Browsing by Author "Euaparadorn, Melody"

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    Distribution of invasive ants and methods for their control in Hawai`i Volcanoes National Park.
    (2016-01-25) Peck, Robert; Banko, Paul; Cappadonna, Justin; Snook, Kirsten; Euaparadorn, Melody
    The first invasive ants were detected in Hawai`i Volcanoes National Park (HAVO) more than 80 years ago. Ecological impacts of these ants are largely unknown, but studies in Hawai`i and elsewhere increasingly show that invasive ants can reduce abundance and diversity of native arthropod communities as well as disrupt pollination and food webs. Prior to the present study, knowledge of ant distributions in HAVO has primarily been restricted to road- and trail-side surveys of the Kīlauea and Mauna Loa Strip sections of the park. Due to the risks that ants pose to HAVO resources, understanding their distributions and identifying tools to eradicate or control populations of the most aggressive species is an important objective of park managers. We mapped ant distributions in two of the most intensively managed sections of the park, Mauna Loa Strip and Kahuku. We also tested the efficacy of baits to control the Argentine ant (Linepithema humile) and the big-headed ant (Pheidole megacephala), two of the most aggressive and ecologically destructive species in Hawai`i. Efficacy testing of formicidal bait was designed to provide park managers with options for eradicating small populations or controlling populations that occur at levels beyond which they can be eradicated. Within the Mauna Loa Strip and Kahuku sections of HAVO we conducted systematic surveys of ant distributions at 1625 stations covering nearly 200 km of roads, fences, and transects between August 2008 and April 2010. Overall, 15 ant species were collected in the two areas, with 12 being found on Mauna Loa Strip and 11 at Kahuku. Cardiocondyla kagutsuchi was most widespread at both sites, ranging in elevation from 920 to 2014 m, and was the only species found above 1530 m. Argentine ants and big-headed ants were also found in both areas, but their distributions did not overlap. Surveys of Argentine ants identified areas of infestation covering 560 ha at Mauna Loa Strip and 585 ha at Kahuku. At both sites, upper boundaries of big-headed ants coincided with lower boundaries of Argentine ants. Significantly, Wasmannia auropunctata (little fire ant) was not detected during our surveys. Formicidal baits tested for controlling Argentine ants included Xstinguish™ (containing fipronil at 0.01%), Maxforce® (hydramethylnon 1.0%), and Australian Distance® (pyriproxyfen 0.5%). Each bait was distributed evenly over four 2500 m2 replicate plots. Applications were repeated approximately four weeks after the initial treatment. Plots were subdivided into 25 subplots and ants monitored within each subplot using paper cards containing tuna bait at approximately one week intervals for about 14 weeks. All treatments reduced ant numbers, but none eradicated ants on any of the plots. Xstinguish™ produced a strong and lasting effect, depressing ant abundance below 1% of control plot levels within the first week and for about eight weeks afterward. Maxforce® was slower to attain maximum effectiveness, reducing ants to 8% of control levels after one week and 3% after six weeks. Australian Distance® was least effective, decreasing ant abundance to 19% of control levels after one week with numbers subsequently rebounding to 40% of controls at four weeks and 72% at 10 weeks. In measurements of the proportion of bait cards at which ants were detected, Xstinguish™ clearly out-performed Maxforce®, reaching a minimum detection rate of 3% of bait cards at one week compared to a low of 19% for Maxforce® two weeks following the second treatment. Although ant abundances were dramatically reduced on Xstinguish™ plots, it is not currently registered for use in the USA. Our results suggest that ant abundance can be greatly reduced using registered baits, but further research is needed before even small-scale eradication of Argentine ants can be achieved. Formicidal baits tested to control big-headed ants included Amdro® (hydramethylnon 0.75%), Xstinguish™ (fipronil 0.01%), Extinguish® Plus (a blend of hydramethylnon 0.365% and S-methoprene 0.25%), and Australian Distance® Plus (hydramethylnon 0.365% and pyriproxyfen 0.25%). Application methods were the same as used for Argentine ants, with baits being applied on two occasions (approximately four weeks apart) on four 2500 m2 replicate plots. All four baits reduced populations to below 2% of control plot levels within one week of treatment. Amdro® was particularly effective as no ants were detected on two of the four Amdro® plots immediately following treatment. Suppression was long-lived in three of the treatments; Amdro®, Australian Distance® Plus, and Extinguish® GENERAL INTRODUCTION Plus all maintained ant abundances at levels less than 1% of control plots over 12 weeks of study. In contrast, ant abundances in Xstinguish™ plots rose to 7% of control plots after four weeks and 20% after 10 weeks. Our results corroborate other recent studies indicating that small populations of big-headed ants can be controlled in natural areas using products registered in the USA.
