Protecting avocado trees from ambrosia beetles by repellents and mass trapping (push–pull): experiments and simulations

Abstract

The polyphagous shot hole borer (PSHB), Euwallacea fornicatus (Eichhoff), is an ambrosia beetle (Coleoptera: Curculionidae) infesting avocado branches Persea americana Mill. in North America, South Africa and Israel. Field experiments were conducted with attractive quercivorol traps and repellents on trees to develop push–pull control methods. PSHBs were collected over the summer from multiple-funnel traps baited with quercivorol in grids of low-, medium- and high-density traps to assess mass trapping interactions and capture trends. Mean catch/trap-week was higher on peripheral outer traps compared to the next inner ring of traps in grids. These ratios and grids were simulated to estimate the circular effective attraction radius (EARc) of multiple-funnel traps and compared to a previous relationship for sticky traps yielding EARc from release rate of quercivorol. The results indicate that multiple-funnel traps have smaller EARc in higher-density grids, likely due to interactions between traps. Tests with verbenone compared to methyl salicylate (MeSA) indicate both are repellents and no evidence for synergism. Dollops of verbenone–MeSA–SPLAT (5% each volatile) were applied monthly at 10- and 40-cm spacings along branched trunks of avocado trees, with release of volatiles declining exponentially over a month. These treatments caused a reduction in both numbers of aggregations/tree and attacks/aggregation to about half that of untreated control trees. Verbenone–MeSA–SPLAT dollops caused localized phytotoxicity on avocado bark, suggesting 8 cm2 plastic bag dispensers containing 0.25 g verbenone are preferred at 40-cm spacing. Push–pull should be done just before flight season to overwhelm natural attraction of single females initiating aggregations.