LABORATORY AND ON-FARM ASSESSMENT OF RESISTANCE TO sitophilus zeamais IN MAIZE GERMPLASM Upenyu MAZARURA and Denash GIGA University of Zimbabwe P.O. Box MP.167 Mount Pleasant, Harare Zimbabwe ABSTRACT The relative 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°C) and relative humidity (70-75%). An index of susceptibility derived from the numbers of F1 progeny and the mean development period was used as the basis for the measurement of susceptibility. significant differences in susceptibility between the maize germplasm was found with indices ranging from 9.3 for Rattray Arnold (1) 8149 (least susceptible) to 14.7 for PNR 6334 (most susceptible). In order to test whether the laboratory results were valid, 14 different maize genotypes were selected and evaluated under field conditions and natural infest- ation pressure. The maize was stored in small jute sacks in small farmers' stores over several months and percent damage and insect population growth monitored regularly. Generally, materials found to be the least susceptible in laboratory tests showed lowest damage in on-farm storage while the most susceptible varieties sustained the greatest damage. INTRODUCTION The maize weevil, Sitophilus zeamais is a serious pest of stored maize causing extensive damage in small farmer storage. Grain protectants such as malathion, pirimiphos-methyl and other organophosphates applied at dilute dusts are widely used by farmers. But because of their costs, hazards and insect resistance there is a need for alternative control strategies. Storing resistant varieties is one such strategy. Many workers have investigated resistance in maize against storage pests under laboratory conditions (e.g. van der Schaaf et al., 1969; Dobie, 1974; Schoonhoven et al., 1972, 1975, 1976) and found that maize differ greatly in their intrinsic susceptibility. Very few studies however, have examined whether the resistance under laboratory conditions do in fact hold under farmers' conditions. It was long been known that resistance to insect attack is strongly correlated with physical factors such as tight husk covers, kernel hardness and low moisture content. Chemical factors such as amylose (Rhine and Staples, 1968) and sugar contents (Singh and McCain, 1963) are also important resistance - 1651 -