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    Limiting factors of five rare plant species in mesic forests, Hawai`i Volcanoes National Park
    (2010-05) Pratt, Linda W.; VanDeMark, Joshua R.; Euaparadorn, Melody
    Five rare or endangered plant species native to Kīpuka Puaulu and Kīpuka Kī were studied for two years to determine their stand structure, patterns of reproductive phenology, success of fruit production, potential pollinators, greenhouse seed germination rates, presence of soil seed banks, impacts of seed-predating rats, seed predation by insects, seedling predation by Kalij pheasant (Lophura leucomelanos), and seedling survival with different treatments. Species monitored were the trees Hibiscadelphus giffardianus (hau kuahiwi), Melicope hawaiensis (manena), M. zahlbruckneri (alani), and Zanthoxylum dipetalum var. dipetalum (kāwa`u), and the vine Sicyos macrophyllus (`ānunu). Limiting factors identified for H. giffardianus were rat predation of seeds, bark-stripping, low fruit production likely resulting from the inter-relatedness of the planted population, and loss of original pollinators. For M. hawaiensis, rat and native insect predation of seeds limited the number of seeds available, and natural seedling recruitment was very low. Pollination was effected by an alien insect species. For M. zahlbruckneri, native insect predation and rat depredation greatly reduced the number of seeds available for germination. The low proportion of flowers that became fruit indicated a lack of successful pollination or self-incompatibility. For S. macrophyllus, rat predation of seeds on the ground and in the seed bank reduced the number of seeds available for natural regeneration. Alien grasses were suspected to limit seedling recruitment. Most floral visitors were alien insect species. Seedling recruitment appeared to be the most vulnerable life stage for Z. dipetalum var. dipetalum. Both alien Kalij pheasants and unknown insect species were implicated as seedling predators/herbivores.
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    Limiting factors of four rare plant species in Ola`a forest of Hawai`i Volcanoes National Park.
    (2010-07) VanDeMark, Joshua R.; Pratt, Linda W.; Euaparadorn, Melody
    Three endangered or candidate endangered plant species native to `Ōla`a Forest (Cyrtandra giffardii, ha`iwale; Phyllostegia floribunda, a mint with no common name; and Sicyos alba, `ānunu) were studied for more than two years to determine their stand structures, short-term mortality rates, patterns of reproductive phenology, success of fruit production, seed germination rates in the greenhouse, presence of soil seed bank, and survival of both natural and planted seedlings. The role of rodents as seed predators was evaluated for S. alba using seed offerings in open and closed stations. A fourth endangered species (Cyrtandra tintinnabula) at a remote site in `Ōla`a was visited to determine its stand structure and mortality rate. Cyrtandra giffardii displayed a stable population structure with many adults and few small or very large plants; the monitored population had a mortality rate of 7.3% over three years. Mortality of plantings from 2003-2004 in a re-introduced population of Phyllostegia floribunda was 21.4%. The stand structure of C. tintinnabula indicated a relatively stable population with both small and large plants present and a short-term mortality rate between visits of 14.5-17.0%. Four groups of S. alba vines were monitored; 3 of these have persisted in place for at least 15 years. All species monitored had annual patterns of flower and fruit phenology, although male inflorescences of S. alba showed a subannual pattern. Successful transition of flowers to fruit was high for P. floribunda (51.5%), moderate