Evaluation of two-leaf sampling units to estimate sugarcane aphid (Hemiptera: Aphididae) economic thresholds in commercial grain sorghum

Authors: LINDENMAYER, JESSICA - Trece, Inc; PAYTON, MARK - Oklahoma State University; GILES, KRISTOPHER - Oklahoma State University; Elliott, Norman - Norm; KNUTSON, ALLEN - Texas A&M University; BOWLING, ROBERT - Channel Agronomy; SEITER, NICHOLAS - University Of Illinois; MCCORNAK, BRIAN - Kansas State University; BROWN, SEBE - Louisiana State University; ROYER, TOM - Oklahoma State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2020
Publication Date: 2/1/2021
Citation: Lindenmayer, J.C., Payton, M., Giles, K.L., Elliott, N.C., Knutson, A.E., Bowling, R., Seiter, N.J., McCornak, B., Brown, S.A., Royer, T.A. 2021. Evaluation of two-leaf sampling units to estimate sugarcane aphid (Hemiptera: Aphididae) economic thresholds in commercial grain sorghum. Journal of Economic Entomology. 114(1):481-485. https://doi.org/10.1093/jee/toaa270.
DOI: https://doi.org/10.1093/jee/toaa270

Interpretive Summary: Sugarcane aphid Melanaphis sacchari is an invasive species that became an economic pest of grain sorghum in the United States in 2013. Effective monitoring and early detection are cornerstones of management for invasive aphid pests. The objective of this study was to identify the location of aphids within the plant canopy that best predict total aphid density on the plant. Sorghum plants from 140 fields located in Arkansas, Kansas. Louisiana, Oklahoma and Texas were sampled during two years. Complete counts of aphids were recorded on every leaf on every plant. For analysis, plant canopies were stratified into three categories: upper, middle, and lower. Two leaves from each stratum were used to develop relationships between aphid numbers per leaf and total aphid density of sugarcane aphids per plant. Analysis of within plant relationships revealed that leaves from the middle strata were best for estimating aphid density. By focusing sampling on leaves in the middle of the plant we can increase likelihood of early detection of the aphid and most accurately determine whether a field needs to be treated with insecticide to suppress the aphid infestation.

Technical Abstract: Sugarcane aphid Melanaphis sacchari Zehntner is a significant economic pest of grain sorghum in the United States. Effective monitoring and early detection are cornerstones for managing invasive pests. The recently developed binomial sequential sampling plan estimates sugarcane aphid economic thresholds (ETs) based on classification whether a 2-leaf sample unit has <= or >= 50 M. sacchari. In this study, we evaluated eight 2-leaf sampling units for potential use in the sequential sampling plan. From 2016 through 2017, whole plant counts of M. sacchari were recorded non-destructively in situ on sorghum plants from 140 fields located in five states. Plant canopies were stratified into three categories. Two leaves from each stratum were used to compare linear relationships between M. sacchari numbers per two-leaf sample unit and total M. sacchari density per plant. Analysis revealed that two randomly selected leaves from the middle stratum accounted more variation for estimating M. sacchari density when compared to two leaves from the other strata. Comparison of eight two-leaf sampling units within plant growth stages were variable in quantifying variation of M. sacchari densities. When growth stages were combined, the standard uppermost + lowermost leaf sample unit and a unit consisting of two randomly selected leaves from the middle stratum revealed little difference in their enumeration of variation in M. sacchari density. Because other sample units were either less predictive and/or more variable in estimating M. sacchari density, we suggest that the (L1+U1) sample unit remain the preferred method for appraising M. sacchari ETs.