title: Efficacy of Topical Application, Leaf Residue or Soil Drench of Blastospores of Isaria fumosorosea for Citrus Root Weevil Management: Laboratory and Greenhouse Investigations.
abstract: The efficacy of topical, leaf residue, and soil drench applications withIsaria fumosoroseablastospores (Ifrstrain 3581) was assessed for the management of the citrus root weevil,Diaprepes abbreviatus(L.). Blastospores ofIfrwere applied topically at a rate of 10⁷ blastospores mL-1on both the larvae and adults, and each insect stage was incubated in rearing cups with artificial diet at 25 °C, either in the dark or in a growth chamber under a 16 h photophase for 2 weeks, respectively. Percent larval and adult mortality due to the infection ofIfrwas assessed after 14 days as compared to untreated controls. Leaf residue assays were assessed by feeding the adults detached citrus leaves previously sprayed withIfr(10⁷ blastospores mL-1) in Petri dish chambers and then incubating them at 25 °C for 2-3 weeks. Efficacy of the soil drench applications was assessed on five larvae feeding on the roots of aCarrizohybrid citrus seedling ~8.5-10.5 cm below the sterile sand surface in a single 16 cm × 15.5 cm pot inside a second pot lined with plastic mesh to prevent escapees. Drench treatments per pot consisted of 100 mL ofIfrsuspension (10⁷ blastospores mL-1), flushed with 400, 900, or 1400 mL of water compared to 500, 1000, and 1500 mL of water only for controls. The mean concentration ofIfrpropagules as colony forming units per gram (CFUs g-1) that leached to different depths in the sand profile per treatment drench rate was also determined. Two weeks post-drenching ofIfrtreatments, larvae were assessed for percent mortality, size differences, and effect of treatments in reducing feeding damage to the plant root biomass compared to the controls. Topical spray applications caused 13 and 19% mortality in larvae and adults after 7 days compared to none in the control after 14 days, respectively. Adults feeding on a singleIfrtreated leaf for 24 h consumed less than the control, and resulted in 100% mortality 35 days post-treatment compared to 33% in the untreated control. Although offered fresh, untreated leaves after 24 h, only adults in the control group consumed them.IfrCFUs g-1were isolated 8.5-10.5 cm below the sand surface for the 1000 and 1500 mL drench rates only, resulting in 2%-4% larval mortality. For all theIfrdrench treatments, no differences were observed in percent larval mortality and size or the effect of treatments in reducing feeding damage to the plant root biomass compared to the controls. These results suggest that the foliar application ofIfrmay be an efficient biocontrol strategy for managing adult populations ofD. abbreviatus; potential alternative larval management strategies are discussed.
authors.affiliation: Indian River Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, 2199 South Rock Road, Fort Pierce, FL 34945, USA. pbavery@ufl.edu.
authors.forename: Pasco B
authors.initials: PB
authors.lastname: Avery
authors.affiliation: Subtropical Insect Research Unit, U.S. Horticultural Research Laboratory, Agricultural Research Service, USDA, 2001 South Rock Road, Ft. Pierce, FL 34945, USA. wayne.hunter@ars.usda.gov.
authors.forename: Wayne B
authors.initials: WB
authors.lastname: Hunter
authors.affiliation: Subtropical Insect Research Unit, U.S. Horticultural Research Laboratory, Agricultural Research Service, USDA, 2001 South Rock Road, Ft. Pierce, FL 34945, USA. david.hall@ars.usda.gov.
authors.forename: David G
authors.initials: DG
authors.lastname: Hall
authors.affiliation: Crop Bioprotection Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, USDA, Peoria, IL 61604, USA. mark.jackson@ars.usda.gov.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Jackson
authors.affiliation: Indian River Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, 2199 South Rock Road, Fort Pierce, FL 34945, USA. capowell@ufl.edu.
authors.forename: Charles A
authors.initials: CA
authors.lastname: Powell
keywords: Diaprepes abbreviatus; Isaria fumosorosea; biological control; blastospores; citrus; soil drench