Investigating IPM tools to manage the invasive mealybug Phenacoccus solenopsis

Abstract: Phenacoccus solenopsis (Hemiptera: Pseudococcidae) is a polyphagous invasive
pest, native to Asia, that is recently threatening horticultural and ornamental protected crops in Mediterranean countries. Because P. solenopsis raises economic concerns, there is a growing interest in exploring sustainable control tools, such as biological control and selective insecticides. After the report of P. solenopsis in Italy, predators such as Cryptolaemus  montrouzieri and Parexochomus nigripennis (Coleoptera: Coccinellidae) and parasitoids such as Anagyrus matritensis and Aenasius arizonensis (Hymenoptera: Encyrtidae) have been recorded as natural enemies of the pest in solanaceous protected crops and ornamental plants in urban environments in Sicily. Because no insecticides are currently authorized on P. solenopsis in Europe, we tested several commercial insecticides and plant essential oils (EOs) on the solenopsis mealybug. We also assayed the non-target effects of the most effective synthetic insecticides and EOs against P. solenopsis towards C. montrouzieri in terms of survival and olfactory response in the laboratory. The host stage selection of A. matritensis was assessed on P. solenopsis through choice and no-choice tests. Assayed systemic insecticides showed high toxicity towards P. solenopsis but negatively affected C. montrouzieri, while EOs had a safer ecotoxicological profile. Anagyrus matritensis parasitized all P. solenopsis stages except the male pupa while the 3rd instar nymph and pre-ovipositing female were the most preferred stages. The results highlighted that careful evaluation of each insecticidal substance should be assessed before its inclusion for the integrated control of P. solenopsis. Preliminary data on A. matritensis will be useful to unravel the biological traits of this new association and implement potential biocontrol applications. Also, the abundant presence in the field of A. arizonensis appears promising for P. solenopsis biocontrol. Overall, an integrated approach holds significant promise to manage the impact of P. solenopsis in newly invaded areas.