Varietal Resistance Against the Rice Water Weevil in Field and Greenhouse Studies

The resistance of commercial rice (Oryza sativa L.) varieties widely grown in Louisiana was assessed against the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), the major insect pest of rice in the United States, in a 5-yr field study that included conventional inbred, herbicide-tolerant, and hybrid varieties. Resistance was evaluated by comparing densities of immature rice water weevils (larvae and pupae) in root-soil core samples taken at two time points after flooding. Randomized block experiments were conducted in two different locations to enable identification of potentially resistant varieties over diverse environments. There were small but significant differences in the resistance of commercial varieties over the 5-yr field study. The variety 'Jefferson' was found to support larval densities 6-70% lower than other varieties, while 'Jupiter' often supported higher larval densities. Greenhouse experiments evaluated adult preference for oviposition and survivorship of larvae on different varieties. Females exhibited limited ovipositional preference for varieties: numbers of weevil eggs per plant differed significantly among varieties in choice tests but not in no-choice tests, while first instar densities in both choice and no-choice tests showed no significant differences among varieties. Analysis of data from both choice and no-choice tests showed that numbers of late instars and pupae differed significantly among varieties, suggesting presence of antibiosis in some cultivars. Our results suggest that none of the varieties tested possess high levels of resistance to rice water weevil infestation, although 'Jupiter' appears to be more susceptible than other varieties and 'Jefferson' appears to be somewhat more resistant.