for C. giffardii (23.3%), and undetermined for S. alba. High percentage viability was demonstrated for seeds of P. floribunda and S. alba (78.5-100% positive to strongly positive in tetrazolium tests), but seed viability was not tested for C. giffardii. Greenhouse germination rates were high for P. floribunda (88.0-92.0%), but variable and relatively low for C. giffardii (0-19.3%) and S. alba (4.0-11.1% in 2007 and 0 in 2008). No soil seed bank was detected for S. alba in 3 seasonal samplings, but P. floribunda was found to have a viable seed bank in April that persisted from at least the previous summer. Rodent predation of S. alba seeds was 93.3% in fruit offerings in accessible bait stations. Mortality of natural seedlings was high for both P. floribunda (90.2%) and S. alba (69.7%). Planted seedlings of P. floribunda produced flowers and fruit in their first year, and reproduction was higher in sunny plots than in shady plots. Mortality was high in both planting treatments, and 2 survival rates did not differ significantly in sun and shade (χ 2 = 0.48, df = 1, p = 0.490). Three planted seedlings of S. alba survived for 12-16 months but did not reproduce. Floral visitors were observed at C. giffardii and P. floribunda using digital video cameras and recorders. In almost 200 hours of observation, no visitors entered the flowers of C. giffardii, although one very small insect, either a micro-wasp (Hymenoptera) or fly (Diptera) was seen on the exterior of a corolla. In almost 300 hours of video observation, three floral visitors were identified at P. floribunda flowers. Honeybees (Apis mellifera) were likely pollinators, as they contacted both anthers and stigma of flowers. The mean visitation rate of honeybees was 0.003 visit/flower/hour, and visit duration ranged from 2 to 17 seconds. Fruitflies (Drosophilidae of undetermined species) crawled around flower interiors, but did not seem to forage for either nectar or pollen. Fruit fly mean visitation rate was 0.006 visit/flower/hour, and visit duration was 28 to 1,424 seconds. The third observed insect visitor was an endemic geometrid moth caterpillar (Lophoplusia giffardi), which was seen feeding on foliage and flowers of P. floribunda. In conclusion, two of the three regularly-monitored rare plant species of `Ōla`a Forest appeared to have more than one limiting factor inhibiting the natural increase in their populations, while for P. floribunda the most important factor was high seedling mortality. Most plants of the monitored C. giffardii population appeared to be hybrids, probably with the more common species C. lysiosepala. Seed germination rates were low, and natural seedlings were not observed. Pollinators were not seen in many hours of observation, indicating that cross pollination is a rare or uncommon event. The re-introduced population of P. floribunda had relatively low mortality, and reproduction was successful with high rates of fruit formation from abundant flowers. Seed germination rates were high, and a soil seed bank was detected. Natural seedling recruitment was observed, but high seedling mortality indicated that this life stage was the most vulnerable in the species. The population of S. alba was small and the vine life form precluded an accurate estimate of the number of adult plants in `Ōla`a Forest. Natural dormancy was likely a factor in the observed low rate of seed germination. No soil seed bank was detected, and alien rodents were implicated as seed predators. Natural recruitment was observed at multiple sites in `Ōla`a, but seedling mortality was high. The cause of seedling mortality was not identified.
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    Limiting factors of four rare plant species in Ola`a forest of Hawai`i Volcanoes National Park.
