Comparison of Relative Bias, Precision, and Efficiency of Sampling Methods for Natural Enemies of Soybean Aphid (Hemiptera: Aphididae)

Abstract

Generalist natural enemies play an important role in controlling soybean aphid, Aphis glycines (Hemiptera: Aphididae), in North America. Several sampling methods are used to monitor natural enemy populations in soybean, but there has been little work investigating their relative bias, precision, and efficiency. We compare five sampling methods: quadrats, whole-plant counts, sweep-netting, walking transects, and yellow sticky cards to determine the most practical methods for sampling the three most prominent species, which included Harmonia axyridis (Pallas), Coccinella septempunctata L. (Coleoptera: Coccinellidae), and Orius insidiosus (Say) (Hemiptera: Anthocoridae). We show an important time by sampling method interaction indicated by diverging community similarities within and between sampling methods as the growing season progressed. Similarly, correlations between sampling methods for the three most abundant species over multiple time periods indicated differences in relative bias between sampling methods and suggests that bias is not consistent throughout the growing season, particularly for sticky cards and whole-plant samples. Furthermore, we show that sticky cards produce strongly biased capture rates relative to the other four sampling methods. Precision and efficiency differed between sampling methods and sticky cards produced the most precise (but highly biased) results for adult natural enemies, while walking transects and whole-plant counts were the most efficient methods for detecting coccinellids and O. insidiosus, respectively. Based on bias, precision, and efficiency considerations, the most practical sampling methods for monitoring in soybean include walking transects for coccinellid detection and whole-plant counts for detection of small predators like O. insidiosus. Sweep-netting and quadrat samples are also useful for some applications, when efficiency is not paramount.

Preceding crop affects soybean aphid abundance and predator–prey dynamics in soybean

“…lacewing and syrphid adults ;Schneider 1969;Haslett 1989;Canard 2001) and may have responded to the aphid honeydew as a nutritional resource, or they may have been foraging for oviposition sites with high prey densities. A surprising result is that O. insidiosus and Hippodamia convergens were uncorrelated with aphid abundance as has been previously documented (Desneux and O'Neil 2008;Harwood et al 2009;Lundgren et al 2013;Bannerman et al 2015), questioning the biological control potential of these predators within this study system. It may also be that the rising abundance of certain aphidophilous taxa may limit the aphid-driven population responses of these less specialized predators through competition or intraguild predation (Gardiner and Landis 2007;Gardiner et al 2011).…”

“…Certain aphidophilous predators had a strong, positive numerical response to aphid populations. Some of these taxa are well known aphidophagous species, such as Harmonia axyridis (Costamagna and Landis 2006;Bannerman et al 2015). Others are more glucophagous (e.g.…”

Predators and alate immigration influence the season-long dynamics of soybean aphid (Hemiptera: Aphididae)

“…assemblage associated with insect pests (Bannerman et al, 2015;Symondson et al, 2002). Here we use the term generalist predators to include both polyphagous species with a wide prey range and stenophagous taxa that are opportunistic feeders on various resources (e.g.…”

“…Soybean aphid has subsequently become a serious economic pest of soybean and has rapidly spread across the soybean producing regions of North America (Ragsdale et al, 2011). In North America, the natural enemy guild associated with soybean aphid varies regionally but always contains a significant generalist predator component (Bannerman et al, 2015;Desneux et al, 2006;Gardiner et al, 2009b;Hallett et al, 2014;Mignault et al, 2006;Ragsdale et al, 2011). More than 50 species of aphidophagous predators and parasitoids feed on A. glycines (Maisonhaute et al, 2017;Ragsdale et al, 2011, and references within), and in many cases provide high levels of suppression (e.g.…”

“…Predators were sampled weekly from 12 June until August during a two-hour period between 8:30 and 16:30. Three methods were used to sample predators and parasitoid mummies: sweep-netting, destructive whole-plant counts, and 25 m walking transects (Bannerman et al, 2015). Each sweep-net sample consisted of 25, 180° sweeps through the soybean canopy along a linear transect, with 4 samples taken per field per week.…”