A study was made to determine the adequate sample size for research on corn resistance to maize weevil, Sitophilus zeamais Motschulsky. To evaluate the damage, the techniques described by Wiseman et alii and by Davis et alii were used. The relative merits of these two methods are discussed. The criteria used to select the sample size was such that a difference between two treatments of ten percent and of twenty percent of the overall mean should be detected by the statistical test, and that each treatment mean could be estimated with a standard error of 0.10 y or 0.20 y. The data were obtained from two laboratory experiments, in 1978/79, and 1979/80, at Instituto Agronômico, Campinas, State of São Paulo, Brazil. The treatments were: cultivar Asteca Prolífico VRPE VII, which is resistant to Sitophilus zeamais, Hmd 7974, a susceptible double hybrid; cultivar Maya XVI and HS 7777. A randomized complete block design with ten replications was used and each plot consisted of five rows of ten ears. The variance components method was used to define the type of sampling. The following minimum sample sizes can be used to detect differences of ten percent of the overall mean, between two treatments means: 6 blocks with 6 rows of 10 ears for the Wiseman method and 10 blocks with 6 rows of 10 ears for the Davis method of evaluation. To detect differences of 0.20 y, it can be used 6 blocks with 2 rows of 7 ears for Wiseman method and 6 blocks with 1 row of 10 ears for the Davis method of evaluation. According to each method of damage evaluation the following minimum sample sizes can be used for estimating the mean damage with 0.10 y as the half confidence interval: a) by Wiseman method, 270 ears for cultivar Asteca, and 70 ears for the cultivars Maya, Hmd 7974 and HS 7777; b) by Davis method, 450 ears for cultivar Asteca, and 300 ears for the other three cultivars. To estimate the mean damage with a 0.20 y as the half confidence interval it can be used: a) by Wiseman method, for cultivar Asteca, 5 blocks with 2 rows of 6 ears; for cultivars Hmd 7974, HS 7777 and Maya, 5 blocks with 2 rows of 3 ears; b) by Davis method, for cultivar Asteca, 5 blocks with 3 rows of 6 ears and for the other three cultivars, 5 blocks with 2 rows of 5 ears.
sample size; corn cultivars; Asteca Prolífico VRPE VII; IAC Hmd 7974; IAC Maya XVI e HS 7777; variance components; mean damage