D3062: Further development of sampling protocols for Melanaphis sorghi in grain sorghum

Current studies indicate that natural enemies provide top-down suppression of sorghum aphids (Melanaphis sorghi), and the combination of all parasitoids and predators appears to be critical for preventing aphids from reaching economic injury levels. Yet, little information exists on integrating natural enemy and aphid density estimates for management decisions. The lack of integration is likely due to IPM sampling plans being based primarily on the spatial distributions of pests alone in the form of abundance estimates or classification of status. Preliminary dynamic thresholds were calculated from empirical field data and controlled experiments. These preliminary thresholds are awaiting field validation. Therefore, this study aimed to quantify whole-field error rates for sorghum aphid dynamic thresholds in Texas and Oklahoma. Seasonal sampling data from multiple locations was used to document percentages of correct predictions and errors relative to aphid populations exceeding economic injury levels. Error rates appear to be driven by the composition of natural enemies rather than the ratio of natural enemies to aphids. Nested ANOVA and Taylors Power Law regressions were utilized to determine variation in natural enemy counts among strata and calculation of aggregation indices. Approximately 80% of the variance in counts for all NEs occurred at the same spatial scale as aphid pests in sorghum.  According to TPL regression analyses, each calculated aggregation index was lower than that of SCA. Therefore, sampling requirements for NEs are expected to be lower or concurrent with those of aphid pests.