This document is a preliminary and exploratory proposal for investigating the populations of the tramp ant Pheidole megacephala, a destructive pest endangering the ecosystem on Kure Atoll, Northwestern Hawaiian Islands.
Recent observations have shown that the big-headed ant Pheidole megacephala has become widespread on Green Island, Kure Atoll, Observations by Gordon Nishida and Beth Flint recorded 26,500 ants per square meter at selected sample sites. While this may not be an accurate indication of the average for Green Island, it is indicative of the large numbers of this ant on Green Island. The ants are not native to the Hawaiian Islands; that is, they are an introduced species.
The ants constitute a manifest threat to the natural ecosystem on Kure. They successfully attack and destroy most other insects, and are often successful in killing new-hatch chicks and possibly other juvenile megafauna. In addition, by supporting the scale that attacks the flora, the ants facilitate destruction of habitat used by other fauna such as the Bonin petrel (BOPE).
The position of the ant in the Kure ecosystem is complex. According to Nishida, the ants feed on the nectar of a scale insect that breeds on the aggressive, introduced plant Verbesina encelioides, which has also overrun the island. The ants protect the scale from parasites and predators. As the V. encelioides populations are reduced by the scale, it moves onto the native naupaka (Scaevola), leaving the typical blackening caused by a fungus growing on the "honeydew" produced by the scales.
Considering the manifest threat of the ants, a program of control or eradication may be indicated. However, the very limited area of Green Island, the adjacency of marine ecosystems, and the presence of endangered megafauna such as the Monk seals and BOPE demand that such a program be carefully planned and executed. Preliminary to decisions on such an action, additional observation and documentation of the infestation and potential consequences of control or eradication are desirable.
During Sep-Oct, 2005, this organization will carry out a 2-week stay on Kure. This provides an opportunity to collect information on the existing populations of Pheidole megacephala, and to test ideas about control and/or eradication. The team consists of 12 persons experienced in field work. While the major activity of the expedition is radio science, the team will devote a portion of its effort to supporting the work of the naturalists on Kure, and participating in collaborative studies such as that described in the present proposal.
The goal of this work is to obtain sufficient information about the extant populations of Pheidole megacephala on Green Island, Kure, to allow decision-making for a plan of control or eradication.
Information that is of interest includes:
The following tasks are among many that could be carried out during the 2005 Cordell Expedition to Kure. It is proposed that the primary responsibility for these tasks rest with the resident naturalist, and that the Cordell group provide manpower and documentation. It is not proposed that all of these tasks be done, but that a selection of such tasks from this or another list be defined and carried out.
1. Mapping of colonies of Pheidole megacephala and relevant community species
It is proposed to carry out a relatively systematic survey of the ant populations, using a GPS unit to record locations and photography to record habitat. Particular effort would be made to examine relatively inaccessible locations, such as areas overgrown with dense vegetation. The emerged area on Green Island is about 200 acres, or about 800,000 sq. m. A 10m grid over the entire island would therefore require 8,000 samples, which is too ambitious for this project.
We propose instead to identify the major habitat types, and make descriptive observations with resolution appropriate for the habitat. Thus, we might define 10 habitat types, and examine two or three 50x50m areas of each habitat type, producing 20-30 descriptions of the ant populations, covering all habitat types. The assumption will then be that the ant populations are similar for each type, and therefore an areal extrapolation to the entire island will be a reasonable estimate of the total population.
2. Response of P. megacephala to selected bait
It is proposed to place selected bait at selected locations and document the response of P. megacephala to the bait, especially the formation of trails that might indicate the locations of nests and the possible overlap of foraging areas of adjacent colonies. The locations will be selected based on previous knowledge of high-density populations. Documentation will be descriptive and diagrammatic, with semi-quantitative estimates of the numbers of ants observed. These observations will be done day and night to obtain information about the diurnal behavior of the ants.
