Geology topics

Robert W. Peck

Publications and source records attributed to Robert W. Peck.

At least 19 recordsLinked to original sources

USGS2026

Dietary composition and diversity in an endemic island bat, the Hawaiian hoary bat (Lasiurus semotus)

Due to the importance of sufficient diets, conservation practices for endangered bats often involve protection and restoration of foraging resources. For insectivorous (or arthropodivorous) bats, detailed knowledge of prey consumption can inform effective management. In this study, we used metabarcoding techniques to investigate the diet of Lasiurus semotus , a primarily insectivorous, solitary foliage-roosting endangered bat endemic to the Hawaiian Islands. To determine diet composition and how it relates to sex, reproductive condition, and habitat, we analyzed 141 guano samples collected from across the Hawaiian archipelago between 2010–2021. We detected 424 arthropod prey items, with Lepidoptera — the most common order (found in 100% of all samples), followed by Blattodea (85%), Coleoptera (42%), Orthoptera (47%), Diptera (33%), and Hemiptera (25%). Coleoptera were more frequent in guano collected from females. Prey richness and evenness at the family-level were similar across sex, reproductive condition, elevation, and land cover type. High variability among samples, and the dominance of Lepidoptera and Kalotermitidae (Blattodea), indicates that local prey abundance may influence L. semotus diet more strongly than prey richness and evenness. Lasiurus semotus consumed both native and non-native arthropods, including several invasive agricultural pests. Our study demonstrates that hoary bats in the Hawaiian Islands consume a wide variety of prey types, likely sought over an extensive range of habitats.

Hawaii↗

USGS2025

Host preferences of non-native Acalolepta aesthetica (Coleoptera: Cerambycidae) on the Island of Hawai'i

1. Understanding the host preferences of non-native polyphagous insects is a key step in anticipating their impacts. 2. We apply a technique from wildlife ecology, a resource selection function, to quantify the host preferences of Acalolepta aesthetica Olliff (Coleoptera: Cerambycidae: Lamiinae) in its non-native range on the Island of Hawaiʻi. We then visually surveyed its preferred host to map its distributional extent and conducted laboratory no-choice tests to assess risks to common native woody species. 3. The preferred host of A. aesthetica was the state tree, Aleurites moluccanus (L.) Willd., the kukui (or candlenut). Cacao ( Theobroma cacao L.) was the second most preferred host. Infestations were also observed in Citrus species, Artocarpus altilis (Parkinson) Fosberg (ʻulu or breadfruit) and Persea americana Mill. (avocado), but preferences among these taxa were statistically indistinguishable. 4. Acalolepta aesthetica females oviposited on all tested species in no-choice trials, but larvae growing within ʻōhiʻa ( Metrosideros polymorpha Gaudich.) and koa ( Acacia koa A. Gray) died. It therefore poses a low risk to these two tree species, which are foundational to Hawaiian native forests. Acalolepta aesthetica was able to complete its development within ʻōlapa ( Cheirodendron trigynum (Gaudich.) A. Heller), which could be monitored if the distribution of A. aesthetica spreads to native forests. 5. The host species preferred by A. aesthetica are highly valued for agricultural, horticultural and cultural uses. Developing monitoring and management techniques for this cerambycid and employing strong biosecurity could prevent human-mediated spread and limit negative impacts to other Hawaiian Islands, the U.S. mainland, and the world.

Hawaii↗

USGS2025

Temporal associations between ambrosia beetles and ʻōhiʻa (Metrosideros polymorpha) artificially inoculated with Ceratocystis lukuohia

Wood boring ambrosia beetles play a central role in the spread of Ceratocystis wilt of ‘ōhi‘a, a fungal disease caused by Ceratocystis lukuohia that kills the bioculturally important ‘ōhiʻa ( Metrosideros polymorpha ) tree. Beetles contribute to the spread of the disease by extruding fungus-infected wood particles (frass). Disease mitigation can benefit from knowledge of ambrosia beetle life-history and fungal survival in affected ‘ōhi‘a. We investigated temporal associations among tree death, the timing and duration of beetle attacks, and the persistence of viable C. lukuohia within intentionally infected (inoculated) ʻōhiʻa at three sites that approximate the elevational range of the disease on the Island of Hawaiʻi. Beetles most frequently attacked inoculated trees at the time when foliage first showed symptoms of infection (yellow leaves; n = 9) although some attacks were observed during earlier (green leaf; n = 3) and later (brown leaf; n = 3) stages of symptom progression. On average, beetles initiated new attacks for nearly one year after trees were inoculated. We tracked active galleries of Xyleborinus saxesenii , Xyleborus ferrugineus and Xyleborus simillimus and found they produced frass with viable C. lukuohia propagules for 122.8 ± 40.0, 275.8 ± 32.7 and 304.2 ± 53.4 days, respectively. Infected ʻōhiʻa felled from our mid-elevation site at the end of the study revealed viable fungal propagules and the presence of X. ferrugineus over two years after trees first appeared symptomatic of infection, suggesting that Ceratocystis wilt of ʻōhiʻa remains a threat to spread from infected trees long after trees succumb to the disease.

