UC Riverside

The Euwallacea fornicatus species complex, collectively known as shothole borers (SHB), is comprised of three major invasive cryptic ambrosia beetles of economic importance. Since their detection, two of these species, the polyphagous shot hole borer (PSHB), Euwallacea fornicatus, and the Kuroshio shothole borer (KSHB), Euwallacea kuroshio, have become established in southern California without effective and cost-efficient control measures. The goal of this dissertation was to find promising natural enemies associated with the E. fornicatus species complex and assess their potential as candidates in a classical biological control program. In chapter 1, I recorded emergence and behavior of parasitoid associated with shothole borer-infested wood material imported from the beetle’s native region. As a result, I identified three parasitoid wasps as natural enemies of PSHB that ions emerged from experimental logs selectively infested with PSHB. In Chapter 2, I attempted to confirm a molecular link between beetles in the E. fornicatus species complex and each parasitoid species using molecular gut content analysis. A large subset of parasitoid wasps from Taiwan, collected from shothole borer-infested wood and yellow panel traps, were sequenced and analyzed for trace amounts of DNA from their host beetles. While a few parasitoid species amplified trace amounts of shothole borer DNA, two braconid parasitoids in the subfamily Euphorinae, along with two parasitoids in the families Bethylidae and Eulophidae amplified shothole borer DNA. In chapter 3, I conducted experiments to identify entomophilic nematodes associated with the E. fornicatus species complex. In doing so, a nematode species in the genus Rhabditolaimus originally detected in Taiwan, the native region to the E. fornicatus species complex, was confirmed to already be established in southern California. Fitness cost experiments indicated adverse effects of this Rhabditolaimus sp. on PSHB brood size when reared in the presence of the nematode. This could be evidence that this nematode is a cryptic factor behind the decline of shothole borer populations in previously-infested regions across southern California.