LEVELS OF RESISTANCE TO THE MAIZE WEEVIL, SITOPHILUS-ZEAMAIS (MOTSCH) IN EXOTIC, LOCAL OPEN-POLLINATED AND HYBRID MAIZE GERMPLASM

The susceptibility of maize germplasm from CIMMYT - Mexico, Malawi and Zimbabwe - to attack by the maize weevil, Sitophilus zeamais (Motsch.) was investigated under controlled temperature (28-degrees-C) and r.h. (70-75%). An index of susceptibility (I), derived from the numbers of F1 progeny and the mean development period was used as the basis for measurement of the susceptibility. The indices of susceptibility of the CIMMYT germplasm ranged from 9.25 for Rattray Arnold (I) 8149 to 14.48 for Poza Rica 7737. Of the 17 collections of Malawi local maize evaluated MLM#20 was the least susceptible (I = 10.72), while MLM#24 was the most susceptible (I = 13.25). The least susceptible of the Zimbabwean germplasm was a local collection of an indigenous maize, Variety 8 (I = 10.61), while the most susceptible was a hybrid PNR 6334 (I = 14.74). Further, the nine Mexican materials and a local hybrid SR 52 were evaluated under field conditions in small farmers' granaries. Rattray Arnold (I) 8149 and Population 68 were the least damaged and produced the lowest numbers of weevils. Maize classified as susceptible in laboratory tests also suffered high damage levels in on-farm storage trials.