Plant defense against fall armyworm in micro‐sympatric maize (<i><scp>Z</scp>ea mays</i> ssp. <i>mays</i>) and <scp>B</scp>alsas teosinte (<i><scp>Z</scp>ea mays</i> ssp. <i>parviglumis</i>)

Abstract

Abstract Maize [ Z ea mays L . ssp. mays ( P oaceae)] was domesticated from B alsas teosinte ( Z ea mays ssp. parviglumis I ltis &amp; D oebley) in present‐day M exico. Fall armyworm, S podoptera frugiperda JE S mith ( L epidoptera: N octuidae), is among the most important pests of maize in M exico and C entral A merica. We compared the strength of plant defenses against fall armyworm between micro‐sympatric landrace maize and B alsas teosinte in the field and laboratory. The field comparison, conducted in M exico, consisted of comparing the frequency of fall armyworm infestation between young maize and B alsas teosinte plants in dryland agricultural fields in which B alsas teosinte grew as a weed. The laboratory comparison contrasted the performance of fall armyworm larvae provided a diet of leaf tissue excised from maize or B alsas teosinte plants that were intact or had been primed by larval feeding. In the field, maize plants were more frequently infested with fall armyworm than B alsas teosinte plants: over 3 years and three fields, maize was infested at a ca. 1.8‐fold greater rate than B alsas teosinte. In the laboratory, larval growth, but not survivorship, was differently affected by feeding on maize vs. B alsas teosinte, and on primed vs. intact plants. Specifically, survivorship was ca. 98%, and did not differ between maize and B alsas teosinte, nor between primed and intact plants. Larvae grew less on intact vs. primed maize, and similarly on intact vs. primed B alsas teosinte; overall, growth was 1.2‐fold greater on maize compared to B alsas teosinte, and on primed compared to intact plants. Parallel observations showed that the differences in growth could not be attributed to the amount of leaf tissue consumed by larvae. We discuss our results in relation to differences in the strength of plant defenses between crops and their ancestors, the relevance of unmanaged B alsas teosinte introgression in the context of fall armyworm defenses in maize, and whether greater growth of larvae on primed vs. intact plants signifies herbivore offense.