The diamondback moth, Plutella xylostella (L.), is a major pest that has developed resistance to many groups of synthetic insecticides. Natural plant products present reliable alternatives for its management. In this study, the activities of essential oils and ethanol extracts from three medicinal plants, i.e., Curcuma longa L. (Zingiberaceae), Cymbopogon nardus (L.) Rendle (Gramineae), and Acorus calamus L. (Acoraceae), from Thailand against P. xylostella were evaluated. Four concentrations of the extracts (i.e., 0.625, 1.25, 2.5, and 5%) were tested. The essential oils and ethanol extracts of Cu. longa, Cy. nardus, and A. calamus exhibited different degrees of activity against P. xylostella. Of these, both the essential oil and ethanol extract of A. calamus at 5% (v/v) concentration exhibited feeding toxicity for P. xylostella larvae, resulting in 100% mortality 1 d after treatment, with a median lethal concentration of 0.528% for the essential oil and 1.074% for the ethanol extract. Furthermore, all concentrations of A. calamus ethanol extract exhibited contact toxicity to the larvae, resulting in >75% mortality 3 d after treatment. All tested extracts, except A. calamus ethanol extract at the 0.625% concentration, exhibited high repellent activity against P. xylostella larvae, while Cu. longa and Cy. nardus ethanol extracts at 5% (w/v) concentration and A. calamus essential oil at 2.5% (v/v) concentration deterred oviposition by P. xylostella adults with an effective repellency >70%. These results indicate that both essential oils and ethanol extracts of these plants have the potential to be developed as insecticides for use in integrated pest management of P. xylostella.
This work investigated acaricidal and repellent activities of Zanthoxylum myriacanthum Wall. ex Hook. f. (Rutaceae) extracts against Tetranychus urticae Koch and Tetranychus truncatus Ehara (Acari: Tetranychidae). Acaricidal activities were tested by spraying the extracts on adult females and eggs, and repellent activity was assessed in paired-choice tests with filter paper treated with the extracts by using adult female mites. Adult mortality 24 h after application of a 12% (w/v) concentration of the hexane extract was 73.3% for T. urticae and T. truncatus, whereas application of the methylene chloride extract caused 85.8% mortality of T. urticae and 85% mortality of T. truncatus. Lower concentrations (6–12%) of the methanol extract yielded low efficacy against T. urticae but exhibited high efficacy against T. truncatus (73.8–95.8%). In general, egg hatch was reduced <50% by 5 d following application of the extracts. Only the 6–12% concentration of the hexane extract caused higher levels of T. truncatus egg mortality ranging 55.4–68.7%. All extracts repelled adult mites over 64% from 5 to 72 h after exposure. However, the percentage of repellency showed no statistical differences in all treatments. Gas chromatography-mass spectrometry (GC-MS) analysis identified that the major chemical compounds in the hexane extract were DL-limonene (29.75%) and sabinene (9.76%), whereas limonene (40.70%) and sabinene (16.60%) were the principal constituents of the methylene chloride extract. Our results demonstrate that Z. myriacanthum dried fruit extracts have potential for controlling T. urticae and T. truncatus and might be developed as acaricides for integrated pest management programs.
Herbivore-induced plant volatiles (HIPVs) are regarded as an indirect plant defense against herbivores, since they attract natural enemies to the infested plant. On the other hand, HIPVs also affect behavioral responses of herbivores. In a previous study, Lytopylus rufipes, a parasitoid of the oriental fruit moth (Grapholita molesta), showed positive responses to pear HIPVs, but the influence of pear HIPVs on G. molesta is still unclear. To better understand these responses, we first tested oviposition preferences of G. molesta to uninfested and infested pear shoots (US and IS, respectively) and uninfested mature leaves (ML) in dual-choice bioassays with a cylindrical tube. Then, preferences to volatile components were also assessed. Results show that G. molesta females preferred US-, IS-, and ML-treated areas compared to the control area (no leaves), respectively. Subsequently, G. molesta females preferred IS over US, and US more than ML when comparing pear tissues. Furthermore, G. molesta females didn’t show any significant preference to individual volatile components, but more eggs were laid in the area treated with a synthetic pear HIPV blend, compared to the hexane-treated area (control). These results indicate that G. molesta females do not avoid infested pear shoots nor HIPVs. Moreover, HIPVs may recruit not only natural enemies, but herbivores to the release point of HIPVs. Thus, it is important to examine the responses of G. molesta females to HIPVs in the field before employing them for pest management.
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