Hawaii↗

USGS2025

Photographic guide to the leaf litter arthropod community of the lowland wet forest ecosystem of the Island of Hawaiʻi

Leaf litter arthropods are important components of the food web in forests, and their presence and diversity can provide information on forest health. There has been very little documentation of the leaf litter arthropods in Hawaiian forest ecosystems. This technical report is a photographic guide to some common arthropods collected from forest leaf litter at the Liko Nā Pilina Hybrid Ecosystems Project study site, a lowland wet forest in Hilo, Island of Hawaiʻi, USA. Leaf litter samples were collected from plots of invaded and experimental restoration communities using two complementary methods (litterbags and quadrats), and arthropods were extracted using Berlese funnels. The field site contained many morphospecies that were rare and locally distributed across plots, and only a few that were very common and widely distributed. The majority of the morphospecies identified were mites. This photoguide is designed to help identify arthropods found in plant litter in Hawaiian lowland forests and it may assist with research and education efforts concerned with the diversity, ecology, or conservation of litter arthropods across the Hawaiian archipelago and other Pacific islands.

Hawaii↗

USGS2025

Abundance of ohiʻa-associated ambrosia beetles in two sites with rapid ohiʻa death outbreaks

ʻŌhiʻa lehua ( Metrosideros polymorpha Gaudich.) is the dominant tree in native Hawaiian forests but is threatened by two pathogenic fungi ( Ceratocystis spp.) which cause Rapid ʻŌhiʻa Death (ROD). Understanding the spread of ROD is vital to informing prevention and management strategies. Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) contribute to the spread of disease by releasing contaminated frass into the environment or carrying fungal spores between trees on their bodies. We quantified the abundance of ʻōhiʻa-associated ambrosia beetles and their potential contributions to fungal spread within two study sites experiencing active ROD outbreaks. We established a grid of beetle traps at each site, cultured trap samples for viable Ceratocystis , and compared the spatial distribution of beetle captures with that of ʻōhiʻa trees showing symptoms of ROD. Nearly all captured ʻōhiʻa-associated beetles were Xyleborinus saxesenii (Ratzeburg) or Xylosandrus crassiusculus (Motschulsky), both introduced species that utilize many plant hosts. For both species, abundance was unrelated to distance to the nearest symptomatic ʻōhiʻa tree. However, at one of our sites, Xylosandrus crassiusculus abundance was higher on one side of a fence line, where there were more symptomatic ʻōhiʻa within a denser and more diverse forest. Culturing the collected samples (beetles, water, and debris) produced instances of Ceratocystis viability in samples both with and without ʻōhiʻa-associated beetles, supporting the potential for transmission via frass carried by wind as well as direct transmission by beetles. The community of ʻōhiʻa-associated beetles we captured differed from previous findings at lower elevation sites, highlighting the complexity of beetlemediated fungal infection risk.