    (2016-01-26) VanDeMark, Joshua; Pratt, Linda; Euaparadorn, Melody
    Three endangered or candidate endangered plant species native to `Ōla`a Forest (Cyrtandra giffardii, ha`iwale; Phyllostegia floribunda, a mint with no common name; and Sicyos alba, `ānunu) were studied for more than two years to determine their stand structures, short-term mortality rates, patterns of reproductive phenology, success of fruit production, seed germination rates in the greenhouse, presence of soil seed bank, and survival of both natural and planted seedlings. The role of rodents as seed predators was evaluated for S. alba using seed offerings in open and closed stations. A fourth endangered species (Cyrtandra tintinnabula) at a remote site in `Ōla`a was visited to determine its stand structure and mortality rate. Cyrtandra giffardii displayed a stable population structure with many adults and few small or very large plants; the monitored population had a mortality rate of 7.3% over three years. Mortality of plantings from 2003-2004 in a re-introduced population of Phyllostegia floribunda was 21.4%. The stand structure of C. tintinnabula indicated a relatively stable population with both small and large plants present and a short-term mortality rate between visits of 14.5-17.0%. Four groups of S. alba vines were monitored; 3 of these have persisted in place for at least 15 years. All species monitored had annual patterns of flower and fruit phenology, although male inflorescences of S. alba showed a subannual pattern. Successful transition of flowers to fruit was high for P. floribunda (51.5%), moderate for C. giffardii (23.3%), and undetermined for S. alba. High percentage viability was demonstrated for seeds of P. floribunda and S. alba (78.5-100% positive to strongly positive in tetrazolium tests), but seed viability was not tested for C. giffardii. Greenhouse germination rates were high for P. floribunda (88.0-92.0%), but variable and relatively low for C. giffardii (0-19.3%) and S. alba (4.0-11.1% in 2007 and 0 in 2008). No soil seed bank was detected for S. alba in 3 seasonal samplings, but P. floribunda was found to have a viable seed bank in April that persisted from at least the previous summer. Rodent predation of S. alba seeds was 93.3% in fruit offerings in accessible bait stations. Mortality of natural seedlings was high for both P. floribunda (90.2%) and S. alba (69.7%). Planted seedlings of P. floribunda produced flowers and fruit in their first year, and reproduction was higher in sunny plots than in shady plots. Mortality was high in both planting treatments, and survival rates did not differ significantly in sun and shade (χ 2 = 0.48, df = 1, p = 0.490). Three planted seedlings of S. alba survived for 12-16 months but did not reproduce. Floral visitors were observed at C. giffardii and P. floribunda using digital video cameras and recorders. In almost 200 hours of observation, no visitors entered the flowers of C. giffardii, although one very small insect, either a micro-wasp (Hymenoptera) or fly (Diptera) was seen on the exterior of a corolla. In almost 300 hours of video observation, three floral visitors were identified at P. floribunda flowers. Honeybees (Apis mellifera) were likely pollinators, as they contacted both anthers and stigma of flowers. The mean visitation rate of honeybees was 0.003 visit/flower/hour, and visit duration ranged from 2 to 17 seconds. Fruit flies (Drosophilidae of undetermined species) crawled around flower interiors, but did not seem to forage for either nectar or pollen. Fruit fly mean visitation rate was 0.006 visit/flower/hour, and visit duration was 28 to 1,424 seconds. The third observed insect visitor was an endemic geometrid moth caterpillar (Lophoplusia giffardi), which was seen feeding on foliage and flowers of P. floribunda. In conclusion, two of the three regularly-monitored rare plant species of `Ōla`a Forest appeared to have more than one limiting factor inhibiting the natural increase in their populations, while for P. floribunda the most important factor was high seedling mortality. Most plants of the monitored C. giffardii population appeared to be hybrids, probably with the more common species C. lysiosepala. Seed germination rates were low, and natural seedlings were not observed. Pollinators were not seen in many hours of observation, indicating that cross pollination is a rare or uncommon event. The re-introduced population of P. floribunda had relatively low mortality, and reproduction was successful with high rates of fruit formation from abundant flowers. Seed germination rates were high, and a soil seed bank was detected. Natural seedling recruitment was observed, but high seedling mortality indicated that this life stage was the most vulnerable in the species. The population of S. alba was small and the vine life form precluded an accurate estimate of the number of adult plants in `Ōla`a Forest. Natural dormancy was likely a factor in the observed low rate of seed germination. No soil seed bank was detected, and alien rodents were implicated as seed predators. Natural recruitment was observed at multiple sites in `Ōla`a, but seedling mortality was high. The cause of seedling mortality was not identified.
