| February 2011. An article in The National newspaper of PNG. It menions that people in the country are finding that red ants were improving the yield and quality of cocoa. A scientist at the Cocoa and Coconut Research Institute (CCI), said there was a possibility red ants were fighting the CPB. He said that black ants were used to fight CPB in Indonesia and Malaysia.
One member thought that the article was propbably referring to the Yellow crazy ant (Anoplolepis gracilipes) that is common in PNG and likes shady moist habitats such as those found under cocoa. There is a booklet published in PNG that describes how this species has been used as a biological control for cocoa pests in the past. Yellow crazy ants are fairly large (about 5-6 mm) and fast moving.
Another possibility is the Little Fire Ant (Wasmannia auropunctata) that is far more damaging and invasive. However, it is only reported in the East Sepik region and Bougaineville, but not East New Britain. Little fire ants are very small (about 1-2 mm) and slow moving.
While Yellow crazy ants are an environmental pest on some islands (e.g., Manus), they do not seem to cause any great problems in PNG. Little fire ants, however, would cause more harm than good in these circumstances, and their propagation should not be encouraged.
The CCI was recommneding the use of Yellow crazy ants in cocoa as far back as 2005, see "Farmers flock to institute’s open day". Post-Courier, Rural Industry Weekly, Thursday, 2 June 2005. And there are a number of publications on the subject:
Anon (1984) Ants Encouraged in Papua New Guinea Cocoa Farms. Tropical Pest Management 30(4), 455-455.
Baker, GL (1976) The seasonal life cycle of Anoplolepis longipes (Jerdon) (Hymenoptera: Formicidae) in a cacao plantation and under brushed rain forest in the northern district of Papua New Guinea. Insectes Sociaux, 23(3), 253-262.
Hassan E (1995) Integrated Pest-Management of Cocoa Weevil Borer in the Northern Province of Papua New Guinea. Zeitschrift Fur Pflanzenkrankheiten Und Pflanzenschutz-Journal of Plant Diseases and Protection, 102(3), 312-319.
Holderness M, Keane PJ, Putter CAJ (1992) Biology and control of Phytophthora diseases of cocoa in Papua New Guinea, Cocoa-pest-and-disease-management-in-Southeast-Asia-and-Australasia. 1992, 171-183; FAO Plant Production and Protection Paper No. 112; 30 ref. Rome, Fao.
Moxon JE (1983) Pests of cocoa - Use of crazy ants for control of Pantorhytes. Harvest 9(3-4), 159.
Room PM (1973) Control by ants of pest situations in tropical tree crops; a strategy for research and development. The Papua New Guinea Agricultural Journal 24(3), 98-103.
Room PM, Smith ESC (1975) Relative abundance and distribution of insect pests, ants and other components of the cocoa ecosystem in Papua New Guinea. Journal of Applied Ecology 12(1), 31-46.
In Solomon Islands, in the 1980s Yellow Crazy Ant (Anoplolepis gracilipes) and Little Fire Ant (Wasmannia auropunctata), plus the weaver/green tree ant (Oecophylla smargadia) were all proposed as control agents for cocoa pod borer and plenty of other pests besides. However, to my mind there is no doubt at all that the Little fire ant is by far and away the most aggressive to other insects and man. Trees or palms occupied by this ant rarely have insect pest problems. Unfortunately, they make harvesting very uncomfortable indeed. The fact that the news article doesn't mention this latter problem may be because it is referring to the Yellow crazy ant.
The article was distributed to the Pacific Invasive Ant Group, and opinions sought. This is what was said:
- Oecophylla is the most likely, the weaver ant, not the Green tree ant as in Australia, because throughout most of its distribution in Asia and parts of Australia it is a bright orange/red, not green. It is also a very common ant in coconuts.
- It could be the weaver ant, as well as the others mentioned. This was the first arthropod deliberately used by humans (in China) as a biocontrol agent. It develops a nest among a number of adjacent trees and attack any other arthropod in the vacinity. The weaver ant is native to northern Australia through to India and up into China. Within this range only one species is acknowledged - Oecophylla smaragdina, but it is very likely that it is actually multiple cryptic species. There is a large number of publications about this ant within cocoa plantations, etc.
Finally, a researcher in PNG who worked on cocoa ants in the '80s (John Moxon) wrote:
Wasmania is likely to be extremely effective in controlling CPB. It is what is called a Dominant species in the “ant-world”, and usually out-competes local Dominants quite easily, with dense contiguous nest populations in their millions. It has a painful sting and so can be a serious problem in cocoa management and surrounding domestic habitations. It should not be intentionally introduced to new locations for pest control purposes - NAQIA and/or DAL/others should be saying this very strongly – it is, after all, a high profile invasive pest species. Where it does occur, eradication is not an easy job.
Oecophylla (Kurukum) is native to PNG and also a Dominant with a bite/sting, but it is less of a problem; it is mainly found on the trees, whereas Wasmania is on both trees and ground, populations are smaller, and the sting is (slightly) less painful than Wasmania. Oecophylla does not roam far from the trees where it nests. It would likely control CPB as they control mirids and Pantorhytes beetles. However, if used, expect a build up of mealybugs, scales, membracids and other homopterns (albeit all very minor pests on mature cocoa).
Kurukums are likely to be already present in most cocoa blocks inter-planted with coconuts in PNG and so management strategies should enhance their effectiveness (e.g., ropes connecting coconut palms with the cocoa trees to serve as “ant highways”, etc). Introductions of Oecophylla could be made into cocoa blocks wothout intercrops, but a regular food source for the ants might need to be established to keep them there (e.g,. mealybugs and scale insects on sour sop trees which also have large leaves for Kurukum nests). Kurukum would be the first choice for biocontrol in PNG.
Although the original article was not about methods of control of the Cocoa pod borer in general, but about ants ion particular, one member suggested that a pheromone was used. It was said that a sex pheromone was available, and that in Indonesia this technology has been practised for the last 2 years, with good results. Also, it is possible to bring about control using Metarhizium anisopliae, an entomofungus and applied to places where the grubs breed.