Efficacy of Beauveria bassiana strain GHA spray applications against coffee berry borer Hypothenemus hampei on Hawaii Island

Authors: WRAIGHT, STEPHEN - Former ARS Employee; GALAINI-WRAIGHT, SANDRA - University Of Hawaii; HOWES, REBECCA - Former ARS Employee; Castrillo, Louela; Griggs, Michael; CARRUTHERS, RAYMOND - University Of Hawaii; SMITH, ROBERT - Smithfarms; Matsumoto Brower, Tracie; Keith, Lisa

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Spray application of the common insect-pathogenic fungus Beauveria bassiana is a major component of an integrated pest management (IPM) program for coffee berry borer (CBB) in Hawaii. Previous studies have assessed the efficacy of Bb sprays; however, none have taken into account the CBB-control contribution of naturally-occurring strains of Bb prevalent in Hawaiian coffee fields. Intensive post-spray field sampling and laboratory processing of samples were conducted to provide a more accurate assessment of Bb efficacy by correcting for this natural activity. Results indicated that each spray of Bb (commercial strain GHA formulated as BotaniGard®) at the rate recommended by the University of Hawaii resulted in approximately 25% mortality of CBB embedded in green coffee berries. Monthly Bb sprays applied within the guidelines of the IPM program, which calls for strict sanitation of coffee fields (removal of all unharvested berries from trees before the start of each season) held crop damage to 10% or less. Post-spray aerial trapping of berry-seeking CBB revealed 30–40% infection, but residual activity was short (= 3 days). Used in combination with sanitation, a half rate of BotaniGard was nearly as effective as the recommended rate. The wild strains of Bb exhibited greater capacity for natural spread and persistence in CBB populations than strain GHA. If amenable to commercial development (mass-producible as safe, user-friendly formulations with good shelf-life), one of these fungi could provide coffee farmers with a more effective biocontrol agent for management of this difficult pest. Recommendations for most effective use of Bb in CBB IPM programs are presented.

Technical Abstract: Beauveria bassiana (Bb) strain GHA is a major component of an integrated pest management (IPM) program for coffee berry borer (CBB) in Hawaii. Efforts to measure effectiveness of GHA spray applications have been complicated by activity of naturally-occurring Bb. Studies were thus designed to provide more accurate efficacy assessments by accounting for this feral activity. BotaniGard® ES + Widespread Max® (WSM) surfactant (2.3 + 0.6 L/ha) were applied via hand-targeted sprayers in commercial coffee fields. Live CBB were collected at various times post spray and monitored for infection. GHA killed 12–15% of founder females collected 1–3 days post spray and 9¬–10% collected after 10 days (infections attributed to secondary transmission); each spray thus resulted in 20–25% mortality. Results were comparable at high- and low-elevation sites. Sprays applied May–August produced similar rates of infection. Peak counts of CBB recently killed by GHA were recorded 4–5 and 12–16 days post spray (reflecting infection by sprayed conidia vs. conidia produced in the field). Cumulative mortality assessed by counts of GHA-killed CBB plateaued at 50–60%, even after numerous sprays, and was attributed to factors unrelated to efficacy. Half rates of BotaniGard/WSM were nearly as effective as full rates. Broadcast sprays from tractor-driven sprayers on intermediate-elevation fields were less effective, but the problem was attributed to crop-architecture-effects on microclimate. Post-spray trapping of host-seeking CBB revealed 30–40% GHA infection, but residual activity was short (= 3 days). Recommendations for use of Bb for CBB IPM are presented.