UC Riverside

Since being detected in California in 2012, Euwallacea whitfordiodendrus and E. kuroshio commonly called shot hole borers (SHB) from Southeast Asia have been causing significant damage in multiple plant species across a range of habitats. Fusarium Dieback (FD) is a disease which results from repeated, local colonization of SHB and inoculation of their symbiotic ambrosia fungi (Fusarium spp., Graphium spp., Paracremonium pembeum) in woody tissues. Rapid molecular detection methods from infested host wood samples have been restricted to identification of the insect vector while management of this pest across their vast host range has been limited due to the cryptic nature of these pests. In addition, beetle-fungus interactions of the two Euwallacea spp. invading California and populations in Southeast Asia have not been explored. The work presented in this dissertation provides a validated real time quantitative polymerase chain reaction (PCR) assay which can detect all plant pathogenic fungi associated with E. whitfordiodendrus and E. kuroshio from pure cultures, avocado wood, and from female mycangia. Evidence from ground surveys indicate fungi from both species detected together on some hosts in Orange and San Diego Counties. Investigation into beetle-fungal associations of Euwallacea spp. in Southeast Asia determined a beetle’s association with their fungal symbionts to be non-exclusive and promiscuous. Both MAT genes were detected from the ambrosia fusaria clade (AFC) Fusarium spp. recovered from the beetles in native regions, while only one mating type (MAT 1-1-1) was determined present in California. We also demonstrated the ability of E. whitfordiodendrus and E. kuroshio to survive utilizing each other’s ambrosia fungi, further indicating the relationship with their fungi can be promiscuous in invaded areas like California. Effective chemical management of the SHB pests in avocado groves was best achieved by use of the insecticide bifenthrin/zeta-cypermethrin.