Wiliwili Research Articles

Reproductive Parameters and Host Specificity of Eurytoma erythrinae (Hymenoptera: Eurytomidae), a Biological Control Agent of the Erythrina Gall Wasp, Quadrastichus erythrinae (Hymenoptera: Eulophidae).

Eurytoma erythrinae Gates & Delvare (Hymenoptera: Eurytomidae) is an important biological control agent of the erythrina gall wasp (EGW), Quadrastichus erythrinae Kim (Hymenoptera: Eulophidae), an invasive species likely originating in eastern Africa that is a threat to Erythrina trees in Hawaii and worldwide. Thousands of Erythrina trees in Hawaii have succumbed to EGW since 2005 and died within a few years of infestation. The endemic wiliwili tree, Erythrina sandwicensis, an important component of Hawaii's dry forests and one of few deciduous native trees, were severely impacted by this wasp. Early during the invasion by EGW it became evident that the endemic species may be driven to extinction, and exploration programs for natural enemies of the EGW started in December 2005. East Africa was selected as the starting point for natural enemy exploration owing to high native Erythina species richness. Several gall formers were found in Tanzania and a putative color variant type of Q. erythrinae was detected in association with three ectoparasitoids. During January 2006, the dominant parasitoid of this gall former was introduced to Hawaii and described as the new species, E. erythrinae. It was found in Ghana and South Africa attacking other gall wasp species on Erythrina. Eurytoma erythrinae was a voracious ectoparasitoid feeding as a predator on 1-5 adjacent EGW immatures to complete its development. Host specificity studies that included seven nontarget gall-forming species showed no evidence of attraction or parasitism by this parasitoid. Mean ± SEM longevity of host-deprived females (40.4 ± 2.2 days) was significantly higher than males (20.5 ± 1.1 days). Host feeding enhanced longevity of ovipositing females (51.3 ± 1.5 days). Female E. erythrinae is synovigenic, with high egg-maturation rate. Peak fecundity (105-239 offspring/female), host feeding biology, short life cycle (18.4 ± 0.1 days), and synchronization with the host were additional desirable attributes of this species. The parasitoid was approved for field release in Hawaii in November 2008. A total of 3998 wasps were distributed on six Hawaiian Islands, with establishment in less than a year. Impacts on high density infestations of EGW were sufficient to prevent tree deaths. Limited rates of parasitism on low-density galled leaves, flowers, and seedpods necessitated the consideration for releasing a second parasitoid, Aprostocetus nitens Prinsloo & Kelly (Hymenoptera: Eulophidae). We report on the reproductive characteristics and host specificity of E. erythinae that could be of importance for classical biocontrol programs in areas with an EGW problem.

Pollination Biology of an Endemic Hawaiian Tree, Erythrina sandwicensis (Fabaceae: Papilionoideae), in a Novel Ecosystem1

Tropical dry forest ecosystems are among the most endangered ecosystems globally. In Hawai‘i, dry forest species are under threat due to habitat destruction, invasive species, and a loss of mutualisms including pollinators. Understanding the pollination biology of species at risk can inform conservation strategies. This study aimed to identify the breeding system and types of floral visitors to Erythrina sandwicensis (Fabaceae) or wiliwili, an iconic Hawaiian tree in decline and with little regeneration. We conducted hand-pollination trials and observed visitors in two sites: a botanical garden and a forest site. We compared fruit set, seed set, seed germination, seedling growth rate, and seedling size across four pollination treatments: open control, autogamy, geitonogamy, and xenogamy. We found that wiliwili is visited by a novel suite of non-native visitors. All treatments produced seeds, but the xenogamous (cross) treatment produced significantly more fruit and seeds than the control or other treatments. Seedlings produced from cross-pollinated treatments were also taller and had wider basal diameters after twenty-eight days of growth. These results indicate that wiliwili employs a mixed-mating system, and that trees are pollen limited. Enhancing current populations of wiliwili to promote cross-pollination could help increase population regeneration.

Classical biological control of the erythrina gall wasp, Quadrastichus erythrinae, in Hawaii: Conserving an endangered habitat

Erythrina gall wasp, Quadrastichus erythrinae (Hymenoptera: Eulophidae) began a global range expansion around 2005, and is considered a significant adventive pest in Asia, Pacific islands, South- and Central America, and North America, including Hawaii. The Hawaii endemic wiliwili tree, Erythrina sandwicensis (Fabaceae) was severely impacted and threatened with extinction, leading to the release of a classical biological control agent, Eurytoma erythrinae (Hymenoptera: Eurytomidae) from southern and East Africa, in 2008. Establishment was confirmed by retrievals of wasps within 1–4 months at all release locations. throughout Hawaii, and reduced impacts to trees within two years. By 2018, the majority of trees sampled incurred less than 33% gall damage to their foliage. E. erythrinae reduced Q. erythrinae damage by >85% in some locations throughout Hawaii and may have contributed substantially to preventing the extinction of this endemic tree.

