William C. Pitt

Biology and impacts of Pacific island invasive species. 11. Rattus rattus, the black rat (Rodentia: Muridae).

Abstract: The black rat, roof rat, or ship rat (Rattus rattus L.) is among the most widespread invasive vertebrates on islands and continents, and it is nearly ubiquitous on Pacific islands from the equatorial tropics to approximately 55 degrees latitude north and south. It survives well in human-dominated environments, natural areas, and islands where humans are not present. Rattus rattus is typically the most common invasive rodent in insular forests. Few vertebrates are more problematic to island biota and human livelihoods than R. rattus; it is well known to damage crops and stored foods, kill native species, and serve as a vector for human diseases. Rattus rattus is an omnivore, yet fruit and seed generally dominate its diet, and prey items from the ground to the canopy are commonly at risk and exploited as a result of the prominent arboreal activity of R. rattus. Here we review the biology of this invasive species and its impacts on humans and the insular plants and animals in the Pacific. We also describe some of the past management practices used to control R. rattus populations on islands they have invaded.

Biology and Impacts of Pacific Island Invasive Species. 5. Eleutherodactylus coqui , the Coqui Frog (Anura: Leptodactylidae)

Abstract: The nocturnal, terrestrial frog Eleutherodactylus coqui, known as the Coqui, is endemic to Puerto Rico and was accidentally introduced to Hawai‘i via nursery plants in the late 1980s. Over the past two decades E. coqui has spread to the four main Hawaiian Islands, and a major campaign was launched to eliminate and control it. One of the primary reasons this frog has received attention is its loud mating call (85–90 dB at 0.5 m). Many homeowners do not want the frogs on their property, and their presence has influenced housing prices. In addition, E. coqui has indirectly impacted the floriculture industry because customers are reticent to purchase products potentially infested with frogs. Eleutherodactylus coqui attains extremely high densities in Hawai‘i, up to 91,000 frogs ha-1, and can reproduce year-round, once every 1–2 months, and become reproductive around 8–9 months. Although the Coqui has been hypothesized to potentially compete with native insectivores, the most obvious potential ecological impact of the invasion is predation on invertebrate populations and disruption of associated ecosystem processes. Multiple forms of control have been attempted in Hawai‘i with varying success. The most successful control available at this time is citric acid. Currently, the frog is established throughout the island of Hawai‘i but may soon be eliminated on the other Hawaiian Islands via control efforts. Eradication is deemed no longer possible on the island of Hawai‘i.

Probabilistic risk assessment for snails, slugs, and endangered honeycreepers in diphacinone rodenticide baited areas on Hawaii, USA

Three probabilistic models were developed for characterizing the risk of mortality and subacute coagulopathy to Poouli, an endangered nontarget avian species, in broadcast diphacinone-baited areas on Hawaii, USA. For single-day exposure, the risk of Poouli mortality approaches 0. For 5-d exposure, the mean probability of mortality increased to 3% for adult and 8% for juvenile Poouli populations. For Poouli that consume snails containing diphacinone residues for 14 d, the model predicted increased levels of coagulopathy for 0.42 and 11% of adult and juvenile Poouli populations, respectively. Worst-case deterministic risk characterizations predicted acceptable levels of risk for nonthreatened or endangered species such as northern bobwhite quail and mallards. Also, no acute toxicity was noted for snails and slugs that feed on diphacinone baits.

Potential predators of an invasive frog (Eleutherodactylus coqui) in Hawaiian forests

In Hawaii, where there are no native reptiles or amphibians, 27 species of reptiles and amphibians have established (Kraus 2003); however, few have been studied to determine their ecological impacts. For example, little is known about the impacts of the Puerto Rican frog, Eleutherodactylus coqui Thomas, that recently invaded (late 1980s) (Kraus et al. 1999), and has established on all four main Hawaiian Islands (Kraus & Campbell 2002). However, there are likely to be consequences because E. coqui can attain high densities (20 570 frogs ha-1 on average in Puerto Rico) and consume large quantities of invertebrates (114 000 prey items ha-1 per night on average in Puerto Rico) (Stewart & Woolbright 1996).