Hawaii↗

USGS2024

Reproductive ecology and egg parasitism of the Samoan swallowtail butterfly

We investigated the reproductive ecology and effects of egg parasitism on the Samoan swallowtail butterfly ( Papilio godeffroyi ), which survives only on Tutuila Island, American Samoa, after having disappeared from the much larger islands of Upolu and Savai‘i in independent Samoa. During monthly surveys of its only known host plant, Micromelum minutum , across eight sites in 2013 and 2014, we collected eggs, eggshells, larvae, pupae, and pupal exuviae. Live specimens were reared under laboratory conditions to determine reproductive outcomes, developmental rates, and sex ratios, as well as parasitoid attack frequencies, brood sizes, and sex ratios. Sixty-six of 448 (14.7%) eggs produced larvae, 47 of which became adults. The sex ratio was approximately even overall and within each developmental stage. Eggs were slightly larger on individual host trees and in host tree stands that yielded more eggs per unit of foliage, indicating that ovipositing females responded to some features of host trees and stands. Eggs hatching female or male larvae were similar in size, and the sexes developed at similar rates. A newly described species of parasitoid wasp, Ooencyrtus pitosina (Encyrtidae), emerged from 73.6% of 382 butterfly eggs that failed to hatch in the laboratory (62.7% of 448 eggs overall). Forty-one other eggs contained dead parasitoid larvae. An additional, unidentified Ooencyrtus wasp species emerged from a single P. godeffroyi egg. No parasitoids were reared from P. godeffroyi larvae or pupae. Of 656 P. godeffroyi eggshells collected in the field and examined in the laboratory, 62.2% showed signs of having been parasitized by O. pitosina. There was no evidence that parasitism rates were density-dependent. O. pitosina brood sizes ranged from 1 to 5, with the sex ratio skewed toward females (2.40 F:1.00 M). Larger parasitoid broods were associated with slightly larger host eggs, indicating that female wasps may adjust brood size according to host egg size or that fewer wasp larvae are able to complete development in smaller eggs. Techniques used to rear both P. godeffroyi and O. pitosina in the laboratory could be applied to a captive-rear, wild-release program, which may facilitate reestablishment of the species in Samoa.

Tutuila Island↗

USGS2024

Climatic drought and trophic disruption in an endemic subalpine Hawaiian forest bird

Overexploitation, habitat conversion, and introduced species have caused unprecedented extinctions and heavily degraded native bird populations in island ecosystems. In the Hawaiian Islands, stemming these losses has proven difficult as the highly specialized avifauna are often impacted – among other things – by poorly understood trophic disruptions as well as persistent climatic shifts. Here we investigate these dynamics by examining the trophic positions of 7 different taxa of producers and consumers across the last century in the subalpine māmane ( Sophora chrysophylla ) forest ecosystem on the island of Hawaiʻi. From museum collections and contemporary sampling, we analyzed the stable nitrogen (δ 15 N) values of producers and consumers to identify trophic and source amino acids and derive trophic enrichment constants specific to this food web. This enables us to reconstruct the diet of the palila ( Loxioides bailleui ), a critically endangered finch whose population recently declined 90 %. Our results show that from 1890 to 2006, the palila trophic position declined from 2.6 to 2.2, with cascading implications for its diet. Bayesian mixing model reconstructions indicate that palila trophic position changes likely arose from a 76 % decline (69.3 % to 16.6 % of diet) in the consumption of native moth caterpillars, and a 172 % increase (30.7 % to 83.4 %) in native plants. From the available ecosystem variables, exploratory Bayesian multiple regressions selected surface temperature changes, and the interactions of surface temperatures with drought and caterpillar parasitism as the primary drivers of these trophic changes. Despite the predicted increases of warming and drought, management interventions may build resiliency in this unique island ecosystem.

Hawaii↗

USGS2024

Factors affecting the density of Metabetaeus lohena (Decapoda: Alpheidae) at a high-density anchialine pool environment on the Kona Coast of the Island of Hawai‘i

Caridean shrimps (Caridea) are the dominant macroinvertebrates in most anchialine ecosystems. Hawaiian anchialine ecosystems, primarily composed of shallow surface pools connected to the ocean via hypogeal networks of cracks, tubes, and other voids, support 10 caridean shrimp species, including two federally listed as endangered. Little is known about most of these species. The objective of this study was to identify factors that affect the abundance and distribution of Metabetaeus lohena (Alpheidae), an uncommon species found across the Hawaiian Archipelago, at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. This park supports the highest concentration of anchialine pools in the State of Hawai‘i and is critical to protecting this threatened ecosystem. During 2017, we measured the density of M. lohena during nighttime surveys, as well as a variety of other biological, physical, and chemical parameters, in 130 pools. Metabetaeus lohena occupied 71.5% of the pools surveyed, with a mean density of 7.32 individuals/m 2 (95% CI = 5.14–9.49). Invasive fish and the endemic shrimp Halocaridina rubra (Atyidae) had the strongest effects on M. lohena density, with negative and positive relations, respectively. In the first estimate of M. lohena density at this scale, our data indicate that Kaloko-Honokōhau supports about 11,480 shrimp (95% CI = 8,054–14,906) in the pools surveyed. Furthermore, our models predict that this park could support an additional 1,695 individuals (95% CI = 955–3,008) for a population of about 13,175 shrimp if fish were removed from 19 pools in which M. lohena are absent.

