Citrus farmers in the Mekong Delta have a long tradition of managing the weaver ant Oecophylla smaragdina (Fabricius). From 1994 to 1998, insecticide use increased significantly (P < 0.01) from 66% to 84% in orchards where O. smaragdina occurred. In 1998, ca 75% of the sweet orange (Citrus sinensis) and 25% of the Tieu mandarin (C. reticulata) orchards had large O. smaragdina populations, due to lower pesticide pressure in the first crop. In orchards with O. smaragdina, farmers sprayed less frequently and used fewer highly hazardous insecticides. Major insecticides used in sweet orange were monocrotophos and alpha-cypermethrin, and those used in Tieu mandarin were methidathion, imidacloprid and fenpropathrin. Expenditure on pesticides was reduced by half when O. smaragdina was abundant, without affecting either the yield or the farmers' income. Therefore, O. smaragdina husbandry is a good example of a traditional practice which should be further promoted as an important component of sustainable citrus production. The experience of those farmers who use no or few pesticides should be drawn upon in developing farmer training programmes or mass media tools to promote IPM in citrus. Farmers practicing ant husbandry were significantly older than those not doing so.

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A survey of mango farmers' knowledge, perceptions and practices in pest management was conducted during the dry season of 1998 in the Mekong Delta, Vietnam. Identification and control of pests was often based on damage symptoms, rather than on recording of causal agents. Damage caused by the seed-borer Deanolis albizonalis (Hampson) was often wrongly attributed to the fruit flies Bactrocera dorsalis Hendel. Nearly all farmers applied calendar sprays of insecticides (97%) and fungicides (79%) from pre-flowering until harvest, with on average 13.4 and 11.6 applications per year, respectively. Pyrethroids were most popular (57%), followed by organophosphates (25%) and carbamates (15%). Around 20% of the insecticides used belonged to WHO Toxicity Class I, while the rest nearly all belonged to Class II. Half of all the target sprays were done with three pyrethroid products only. Farmers' estimated yield loss due to insect pests was strongly correlated to estimated pest severity. Due to pesticide sellers' recommendations, farmer's sprayload significantly increased from 26 to 37 sprays per year, whereas the number of insecticide products used per farmer increased from 2.6 to 3.9 with advice from extension staff and media. Expenditure for pesticides was correlated with that of fertilizers. There was no relationship between the amount of pesticides sprayed and yield. On-farm research is needed to evaluate whether significant savings can be obtained given a more judicious use of pesticides. Only 10% of the 93 participating farmers knew about natural enemies, all of which were predators.

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 430% 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.

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