Attractants of ambrosia beetles in the Euwallacea fornicatus species complex
Abstract: Laboratory and field evaluations of semiochemicals associated with ambrosia beetles in the Euwallacea fornicatus species complex (Coleoptera: Curculionidae: Scolytinae) were conducted. Crossing experiments were conducted between beetles from three invasive populations of cryptic species in the USA. The beetles were collected from a population in Florida, referred to as the tea shot hole borer (TSHB), and two areas in California, referred to as the polyphagous shot hole borer (PSHB) and the Kuroshio shot hole borer (KSHB). Crossing experiments showed only a limited ability of PSHB to hybridize with the other two beetles. Behavioral bioassays of PSHB to diet, diet + fungus, and diet + fungus + beetles revealed the presence of odor-mediated behavior to the latter two treatments. Volatile collections of diet + fungus revealed a compound not present in diet without fungus, p-2-menthen-1-ol, which has four stereoisomers. Lures containing all four stereoisomers, including the one called quercivorol, were field tested in avocado groves in both FL and CA, and found to attract TSHB, PSHB, and KSHB. The addition of high release ethanol in PSHB-infested groves reduced attraction of PSHB. The four stereoisomers contained in the lures were synthesized individually and tested for attraction in Y-tube bioassays. Two stereoisomers were found to be repellent, and the other two were found to be attractive. Modifying lure blend ratios to maximize the attractive stereoisomers and minimize the repellent ones allowed for improvement of lures and capture rates in the field. Volatile collections of diet + fungus + beetles contained compounds that were absent in volatile collections from just diet + fungus. Two compounds were identified and synthesized, and a blend of the two synthetic compounds was tested in the Y-tube and found to be attractive to PSHB. A quantitative analysis of the three species revealed that each species had the same two compounds but at different ratios.