Semisynthesis and Pesticidal Activities of Derivatives of the Diterpenoid Andrographolide and Investigation on the Stress Response of Aphis citricola Van der Goot (Homoptera: Aphididae)

To discover natural-product-based pesticides, 7β-oxycarbonylandrographolide derivatives were stereoselectively constructed from a labdane diterpenoid andrographolide. Among them, 2′-(n)Pr-1′,3′-dioxin-7β-oxy(m-Cl)benzoylandrographolide (IIc), 2′-(n)Pr-1′,3′-dioxin-7β-oxyacetylandrographolide (IIf), 2′-(p-Me)Ph-1′,3′-dioxin-7β-oxy(o-Cl)benzoylandrographolide (Vb), and 2′-(p-Me)Ph-1′,3′-dioxin-7β-oxy(m-Cl)benzoylandrographolide (Vc) against Mythimna separata displayed the most promising growth inhibitory activity; 2′-(n)Pr-1′,3′-dioxin-7β-oxy(o-Cl)benzoylandrographolide (IIb: LC50 = 0.406 mg/mL) and IIc (LC50 = 0.415 mg/mL) exhibited the most pronounced acaricidal activity (andrographolide; LC50: 5.106 mg/mL) and good control effects against Tetranychus cinnabarinus; compounds Ic, IIe, and Va–c (LD50 = 0.035–0.039 μg/nymph) showed potent aphicidal activity (andrographolide: LD50 = 0.178 μg/nymph), and compounds IIe and Vb showed good control effects against Aphis citricola. Moreover, it was found that Hsp70 of A. citricola was an important gene involved in stress response to andrographolide and its derivatives.