Do organic silicon and imidacloprid synergistically induce toxicity to the new invasive mealybug Phenacoccus solenopsis Tinsley on Portulaca grandifora plants?

Abstract

In this study, the efects of organic silicon (Si) on the toxicity of imidacloprid to a new invasive mealybug, Phenacoccus solenopsis(Hemiptera: Pseudococcidae), infesting Portulaca grandifora (Caryophyllales: Portulacaceae) plants were evaluated using spotting anddipping methods under laboratory and feld conditions to improve management strategies for solenopsis mealybug. Results showedsignifcant synergistic efects of 0.06% organic Si with imidacloprid solution against third-instar P. solenopsis nymphs and adult females.However, the percentage mortalities increased remarkably afer P. solenopsis was exposed to 100, 50, and 25 mg a.i./L of imidaclopridcombined with organic Si. For the third-instar nymphs, these values increased to 100%, 100%, and 92.5%, respectively; for the adultfemales, these values increased to 100%, 100%, and 82.4%, respectively. Afer 5 days, the percentage mortalities reached 84.7%, 56.1%,and 39.7% when the third-instar nymphs were exposed to 100, 50, and 25 mg a.i./L of imidacloprid solution, respectively. Te percentagemortalities reached 57.5%, 38.9%, and 26.2% when adult females were exposed to the same imidacloprid solutions, respectively. OrganicSi alone elicited toxicity to P. solenopsis. Te percentage mortalities of the frst-, second-, and third-instar nymphs and the adult femaleswere 76.9%, 47.5%, 39.2%, and 18.9%, respectively. Field data showed that imidacloprid combined with organic Si caused sustainablecontrol of P. solenopsis. Te percentage mortalities of P. solenopsis reached maximum values (approximately 99.9%) afer 21 days. Tus,the combined treatment with imidacloprid and organic Si is synergistically more efective than the individual use of these substancesagainst third-instar P. solenopsis nymphs and adult females.