Controlling factors of environmental flooding, soil pH and Diaprepes abbreviatus (L.) root weevil feeding in citrus: Larval survival and larval growth

The underlying influences of soil flooding, pH level and soil-inhabiting Diaprepes abbreviatus (L.) root weevil larval feeding in citrus were examined in two separate greenhouse studies, rootstock flooding Diaprepes-larvae (RFD) and liming rootstock flooding Diaprepes-larvae (LRFD). Our objectives were to determine the combined effects of soil flooding and pH level on survival and growth of Diaprepes root weevil larvae to gain insights of insect-environmental relations for the weevil control. We used a Floridana sandy loam (pH 4.8) from a citrus grove infested by Diaprepes root weevil in center Florida. The RFD experiment consisted of two citrus rootstocks (Swingle and Smooth Flat Seville), three flooding durations (0, 20, and 40 days) and two larval infestation rates (0 and 5 larvae) for 40-day feeding. The LRFD experiment consisted of two citrus rootstocks (Swingle and Carrizo), three pH levels (non-limed control, and target pH 6 and 7), two flooding durations (0 and 40 days), and two larval rates (0 and 5 larvae) for 56-day feeding. Dolomite (54% CaCO3 and 46% MgCO3) was used for soil liming in the LRFD. Treatments were arranged with 15 replicates in a completely randomized design. In the RFD, flooded soil pH was 0.3 units higher than nonflooded soil and larval survival was the lowest in the longest flooded treatment (P < 0.05). In the LRFD, soil pH increased 0.5–0.9 units for the target pH 6, and 0.7–1.1 units for the target pH 7. The effects of rootstock, liming and flooding treatments and their interactions were significant on soil pH and larval survival (P < 0.05). Larval survival decreased from 80% to 60% with increasing soil pH from 4.8 to 5.7. Total larval weight per seedling decreased significantly from 0.060 g to 0.012 g when the soil pH increased from 5.1 to 5.7. Flooding reduced larval survival and growth, and increasing acidic soil pH by 1 unit would be an option for controlling soil acidity and for promoting integrated management of Diaprepes root weevil in citrus. # 2006 Elsevier B.V. All rights reserved.