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Twospotted spider mites, Tetranychus urticae K., are pests of maize, Zea mays L., in some areas of the USA. Resistant genotypes are needed to reduce plant damage caused by this pest. Two laboratory and three field experiments were conducted in 1986 to determine the resistance‐susceptibility of maize genotypes to an artificial infestation by the twospotted spider mite. Inbred line 41:25046 was highly resistant to the twospotted spider mite in both laboratory and field tests. This inbred exhibited a high degree of antibiosis against the mite; few mites survived, and little leaf damage resulted from the artificial infestation. This inbred also is highly resistant to the European corn borer, Ostrinia nubilalis Hiibner, and has been used as a nonrecurrent parent to develop several genotypes of maize resistant to this pest. Our data show that 41:25048 also could be used to develop genotypes of maize resistant to twospotted spider mites. Nine other genotypes had intermediate or susceptible reactions to twospotted spider mites, with Mol7 being the most susceptible.

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Chromosomal interchanges were used to determine which chromosome arms of resistant corn inbreds, C.I.31A and B49, carry genes for resistance to European corn borer leaf feeding. All corn plants were infested manually with corn borer egg masses in field studies conducted in 1961 through 1964.Resistant inbred C.I.31A was found to possess a gene or genes contributing to resistance on the short arm of chromosomes 1, 2, and 4, and on the long arm of chromosomes 4 and 6. Resistant inbred B49 appears to have genes for resistance on these same chromosome arms (possibly allelic to those of C.I.31A) plus an additional gene for resistance on the long arm of chromosome 8.