Marie-Stéphane Tixier

Status of two cryptic species, Typhlodromus exhilaratus Ragusa and Typhlodromus phialatus Athias‐Henriot (Acari: Phytoseiidae): consequences for taxonomy

Typhlodromus phialatus and T. exhilaratus are morphologically close species. Their differentiation is based on the shape of the insemination apparatus and on idiosomal setae length. However, the setae length values are often intermediate between these two species and do not allow accurate identification. Furthermore, the handful of differences in insemination apparatus shape are also questionable as a means of differentiation. Synonymy between these species has thus been questioned. Three experiments were carried out. Idiosomal seta length measurements, molecular tests and cross experiments were conducted for three populations, identified as T. exhilaratus and T. phialatus according to the shape of their insemination apparatus. The results show that the variation range of seta lengths is great and that these criteria do not allow accurate separation of these populations into two species. However, molecular tests show a species‐level nucleotide differentiation between them. Cross experiments confirm this result, showing complete reproduction incompatibility between the mites bearing different insemination apparatus shapes. Therefore, T. exhilaratus and T. phialatus could be considered to be two valid species and the insemination apparatus could be considered as a pertinent diagnostic criterion at the specific level.

On the specific identity of specimens of Phytoseiulus longipes Evans (Mesostigmata: Phytoseiidae) showing different feeding behaviours: morphological and molecular analyses.

This paper focuses on the differentiation of specimens, identified as Phytoseiulus longipes, collected in four countries: Argentina, Brazil, Chile and South Africa. Two of these populations are known to feed and develop on Tetranychus evansi, whereas the two others do not. As morphologically similar specimens can sometimes belong to different species and because differences in predatory behaviours exist among the four populations considered, we tested for the presence of cryptic species. Morphological and molecular experiments (12S rDNA) were carried out. The four studied populations of P. longipes could be morphologically differentiated thanks to a combination of characters. However, these morphological differences are very small. The two populations that feed and develop on T. evansi (from Argentina and Brazil) are morphologically closer to each other than to the two other populations. Genetic distances among the four populations of P. longipes were very low, suggesting that despite their different feeding habits, all specimens belong to the same species. However, the populations associated with T. evansi showed some genetic differentiation from those that do not use this pest. This is the first time that this type of differentiation has been reported for the family Phytoseiidae. These results are of primary importance to ensure the success of biological control programs and to develop strains adapted to both crops and prey species.

Egg hatching response to a range of air humidities for six species of predatory mites

The efficiency of biological control agents is often affected by local conditions such as low relative humidity (r.h.). This is especially true for mites of the family Phytoseiidae, and particularly for their egg stage. A key issue in biological control is thus to assess the drought tolerance of phytoseiid species that are (or that will be) commercialized. In this study, we evaluated the egg hatching response to a humidity range for six species of Phytoseiidae, by assessing the relative air humidity and vapour pressure deficit (VPD) at which 50% of the eggs hatch: r.h.50 and VPD50. Typhlodromus athiasae Porath & Swirskii and Phytoseiulus longipes Evans (Argentinean strain) were the most drought‐tolerant, with a r.h.50 of 43% (VPD50 = 18.2 hPa) and 43% (18.1 hPa), respectively. The most drought‐sensitive species were Amblyseius swirskii (Athias‐Henriot) (63%, 11.4 hPa), Phytoseiulus macropilis (Banks) (69%, 9.8 hPa), and Phytoseiulus persimilis Athias‐Henriot (70%, 9.4 hPa). Neoseiulus idaeus Denmark & Muma and P. longipes (Chilean strain) showed intermediate responses with 49% (16.1 hPa) and 50% (15.9 hPa), respectively. These results were similar to what had been obtained for the same species by other authors. However, unexpected inter‐ and intraspecific differences uncorrelated to climatic conditions of the area of origin were observed. The possibility to localize species and/or populations that could be efficient as biological control agents under dry conditions is discussed.

