Chemical control does not outperform weaver ant biocontrol in Thai mango production

Oecophylla smaragdina weaver ants are important biocontrol agents of fruit crops but their mutualistic association with honeydew-producing insect pests (HPIs) can result in an ineffectual crop protection. We tested the hypothesis that diluted molasses provisioning will disrupt the association of O. smaragdina with HPIs, and will result in improved pest control, mango yield, and edible queen larvae and pupae (ant eggs) yield in comparison to sugar water provisioning, chemical control (cypermethrin), and control group ( i.e. , weaver ants only). The impact of these four experimental groups was tested in a mango ( Mangifera indica ) orchard in Kalasin province, Thailand, from October 2023 until June 2024 on 1) weaver ant presence; 2) HPIs abundance; 3) abundance of weaver ants tending HPIs, sugar, and molasses; and 4) mango and queen larvae and pupae yields. Ten weaver ant colonies were used in each of the sugar, molasses, and control groups. Sugar/molasses were provisioned in rubber collecting bowls. Twenty trees were used for the cypermethrin group and were sprayed twice during the mango season. The mean mango yield per tree was 74.8 ± 20.6 kg in the molasses group, 77.3 ± 19.6 kg in the sugar group, 80.9 ± 38.4 kg in the cypermethrin group, and 82 ± 11.3 kg in the control group. There was no statistically significant difference between the four treatments. Due to extreme heat and severe lack of rain from 2023 until April 2024 the nature calendar was disrupted. The production of queen larvae and pupae was negatively affected: 11 of the 30 colonies that were monitored did not produce ant eggs. The remaining 19 colonies produced extremely small amounts. The potential additional value that sugar/molasses provisioning could have on weaver ant performance was thus not actually tested due a disrupted nature calendar. Nevertheless, chemical control did not outperform O. smaragdina biocontrol in mango production.