Examining factors influencing varietal resistance to Rhyzopertha dominica (F.) in stored rice

Host-plant resistance is an important pest management tool that is often overlooked in stored grain systems where the mechanisms of resistance are poorly understood. Here, we evaluated 13 varieties of rice for resistance toward the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), one of the most devastating pests of stored rice. Over a two-month period, we measured each variety's damage by adult beetles and larvae, as well as progeny counts, progeny mass, and days to eclosion. We found large differences among varieties, with over 5-fold differences in damage by adults and 14-fold differences in larval damage. Subsequently, we evaluated the physical and nutritional characteristics of these varieties and compared these qualities with our susceptibility data. We found that while nutritional components of a variety did not affect susceptibility, the physical characteristics of the grain did. Varieties with longer, thinner grains were more susceptible to damage by R. dominica adults, while varieties with wide, stout grains were more resistant. Finally, we ran another resistance assay comparing single varieties to mixes of two varieties. We found that varietal mixes generally did not create any sort of associational resistance or susceptibility, expect in one instance. Mixes containing Jazzman 2 and CL151 received less damage from R. dominica adults and larvae than would be expected from the mixture. By understanding stored rice varietal resistance, growers can better anticipate pest impacts. Moreover, by understanding the mechanisms underlying resistance, resistant varieties can be more easily selected and bred to prevent insect infestation.