Within-Plant Distribution of Soybean Aphid (Hemiptera: Aphididae) and Development of Node-Based Sample Units for Estimating Whole-Plant Densities in Soybean

Abstract

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is capable of reducing soybean, Glycine max (L.) Merr., yield up to 40% during severe outbreaks. Frequent sampling, which can be costly and time-consuming, is essential to making informed management decisions. However, one way to decrease sampling effort is to use a reduced sample unit when possible. The objectives of this study were to describe the vertical distribution of soybean aphid within soybean over time and to define node-based sample units of varying sizes by testing the ability of selected units to accurately estimate whole-plant aphid density. Within-plant distribution of soybean aphid changed significantly with time. However, the average nodal position where soybean aphids were found on soybean remained within the top half of the plant at all three locations studied across all sample dates. Consequently, selecting the node with the highest aphid density multiplied by the total number of infested nodes (N(MAX)') was the best predictor of aphids on remaining soybean components in both the original (r2 = 0.855) and validation (r2 = 0.824) data sets. For sample units that included more than a single node to estimate densities, a weighted formula, which incorporated changes observed in the within-plant aphid distribution, improved model performance (higher r2 values) and reduced variability around parameter estimates compared with a node-averaged formula. Our results suggest that smaller sample units provide reliable estimations of whole-plant aphid density throughout the growing season for differently maturing soybean, which is essential to their use in pest management decisions and development of future sampling plans.

Non-target impacts of soybean rust fungicides on the fungal entomopathogens of soybean aphid

“…Within-cage aphid densities were estimated weekly. In the R2 experiment, whole-plant counts were employed to estimate density, and in the R5 experiment, we used a node-based sampling plan developed by McCornack et al (2008), in which aphids present on three specific nodes of the plant were counted and used to estimate the total per plant aphid density. Fungal inoculum was introduced into cages as laboratory-infected soybean aphids on 29 June and 14 August for the R2 and R5 experiments, respectively.…”

Population Distribution and Density of Pentalonia nigronervosa (Hemiptera: Aphididae) Within Banana Mats: Influence of Plant Age and Height on Sampling and Management

“…The distribution of P. nigronervosa throughout the entire banana mat (from the largest "mother" plant to the smallest sucker) has not been quantiÞed. For aphids, describing the within-plant distribution is critical to the development of a sampling plan and for their successful management (McCornack et al 2008). In Hawaii, P. nigronervosa poses a threat to banana productivity mainly through its role as a virus vector; and although sampling should be designed for optimal detection of vector populations rather than quantiÞ-cation of aphid numbers per banana plant, knowing the distribution of aphids within the various plant stages is critical for developing a successful scouting protocol and management plan.…”

Potential of Suction Traps As a Monitoring Tool for <I>Aphis glycines</I> (Hemiptera: Aphididae) in Soybean Fields

“…For these plants, the numbers of aphids per plant were estimated using the linear relation between the sum of aphids on the three nodes (x) and on the whole plant (y), as determined from a sample of 120 plants (y ϭ 3.76x, r 2 ϭ 0.85; Yoo and OÕNeil 2009). Sampling three nodes per plant provides reasonable estimates (r 2 Ͼ 0.500, P Ͻ 0.0001) of aphid densities for plants sampled between early vegetative growth to full pod set (table 4 in McCornack et al 2008).…”