Not Seeing the Mites for the Hairs. Comment on Möth Et Al. Unexpected Effects of Local Management and Landscape Composition On

insects Comment Not Seeing the Mites for the Hairs. Comment on Möth et al. Unexpected Effects of Local Management and Landscape Composition on Predatory Mites and Their Food Resources in Vineyards. Insects 2021, 12, 180 Peter Schausberger Department of Behavioral and Cognitive Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria; [email protected] 1. Synopsis Möth et al. (2021) [1] investigated the effects of pest management regime (integrated vs. organic), and field and landscape elements on plant-inhabiting mite abundance and pollen deposition in vineyards. One of their main conclusions, dubbed “unexpected”, is higher predatory mite abundance and pollen deposition in integrated rather than organic vineyards. Möth et al. (2021) [1] sampled leaves from highly diverse grape varieties, Citation: Schausberger, P. Not Seeing however, varieties and associated variability in mite microhabitat quality, which is largely the Mites for the Hairs. Comment on determined by leaf surface morphology, were neglected in sampling plans and analyses. Möth et al. Unexpected Effects of However, leaf surface morphology is a decisive factor for the occurrence and abundance Local Management and Landscape of grape-inhabiting mites. Retrospectively scrutinizing the diversity and heterogeneity of Composition on Predatory Mites and sampled varieties and associated differences in leaf morphological characteristics, that is, Their Food Resources in Vineyards. hairiness of the leaf underside, revealed higher microhabitat quality in vineyards subjected Insects 2021, 12, 180. Insects 2021, 12, to integrated pest management than in those subjected to organic pest management. In- 671. https://doi.org/10.3390/ tegrating leaf hairiness as an explanatory variable into analyses challenges the claims by insects12080671 Möth et al. [1] and puts the “unexpected” into perspective. Erect hair grades of the leaf underside had strong explanatory power and significantly influenced three of four dependent Academic Editors: Giovanni Burgio, variables, that is, abundance of phytoseiid and eriophyid mites and pollen deposition on David G. James and Daniele leaves. Re-analysis suggests only weak effects of pest management regimes. These effects Sommaggio are further undermined when considering that increased hairiness of the leaf underside may exert inter-related additive or synergistic effects on mite abundance, due to hampering Received: 29 March 2021 pesticide deposits, increased provisioning of shelters, enhanced trapping of air-borne mites, Accepted: 21 July 2021 Published: 26 July 2021 and mite and pollen retention on leaves. I conclude that non-consideration of microhabitat quality may blur causal relationships between the occurrence of plant-inhabiting target organisms and larger-scale environmental variables. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 2. Background published maps and institutional affil- iations. Möth et al. (2021) [1] investigated the influence of integrated versus organic pest management regimes as well as field and landscape elements on mite abundance and pollen deposition in Eastern Austrian vineyards. They examined the relevance of environmental factors at various spatial scales such as interrow vegetation type and cover at the field scale, and landscape scale factors such as surrounding vineyards and forests Copyright: © 2021 by the author. Licensee MDPI, Basel, Switzerland. on mite abundance and pollen deposition on grape leaves. Pest management regimes This article is an open access article were characterized by various sub-variables such as frequency and toxicity of the applied distributed under the terms and products. The main conclusions by Möth et al. (2021) [1], dubbed “unexpected”, is higher conditions of the Creative Commons abundance of phytoseiid mites, primarily Typhlodromus pyri, and tydeid mites, primarily Attribution (CC BY) license (https:// Tydeus goetzi, and higher pollen deposition in integrated than organically pest-controlled creativecommons.org/licenses/by/ vineyards. Möth et al. (2021) [1] explain their findings by a mite-friendlier and more pollen 4.0/). favorable integrated pest management regime because of fewer sprays and lower toxicity Insects 2021, 12, 671. https://doi.org/10.3390/insects12080671 https://www.mdpi.com/journal/insects Insects 2021, 12, 671 2 of 9 of the applied products. Mite-promoting field and landscape factors put forward were a high percentage of vineyards surrounding the target (sampled) vineyard and sponta- neous as compared to seeded interrow vegetation. Lacking report of the sampled grape varieties and associated lacking consideration of the microhabitat quality of the leaves of the sampled vineyards prompted