Toxicity of Mentha pulegium essential oil and chemical pesticides toward citrus pest scale insects and the coccinellid predator Cryptolaemus montrouzieri

Applying botanical extracts with potential insecticidal actvity has long been considered a promising eco-friendly alternative to the use of chemical insecticides. In the present study, we evaluated the contact toxicity of Mentha pulegium essential oil (applied at either 2.73 mg/L, 9.56 mg/L, 13.65 mg/L, 27.31 mg/L, or 40.96 mg/L) toward three pest scales, Planococcus citri, Aonidiella aurantii, and Chrysomphalus aonidum, and two chemical insecticides, chlorpyrifos (100 mL/hL) and spirotetramat (120 mL/hL), against P. citri and A. aurantii under laboratoty conditions. Toxicity of M. pulegium essential oil and both insecticides was also assessed on the coccinellid predator Cryptolaemus montrouzieri. The highest mortality rates for all scale insect nymphs (> 97% for A. aurantii and 100% for P. citri or C. aonidum) were obtained following essential oil application at a dose of 40.96 mg/L. Lowest mortality rate (3.6 ± 0.92%) of C. montrouzieri adults was induced by an essential oil application at a dose of 8.95 mg/L, compared to either dose 11.26 mg/L or 17.66 mg/L. Both chemical insecticides significantly affected survival of mealybug and armored scale insect nymphs until 21 days after treatment. Chlorpyrifos, being highly effective against P. citri and A. aurantii, was significantly more toxic than spirotetramat toward both A. aurantii nymphs and predatory C. montrouzieri adults until three weeks after treatment. Using M. pulegium essential oil in combination with spirotetramat could be recommended for eco-friendly, sustainable control of P. citri, A. aurantii and C. aonidum in citrus orchards while minimizing harmful side effects on C. montrouzieri. © 2022, African Association of Insect Scientists.