Selectivity of essential oils to the egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

ABSTRACT The diversity of arthropod pests has required the combined use of various control methods. The application of essential oils showing insecticidal, repellent or phage-inhibiting activity, together with the release of natural enemies, can improve integrated pest management provided the oils display selectivity. The aim of this study was to evaluate the selectivity of the oils of rosemary pepper [Lippia origanoides Kunth (Verbenaceae)], citronella [Cymbopogon winterianus Jowitt. (Poaceae)] and lemongrass [C. citratus (DC) Stapf.] for Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae), comparing five concentrations (0.01, 0.05, 0.1, 0.5 and 1.0%), and a control (neutral detergent at 1.0%). Residual toxicity was evaluated using adult mortality, calculating lethal concentrations (LC50) in addition to the reductions in parasitism in eggs of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) and selectivity for the par asitoids. The three oils showed selectivity for the parasitoid T. pretiosum, resulting in a mortality rate of between 17.2% (rosemary pepper) and 32.2% (lemongrass) at the lowest concentration. The essential oil of rosemary pepper stood out with an LC50 of 0.43%, a reduction of only 22% in parasitism (Class 1 - Innocuous) and 88.0% emergence, at a dose of 0.01%. The LC50 of the lemongrass oil was 0.15%, with a 34.0% reduction in parasitism (Class 2 - Slightly harmful) and 74.0% emerged adults. For the citronella oil, the LC50 was 0.12%, with a reduction of 46.0% (Class 2 - Slightly harmful) and emergence of 62.0%. The selectivity of the essential oils makes possible to release T. pretiosum, integrating biological control with botanical insecticides, as long as non-sprayed eggs are parasitised by T. pretiosum.

摘要 节肢动物害虫的多样性使得多种防治手段联合施用成为必要之举。将兼具杀虫、驱避或抑菌活性的精油与天敌释放手段联用，若精油具备选择性，则可提升害虫综合治理（integrated pest management）的效果。本研究旨在评估迷迭香胡椒精油[Lippia origanoides Kunth，马鞭草科(Verbenaceae)]、香茅精油[Cymbopogon winterianus Jowitt，禾本科(Poaceae)]及柠檬草精油[C. citratus (DC) Stapf.]对草地贪夜蛾寄生蜂Trichogramma pretiosum Riley（膜翅目Hymenoptera：赤眼蜂科Trichogrammatidae）的选择性，设置5种浓度梯度（0.01%、0.05%、0.1%、0.5%及1.0%）及1.0%中性洗涤剂对照组。本研究以成虫死亡率评估残留毒性，计算致死中浓度（LC50），同时分析其对草地贪夜蛾（Spodoptera frugiperda (J. E. Smith)，鳞翅目Lepidoptera：夜蛾科Noctuidae）卵的寄生率抑制效果及对该寄生蜂的选择性。结果表明，三种精油均对赤眼蜂（T. pretiosum）表现出选择性：在最低浓度下，成虫死亡率介于17.2%（迷迭香胡椒精油）与32.2%（柠檬草精油）之间。在0.01%剂量下，迷迭香胡椒精油的LC50达0.43%，寄生率仅降低22%（属于1级——无危害），成虫羽化率为88.0%，表现最为突出；柠檬草精油的LC50为0.15%，寄生率降低34.0%（属于2级——轻微危害），成虫羽化率为74.0%；香茅精油的LC50为0.12%，寄生率降低46.0%（属于2级——轻微危害），成虫羽化率为62.0%。只要未施药的卵可被赤眼蜂寄生，这些精油的选择性即可支持赤眼蜂的释放，实现生物防治与植物源杀虫剂的协同应用。