Efficacy of Rodenticide Baits for the Control of Three Invasive Rodent Species in Hawaii

We tested the efficacy and palatability of nine commercial rodenticide bait formulations on Polynesian rats (Rattus exulans), roof rats (R. rattus), and house mice (Mus musculus). Efficacy varied by rodenticide tested and rodent species. Generally, rodenticides were more effective against mice than for either of the rat species, and mice tended to consume more rodenticide bait than the laboratory chow alternative food. Efficacy was generally highest for the second-generation anticoagulants tested; however, this varied across products and one-first-generation rodenticide had similar effectiveness. Bait acceptance (palatability) also varied both by rodenticide and by rodent species. Acceptance was the lowest for the acute rodenticides. Bait acceptance appeared to substantially affect the efficacy of rodenticides; materials that were not well accepted produced lower mortality rates. Rodenticide products currently registered for use in Hawaii performed less effectively in this study than other available products not yet registered. Although markets for rodent control products for use on islands are limited, there are advantages to having additional products registered for island use in agriculture, conservation, and public health.

Invasive litter, not an invasive insectivore, determines invertebrate communities in Hawaiian forests

In Hawaii, invasive plants have the ability to alter litter-based food chains because they often have litter traits that differ from native species. Additionally, abundant invasive predators, especially those representing new trophic levels, can reduce prey. The relative importance of these two processes on the litter invertebrate community in Hawaii is important, because they could affect the large number of endemic and endangered invertebrates. We determined the relative importance of litter resources, represented by leaf litter of two trees, an invasive nitrogen-fixer, Falcataria moluccana, and a native tree, Metrosideros polymorpha, and predation of an invasive terrestrial frog, Eleutherodactylus coqui, on leaf litter invertebrate abundance and composition. Principle component analysis revealed that F. moluccana litter creates an invertebrate community that greatly differs from that found in M. polymorpha litter. We found that F. moluccana increased the abundance of non-native fragmenters (Amphipoda and Isopoda) by 400% and non-native predaceous ants (Hymenoptera: Formicidae) by 200%. E. coqui had less effect on the litter invertebrate community; it reduced microbivores by 40% in F. moluccana and non-native ants by 30% across litter types. E. coqui stomach contents were similar in abundance and composition in both litter treatments, despite dramatic differences in the invertebrate community. Additionally, our results suggest that invertebrate community differences between litter types did not cascade to influence E. coqui growth or survivorship. In conclusion, it appears that an invasive nitrogen-fixing tree species has a greater influence on litter invertebrate community abundance and composition than the invasive predator, E. coqui.

Invasive Predators: a synthesis of the past, present, and future

Invasive predators have had devastating effects on species around the world and their effects are increasing. Successful invasive predators typically have a high reproductive rate, short generation times, a generalized diet, and are small or secretive. However, the probability of a successful invasion is also dependent on the qualities of the ecosystem invaded. Ecosystems with a limited assemblage of native species are the most susceptible to invasion provided that habitat and climate are favorable. In addition, the number of invasion opportunities for a species increases the likelihood that the species will successfully establish. The list of routes of entry or pathways into many ecosystems continues to grow as transportation of goods into even the remotest areas become common. Species may enter new areas accidentally (e.g., hitchhikers on products) or as intentional introductions (e.g., sport fish). Pet releases, either accidental or intentional, are a growing area of concern as exotic pets become common and the desire for new or different species grows. Several invasive predators have had major effects on prey populations around the world (e.g., black rats, feral cats, mongoose) or have had devastating effects in isolated areas (e.g., brown treesnakes, Nile perch). Although management of established species has been a priority, eradication has been extremely difficult once a species has become widely distributed. However, little resources are directed toward interdiction efforts, removing incipient populations, or preventing new introductions. The regulation of animal movement in most countries and the inspection of products being moved were not developed to protect native ecosystems. Thus, species may be moved with relative ease between regions and countries. The most cost effective approach to invasive species management is to prevent new species from becoming established by providing funding for interdiction efforts, research prior to a species becoming widespread, and restricting the movement of species.

