Pesticidal character of phytoecdysteroids fromAjuga multiflora Bunge (Labiatae) on larvae ofCryptorrhynchus lapathi L. (Coleoptera: Curculionidae)

Abstract

Eight kinds of phytoecdysteroids extracted from different parts ofAjuga multiflora Bunge (Labiatae) that were collected from different places at different time were tested for killing effects on the 2-instar larvae ofCryptorrhynchus lapathi L by adding them to the artificial diet of larvae. The experimental results indicated that adding 1–3-mL phytoecdysteroids to the artificial diet could lead 58%–100% of 2-instar larvae ofC. lapathi to death within 24 days. The phytoecdysteroids extracted from the whole plant ofA. multiflora which was collected before flowering time were much more effective than those extracted from the plants collected at flowering and after flowering periods, and the modified mortality rate of larvae reached 65.22%, 85.07%, and 98.11% at the dosage level of 1-mL, 2-ml, and 3-mL extracts, respectively. The extract made from root ofA. multiflora plant was more effective in killing efficiency than those from stem and leaves, and the average death rates of larvae were up to 100%, 98.20% and 98.32% at dosage levels of 1-mL, 2-mL, and 3-mL extracts, respectively. The killing speed of the extracted phytoecdysteroids was slower than that of triflumuron, hexaflumuron or deltamethrin emulsifiable concentrate. The mortality rate of larvae is closely related to the feeding duration on the diets containing phytoecdysteroids. Feeding on the diets with addition of phytoecdysteroids for 16 days, more than 80% of treated 2-instar larvae ofC. lapathi were led to death. The killing effect of the extracts was little affected by the growth areas ofA. multiflora plant and the adding way to artificial diet.

Keywords

Ajuga multifora Bunge / Cryptorrhynchus lapathi L / Larva / Phytoecdysteroid / S767.3 / S763.38 / A