Hawaii↗

USGS2024

Distribution of yellow crazy ants (Anoplolepis gracilipes) and notes on other ant species at Wake Atoll, 6-21 October, 2023

Wake Atoll, located in the central Pacific Ocean, is a tropical coral atoll comprised of three islands totaling 696 ha of emergent land. Wake Atoll supports at least 17 species of non-native ants, but one species, the yellow crazy ant ( Anoplolepis gracilipes ), is especially harmful to ecosystems, including seabirds, which are federally protected species and nest throughout Wake Atoll. Our objective was to map the distribution of yellow crazy ants (YCA) across Wake Atoll to provide U.S. Air Force managers with information that could inform an eradication strategy for this species. In addition, we documented the presence of other ant species identified during our survey. We used a 50 x 50-m cell-based sampling grid to survey for YCA and other ant species. YCA were widespread across the atoll, occupying all three islands and were detected in 566 of the 3,675 (15.4%) cells surveyed, covering an area of about 142 ha. The highest proportion of cells containing YCA was on Wilkes Island (99 of 400 cells or 24.8%), followed by Wake Island (395 of 2,760 cells or 14.3%) and Peale Island (72 of 518 cells or 14.0%). YCA detections on Wilkes Island were restricted to Wilkes South (99 of 202 cells or 49.0%); no YCA were found on Wilkes North, an important area that supports the most diverse assemblage of nesting seabirds on Wake Atoll. Based on technologies developed to eradicate YCA from Johnston Atoll and elsewhere, eradicating YCA from Wake Atoll appears technically feasible. The occurrence of discrete populations (i.e., clusters of occupied cells separated from other clusters of occupied cells) within and among islands could allow a stepwise strategy where the short-term outcome of the treatment of one population is independent of the outcome of another treatment. Without action, the high-density YCA population on Wilkes South could breach the narrow (~50 m), sometimes dry, channel separating Wilkes North and South, posing a serious threat to nesting seabirds present on Wilkes North. Eradicating YCA from Wilkes South would create a buffer from YCA and reduce the threat of northward movement of YCA. We also detected 12 ant species other than YCA during our survey, including Lepisiota frauenfeldi , a new record for the atoll.

Hawaii Cooperative Studies Unit Technical Report↗

USGS2023

The use of semiochemicals for attracting and repelling invasive ambrosia beetles (Coleoptera: Curculionidae) in ʻōhiʻa (Metrosideros polymorpha) forests

Early detection of invasive species is critical for preventing ecological and economic damage and maintaining ecosystem health. In Hawaiʻi, a complex of generalist ambrosia beetle species in the tribe Xyleborini (Coleoptera: Scolytinae) are threatening the health and productivity of forests and crops due to their association with tree diseases such as rapid ʻōhiʻa death (ROD) and key agricultural commodities including coffee and macadamia. We conducted trapping experiments to determine the efficacy of semiochemicals to attract and repel Xyleborini ambrosia beetles within two ʻōhiʻa ( Metrosideros polymorpha ) forests on the Island of Hawaiʻi. We compared the attraction of beetles to 100% ethanol and a 1:1 mixture of ethanol: methanol at Waiākea Forest Reserve and ʻŌlaʻa Forest in Hawaiʻi Volcanoes National Park. In addition, we tested the extent to which verbenone and verbenone + methyl salicylate repellents (SPLAT® Verb and SPLAT® Beetle Guard, respectively) deterred beetles from baited traps at Waiākea Forest Reserve in two separate experiments. For all invasive ambrosia beetle species, including Xyleborinus saxesenii , Xyleborus affinis , Xyleborus ferrugineus , Xyleborus perforans, Xylosandrus compactus , and Xylosandrus crassiusculus , more beetles were captured in traps baited with 100% ethanol than 1:1 ethanol: methanol. Across all species, both repellents were effective, with fewer beetles captured in traps equipped with repellents. Our research demonstrates the utility of semiochemicals for attracting and repelling invasive ambrosia beetle species in Hawaiʻi, and the potential use of these tools for early detection and management strategies.

