Pest Manag Sci. 2022 Oct 30. doi: 10.1002/ps.7262. Online ahead of print.
BACKGROUND: Oryzophagus oryzae (Costa Lima) (Coleoptera: Curculionidae) is a major pest of flooded rice paddies throughout South America, and species with very similar life histories are present in many rice-producing regions of the world (collectively referred to here as RWWs). The damage caused by RWW larvae on rice cultivars with contrasting levels of resistance (‘BRS Pampa CL’= “Pamp”: susceptible, ‘BRS Atalanta’= “Atal”: resistant-antibiosis) was evaluated in two consecutive years in the field under seven infestation levels: 0, 2, 4, 6, 8, 10, and 20 adult couples per cage with plants.
RESULTS: Higher densities of adults increased the number of leaf-feeding scars and larvae on roots, respectively, at the rate up to 2.14 and 2.75 in “Pamp” and 2.23 and 2.48 in “Atal”, with the total number of larvae generated being lower in “Atal”. Grain yield was negatively impacted with increasing larval density on the roots, mainly by decreasing root volume and the number of grains per panicle. Root injury intensity and yield loss showed a non-linear relationship. It was found that significant yield losses occurred from 8.37 larvae per plant in “Pamp” and 9.80 larvae per plant in “Atal”.
CONCLUSION: The results provided the first evidence of a tolerance limit for RWW larval damage that, even though similar between cultivars of contrasting resistance, corresponds to twice the current conventional level for larval control in Brazil. We also discuss here the potential of applying tolerance limits to manage the RWW adult population in rice fields. This article is protected by copyright. All rights reserved.