Occurrence and Abundance ofLissorhoptrus oryzophilus(Coleoptera: Curculionidae) Relative to Field Borders in California Rice

Abstract

Field experiments were conducted during 2009 and 2010 on commercial rice fields in the Sacramento Valley of California to validate observations regarding the prevalence of immature populations of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), near field borders, and to assess their impact on yield. In 5 commercial fields, insecticide-treated and untreated plots were established 4.5, 30 and 60 m from one edge of the field. Soil core samples were collected on 2 dates and inspected for L. oryzophilus immatures. Rice yields were determined by harvesting 15 m2 plots in 2009 or 1 m2 per plot in 2010. Analysis of variance (ANOVA) showed that in most locations, immature populations were higher in plots 4.5 or 30 m from the field's edge than in plots 60 m from the field's edge. Yields from treated and untreated plots did not differ significantly. Linear regression of immature populations and rice grain yield per plot per location did not yield a significant, inverse density-yield relationship. Results indicate that border applications of insecticides for L. oryzophilus management are appropriate; however, growers are advised to inspect their fields to confirm border populations and effects on yield. Research needs regarding sampling and economic thresholds are discussed.