Hawaii↗

USGS2023

Twenty-five years of change in forest structure and nesting behavior of Hawaiʻi ʻelepaio

Long-term ecological studies are invaluable for detecting changes over time. Forest restoration has been a conservation priority in Hawaiʻi, where invasive species have negatively impacted native bird habitat. During 1993–1994, a study was conducted of Hawaiʻi ʻelepaio ( Chasiempis sandwichensis ) nest site selection and forest composition in mesic montane forest along Mauna Loa Road in Hawaiʻi Volcanoes National Park. We returned to the site and repeated the methods used in the earlier study to record Hawaiʻi ʻelepaio nest site selection (tree species, tree and nest height, and tree girth [diameter at breast height, DBH]) from 2015 to 2017, and measured forest composition (tree density, relative abundance, height, and DBH) in 2019. Three times as many nests were found in ʻaʻaliʻi ( Dodonaea viscosa ) as in koa ( Acacia koa ) in both time periods. Heights of koa and ʻaʻaliʻi did not change, but their DBH increased over time. The relative height of nests in ʻaʻaliʻi trees did not change, but nests in koa were placed higher in the crown during the later study. Overall tree density increased from 1,619 (95% confidence interval [CI] = 1,499–1,740) trees/ha to 2,583 (95% CI = 2,176–3,096) trees/ha. Koa relative abundance was 53% of total trees earlier and 45% later, ʻaʻaliʻi remained at 47%, and māmane ( Sophora chrysophylla ) increased from 0 to 8% over time. Our results indicate that changes in forest composition affect nesting behavior, but in ways that are not necessarily simple or consistent.

Restoration Ecology↗

USGS2023

Ooencyrtus pitosina (Hymenoptera: Encyrtidae)–A natural enemy of Samoan swallowtail butterfly Papilio godeffroyi (Lepidoptera: Papilionidae)

A new species of encyrtid wasp, Ooencyrtus pitosina Polaszek, Noyes & Fusu sp. n., (Hymenoptera: Encyrtidae: Encyrtinae) is described as a gregarious parasitoid in the eggs of the endemic Samoan swallowtail butterfly Papilio godeffroyi (Lepidoptera: Papilionidae) in the Samoan archipelago. It is described here because it is an important natural enemy of this butterfly, and to facilitate identification for future work with this parasitoid and its host.

Tutuila Island↗

USGS2023

Reproductive response of the Samoan swallowtail butterfly to variability in host plant and habitat characteristics

The Samoan swallowtail butterfly ( Papilio godeffroyi ) has become restricted to Tutuila Island, American Samoa. Factors driving its extirpation on other islands may be partly due to the availability and suitability of habitat, given the singular association we observed of P. godeffroyi with its host plant, Micromelum minutum. We expected that as a host plant specialist, P. godeffroyi might respond to variation in the physical traits and habitat context of M. minutum , which could help identify conservation opportunities throughout its present and former range. Because the ecology of P. godeffroyi is largely unknown, we conducted systematic surveys during 15 months in 2013 and 2014 on Tutuila to investigate its reproductive response to the physical and phenological variability of individual host trees and to the structural and geographical variability of the stands in which they occurred. We searched foliage for eggs, larvae, and pupae and monitored seasonal trends in herbivory and production of leaves, flowers, and fruits on 117 host trees in 8 rainforest stands, mostly within the National Park of American Samoa (NPSA), starting in March 2013 and ending in August 2014. We observed high variability in butterfly reproductive output between individual trees and stands, due largely to a strong negative relationship between leaf biomass (at both tree and stand levels) and oviposition density (number of eggs per foliar biomass) and frequency (number of eggs per survey). Distribution patterns of larvae and pupae were less distinct but generally followed trends in oviposition. Our findings indicate that the butterfly is reproducing widely across Tutuila and is likely to respond positively to management to increase the availability of small host trees in low-density stands. Thus, the species is a good candidate for conservation management focusing on habitat.