3. Search for other ant species
It is proposed to collect individual amts at the bait stations, and preserve them for verification of species. Using a dissecting microscope, preliminary identifications can be made during the occupation on Kure. If a species other than Pheidole megacephala is encountered, a concentrated search of the location of collection could be done to document the extent of the new species. The experiments described by E. O. Wilson, in which the bait was alternately shaded and exposed, resulting in alternating attraction of different species, may not elicit attraction of potential alternate species, since we have no knowledge of what species might be present. However, an equivalent test could be made by placing bait in different exposures, and documenting any differences in attracted ants.
4. Response of P. megacephala to habitat destruction
It is proposed to test the response of Pheidole megacephala to destruction of habitat, particularly destruction of flora that support the scale. One procedure would be to identify an area with a particularly vigorous ant population, and one that is clearly supported by scale. Complete clearing of the vegetation (presumably Verbesina encelioides) would be done manually. The response of the ants would be documented immediately following clearing, and periodically during the occupation in the fall of 2005. This would be followed by observation of the ant populations during later visits by Kure officials.
5. Response of P. megacephala to selected formicides
It is not known whether agency options for control or eradication would permit the use of formicides, and this organization (Cordell Expeditions) is cognizant of the sensitivity to toxics in the environment at Kure. Therefore, the following proposal is offered without knowing previous positions or sensitivities, and it is understood that it may not be an option.
It is proposed to test the response of Pheidole megacephala to selected formicides. This would be done by placing formicidal bait at selected locations, and observing the ant populations over a period of weeks.
The selection of the formicide is crucial. Among several compounds commercially available, one, namely hydramethylnon, appears to be appropriate for consideration in this case. The chemical is marketed under trade names AC 217,300, Amdro, Combat, Maxforce, and Wipeout. It was developed by Prof. David Williams and colleagues. Some information from the commercial sources of this product is appended to this proposal.
Considerable information about the safety and toxicity of hydramethylnon are available (e.g., http://www.epa.gov/iris/subst/0207.htm). A general description of its use and risks is appended to this proposal. Two aspects stand out in these descriptions:
(1) Hydramethylnon shows almost no toxicity to fauna other than ants and related insects. That is, it is very safe, when used according to directions, with birds, mammals, and other fauna.
(2) Hydramethylnon degrades rather rapidly in the environment. Its soil half-life is generally between one week and one month, even faster in water. It does not accumulate in vegetation, and does not contaminate groundwater.
These factors indicate that hydramethylnon may be an acceptable risk to use in an ant control/eradication program at Kure, and based on that, we propose to deploy formicide-baited stations at selected locations, and document the response of the ant populations. If more than one acceptable formicide is available, we proposed to deploy stations with different fomicides and document any difference in response of the ants.
The Cordell group is experienced in field work and documentation, and will compile all relevant information about the field work done during the 2005 expedition. This will include description of the experimental procedure, the materials and methods used, the observations, and a statistical analysis of the results. Interpretation of the data in terms of the ecology of Kure, and any recommendations for future study or actions, will be left to the resident naturalist and the agencies managing the terrestrial environment at Kure.
Cordell Expeditions will not ask for compensation for the work described here. However, there are two practical limits to the effort:
(1) Out-of-pocket expenses associated with purchase of chemicals, baited stations, traps, etc, should be borne by the appropriate agency with authority at Kure.
(2) The amount of time associated with this effort cannot severely impact the primary activities of the Cordell group. That is, the group has responsibilities to its sponsors to deliver its primary objective, and the work described in this proposal cannot significantly reduce that obligation. This proposal is meant to describe work that can be done by the Cordell team while not otherwise engaged. The effort might be an hour per day, per person, although this may be highly variable, depending on conditions.
This proposal was written by Dr. Robert W. Schmieder, following a meeting with Cynthia Vanderlip in February 2005. As such, it is unsolicited and subject to change. Revision of this proposal, for instance to more narrowly focus the goals, can be done. Please contact Dr. Schmieder at: