Progress 10/01/04 to 09/30/07
Outputs
OUTPUTS: Introduced to the Hawaiian Islands in 1988, the Puerto Rican coqui frog, Eleutherodactylus coqu, has reached population densities far exceeding those in their native range. Because of the lack of potential predators and competitors, E. coqui in Hawaii is an introduction of a new voracious predator. Studies in Hawaii discovered that plots in heavily forested areas where the coqui frog has become well established yield population estimates of frog density 3 times the estimates reported from native populations in Puerto Rico. We suggested that the apparent lack of native or exotic predators in Hawaii and abundance of suitable retreat sites contribute to achievement of unusually high population densities of E. coqui in Hawaii compared with Puerto Rico. At Lava Tree State Monument, Pāhoa, Hawaii, 100 pvc (polyvinyl chloride) pipes serving as artificial retreat and nesting sites were observed every two-weeks for frogs and eggs from February 2005 to August 2006. A total of a
770 frogs were collected from within a 400 meter square area. Average occupancy of retreats was 20.7% per survey (range 1-42%). In addition to frogs, 249 egg clutches (5044 eggs) were recovered during surveys. Before the placement of pvc pipes, the difference between the pvc retreat plot and an untreated 400m2 plot in mean number of new frogs captured on four consecutive night surveys ranged from 17.5 to 27.3 frogs/night. At the conclusion of the study the difference had become -11.0 frogs/night; the plot where pvc traps were placed had as many as 27 more frogs found a night at study inception and after 18 months of collection from pvc retreats the untreated plot had 11 more frogs collected per night. These field results demonstrate that collecting frogs and eggs in artificial pvc retreat and nesting sites can significantly impact coqui frog populations. We tested the enemy release hypothesis as it relates to the invasive Puerto Rican frog, Eleutherodactylus coqui in Hawaii. We
collected parasite data on 160 individual coqui frogs collected during January-April 2006 from eight populations in Puerto Rico and Hawaii. Results were consistent with the enemy release hypothesis. Puerto Rican coqui frogs had higher species richness of parasites than Hawaiian coqui frogs. Parasite prevalence and intensity were significantly higher in Hawaii, however this was likely a product of the life history of the dominant parasite and its minimal harm to the host. This suggests that the scarcity of parasites may be a factor contributing to the success of E. coqui in Hawaii. Hawaii has no native amphibians, and with careful and extensive testing, a parasite that specifically targets amphibians with no transmission to other hosts may be a means of managing the invasion of E. coqui in Hawaii. New knowledge was disseminated to communities and nursery growers by participating in community meetings, annual conferences of the nursery industries in Hawaii, and participating in annual
invasive species and conservation conferences in Hawaii.
PARTICIPANTS: Collaborators and contacts: Dr. William J. Mautz, Professor Department of Biology University of Hawaii at Hilo Hilo, HI 96720 Mr. Kyle Onuma, Specialist Hawaii Dept. of Agriculture Plant Pest Control Branch 16 East Lanikaula St. Hilo, Hawaii 96720 Ms. Karen Shiroma, Coqui Frog Program Manager, County of Hawaii 25 Aupuni Street Hilo, HI 96720
TARGET AUDIENCES: PVC trap methods for the coqui frog were presented at invasive species conferences, placed on web pages, and published as an outreach bulletin (See http://www.ctahr.hawaii.edu/coqui/index.asp). PVC trap methods were shared with private, county, state and federal landowners as an effective nonchemical method for reducing coqui frogs populations.
Impacts
The pvc (polyvinyl chloride) trap was found to be an effective and economical nonchemical control against the coqui frog. These traps are an alternative to toxic citric acid that must contact the coqui frog to be effective. Internal parasites discovered on coqui frogs in Puerto Rico may provide an effective biological control that is specific only to coqui frogs and will provide a long term, environmentally acceptable control of the coqui frog.
Publications
- Marr, S. 2006. The role of parasites in the invasion of the Puerto Rican tree frog (Eleutherodactylus coqui) in Hawaii. M.S. Thesis, University of Hawaii at Hilo.