Tutuila Island↗

USGS2023

Ambrosia beetles (Coleoptera: Curculionidae) can directly transmit the fungal pathogens responsible for Rapid ʻŌhiʻa Death

The ecologically and culturally vital tree species, ʻōhiʻa lehua ( Metrosideros polymorpha ), is threatened by the fungal pathogens Ceratocystis lukuohia and Ceratocystis huliohia , the causal agents of the disease complex called Rapid ʻŌhiʻa Death (ROD). Four invasive ambrosia beetle (Coleoptera: Curculionidae: Scolytinae) species in the Xyleborini tribe colonize ROD Ceratocystis -infested ‘ōhiʻa and produce inoculum through their frass; however, the potential for direct transmission of the ROD fungi by these beetles was unknown. We fulfilled Leach's rules to support insect transmission of ROD by documenting the visitation of these ambrosia beetles to healthy ‘ōhiʻa trees, culturing C. lukuohia and C. huliohia from the ROD-associated beetles using three different collection methods at multiple study sites, and challenging healthy ʻōhiʻa seedlings with beetles that were exposed to both C. lukuohia and C. huliohia cultures. We documented all four invasive ROD-associated ambrosia beetle species including Xyleborinus saxesenii , Xyleborus affinis , Xyleborus ferrugineus , and Xyleborus perforans to regularly visit healthy ʻōhiʻa trees on sticky traps. Viable Ceratocystis propagules were isolated from all species, and C. lukuohia was most commonly isolated of the two ROD-causing fungi. Consistently across all collection techniques, ROD Ceratocystis spp. were detected on just under 3% of all assayed beetles, with the highest detection rate from X. affinis . All four beetle species were capable of directly transmitting both pathogens to healthy ʻōhiʻa seedlings with a high rate of transfer. Ceratocystis spp. are highly virulent pathogens in trees, and a single inoculation can result in tree death, therefore any direct transmission is a cause for concern. After meeting the criteria of Leach's rules, we propose that Xi. saxesenii , X. affinis , X. ferrugineus , and X. perforans are vectors of C. lukuohia and C. huliohia , particularly in areas of high ROD pressure and tree stress.

Hawaii↗

USGS2023

Carbon dioxide (CO2) gas and eDNA monitoring as tools for eradicating invasive fish from anchialine pools in Hawai‘i

Invasive fish can profoundly affect communities they invade. In Hawai‘i, invasive fishes have become established in many anchialine pools, threatening the persistence of resident invertebrates, including several endangered species. Tools to eradicate invasive fishes from these pools are lacking. This study tested the efficacy of carbon dioxide (CO2) gas diffused into anchialine pool water as a method to eradicate invasive Mozambique tilapia (Oreochromis mossambicus), guppies (Poecilia reticulata), and western mosquitofish (Gambusia affinis). We first conducted aquarium trials to identify how these fishes were affected by elevated CO2 and the concomitant reduction in pH. We then carried out field trials in pools containing these fish in one pool each at two national historical parks on the Island of Hawai‘i during July 2021–January 2022. We also developed environmental DNA (eDNA) protocols to detect fish that may have survived CO2 treatments. The effect of CO2 on fish behavior varied among species; at pH 5.3 (CO2 = 255 mg/L) for tilapia and 5.0 (CO2 = 488 mg/L) for tilapia, guppies, and mosquitofish, all generally lost their ability to swim, showed slow or no gill movement, and altered their position in the water column. No tilapia survived the trials (n = 4 and 6 individuals at pH 5.3 and 5.0, respectively). In contrast, 41.7% (n = 12) of adult guppies and 66.7% (n = 12) of adult mosquitofish survived treatment at pH 5.0. In the field we were unable to reduce anchialine pool water pH below 5.7. Regardless, we were able to eradicate tilapia from one pool over four sequential treatments. Post-treatment eDNA assessments supported visual surveys, confirming our results. We were not able to eradicate guppies and mosquitofish. Results from this study show that CO2 can be an effective tool for eradicating invasive tilapia from anchialine pools, and post-treatment eDNA assessments can provide managers with a method for evaluating the success of eradication efforts.

Hawaii↗

USGS2023

Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae and Platypodinae) associated with rapid ohia death and mixed Metrosideros polymorpha forests on the Island of Kauai, Hawaii

Xyleborini (Coleoptera: Curculionidae) beetles on the island of Kauaʻi, Hawaiʻi, are of interest due to their role in the fungal disease complex, rapid ʻōhiʻa death (ROD), and the unique radiation of endemic ambrosia beetles found across the Hawaiian archipelago. We investigated the status of RODassociated and native ambrosia beetles on Kauaʻi by rearing beetles from bolts collected from ROD-Ceratocystis infested ʻōhiʻa lehua (ʻōhiʻa; Metrosideros polymorpha) trees and trapping in mixed ʻōhiʻa forests. Beetles associated with ROD on Kauaʻi include Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xyleborus perforans, Xylosandrus crassiusculus, and Crossotarsus externedentatus. Xyleborus perforans was most abundant in ʻōhiʻa bolts followed by Xyleborus ferrugineus. From trap captures, we identified new island records of the native Xyleborus beetles including Xyleborus dubiosus, Xyleborus oahuensis, and Xyleborus tantalus. Xylosandrus crassiusculus was most abundant in traps. Additional work could contribute to understanding and mitigating the spread of ROD on Kauaʻi and to documenting the endemic Xyleborus beetles.

