Molasses provisioning to disrupt the mutualistic association of the biocontrol agent Oecophylla smaragdina weaver ants with honeydew-producing pest insects in mango in Thailand

Project Information

MolassAnt

Grant agreement ID: 101067706

DOI

10.3030/101067706

Project closed

EC signature date 31 May 2022

Start date 1 October 2022

End date 30 September 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 238 032,96

Coordinated by

KATHOLIEKE UNIVERSITEIT LEUVEN
Belgium

Periodic Reporting for period 2 - MolassAnt (Molasses provisioning to disrupt the mutualistic association of the biocontrol agent Oecophylla smaragdina weaver ants with honeydew-producing pest insects in mango in Thailand)

Reporting period: 2024-10-01 to 2025-09-30

Summary of the context and overall objectives of the project

Weaver ants (Oecophylla smaragdina) can protect a large variety of tree crops, including pomelo, mango, and cashew, in Thailand, by preying upon or deterring pest insects in the tree crown such as fruit flies and leaf miners to the economic benefit of farmers. Furthermore, weaver ant queen brood is a profitable, organic, and culturally valued food and seasonal by-product of crop trees in Thailand. The market value of queen brood is 3.5 times higher than that of beef, 10 times higher than that of chicken, and 13 times higher than that of rice in Thailand. A major disadvantage of weaver ant biocontrol is the mutualistic association of ants with honeydew-producing Hemipteran pests, including aphids, scale insects, mealybugs, and leafhoppers that can result in an ineffectual protection of tree crops. In a 22-month experiment, I will disrupt the mutualistic association of weaver ants and honeydew-producing Hemipteran pests in mango in Thailand by provisioning sugarcane molasses, a high quality carbohydrate source, as a honeydew alternative which will eventually result in improved pest control, mango yield, and queen brood yield in accordance with the calls of the European Union and the Thai government for ecologically sustainable production of high quality and safe food for import and export.
I tested the overarching hypothesis that sugarcane molasses provisioning will disrupt the mutualistic association of O. smaragdina with honeydew-producing insect pests, and will eventually result in improved pest control, mango yield, and queen brood yield in comparison to sugar provisioning, weaver ants only (control group), and chemical control (deviation, see Section 5). Specifically, I have evaluated the impact of molasses and sugar provisioning in mango in Thailand on 1) weaver ant presence in the trees, 2) abundance of honeydew-producing insect pests, 3) weaver ant tending of honeydew-producing insect pests, and 4) quantity, nutritional quality, and microbiological quality of mangoes and queen brood.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The Mangifera indica (kaew kamin variety) mango orchard was located at JR Farm, Yang Talat District, Kalasin Province, Thailand (16° 29' 55.3"N, 103° 24’ 44.8”E). A section of the farm was used as experimental area with 204 trees of 12–15 years old. Four experimental treatments were applied for nine and a half months: (i) diluted molasses provisioning of weaver ants, (ii) 50% sugar solution provisioning of weaver ants, (iii) no molasses/sugar provisioning of weaver ants (control), and (iv) chemical control (deviation). The sugar water and diluted molasses had a similar sugar content of 50° and 48° Brix respectivally. I used 10 weaver ant colonies per treatment (sugar, molasses, and control) and each colony had access to six trees that were connected by nylon rope (Ø = 8 mm). Colony boundaries were determined. I used 20 trees for the chemical control group. An additional four trees served as a barrier between the chemical control group and the three weaver ant groups. In each weaver ant colony, I selected two trees for parameter evaluation which always included the queen tree. These two trees were examined twice per month. Up to three honeydew-producing insect aggregations were sampled on panicles (and undersides of leaves at the base of the panicles; one aggregation per panicle) in the two selected trees in each colony. Molasses and sugar were provided in rubber collecting bowls with pebbles (I found that pebbles avoided the drowning of ants). The bowls were attached to primary branches or trunks with iron wire. About 100 ml of these liquids were provided at the queen tree of each colony in the sugar and molasses groups. I refreshed the liquids twice per week.
To test the effect of provisioning molasses and sugar, I have evaluated a comprehensive list of parameters including assessments of ant presence (activity); target honeydew-producing insect pest abundance; ant tending of target honeydew-producing insect pests and molasses and sugar feeders; and mango and queen brood quantity, nutritional quality, and microbial quality.
I successfully conducted the methodology. There was no statistically significant difference between the four experimental treatments in terms of mango production. Thus, weaver ants performed as good as chemical control in protecting mango fruits from pest insects. However, even though worker ant populations were normal, queen brood production did not occur due to a disrupted nature calendar that had extreme negative consequences for Thai agriculture in general. Mango production was seemingly normal probably because the kaew kamin variety performs well in very dry conditions and because I used flowering hormones. Present scale insects were Coccus hesperidum, C. viridis, and two unidentified Parasaissetia species. The analyses of other parameters are ongoing.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

My innovative and highly novel project has not significantly improved our scientific knowledge of how to use a carbohydrate source (here molasses) to disrupt mutualistic ant-Hemiptera associations (here O. smaragdina weaver ants) since a disrupted nature calendar negatively affected the use of molasses and queen brood production. This was in contrast to the pre-testing of the methodologies in year 1 when weaver ants did make use of molasses. This has not further assisted Biobest, Belgium, in their O. longinoda weaver ant project of disrupting ant-Hemiptera associations in Senegal. The MolassAnt underlying idea of a dual production system of tree crops (here mango) and queen brood is in line with Thai practices of harvesting queen brood in tree crop plantations and thus supported and build on Thai culture. It has limitedly improved plantation economics by reducing the money spent on chemical control of insect pests (the owner of JR Farm has now adopted weaver ant biocontrol). However, the potential additional income through queen brood production could not be assessed. The dual production system will have reduced the ecological footprint of at least the Thai mango producers of JR Farm within the first year after the project because the owner has already stopped using chemical control in favour of weaver ant biocontrol. His reasons include that weaver ant biocontrol performs equally well as chemical control in mango production and that chemical control is more expensive than weaver ant biocontrol (he does not do sugar/molasses provisioning). I suspect that a snowball effect might take place in the first five years after the project in at least Yang Talat District, Kalasin, Thailand (the location of the research site JR Farm), through the owner of JR Farm (a bottom-up effect). The project has not yet significantly aided Biobest, Belgium, in exploring the development of a commercial ant feed product analogous to Biobest’s popular honeybee sugar-solution Biogluc® because weaver ants at JR Farm did not use molasses during the experiment in year 2. The experiment was an invalid test due to the disrupted nature calendar, with respect to the effects of sugar/molasses provisioning on mango and queen brood yield. The experiment needs to be repeated.