the larvae and adults to six concentrations (0, 100, 200, 300, 400, and 500) of infective juveniles (IJs) per mL. The median lethal concentration (LC₅₀) values for each nematode species against the larvae and adults of X. luteola were 167.59 and 6.73 IJ·mL<sup style="text-align: justify;">–1</sup> for S. feltiae, 218.23 and 204.09 IJ·mL<sup style="text-align: justify;">–1</sup> for S. carpocapsae, and 338.66 and 70.29 IJ·mL<sup style="text-align: justify;">–1</sup> for H. bacteriophora, respectively. Also, the median lethal time (LT₅₀) values for each nematode species against the larvae and adults of X. luteola were 44.51 and 22.23 h for S. feltiae, 50.78 and 36.17 h for S. carpocapsae, and 67.64 and 34.71 h for H. bacteriophora, respectively. The S. feltiae nematode was the most effective species in controlling the larvae and adults of the elm leaf beetle, X. luteola. Based on these and other results, the research could be expanded on the prospects of using entomopathogenic nematodes, especially S. feltiae, in managing of the elm leaf beetle, X. luteola.