Hawaii↗

USGS2022

Hypotheses and lessons from a native moth outbreak in a low-diversity, tropical rainforest

Outbreaks of defoliating insects in low-diversity tropical forests occur infrequently but provide valuable insights about outbreak ecology in temperate environments and in general. We investigated an extensive outbreak of the endemic koa moth ( Scotorythra paludicola ), which defoliated endemic koa trees ( Acacia koa ) over a third of their range on Hawai‘i Island during 2013 and 2014. At Hakalau Forest National Wildlife Refuge, we observed the dynamics of the outbreak and its effects on host trees, nutrient cycling, and insectivorous consumers in reforestation stands of densely planted koa and in natural forest stands of mixed koa and ‘ōhi‘a ( Metrosideros polymorpha ). Contrary to predictions of the resource concentration hypothesis, caterpillar biomass and defoliation severity were greater in the natural forest sites, where koa density was relatively low. Caterpillars preferentially consumed the most palatable koa foliage type (phyllodes), and koa initially refoliated with the least palatable foliage type (true leaves). Lightly defoliated small trees refoliated more quickly than did heavily defoliated ones but the opposite was true for large trees, which also produced a greater proportion of phyllodes. Mortality was greatest for heavily defoliated small koa. Caterpillar frass caused larger increases in soil nitrogen (N) than phosphorus (P) availability, with the greatest N increases in fine-textured soils. Foliar N increased in alien grasses under koa canopies compared to grasses away from koa and to native woody understory species. Bird activity was influenced by ‘ōhi‘a flower abundance and the severity of koa defoliation; birds switched to outbreaking caterpillar prey, and they gained weight during the outbreak. Bat foraging times decreased during the outbreak, apparently because they became satiated quickly each night. Parasitoid wasps increased with caterpillar abundance but had little influence on outbreak dynamics. Reducing alien grass cover and increasing tree diversity would likely reduce the impacts of insect outbreaks and similar perturbations to native forests.

Hawai'i↗

USGS2022

Rapid ʻŌhiʻa Death in Hawaiʻi

Ceratocystis lukuohia and Ceratocystis huliohia are two newly recognized fungi that have arrived in Hawai‘i and are causing a serious vascular wilt and canker disease, respectively, of ‘ōhi‘a trees ( Metrosideros polymorpha ), the most common and important tree species in Hawai‘i. Management of these diseases has presented challenges due to unique etiological aspects and the exceptionally pathogenic nature of one of these fungi ( C. lukuohia ) once it gains access to the tree’s vascular tissue. Careful study of the spread of the pathogens has resulted in an understanding of the role of ambrosia beetles and the frass they produce that carries the pathogen, as well as the wounding of trees by many different agents by which the pathogen can access and infect the vascular tissue. A variety control measures are being used. These include a state-of-the-art monitoring program to detect diseased and recently killed trees and molecular biology approaches that can confirm if a given tree was infected by Ceratocystis . Based on monitoring more than one million trees have been estimated as killed by the diseases to date. A major part of the program includes the deployment of a field crew that seeks out and fells large infected ‘ōhi‘a trees as these trees are the main source of most of the infective Ceratocystis -laden frass. Long-term control measures also include fencing of some forests to reduce the amount of wounding to ‘ōhi‘a trees by feral cattle and pigs that allows entry of the fungi and quarantine restrictions to ensure there will be no inter-island movement of the pathogens in ‘ōhi‘a products. Finally, methods are also being developed to restore ‘ōhi‘a forests affected by these diseases by determining effective regeneration practices and developing genetically resistant ‘ōhi‘a stock. Hawai‘i has an active extension program dedicated to providing information on how residents and visitors can contribute to protecting ‘ōhi‘a trees from these diseases. More than 500,000 people have participated in this program. Hawai‘i residents have a very deep appreciation for this tree species and do what they can to help prevent these diseases from destroying more of their most treasured tree species.

Hawai'i↗