Direct and indirect influences of the weaver ant Oecophylla smaragdina on citrus farmers' pest perceptions and management practices in the Mekong Delta, Vietnam

Abstract

In the Mekong Delta, Vietnam, the predatory weaver ant Oecophylla smaragdina was abundant in about 75% of the sweet orange and 25% of the Tieu mandarin orchards. With a three-level scale (low, moderate, high), farmers assessed the incidence, severity and yield loss of fruit caused by major pests. With abundant O. smaragdina, sweet orange farmers assessed a lower pest infestation or yield loss for the citrus stinkbug Rhynchocoris humeralis, the aphids Toxoptera aurantii and T. citricidus, the leaf-feeding caterpillars Papilio spp., and inflorescence eaters. In Tieu mandarin, the use of agrochemicals was higher than in sweet orange, and pest risk assessment was not correlated with ant abundance, except for aphid infestation, which was rated lower. The number of sprays targeting a particular pest was positively correlated both with pest incidence and severity ratings and was negatively correlated with ant abundance. Irrespective of O. smaragdina abundance, citrus leafminer Phyllocnistis citrella was one of the major spray targets. Citrus red mite Panonychus citri was the most important target in Tieu mandarin, accounting for >30% of all target sprays. Stimulating O. smaragdina as a biological control agent in Tieu mandarin will only be successful when citrus leafminer and mites can be controlled simultaneously without excessive chemical treatments. The concept of ant predation, well known by most farmers, could be used as a starting point to educate farmers about the existence and role of predatory mites. Farmer participatory training and research that focuses on experiential learning and field observations offers a promising approach to enhance farmers' perceptions of pests, their ecological causalities and non-chemical alternative management options.