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    Status and limiting factors of three rare plant species in the coastal lowlands and mid-elevation woodlands of Hawai`i Volcanoes National Park.
    (2016-01-26) Pratt, Linda; VanDeMark, Joshua; Euaparadorn, Melody
    Two endangered plant species (Portulaca sclerocarpa, `ihi mākole, and Sesbania tomentosa, `ōhai) and a species of concern (Bobea timonioides, `ahakea) native to the coastal lowlands and dry mid-elevation woodlands of Hawai`i Volcanoes National Park were studied for more than two years to determine their stand structure, short-term mortality rates, patterns of reproductive phenology, success of fruit production, seed germination rates in the greenhouse, presence of soil seed bank, and survival of both natural and planted seedlings. The role of rodents as fruit and seed predators was evaluated using exclosures and seed offerings in open and closed stations or cages. Rodents were excluded from randomly selected plants of P. sclerocarpa and from branches of S. tomentosa, and flower and fruit production were compared to that of adjacent unprotected plants. Tagged S. tomentosa fruit were also monitored monthly to detect rodent predation. Natural populations of all three rare plant species showed declines over the period of monitoring. Bobea timonioides had the stand structure of a senescent population, and about a third of these long-lived trees have died since a previous survey 13 years ago. The size of monitored natural P. sclerocarpa plants decreased during the study, and mortality rate was 23% over two years. A comparison of current and long-term population data showed the same declining trend. Stand structure and mortality of natural S. tomentosa could not be determined at Kīpuka Nēnē, but half of monitored plants died over a year at coastal `Āpua Point. Portulaca sclerocarpa and S. tomentosa showed pronounced seasonal patterns in their reproductive phenology, and B. timonioides appeared to have a continuous pattern of flower and fruit production. Buds and flowers of P. sclerocarpa at its natural population peaked during spring and fall months, and fruit capsules were borne most of the year. At the upland S. tomentosa site, peak bud and flower production occurred in spring and summer, and greatest fruit abundance was in summer and winter months. The coastal site for this species showed greatest flowering in the fall and mature fruit were persistent year-long. Fruit set was high for P. sclerocarpa, very low for S. tomentosa, and undetermined for B. timonioides. Pollination was studied for only S. tomentosa at Kīpuka Nēnē, where six insect species were floral visitors, and native Hylaeus, or yellow-faced bees, and Apis mellifera honeybees were found to be transporting pollen of the rare plant. Seed germination rates determined by greenhouse studies were moderately high for B. timonioides and S. tomentosa and low but variable for P. sclerocarpa. Field-sowed seeds of B. timonioides and P. sclerocarpa did not germinate, but up to 31% germination was observed for S. tomentosa seed-sowing trials. No difference in germination or seedling survival was observed for S. tomentosa in plots with and without grass. A small seed bank was detected for S. tomentosa during one season at both Kīpuka Nēnē and `Āpua Point. Mortality of planted seedlings or cuttings was high for all three rare species, but recent plantings of P. sclerocarpa seedlings showed a low mortality rate at one site. Natural seedlings were observed at two P. sclerocarpa planting sites, but all succumbed during dry periods. Rodents were found to be seed predators of both P. sclerocarpa and S. tomentosa, but had no detected impact on B. timonioides. A third of tagged seed pods of S. tomentosa displayed signs of rat predation, and another third disappeared. The most important limiting factors identified for P. sclerocarpa were loss of seeds to rodent predation and low seedling recruitment. Sesbania tomentosa shared these two limiting factors and also lost flowers to alien insect predation and displayed very low fruit set caused by either a lack of effective pollination or self-compatibility problems. Lack of natural seedling recruitment, perhaps caused by current harsh site conditions, appeared to be the most significant limiting factor for B. timonioides.
