Biologia 67/3: 546—560, 2012 Section Zoology DOI: 10.2478/s11756-012-0025-x Measuring the host specificity of plant-feeding mites based on field data – a case study of the Aceria species Anna Skoracka1 &Lechoslaw Kuczynski´ 2 1Department of Animal Taxonomy and Ecology, Institute of Environmental Biology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61–614 Pozna´n, Poland; e-mail: [email protected] 2Department of Avian Biology, Institute of Environmental Biology, Faculty of Biology, Adam Mickiewicz University, Umul- towska 89, 61–614 Pozna´n, Poland; e-mail: [email protected] Abstract: For the majority of eriophyoid species, host ranges have been established purely on the basis of collection records, usually without quantitative data. The aim of this study was to: (1) quantitatively examine published literature to explore whether relevant analyses of field-collected quantitative data were used to assess host specificity of herbivores; (2) propose a protocol for data analysis that could be applied to plant-feeding mites; (3) analyse host specificity of the grass-feeding Aceria species as a case study. Field data were collected in Central and Northern Europe over a period of 11 years, and included 73 grass species. For the eight Aceria species found, infestation parameters and host specificity indexes were assessed. Accumulation curves were calculated to study how the sampling effort influenced estimates of host specificity indexes. A literature analysis showed that among the studies that declared an aim of estimating the host range only 56% of them applied any quantitative analysis or informed on estimation reliability. The analysis of field-collected data and its interpretation showed the most complete and reliable conclusions about the host specificity of Aceria species when all indices were considered and, if available, other information about the mite’s ecology and biology. It was shown that estimates of host specificity could be strongly affected by sampling effort, and that several hundreds of samples should be collected for measuring the host specificity of grass-infesting mites, at least. Recommendations regarding host specificity estimation on the basis of field data are given. Key words: Eriophyoidea; host range; infestation parameters; normalized Rohde index; Rohde index; sampling effort; taxonomic index Introduction that all host species used by a parasite are evenly in- fested. However, the hosts may differ on two funda- Host specificity is a key ecological trait of herbivore mental levels: ecological (some host species are used species as it defines their resource base, which in turn more intensely than others) and phylogenetic (some influences the population dynamics and interactions host species are closely related, whilst others are dis- of herbivores with other organisms. In addition, host tantly related). Thus, the number of host species (i.e., specificity reflects past evolutionary interactions be- host range) is in fact only a crude measure of host speci- tween the herbivore and plant lineages, thus giving ficity (Poulin 2007). A useful measure of host speci- hints about the role of historical processes in shaping ficity requires taking the level of parasite infestation ecological communities (Novotny et al. 2002). Hence, a and between-host relationships into account (Poulin & proper estimation of host specificity is one of the ma- Mouillot 2003). jor research tasks in the study of plant-herbivore inter- Estimation of the host specificity of herbivores can actions, allowing an understanding of the evolution of be based on field surveys (e.g., Gassmann et al. 2008; feeding specialization (Poulin 2007). Duyck et al. 2009). A measure of the host specificity on The term ‘host specificity’ has been used in differ- the basis of field data should take into account how ent contexts with many interpretations. According to heavily and how frequently the various host species the most widely accepted definition, host specificity is are infested by a given herbivore species. Ranking host the extent to which a parasite taxon is restricted in species according to herbivore abundance shows which the number of host species used (Poulin 2007). The hosts are used more intensively among the spectrum of term ‘host specificity’ has occasionally been used as all available hosts. Information on whether a herbivore an alternative to the term ‘host range’, however, it is utilizes its various hosts species equally or whether it useful to distinguish both terms. The number of host concentrates on only one or few of them would be valu- species infested by a parasite should be referred to as able for examination of host use (Poulin 2007). The the host range (Lymbery 1989). This measure assumes host range that indiscriminately includes all host plant c 2012 Institute of Zoology, Slovak Academy of Sciences Host specificity of plant-feeding mites 547 records becomes rapidly dominated by marginal hosts from 1988 to November 2009 were selected by search- and accidental events (Novotny & Basset 2005). Thus, ing the SCOPUS database (http://info.scopus.com ) us- it is obvious that the assessment of the host specificity ing the following query: TITLE-ABS-KEY(”host range” basedonfieldobservationsrequires the collection of OR ”host-range” OR ”host specificity”) AND TITLE-ABS- quantitative data. KEY(”herbiv*” OR ”plant feed*” OR ”plant-feed*” OR ”phytophag*”) AND (LIMIT-TO(DOCTYPE,”ar”) OR Eriophyoid mites are an important component of LIMIT-TO(DOCTYPE,”ip”) AND (LIMIT-TO herbivore fauna in all plant assemblages and they are of (SUBJAREA,”AGRI”) OR LIMIT-TO(SUBJAREA, great practical importance as plant pests or agents in ”ENVI”). By using a more human-readable format, all pa- the biological control of weeds (Smith et al. 2010; Van pers were searched within the title, abstract or keywords Leeuwen et al. 2010). Nevertheless, most associations for: between eriophyoid mites and their plant hosts remain 1. at least one occurrence of the following terms: ”host poorly understood. Most eriophyoid species are com- range”, ”host-range”, ”host specificity”, monly regarded as highly specialized mites with narrow 2. at least one occurrence of the terms beginning with: host specificity, and only a few species are known as gen- ”herbiv”, ”plant feed”, ”plant-feed”, ”phytophag”. eralists with wide host ranges (Oldfield 1996; Skoracka Subsequently, both search criteria were combined – only papers fulfilling both of them (i.e., dealing with any et al. 2010). However, most information about the host aspects of host range or host specificity studied on plant- ranges of eriophyoid mites was based on single sam- feeding organisms) were selected. Thereafter, only research pling occasions without quantitative data. In this way, articles (either published or in press in November 2009) were the degree of host specificity of eriophyoid species could taken into account. Finally, the whole set of papers was lim- be under or overestimated due to inefficient sampling. ited to cover only the subject areas of “Agricultural and Bi- Detailed information on host plant range is scarce and ological Sciences” or “Environmental Science”. This whole limited to several species (mostly potential agents for query can be replicated by pasting it into the “Advanced the biological control of weeds) for which laboratory Search” window in the Scopus web interface. tests were applied (Smith et al. 2010). Rearing eriophy- According to the query used, 312 articles were found oid mites is very labour intensive due to their extreme on the SCOPUS database. The abstracts of all articles were screened for the aims of the study, the group of organisms minuteness and hidden life-style (Oldfield 2005), and studied and the methods used. Among the articles, 47 con- this is probably the reason for the rarity of laboratory sidered groups other than herbivores, e.g. parasitoids, plant data on eriophyoid specificity. However, field studies or animal parasites, and viruses, and were excluded from gathering quantitative data on eriophyoid mites have further analysis. Among the 265 remaining articles related also rarely been done (Skoracka et al. 2010; Smith et al. to herbivores, 208 were excluded from further analysis be- 2010). This deficiency in reliable host specificity infor- cause: (1) they did not examine host range/specificity on mation is in contrast with the diversity and importance the basis of field-collected data (they were based on molec- of eriophyoid mites, as well as with the great number of ular data – 21 articles, morphometric data – 6, experimental analogous studies targeting other herbivores (e.g., Diaz methods – 154 articles); (2) they were based on literature reviews (27 articles). et al. 2008; Duyck et al. 2009; Pratt et al. 2009) or an- From the selected 57 papers we noted: (1) the appli- imal parasites (e.g., Britton et al. 2009; Hellgren et al. cation of other methods (e.g., laboratory testing); (2) the 2009; Malenke et al. 2009). group of herbivores studied; (3) whether the aim of the study There were two main aims of this study. First, was to measure the host range or host specificity; (4) the we quantitatively examined published literature to de- application of any quantitative analysis, statistical test or termine whether quantitative field-collected data were any measures of the reliability of estimates; (5) information used by researchers to estimate the host range or host about the sample size. specificity of herbivores and what statistical analysis was applied to this data. Second, considering both the Field study value of field-collected quantitative data and the insuf- Field samples were collected between July 1998 and Octo- ficiency of such data for eriophyoid mites, we present ber 2009 from 404 localities in Central and Northern Europe results of an extensive long-term field study on grass- (Czech Republic, Denmark, Finland, Lithuania, Norway, Poland, Sweden, Ukraine). Shoots of a given grass species feeding Aceria species. It was our intention: (1) to ap- were collected by a cut just above the ground, put into plas- ply ecological parameters and indexes to obtain infor- tic bag and transported to the laboratory.