The emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is one of the most destructive invasive
forest pests in North America, where it has killed hundreds of millions of ash (Fraxinus spp.) trees since its first detection
in 2002. Native to Asia, female EAB adults lay their eggs between bark crevices or under loose bark of their host trees.
Because of this cryptic egg-laying behavior, field detection of EAB eggs has been extremely difficult, resulting in knowledge
gaps of EAB egg-laying behavior. Here, we determined the effective bark crevice size that EAB females oviposit under through trials with coffee filter paper covered with mesh screening in a no-choice experiment. We then conducted a choice experiment where we wrapped an ash log with polypropylene ribbons at different tightness treatments as oviposition stimulants. We found that female EAB oviposited onto coffee filter paper through mesh pores ranging from 0.6 x 0.6 mm (0.36 mm2) to 1.4 x 1.4mm (1.96 mm2), but not 0.2 x 0.2 mm (0.04 mm2). Females also oviposited more on logs wrapped with ribbon at a moderate gap width (0.5 mm) than on logs with loose gaps (1 mm) or logs with tight gaps (0.06 mm), which was smaller than our measured ovipositor widths. Our findings suggest that female EAB prefer gap sizes that are relatively tight so long as they are large enough to allow insertion of the ovipositor. These results have implications for development of effective traps to detect EAB eggs in the field.
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