Mesh exclusion bags are increasingly being adopted by Florida citrus growers to protect young citrus trees from Asian citrus psyllid, Diaphorina citri Kuwayama, and Huanglongbing disease. These mesh bags exclude larger insects such as D. citri but may allow entry of minute insects. Hibiscus mealybugs, Nipaecoccus viridis (Newstead), have been observed thriving in the micro-habitat created by these covers on trees. Entomopathogenic fungi (EPF) and insect growth regulators (IGRs) are effective against several mealybug species under various growing conditions, but their efficacy against N. viridis or within the microclimate within exclusion bags is unknown. Therefore, we evaluated various formulations of entomopathogenic fungi with and without IGR against N. viridis using laboratory bioassays. We then conducted semifield bioassays to determine effectiveness of EPF formulations alone and in combination with an IGR applied to citrus trees enveloped within mesh bags under field conditions. Survival probabilities of N. viridis nymphs exposed to all Beauveria bassiana-based products tested were comparable to malathion under laboratory conditions and reduced survival as compared to controls (water only). Under field conditions, mortality of N. viridis nymphs on leaves sprayed with each fungal formulation tested was significantly greater than on control treatments (Water, Suffoil X, 435 oil) up to four weeks post application. There were no differences in the colony forming units per leaf area amongst all fungal treatments. Formulated B. bassiana-based products applied alone or combined with an IGR should be effective tools for managing N. viridis populations on young citrus trees protected with mesh exclusion bags.
Keywords: citrus; entomopathogenic fungi; exclusion; mealybug.
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