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    Status and limiting factors of two rare plant speices in montane dry communities of Hawai`i Volcanoes National Park.
    (2016-01-25) Pratt, Linda; VanDeMark, Joshua; Euaparadorn, Melody
    Two rare plants native to montane dry forests and woodland communities of Hawai`i Volcanoes National Park (HAVO) were studied for more than two years to determine their stand structure, short-term mortality rates, patterns of reproductive phenology, success of fruit production, floral visitor composition, seed germination rates in the greenhouse, and survival of both natural and planted seedlings. Phyllostegia stachyoides, a shrubby Hawaiian mint (Lamiaceae) that is a species of concern, was studied within two small kīpuka at a natural population on the park’s Mauna Loa Strip, and three plantings at sites along the Mauna Loa Road were also monitored. Silene hawaiiensis, a threatened shrub species in the pink family (Caryophyllaceae), was monitored at two natural populations, one on Mauna Loa at the Three Trees Kīpuka and the second on Kīlauea Crater Rim south of Halema`uma`u. Silene hawaiiensis plantings were also made inside and outside ungulate exclosures at the park’s Kahuku Unit. Phyllostegia stachyoides appeared to have a relatively stable natural population in HAVO with approximately 19% adult plant mortality over three years and recruitment of natural seedlings. Despite high mortality (~98%), some seedlings persisted for more than a year, and recruitment of new plants into the population exceeded the losses of adult plants. Flowering and fruiting phenology was annual and seasonal with peak appearance of buds and flowers in spring and greatest abundance of mature fruit in the summer and fall. Successful production of green fruit from buds and flowers was very high (45%), and green fruit transitioned to mature fruit at a rate of 17.8%. Five insect species were observed visiting flowers, and those with the greatest visitation rates were the alien hover fly Allograpta obliqua (Syrphidae) and the endemic yellow-faced bee Hylaeus difficilis (Colletidae). Both insect species were shown to be carrying pollen of P. stachyoides. Seed germination rates in the greenhouse were variable but ranged as high as 80.4%. Mortality of seedlings planted at three sites along the Mauna Loa Road was very high (~90%) within 2–3 years of planting. There was no significant difference in the mortality or growth of seedlings planted in areas with little grass compared to those in adjacent areas with high grass cover. Silene hawaiiensis had a stable population structure at the Mauna Loa study area, but its population structure at the Kīlauea study site was flat to declining. Mortality of adult plants was low on Mauna Loa (6.5%), but was greater than 30% at the Kīlauea Crater Rim site. Among regularly monitored plants at the Kīlauea site, losses were observed in all size classes between 2006 and 2008. Natural seedling recruitment was observed in stand structure plots at both sites between 2006 and 2007, but numbers of seedlings were low and did not compensate for losses of adult plants. Reproductive phenology was annual with buds and flowers observed in summer and fall, and fruit formed in the fall and winter. The production of immature fruit capsules from buds and flowers was high (51.2%) and tagged immature fruit became mature fruit at a high rate of 66.7%. Floral visitation rates were very low in timed observations and only three insect species were identified visiting S. hawaiiensis flowers: native yellow-faced bees Hylaeus difficilis and H. volcanicus, and the alien hover fly Allograpta exotica. A seed dispersal experiment at the Kīlauea Crater Rim site demonstrated that wind dispersed seeds could travel at least 40 m from S. hawaiiensis plants with mature open capsules. Seed germination rates varied from 7.0 to 73.0% in greenhouse trials. Mortality of planted seedlings at Kahuku was not significantly greater outside ungulate exclosures than inside, but growth in height and production of reproductive structures was significantly greater in protected areas inside exclosures. In the current study, the seedling stage was the most vulnerable part of the life cycle for both P. stachyoides and S. hawaiiensis, and low seedling recruitment appeared to be the most important limiting factor for these species.