A Fourth Contribution to the Study of HawaiianOrthotylus(Heteroptera: Miridae): New Species, Addenda, Revised Checklist, and Key to thePerrottetia-Feeding Species

Supplemental data and addenda are provided to complement and correct the work of Polhemus (2011) dealing with Hawaiian Orthotylus species. The following new species are described, accompanied by illustrations of key morphological characters, distribution maps, and color dorsal habitus photographs: O. erythrinae from Oahu, which feeds on Erythrina sandwicensis, and O. broussaisiae from Kauai, which feeds on Broussaisia arguta. Additional distribution records are provided for O. dubautiae D. Polhemus, O. hedyotivorus D. Polhemus, and O. kopikoides D. Polhemus. The name Orthotylus perrottetioides is proposed as a replacement name for Orthotylus perrottetiopsis Polhemus 2011, which due to a lapsus is a primary homonym of Orthotylus perrottetiopsis Polhemus 2003, and addenda to Polhemus (2011) related to this change are detailed. A revised key to Hawaiian species of Orthotylus occurring on Perrottetia is provided, accompanied by color dorsal habitus photographs of the males and females of the four known Perrottetia-feeding Hawaiian species. A revised checklist and updated of Hawaiian Orthotylus species, host plants, and islands of occurrence is also provided.

Effectiveness of Erythrina gall wasp biocontrol and implications for the recovery of threatened Wiliwili trees (Fabaceae: Erythrina sandwicensis)1

Abstract Wiliwili (Erythrina sandwicensis), an endemic Hawaiian dry forest tree species, is threatened by an invasive gall-forming wasp (Quadrastichus erythrinae) first detected in Hawai‘i in 2005. Eurytoma erythrinae, a predator of Q. erythrinae from Tanzania, was selected as a biological control agent and was released at sites throughout the Hawaiian Islands. To assess the effectiveness of this biocontrol release, we measured the extent of damage attributable to Q. erythrinae wasps in 124 E. sandwicensis trees at the Waikoloa Village Dry Forest Recovery Project before (January, 2009) and after (January, 2011) the release of the parasitoid wasp at this site. Because host spatial distribution has important consequences for the establishment and success of natural enemies such as parasitoids, we took a spatially explicit approach to account for the potential spatial heterogeneity in E. sandwicensis. We observed an increase in galling damage across the population and 21 trees became completely defoliated be...

Evaluation of a commercially available ELISA kit for quantifying imidacloprid residues in Erythrina sandwicensis leaves for management of the Erythrina gall wasp, Quadrastichus erythrinae Kim

The erythrina gall wasp (EGW), Quadrastichus erythrinae Kim 2004, was first detected in Hawaii in 2005 and has been infesting and killing Erythrina trees throughout the island chain since. It is believed EGW originated from Africa (Messing et al. 2009). Its host range appears to be limited to Erythrina; its geographic range already includes much of Asia and the Pacific. In North America, EGW has recently become established in south Florida and it is expected that introductions will occur to southern California (Smith et al. 2007). Observations indicate that a highly favored host is E. variegate L., but numerous species, including the Hawaiian endemic, E. sandwicensis O. Deg are severely injured and killed. Erythrina are warm-loving plants with about 115 species in the genus. It is expected that EGW will expand its geographic range to meet that of its host Erythrina with some restrictions due to climate (Li et al. 2006).

Impact of the newly arrived seed-predating beetle Specularius impressithorax (Coleoptera: Chrysomelidae: Bruchinae) in Hawai?i

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.

Application of an Enzyme-linked Immunosorbent Assay for the Analysis of Imidacloprid in Wiliwili Tree, Erythrina sandwicensis O. Deg, for Control of the Wasp Quadrastichus erythrinae

A monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) for the neonicotinoid insecticide imidacloprid was evaluated for its reproducibility, accuracy, and comparability to results from a conventional high-performance liquid chromatography (HPLC) for the analysis of imidacloprid in the endemic wiliwili tree (Erythrina sandwicensis O. Deg) found in dryland forests and landscapes in Hawaii. Imidacloprid was applied to these wiliwili trees in an attempt to control the newly introduced erythrina gall wasp, Quadrastichus erythrinae Kim. Leaf samples were freeze-dried and extracted with acidic aqueous methanol followed by methylene chloride partitioning. After solvent removal, the extract residue was reconstituted in 1 mL of water/methanol (1:1, v/v) for ELISA; no significant matrix interference was observed at 10-fold or more dilution. The average recoveries of imidacloprid from fortified samples ranged from 78% to 100% by ELISA. The correlation between the ELISA and HPLC results was excellent (r2 = 0.98). Imidacloprid was detected with the ELISA in all treated samples and its level varied in the samples among different treatments and in those from different parts of the trees. The infestation severity rating of leaf samples was inversely related to the concentration of imidacloprid. It is clear that imidacloprid effectively controls the wasps. The ELISA is a suitable method for quantitative and reliable determination of imidacloprid in wiliwili trees and the application provides information to understand how to control the wasps.

Induced Isoflavonoids of Erythrina sandwicensis

Abstract Two new phytoalexins isolated from the fungus-inoculated leaflets of Erythrina sandwicensis have been identified as (—)-6aS; 11 aS-3,6 a,9-trihydroxy-10-isopentenylpterocarpan (sandwicar-pin) and (—)-6aR; 11 aR-3-hydroxy-9-methoxy-10-isopentenylpterocaipan (sandwicensin). These compounds co-occur with several known pterocarpan (demethylmedicarpin, 3,6a,9-trihydroxy-pterocarpan, phaseollidin and cristacarpin) and isoflavan (demethylvestitol and isovestitol) deriva­ tives. The preparation and spectral (UV, MS) characteristics of 3-methoxy-9-hydroxy-10-isopen-tenylpterocarpan are also described.