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Progress 10/01/05 to 09/30/06
Outputs
The stomach contents of 48 adult coqui frogs from Lava Tree State Monument (Pahoa, HI, elevation 180 m, annual rainfall 297 cm) were determined by dissecting and identifying the arthropods in the stomach of frogs. Approximately 10 orders and 23 families of arthropods were identified. The most frequently consumed insects were of the orders Hymenoptera (23%, primarily Formicidae), Coleoptera (23%), Hemiptera (13%), and Diptera (11.7%). Remnants of snails (Styllomatophora) were also recovered from the gut contents of two frogs. These findings verified that, at this location, the coqui frog is primarily foraging on forest floor-dwelling arthropods. A study was conducted to determine the efficacy of a lower 8% citric acid rate with the addition of pyrethrins and piperonyl butoxide. Citric acid was as effective at 8% as 16% concentration in preventing coqui frog eggs from hatching (100% mortality). Pyronyl Crop Spray (6% pyrethrins, 60% piperonyl butoxide) at 1.8 ml/L) were
not effective in reducing egg hatch (93% hatching rate); however, all froglets died upon contact with pyrethrins after hatching. When eggs were treated with both pyrethrins and 8% citric acid, there was 100% mortality compared to 100% hatch among untreated controls. Other researchers had found that Pyronyl at 1.8 ml/L plus 8% citric acid is as effective against adult coqui frogs as 16% citric acid alone. Reducing the concentration of citric acid from 16% to 8% significantly reduced phytoxicity to sensitive plants. Hot water treatment (45 C for 5 min) is effective in killing coqui frogs and their eggs, most ornamental plants can tolerate this treatment without heat injury. A thermal study with various species of ornamental potted plants observed no heat injury at 45 C to Podocarpus gracilor, Salvia leucantha, Lantana montevedensis, bromeliad Puna Gold, Sida fallax, Nephrolepis exaltata, Phymatosorus grossus, and Beallara (Oncidiinae) and Epicattleya (Laeliinae) orchids.
Impacts
The diet of coqui frogs was determined to consist primarily of forest floor dwelling arthropods which will greatly assist in developing control strategies based on depleting food supply. An effective non-phytotoxic pesticide (pyrethrins, piperonyl butoxide, and citric acid) was developed agains the coqui frog that can be used as a quarantine treatment on potted plants.
Publications
- Coqui Frog Working Group. May 2006. Coqui Frog Control for Homeowners. University of Hawaii at Mānoa, CTAHR. Office of Information Services. MP-5. 2 pp.
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Progress 10/01/04 to 09/30/05
Outputs
The efficacy of hydrated lime was evaluated on coqui frog eggs. Egg clusters (4-5 d old) were divided in two masses and placed in identical petri dishes upon moistened paper towels; one egg mass was treated with hydrated lime (50 lb/100 gal) and the other egg mass was left untreated. Observations were taken 3, 6 and 9 d after treatment. Three days after treatment, the treated egg mass turned white with no signs of embryonic development compared to the untreated eggs. Six days after treatment, the treated eggs began to decay, and by 9 days fungus had developed on the deteriorating mass. The untreated eggs hatched 9 days after treatment. Hydrated lime effectively prevented coqui frog eggs from hatching. There was 100% mortality among treated eggs from 3 to 10 d old (n=145); however, 2 out of 16 (12.5%) eggs treated at 13-d old hatched. Among untreated eggs, there was a 97% hatching rate (n=94). The rate of hydrated lime application was decreased to 25 lb/100 gal with
identical results: 100% mortality among treated eggs from 4-10 d old (n=127). No phytotoxicity from hydrated lime was observed on a variety of plants, however, the suspension dried to a semi-permanent white residue, which poses an aesthetic predicament with ornamental plants. These data were submitted by the HDOA to the Environmental Protection Agency (EPA) requesting a quarantine exemption to use hydrated lime to control coqui frogs in Hawaii. After solicitation of public comment and a request for more supporting data, EPA approved an emergency exemption to allow the use of calcium hydroxide (CA(OH)2), commonly known as hydrated lime, to control coqui frog infestations in Hawaii. This approval allows nurseries, property owners and government agencies to use hydrated lime in outdoor nurseries, residential areas, resorts and hotels, parks, forest habitats and natural areas to control coqui frogs and greenhouse frogs.
Impacts
Citric acid is available for use against the coqui frog, but its expense at 10 times the cost of hydrated lime restricts its feasibility to spot treatments over small areas with a few frogs. Submission of data supporting hydrated lime's efficacy on coqui frog eggs and lack of phytotoxicity was critical in obtaining the emergency exemption from EPA. Hydrated lime is an equally effective and more economical chemical control agent available for use on a larger scale (nurseries, county and state parks, forest reserves).
Publications
- No publications reported this period
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