Laboratory Screening of Selected Entomopathogenic Fungi, Bioinsecticide, and Insect Growth Regulator Against Hibiscus Mealybug, Nipaecoccus viridis (Newstead)

Abstract

Orange | Citrus sinensi Hibiscus mealybug | Nipaecoccus viridis (Newstead) The goal of this screening is to evaluate several biological insecticides that are registered for use on various insect pests in Florida citrus production that are likely to have field efficacy for a recently established invasive, highly damaging mealybug pest in citrus. We also tested an insect growth regulator, buprofezin, a chitin synthesis inhibitor that is labeled for use in citrus that has shown efficacy on native mealybugs. All tests were completed in the laboratory over the course of 8 mo (Dec 2019 to Jul 2020) with a break in testing as our research station was closed temporarily for COVID-19. Assays consisted of fully expanded but not hardened citrus leaves (cv. Valencia) that were dipped into a designated insecticide at the maximum label rate and allowed to dry. Leaf petioles were then immersed in water in a 1.5 ml Eppendorf tube and secured with Parafilm™. Leaves were then placed into individual Petri dishes (Falcon Corning Petri Dish 150 × 15 mm, Fisher Scientific, United States) and ten 2nd to 3rd instar mealybug nymphs were transferred onto the leaf surfaces using a camel hair brush (#2 FM Brush Co., New York, United States). Petri dishes were sealed with Parafilm to prevent mealybugs from escaping and held under controlled conditions (25 ± 5°C; 70-80% RH and 16:8 (L:D) h photoperiod). Mortality was assessed under a ster-eomicroscope (Leica MZ6, Leica Microsystems Inc., IL, United States) every 24 h for 168 h; mean number of mealybugs dead per dish at 3, 5, and 7 DAT are presented here in Table 1. Five replicate bioassays per product were performed for a total of 50 mealybugs tested for each insecticide with a water control. Data were analyzed using a 2-way ANOVA (R v4.0.0) with means separated with Fisher's LSD at P ≤ 0.05. Materials tested had a range of efficacy for mortality of Nipaecoccus viridis in controlled laboratory bioassays. BotaniGard MAXX (Beauveria bassiana strain GHA and pyrethrin) had the highest mean mortality at all three time points. The two other materials with B. bassiana strain GHA, BoteGHA ES, and BotaniGard ES performed almost as well as BotaniGard MAXX. The lowest efficacy of any of the materials tested was PFR-97, which is used for control of several species of mealybugs in greenhouses. However, given the data presented here, PFR-97 does not look like a viable option for control of N. viridis. 1 1 This research was supported in part by industry gifts of pesticides, including entomopathenogenic fungi.