Dipentene

(+)-α-Pinene (98%), α-pinene (98%), (S)-(−)-limonene (96%), dipentene, (S)-(−)-citronellal (96%), (±)-citronellal (≥95%), (−)-linalool (≥95%), linalool (97%), (−)-terpinen-4-ol (≥95%), and terpinen-4-ol (≥95%) were purchased from Sigma-Aldrich (Darmstadt, Germany). HPLC-grade n-hexane was supplied by QREC (Asia) Sdn. Bhd. (Selangor, Malaysia).

A 90-mm filter paper (100-0011, Advantech, Tokyo, Japan) was placed in each insect-culture dish (ICD), with 1 mL of PEG400 (Sigma Chemical Co., St. Louis, MO, USA) as an untreated control. Cloves (5.6 mg/mL as eugenol, Sigma Chemical Co.), cypress oil (49 mg/mL as dipentene, Sigma Chemical Co.), shrubby sophora (22.5 mg/mL as matrine, Sigma Chemical Co.), pyrethrins (1 mg/mL, Sigma Chemical Co.), ivermectin (1.0 mg/mL) + allicin (0.5 mg/mL), and ivermectin (0.25 mg/mL) + allicin (1.0 mg/mL) were applied to the filter papers in different ICDs using a micropipette. The concentrations of these active ingredients were selected based on their effective concentrations in commercially available products. On a working bench, the filter papers were left to soak the drug solution for 30 min and then partially dried. PRMs (20 individuals) were transferred to each ICD (Figure 5). The PRMs and drug-containing ICDs were stored in insulated foam containers at 25 °C and 70% humidity, and the death rates of PRMs were recorded after 2, 24, and 48 h of treatment. The described method is based on the “contact filter paper susceptibility and resistance test” outlined in the guidelines for insecticide efficacy testing [22 ].