Mortality rates and feeding behavior of adult Myllocerus undecimpustulatus undatus Marshall (Coleoptera: Curculionidae) exposed to four biopesticides on peach foliage in field cages

Abstract

Mortality and feeding damage of Myllocerus undecimpustulatus undatus Marshall (Coleoptera: Curculionidae) exposed to four biopesticides on peach foliage in field cages were assessed at two sites in Florida. Two branches (one for caging weevils and one with no cage) with 6–8 leaves without evidence of herbivory were tagged on each of 25 trees at each site. Before treatment applications, one leaf was collected from each uncaged branch for a baseline assessment of endemic entomopathogenic fungal propagules and spray drift. Treatments were three entomopathogenic fungus-based formulations (BotaniGard®ES, PFR-97™ 20 % WDG, and Met52® EC), one azadirachtin formulation (AzaMax™), and distilled water as a control. Branches tagged for caging were sprayed with either one of the three fungal biopesticide treatments at a concentration of 10⁷ propagules per ml, an azadirachtin formulation, or distilled water until runoff and then allowed to air dry. One leaf was randomly selected from each sprayed branch for propagule deposition assessment. Five adult M. undecimpustulatus undatus were placed in each cage (five cages per treatment) and left for 15 days after which survivorship and herbivory were assessed across three trials at each site (15 total replicates per treatment per site). All biopesticide treatments resulted in higher weevil mortality compared to the water control. BotaniGard caused approximately four times higher mortality than the other fungal treatments and 78 % mycosis. Mean damage rating index values were highest in the control treatment, followed by BotaniGard ≥ PFR-97 ≥ Met52 = AzaMax. The high mortality rates caused by BotaniGard and reduced feeding caused by AzaMaz suggest that adult M. undecimpustulatus undatus populations might be managed in the field by combining these two biopesticides.