Prior to 2001, seed predation was virtually absent in the endemic Wiliwili Erythrina sandwicensis (Fabaceae: Degener), dominant tree species of lower-elevation Hawaiian dryland forests. The African bruchine chrysomelid Specularius impressithorax (Pic) (Coleoptera: Chrysomelidae: Bruchinae) was first detected in Hawai?i in 2001 and became established on all main islands within the next two years. The mode of entry for this invasive Erythrina seed predator into Hawai?i is unknown, but likely occurred with the importation of trinket jewelry from Africa containing characteristically brightly-colored Erythrina seeds. The initial establishment of this insect likely occurred on a non-native host, the widely cultivated coral tree E. variegata. Within three years of its first record, S. impressithorax accounted for 77.4% mean seed crop loss in 12 populations of Wiliwili on six main Hawaiian islands. Specularius impressithorax, dispersed through international commerce and established via E. variegata, has become a threat to a unique Hawaiian forest type and may threaten other Erythrina, especially New World representatives.

Coffee is one of the most economically valuable specialty crops for which Hawaii is famous. It is produced commercially on >6,900 acres across six islands by more than 1,470 growers. It has a raw crop value of $55.9 million, while the value-added benefits of coffee-related industries exceed $148.5 million (USDA, 2021). In addition to high product quality, Hawaii also has the distinction of being the last major coffee growing region that is free of coffee leaf rust (CLR), a highly damaging disease caused by the obligate parasitic fungus Hemileia vastatrix Berk. & Broome. On October 21, 2020, a coffee grower in Maui County, Hawaii reported the presence of coffee leaf rust-like symptoms on coffee plants (var. ‘Typica’) at their farm with many trees heavily defoliated. Foliar symptoms consisted of yellowish-orange, circular lesions that often coalesced. On abaxial surfaces, these lesions appeared powdery. Urediniospores were mostly reniform, (25)27-34(36) × (17)18-28(29) µm, strongly echinulated on the upper (convex) surface and smooth on the lower (concave) surface, with hyaline to pale yellow-orange walls. Urediniospores incubated in molecular grade water for 10 min at 95 oC served as template for PCR targeting the internal transcribed spacer region of fungi using primers ITS1/ITS2, ITS3/ITS4, and ITS1/ITS4 (White et al., 1990). Amplification products underwent direct Sanger-based sequencing. Following primer sequence trimming, the sequence reads were assembled using CAP3 (Huang and Madan, 1999) and deposited in GenBank (Accession MW228837). Blastn analysis revealed > 99% nucleotide identity with isolates of H. vastatrix from Mexico (eg. KX260251) and Brazil (eg. MF627828). A voucher material from which both the morphological and molecular assays were performed was deposited in the National Fungus Collection (BPI 924818). Subsequent surveys on the islands of Hawaii, Lanai, and Oahu revealed the presence of coffee plants with symptoms of coffee leaf rust. To confirm pathogenicity, urediniospores from a symptomatic plant growing in Holualoa, Hawaii, were collected in gelatin capsules using a G-R Electric Manufacturing Portable Vacuum Pump with a mini cyclone spore adapter. The concentration of spores was adjusted to 1 x 105 spores/ml in sterile water using a Brightline Hemocytometer. The spore suspension was brushed onto the abaxial side of leaves from two C. arabica var. ‘Typica’ plants using a camel hair paintbrush. Two control plants were mock-inoculated with sterile water. Plants were placed in a dark humid chamber set at 22 oC for 48 hours, after which it was adjusted to 12 hours light under cool white fluorescent lighting. After 20 days small, chlorotic spots were visible on the adaxial leaf surface and a few spots contained orange urediniospores on the abaxial surface. Lesions expanded by day 34, followed by necrosis of the center area of several leafspots and leaf abscission was observed at day 70. The experiment was conducted twice. H. vastatrix was confirmed by both morphological and molecular examination of urediniospores recovered from the observed lesions. All mock-inoculated control plants remained asymptomatic. To our knowledge, this is the first report of CLR on coffee in Hawaii. This discovery is of great concern since CLR threatens not only the yield and quality of Hawaii-grown coffee, but also the economic viability of this historic and culturally important industry. Statewide monitoring for CLR continues and further work is needed to mitigate the impact of this discovery through the development of short- and long-term management strategies.

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Hawaii has long been one of the last coffee-producing regions of the world free of coffee leaf rust (CLR) disease, which is caused by the biotrophic fungus Hemileia vastatrix. However, CLR was detected in coffee farms and feral coffee on the island of Maui in February 2020 and subsequently on other islands of the Hawaiian archipelago. The source of the outbreak in Hawaii is not known, and CLR could have entered Hawaii from more than 50 coffee-producing nations that harbor the pathogen. To determine the source(s) of the Hawaii inoculum, we analyzed a set of eleven simple sequence repeat markers (SSRs) generated from Hawaii isolates within a dataset of 434 CLR isolates collected from 17 countries spanning both old and new world populations, and then conducted a minimum spanning network (MSN) analysis to trace the most likely pathway that H. vastatrix could have taken to Hawaii. Forty-two multilocus genotypes (MLGs) of H. vastatrix were found in the global dataset, with all isolates from Hawaii assignable to MLG 10 or derived from it. MLG 10 is widespread in Central America and Jamaica, making this region the most probable source of inoculum for the outbreak in Hawaii. An examination of global weather patterns during the months preceding the introduction of CLR makes it unlikely that the pathogen was windborne to the islands. Likely scenarios for the introduction of CLR to Hawaii are the accidental introduction of spores or infected plant material by travelers or seasonal workers, or improperly fumigated coffee shipments originating from Central America or the Caribbean islands.

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