Leek, Allium ampeloprasum L., is susceptible to attack by onion thrips, Thrips tabaci Lindeman, that reduce yield and quality. Intercropping has been proposed as a strategy for reducing negative effects of pests on one or all crops in a system. The objective of the study was to assess the effect of intercropping maize, Zea mays L., and leek on abundance of thrips and production and morphology of both crops, but emphasizing effects on leek. The experiment was done during spring 2016 in northwestern Mexico, under extreme climatic conditions characteristic of desert environments and high soil salinity. Two maize varieties (sweet and field) at zero, three, five, and 10 plants per square meter were intercropped with a fixed number of 10 leek plants per square meter. The response variables were thrips abundance and plant yields and morphology characteristics. Maize reduced abundance of thrips on leek, with 5.6, 2.6, 2.2, and 1.5 thrips for 0, 3, 5, and 10 maize plants m^-2, respectively; i.e., the closer together the maize plants, the less abundant were thrips on leek, but leek yields were less with more maize plants (plant competition) per meter, with 12,075, 4,875, 4,581, and 4,159 kg ha^-1, respectively. Leeks intercropped showed morphological adjustments compared with a leek monoculture, indicating negative effects of competition with maize, instead of benefiting from the microenvironment (cooler leek canopy temperatures) created by maize. Maize was effective at reducing abundance of thrips but severely out-competed leeks. Further testing is needed on less competitive secondary crop species in main crops in a region to reduce pest abundance naturally without decreasing yield potential of associated crops.