Potential of plastic barriers to control Andean potato weevil Premnotrypes suturicallus Kuschel

In potato production systems of the high Andes, Andean potato weevils of the genus Premnotrypes and Rhigopsidius are the most important potato pests. The adults are flightless insects that migrate to potato fields during the potato-growing season, where the larvae damage a high proportion of the tuber harvest. We tested the hypothesis that plastic barriers established at field borders at sowing time are effective management tools to stop Andean potato weevil migration into potato fields, with a consequent reduction in Andean potato weevil tuber damage. In addition, we studied the effect of barriers on carabids, which represent an important insect family in the Andes and are natural enemies of Andean potato weevils. The studies were carried out in 21 on-farm experiments in two villages in the Central Highlands of Peru. The effect of plastic barriers was compared to farmers' practice, consisting of 1-4 insecticide applications per potato-growing season, in participatory research in fallow-potato and potato-potato rotation systems in which the Andean potato weevil Premnotrypes suturicallus Kuschel is endemic. Plastic barriers proved to be highly effective in stopping weevil migration. In screen house experiments only a small proportion (13%) of weevils was able to escape from plastic heights of 25cm. A height of 50cm could not be overcome, which was the height used in the on-farm field experiments. The combination of plastic barriers with pitfall traps installed close to the plastic significantly increased the number of Andean potato weevil catches, and proved an effective technology for mass trapping of Andean potato weevil adults. Plastic barriers also affected and increased the number of carabids, mainly of the genus Blennidus, in the pitfall traps. The proportion of carabids was 4-5 times higher in the location in which a lower number of Andean potato weevils and damaged tubers were observed. The results suggest that carabids are important predators of Andean potato weevils. The plastic barriers effectively reduced Andean potato weevils-caused potato tuber damage at harvest. Compared to the farmers' practice of using insecticides, the barriers were equally effective in fallow-potato rotation systems. In potato-potato rotation systems the combination of plastic barrier with one application of insecticide was superior to farmers' practice using 3-4 insecticide applications. The costs for plastic barriers were calculated to be equivalent to two or three insecticide applications per hectare. Plastic barriers are proposed as a new effective component for Integrated Pest Management of Andean potato weevils.