HORTICULTURAL ENTOMOLOGY Interactions of Light Intensity, Insecticide Concentration, and Time on the Efficacy of Systemic Insecticides in Suppressing Populations of the Sweetpotato Whitefly (Hemiptera: Aleyrodidae) and the Citrus Mealybug (Hemiptera: Pseudococcidae)

The impact of light intensity on the uptake and persistence of the systemic neonicotinoid insecticides, imidacloprid and dinotefuran, were evaluated in poinsettia (Euphorbia pulcherrima Willd.) and yellow sage (Lantana camara L.). Insecticide residues were measured in leaves sampled from the treated plants at four time intervals after treatment to determine the relationship between insecticide concentration andefÞcacy against two insect pests: sweetpotatowhiteßy,Bemisia tabaci Gennadius, and the citrus mealybug, Planococcus citri Risso. The insecticides were evaluated at their respective label rate and at the comparable label rate of the other insecticide under two different light environments: ambient and shade. Theuptake of dinotefuran into yellow sagewasmore rapid at both treatment rates than both rates of imidacloprid, resulting in higher percent mortality of whiteßy nymphs (89.8Ð100) compared with imidacloprid (14.1Ð89.2) across all 4 wk. Additionally, plants that received both rates of dinotefuran had fewer whiteßy pupae ( 1.0) at week 4 compared with imidacloprid-treated plants (23.7Ð25.3). The uptake of dinotefuran into poinsettia plantswas also more rapid and resulted in quicker and higher percent mortality of whiteßy nymphs (89.5Ð99.6) compared with imidacloprid (14.1Ð89.2) across all 4 wk. However, despite efÞcient uptake, the efÞcacyof both systemic insecticideswas less for citrusmealybugwherepercentmortality valueswere 50% among all the treatments across the 4 wk. The use of the two systemic insecticides evaluated in regards to pest management in horticultural cropping systems is discussed.