Morphological and molecular diagnostics of Phytoseiulus persimilis and Phytoseiulus macropilis (Acari: Phytoseiidae)

This study focuses on the diagnostics of two natural enemy species, belonging to the genus Phytoseiulus in the family Phytoseiidae (sub-family Amblyseiinae): P. macropilis and P. persimilis. These two species are of primary importance in biological control all over the world. However, they are morphologically very similar and specific diagnostics is difficult. This study utilizes mitochondrial molecular markers (12S rRNA and Cytb mtDNA) to differentiate these two species. Morphological analyses showed significant differences between P. persimilis and P. macropilis for 17 morphological characters of the 32 considered. However, despite these significant differences, the ranges of all characters overlap. Only the serration of the macroseta on the basitarsus (StIV) allows the differentiation between P. persimilis and P. macropilis. Despite these small morphological differences, molecular results, for both mitochondrial DNA fragments considered (rRNA and Cytb mtDNA), showed a clear delineation between the specimens of P. macropilis and P. persimilis. This study emphasizes (i) that only one morphological character (serration of the seta StIV) clearly separates these two species, and (ii) the usefulness of an automatical molecular and simple diagnostic tool for accurate differentiation of the two species and ensure the morphological diagnostics. Further studies are proposed, including more DNA sequences especially for P. macropilis.

Integrative taxonomy demonstrates the unexpected synonymy between two predatory mite species: Cydnodromus idaeus and C. picanus (Acari : Phytoseiidae)

Species of the mite family Phytoseiidae are well known as predators of mite pests all over the world. Their identification is thus of great interest for biological control. The specimens examined in this study belong to the species Cydnodromus idaeus (described from Brazil) and C. picanus (described from Chile). They were collected together on the same plant in Argentina. These species are mainly differentiated by the presence/absence of the dorsal solenostomes (gland openings) gd2. Some morphometric differences were observed between the Argentinian specimens and the type material of C. idaeus and C. picanus; however, they were not sufficient to support a species separation. Morphological and molecular analyses with two mtDNA (12S rRNA, CytB) and a nuclear DNA (ITS) marker showed no difference between Argentinian specimens with and without the solenostome gd2. Also, molecular differentiation between these latter specimens, C. picanus and C. idaeus, was very low, suggesting that all these individuals belong to the same species. Biological experiments confirm these results, as 75% of the progeny resulting from females with gd2 had gd2 present whereas all the descendants resulting from the females without gd2 had gd2 present too. The presence/absence of this solenostome seems thus to be variable within a species and cannot be used diagnostically. We conclude that all specimens from Argentina belong to C. idaeus and that C. picanus is a junior synonym of C. idaeus. The present results were unexpected as the presence/absence of solenostomes is used in Phytoseiidae identification keys and as one of a suite of diagnostic characters for discriminating between species. The consequences of these findings for the taxonomy of Phytoseiidae are discussed.

A new species of the genus Euseius Wainstein (Acari: Phytoseiidae) from France

The identity of specimens belonging to the genus Euseius found on several trees in France is investigated. Previous molecular and morphological analyses have shown that the new species herein described is different from Euseius stipulatus. Among the 187 species belonging to the genus Euseius, four of them (Euseius querci, Euseius amissibilis, Euseius kirghisicus and Euseius longiverticalis) seem to be morphologically close to this new species. However, none were very similar. This paper reports the description of this new species: Euseius gallicus sp. nov. Kreiter and Tixier.

Management of Phytophagous Mites in European Vineyards

The first infestations of spider mites in European vineyards were detected in the second half of the nineteenth century after the invasion of powdery mildew, downy mildew and phylloxera from North America. Serious problems associated with Tetranychus urticae Koch were detected in Italy and Austria and local outbreaks of Panonychus ulmi (Koch) were recorded. At that time the eriophyid Colomerus vitis (Pagenstecher) was known but not considered important, probably because sulfur was largely used to control grape diseases. Two additional species were described at the beginning of the twentieth century: the spider mite Eotetranychus carpini (Oudemans) and the eriophyid Calepitrimerus vitis (Nalepa). At that time, problems with mites injurious to grapes were negligible but the situation suddenly changed after World War II. Most of these problems were immediately associated with the extensive use of chlorinated hydrocarbon insecticides and later, by ethylene-bis-dithiocarbamate fungicides (EBDC). Three spider mite species were involved in the outbreaks: E. carpini, P. ulmi and T. urticae (Rambier 1958; Rota 1962; Zangheri and Masutti 1962). Most researchers of the time thought that mite outbreaks were due to the detrimental effects of pesticides on natural enemies of spider mites. However, there was little evidence to support this fact. Meanwhile, according to Chaboussou (1965) infestations were caused by changes in plant physiology induced by organic pesticides, favorable to mite demographic parameters (‘trophobiosis’). Chaboussou (1965) and others also tried to classify the most common pesticides according to their effect on spider mites. However, contradictory results were reported and no scientific proof could be obtained, and trophobiosis remained a matter of great debate among entomologists.