Biology and Impacts of Pacific Island Invasive Species. 8. Eleutherodactylus planirostris, the Greenhouse Frog (Anura: Eleutherodactylidae)

Abstract: The greenhouse frog, Eleutherodactylus planirostris, is a direct-developing (i.e., no aquatic stage) frog native to Cuba and the Bahamas. It was introduced to Hawai‘i via nursery plants in the early 1990s and then subsequently from Hawai’i to Guam in 2003. The greenhouse frog is now widespread on five Hawaiian Islands and Guam. Infestations are often overlooked due to the frogs quiet calls, small size, and cryptic behavior, and this likely contributes to its spread. Because the greenhouse frog is an insectivore, introductions may reduce invertebrates. In Hawai‘i, the greenhouse frog primarily consumes ants, mites, and springtails and obtains densities of up to 12,500 frogs ha-1. At this density, it is estimated that they can consume up to 129,000 invertebrates ha-1 night-1. They are a food source for the nonnative brown tree snake in Guam and may be a food source for other nonnative species. They may also compete with other insectivores for available prey. The greatest direct economic impacts of the invasions are to the nursery trade, which must treat infested shipments. Although various control methods have been developed to control frogs in Hawai’i, and citric acid, in particular, is effective in reducing greenhouse frogs, the frogs inconspicuous nature often prevents populations from being identified and managed.

The effect of cooking on diphacinone residues related to human consumption of feral pig tissues

We examined feral pig tissues to determine whether the potential hazard of consuming meat from pigs previously exposed to diphacinone rodenticide baits was reduced by cooking. Residue levels were measured in cooked and uncooked tissues of feral pigs exposed to sub-lethal quantities of the anticoagulant rodenticide. Pigs were provided large amounts of baits or untreated food to consume, then euthanized prior to the onset of symptoms indicative of rodenticide poisoning or sickness. For analysis, we grouped pigs into three levels of mean diphacinone consumption: 0, 3.5, and 7.4 mg/kg. None of the pigs displayed obvious signs of toxicity during the study period. The highest concentrations of diphacinone were found in liver tissue. Cooking had little effect on residual diphacinone concentrations. The hazards to humans and pets from meat from feral pigs that consumed the rodenticide diphacinone are not reduced by cooking; consumption of pig meat obtained from areas with active rodent control programs should be avoided.

Detection of Angiostrongylus cantonensis in the Blood and Peripheral Tissues of Wild Hawaiian Rats (Rattus rattus) by a Quantitative PCR (qPCR) Assay.

The nematode Angiostrongylus cantonensis is a rat lungworm, a zoonotic pathogen that causes human eosinophilic meningitis and ocular angiostrongyliasis characteristic of rat lungworm (RLW) disease. Definitive diagnosis is made by finding and identifying A. cantonensis larvae in the cerebral spinal fluid or by using a custom immunological or molecular test. This study was conducted to determine if genomic DNA from A. cantonensis is detectable by qPCR in the blood or tissues of experimentally infected rats. F1 offspring from wild rats were subjected to experimental infection with RLW larvae isolated from slugs, then blood or tissue samples were collected over multiple time points. Blood samples were collected from 21 rats throughout the course of two trials (15 rats in Trial I, and 6 rats in Trial II). In addition to a control group, each trial had two treatment groups: the rats in the low dose (LD) group were infected by approximately 10 larvae and the rats in the high dose (HD) group were infected with approximately 50 larvae. In Trial I, parasite DNA was detected in cardiac bleed samples from five of five LD rats and five of five HD rats at six weeks post-infection (PI), and three of five LD rats and five of five HD rats from tail tissue. In Trial II, parasite DNA was detected in peripheral blood samples from one of two HD rats at 53 minutes PI, one of two LD rats at 1.5 hours PI, one of two HD rats at 18 hours PI, one of two LD rats at five weeks PI and two of two at six weeks PI, and two of two HD rats at weeks five and six PI. These data demonstrate that parasite DNA can be detected in peripheral blood at various time points throughout RLW infection in rats.