writing this comment. Grape varieties strongly differ in leaf surface morphology and thus microhabitat quality for plant-inhabiting mites. Leaf surface morphology is generally acknowledged to be a decisive factor for the occurrence and abundance of plant-inhabiting arthropod, especially mite, populations and pollen deposition [2–4]. The target animals sampled by Möth et al. (2021) [1], plant-inhabiting mites, have body lengths of 0.2 (for eriophyid mites) to 0.5 mm (for phytoseiid mites) [5]. During the vegetative periods, the microhabitats of these mites are the leaves, and here, mainly the undersides. These animals thus primarily experience the leaf surfaces as their landscapes [6], in which they forage, reproduce and interact with other organisms. As with most ecological processes and patterns, scale is a critical issue when investigating environmental factors influencing the occurrence and abundance of plant-inhabiting mites in local fields. For plant-inhabiting mites, relevant spatial scales range from the microscale (sites within leaves to whole leaves) over intermediate scales such as whole plants to other plants within the vineyard, to the macroscale such as vegetation surrounding the vineyard and other local and regional landscape elements. Of primary importance, no matter of the ecological scale, are the microhabitats where the target animals, plant-inhabiting mites, primarily live and spend most of their lives, because some leaves provide microhabitats that are suitable for colonization, establishment and growth of their populations whereas others do not. If the leaf microhabitat is unsuitable, the surrounding field and landscape elements may be highly favorable for mites dispersing into the sampled sites yet the organisms in questions will not settle and reproduce, and as populations grow there [7]. In general, when developing sampling protocols and experimental designs for field and landscape studies, and deciding which factors should be included in analysis, the experimenter should project one’s view of the world into the target organism [8,9]. It has been stressed repeatedly that understanding of large-scale ecological processes and patterns is critically enhanced by mechanistic understanding of individual and population level processes at smaller spatial scales, such as the microhabitat level [8,10]. For the animals and study in question [1], if the leaf features determining microhabitat quality from a mite-centered perspective are not accounted for, blurred or erroneous conclusions about the influence of pest management, and larger spatial scale factors at the field and landscape levels on those mites may be drawn. The sampling unit by Möth et al. (2021) [1] was 20 leaves per vineyard but the sampled vineyards consisted of 10 highly diverse grape varieties that were not homogenously distributed between integrated and organic vineyards (Möth, personal communication, Table S1). Thirteen of the 16 pairs of integrated and organic vineyards within a prede- fined radius of investigation had heterogeneous varieties and three had homogeneous varieties (Table S1). There is ample evidence that grape leaves differ in their quality as mite microhabitat among grape varieties [3,4]. For predatory mites, numerous studies have shown that one highly critical factor is the leaf surface morphology, and here, especially the occurrence and density of trichomes, bristles and domatia-like structures on the abaxial side of the leaf [11,12]. The dominant predatory mite species in vineyards of central Europe including Austria is T. pyri, which is known to thrive on grape varieties with pubescent and/or domatia-rich leaf undersides [13–15]. If the encountered microhabitat features are unfavorable, T. pyri does not successfully colonize and establish, and their populations do not grow, on those plants [16]. In consequence, and at a larger spatial scale, species-specific adaptations to leaf microhabitat features may even result in two adjacent vineyards of different varieties being populated by different predatory mite species or sustaining largely differing predatory mite abundances [7,13,14,17,18]. Insects 2021, 12, 671 3 of 9 Based on the diversity and heterogeneous distribution of grape varieties within and between pairs of integrated and organic vineyards sampled by Möth et al. (2021) [1], I hypothesized that (i) grape variety-associated leaf morphological traits, i.e., hairiness of the leaf underside, differed between vineyards under organic and integrated pest management regimes, (ii) hairiness of the leaf underside has major explanatory power for the observed patterns of mite abundance and pollen deposition in Eastern Austrian vineyards, and (iii) addition of leaf hairiness as an independent variable in statistical modeling changes

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