Statistical approaches to assess intraspecific variations of morphological continuous characters: the case study of the family Phytoseiidae (Acari: Mesostigmata)

Statistical methods for delimiting species with morphological data remain woefully understudied. The present study presents statistical approaches to study the intraspecific variations of continuous characters used in species diagnosis. For this, the data set comprised 14 species of the mite family Phytoseiidae (Acari: Mesostigmata) and 23 continuous characters (seta lengths). The statistical approaches aim to determine (i) how intraspecific variations differ depending on the characters and species considered, and (ii) how to choose the number of specimens to be considered for characterizing intraspecific boundaries. The means of the related confident limits at 95% (rCL95) of the 14 species and the 23 setae are around 20%, suggesting that 95% of the specimens of a same species are included in the interval μ ± 0.2μ. No relationship was found between seta variations and the number of specimens considered for each species, nor for seta variations and their position on the mite body. However, a correlation between seta lengths and rCL95 means was observed. An abacus was proposed to determine the coefficient that must be applied to mean seta length to calculate the lower and upper limits of the interval that will include 95% of the specimens of a same species. The higher the precision around the mean, the higher the number of specimens considered. Furthermore, this number varies considerably depending on the characters and species considered for high precisions. However, for a priori error around the mean of 15%, the number of specimens needed to characterize the intraspecific variation is quite homogeneous and ten specimens would be required. I discuss the utility of such results to resolve some persistent problems in the alpha‐taxonomy of the family Phytoseiidae but also of other taxa.

Rates of description of Phytoseiidae mite species (Acari: Mesostigmata): space, time and body size variations

This study aims to analyse the degree of completeness of world inventory of the mite family Phytoseiidae and the factors that might determine the process of species description. The world data set includes 2,122 valid species described from 1839 to 2010. Species accumulation curves were analysed. The effect of localisation (latitude ranges) and body size on the species description patterns over space and time was assessed. A low proportion of species seems remain to be described, but this trend could be explained by a critical reduction in the number of specialists dedicated to the study of those mites. In addition, this trend refers to the areas where phytoseiids have been well studied around the world, and it may change considerably if the study of these mites would be intensified in some areas. The number of newly described species is lower near the tropics, and their body size is also smaller. Differences in body size were noted between the three sub-families of Phytoseiidae, the highest mean body lengths of adult females being observed for Amblyseiinae, the most diverse family. In the future, collections would have certainly to take into consideration such conclusions for instance in using more adequate optical equipment especially for field collections. The decrease in the number of phytoseiid mite described was confirmed and the factors that could explain such a trend are discussed. Information for improving further inventories is provided and discussed, especially in relation to sampling localization and study methods.

The puzzle of DNA sequences of Phytoseiidae (Acari : Mesostigmata) in the public GenBank database

The public database GenBank is an increasingly important source of sequence data for diagnostic and phylogenetic research; however, not all deposited sequences are necessarily correctly ascribed to a source species. We considered the example of the mite family Phytoseiidae to determine how the corresponding sequences could be accurately exploited. Phytoseiidae mites are well known worldwide for their ability to control certain mite and insect pests. The number of molecular approaches, especially for diagnostic purposes, has increased over the past decade, leading to an increase in the number of sequences registered in the GenBank database. The aim of the present paper was to evaluate the validity of the DNA sequences presently assigned to Phytoseiidae species in this database. Three hundred and fifty-one sequences, corresponding to the four most frequently registered DNA fragments (ITS, COI, Cytb and 12S rRNA), were considered. DNA extraction, amplification and sequencing were performed for the fragments 12S rRNA and ITS for Amblyseius andersoni, A. swirskii, Iphiseius degenerans, Euseius ovalis, E. stipulatus, Neoseiulus cucumeris and Typhlodromus pyri, as some identifications were questionable. Numerous problems were evident based on genetic distance analyses of these sequences. First, nomenclatural problems were encountered, preventing the correct identification of the taxa sequenced in one case. Suspected misidentifications were frequent, stressing the importance of voucher specimen availability. For the 12S rRNA fragment, sequences assigned to three Phytoseiidae species were those of their prey (Astigmata), underlining the care that must be taken when manipulating the DNA of such predators (sterile conditions and specific PCR primers). Finally, sequences of two regions of the COI mtDNA were encountered, leading to alignment problems between sequences of a same gene and same species. These results are discussed in relation to responsibilities of authors in terms of taxon identification and the great utility of open access DNA sequence databases, such as GenBank, for improving taxonomic identifications and advancing scientific research.