The root weevil, Diaprepes abbreviatus (L.), originated in the Caribbean and is now a major pest of citrus, other crops and ornamentals in Florida. Young larvae feed on fibrous roots, move to larger roots as they grow, and pupate in the soil after 9-11 instars. We examined the influence of larval age, weight and instar on the susceptibility of D. abbreviatus to the entomopathogenic nematode, Steinernema riobrave Cabanillas, Poinar and Raulston. Diaprepes larvae belonging to different age cohorts were obtained from the USDA rearing facility in Fort Pierce, FL. Each larva was weighed and the head capsule measured according to standard procedures. Larval instar was determined on the basis of head capsule width. Larvae were placed in individual 25-dram snap-cap vials in Candler sand with 8% moisture by weight, and S. riobrave was applied at rates of 100 to 500 infective juveniles per container. Treatment containers were incubated at 24 °C and mortality was checked after 9-12 days. Mortality varied significantly among instars and decreased markedly in later instars. Within instars, mortality was not related to larval weight or age. The mechanisms responsible for differential susceptibility of larval instars are unknown but this phenomenon could have implications for the timing of nematode applications for weevil control in Florida citrus.
Species 1: Coleoptera Curculionidae Diaprepes abbreviatus (Diaprepes root weevil)
Species 2: Rhabditida Steinernematidae Steinernema riobrave (entomopathogenic nematode)
Keywords: biological control
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