|
The Big-headed ant (BHA) is an introduced and highly invasive species that can significantly impact native ecosystems if it becomes widespread and abundant. It was first identified on Aride by ant expert Dr Brian Fischer in February 2010 and fortunately, it appeared not to have spread too much up the hill by May 2010 and it was still deemed necessary and plausible by ICS to eradicate it at that stage. This project is being funded largely by James Cadbury and a portion from the US Embassy Self-help programme.
The eradication was envisaged in three phases: (1) Scoping phase determining the exact level of the infestation and feasibility of eradication (2) Treatment using toxic formicide baits (3) Post-treatment assessment. The proposed eradication of BHA will completely obliterate ants from a 8.8ha area, consequently the whole island, allowing other ant species to recolonise from the remaining 59.2ha of Aride Island, while ensuring the maximum precautions are taken to minimize the already very low risk of secondary poisoning to other non-target species. Approval was granted by Environment Department to eradicate this species from Aride following completion of Phase 1 and production of the eradication plan in 2012. We have encountered several delays which has caused us to push back the timing of the implementation of Phase 2. These delays have been due to a combination of factors: difficulties in acquiring and shipping the materials to Aride to build the bait stations, high staff turnover on Aride and no one with the appropriate expertise on Aride at the right time to coordinate the eradication process. Phase 2 commenced in October 2013 before the start of the rainy season and we have may significant headway since. |
|
It has been a very long and demanding eradication programme. It has taken much longer than we had anticipated but we are starting to see the light at the end of the tunnel. Some difficulties that we have encountered include:
- Weather was a large problem in 2015 as it was a very wet year and the bait was ruined if it got wet, so it could only be deployed if there were at least 5 days of favourable weather forecast.
- It was crucial to have a well trained team of people who a re vigilante and can identify ants properly and also place the baiting lines accordingly. We found that misidentification was an ongoing issue.
- Most of the treated areas were very rocky and full of tall ferns or thick undergrowth making the application slow and difficult, and if the bait station was not placed in roots or under a rock, the string was off the ground with the bait stations inaccessible to the ants.
- The method of using tuna bait to find ants worked when checking for abundance and the edge of the perimeter, but when looking for individual missed nests it would be impossible to use this method as they are not always attracted to the bait and it would take too much time to place and collect every 3m of 7 hectares
- Hermit crabs were attracted to the bait and made large holes in the bait stations, destroying a considerable number. Birds also liked to eat it if they could find it, and Moorhens had a habit of removing the bait stations along with the Hermit crabs, leaving some sections vulnerable. Mice got into the bags of Seige and fouled it.
- After exposure to the sun, some of the strings decayed and the elastic bands perished very quickly. Another method was adopted of attaching the pipes to the string by taking one end off of the pipe, putting the string in the bend and replacing the end piece. The person placing the pipes then had to make 3 large steps to approximately 3m, which worked most of the time and gave the added advantage of being able to place them nearer tree bases etc. However an occasional person was unable to judge 3m accurately and placed them too far apart, so some follow up checking was needed.
After each part was treated, the area was checked for remaining ants approximately 2 weeks later. An occasional nest was found and re-treated individually. The preliminary result looks very good: the poison for the most part took only 3 days before it was noticed the ants were absent except in the high density areas where it took over 1 week.
Nesting birds, especially White tailed tropicbirds and fallen Lesser Noddy chicks were regularly seen covered in biting ants before the treatment, and after were ant free.
Some trees, fruit and vegetables were highly infested with hemipteran species before the treatment and were growing poorly, mostly crops but also the Hibiscus species, Pisonia and Morinda Citrofolia. After the treament there was a marked improvement especially in the garden. Where the Guava, Aubergine and Bullocks Heart previously had only a few sick fruit and were growing slowly, they suddenly grew much bigger and produced plenty of fruit. The endemic Rothmania Annae were unaffected.
Nesting birds, especially White tailed tropicbirds and fallen Lesser Noddy chicks were regularly seen covered in biting ants before the treatment, and after were ant free.
Some trees, fruit and vegetables were highly infested with hemipteran species before the treatment and were growing poorly, mostly crops but also the Hibiscus species, Pisonia and Morinda Citrofolia. After the treament there was a marked improvement especially in the garden. Where the Guava, Aubergine and Bullocks Heart previously had only a few sick fruit and were growing slowly, they suddenly grew much bigger and produced plenty of fruit. The endemic Rothmania Annae were unaffected.
The whole original area will be thoroughly checked for any remaining BHA during 2016, by slowly checking rocks and trees for ants, section by section by Melinda Curran. If it is an impenetrable area of thick undergrowth then the Tuna bait method will be used.
The entry point where people arrive and the visitors BBQ area on the island both need to be checked for BHA and Crazy Yellow Ants regularly. Stricter bio-security measures are now in force but ants can easily arrive on the island without being noticed as they are so small. It is believed that BHA probably arrived in wood brought by local boatmen who make visitors BBQs, so bringing wood and coconuts has now been banned. BHA kill other ants, which may be a reason that the Crazy Yellow Ant has not yet been recorded on Aride, there will now be a greater risk of this species occurring if bio-security measures are not followed.
The entry point where people arrive and the visitors BBQ area on the island both need to be checked for BHA and Crazy Yellow Ants regularly. Stricter bio-security measures are now in force but ants can easily arrive on the island without being noticed as they are so small. It is believed that BHA probably arrived in wood brought by local boatmen who make visitors BBQs, so bringing wood and coconuts has now been banned. BHA kill other ants, which may be a reason that the Crazy Yellow Ant has not yet been recorded on Aride, there will now be a greater risk of this species occurring if bio-security measures are not followed.
