Tolerance to herbivory by a stemboring caterpillar in architecturally distinct maizes and wild relatives

In a screenhouse experiment in southwest Mexico, two maize cultivars were infested, a land-race and a modern high-yielding variety, and two wild teosintes, Zea diploperennis and Zea mays parviglumis, with newly hatched larvae of the stemborer, Diatraea grandiosella. While subsequent damage levels, when corrected for differences in plant size, were highest in the wild perennial, Zea diploperennis, this taxon showed the lowest absolute and proportional reductions in growth and reproduction, i.e., it was most tolerant to the damage. Higher growth rates were not associated with tolerance. Rather, a greater number of tillers and leaves in the wild taxa allowed for compartmentalization of damage and greater developmental plasticity. These results, when combined with previous findings on effective defense patterns, indicate that tolerance in maizes and wild relatives may be positively associated with defense against stemboring by the same insect. Because the probable mechanisms for defense (tissue fiber) and tolerance (plant architecture) are unrelated, a positive association is contrary to the predictions of some optimal defense theories, which posit a negative relationship between tolerance and defense.