Agistemus aimogastaensis sp. n. (Acari, Actinedida, Stigmaeidae), a recently discovered predator of eriophyid mites Aceria oleae and Oxycenus maxwelli, in olive orchards in Argentina

Abstract A new species, Agistemus aimogastaensis, is described with the aid of optical and Scanning Electron Microscopy. This mite is an important predator of two eriophyid mites (Aceria oleae and Oxycenus maxwelli) in olive orchards (Olea europaea, variety Arauco) in La Rioja Province. The problems related to eriophyids in olive orchards in Argentina are highlighted and photos of the damage on leaves and fruit are included.

Little is known about Agistemus species as predators of eriophyid mites in Olive orchards (Momen 2012;Abou-Awad et al. 2010) and this is the first report of this genus from olive orchards in Argentina.
The genus Agistemus was erected by Summers (1960) based on type species Caligonus terminalis Quayle 1912. Grandjean (1944) published a work on the family Stigmaeidae, and established a series of characteristics with reference to legs and palp chaetotaxy. Further contributions to the present definition of the family were made by Gonzalez-Rodriguez (1961, 1963, 1965 and Summers and Ehara (1965).

Material and methods
All specimens were collected individually from tree surfaces (vegetative buds, leaves, inflorescences, or fruits) and preserved in 70% ethanol. Specimens studied by means of light microscopy were macerated in lactic acid and observed in the same medium, using the open-mount technique (cavity slide and cover slip) as described by Grandjean (1949) and Krantz and Walter (2009). Drawings were made using an Olympus BHC compound microscope (Rungis, France) equipped with a drawing tube. Some specimens were studied by means of a Scanning Electron Microscope (SEM). For this purpose, specimens preserved in ethanol were carefully rinsed by sucking them several times into a Pasteur pipette, and these were then transferred to buffered glutaraldehyde (2.5%) in Sörensen phosphate buffer: pH 7.4; 0.1 m for 2 hours. After postfixation for 2 hours in buffered 2% OsO 4 solution and rinsing in buffer solution, all specimens were dehydrated in a series of graded ethanols and dried in a critical point apparatus. Specimens were mounted on Al-stubs with double-sided sticky tape and then gold coated in a sputter apparatus (Alberti and Fernandez 1988;Fernandez 1990a, 1990b;Alberti et al. 1991;Fernandez et al. 1991;Alberti et al. 1997;Alberti et al. 2007). For a study of the genito-anal plates and genital structures, specimens were dissected and monitored during the lactic acid maceration process (in warm 70% lactic acid) before being stained with chlorazol black E, a well-known stain (Coineau 1974). Measurements taken: total length (tip of rostrum to posterior edge of notogaster) and width (widest part of notogaster) in micrometres (μm). Leg chaetotaxy studies made using standard, polarized and phase contrast microscopes. Setal formulae of the legs include the number of solenidia (in parentheses); Setal length measured with SEM.
Material examined. Holotype female and 2 female paratypes, Aimogasta, Province de La Rioja, Argentina 11-NOV-2012 deposited in Instituto Nacional de Tecnologia Agropecauria (INTA), Aimogasta, La Rioja Argentina; 4 Paratype females, same date and locality as holotype deposited in Museum National d'Histoire Naturelle, Paris, France and 4 paratypes, same date and locality as holotype deposited in Geneva Natural History Museum, Switzerland. All preserved in 70% ethanol. All type specimens were collected from vegetative buds, leaves, inflorescences and fruit of Olea europaea, variety Arauco.
This species most closely resembles Agistemus collyerae Gonzalez-Rodriguez 1963, principally in relation to the setation of leg IV. However A. aimogastaensis can be easily differentiated from the latter on account of the disposition and shape of propodosomal, metapodosomal, humeral and intercalar plates; as well as the length and disposition of dorsal setae. Specific characters given by Gonzalez-Rodriguez for A. collyerae in relation to the unusual lengths of the ag 2 setae (pg 2 sensu Gonzalez-Rodriguez 1963) and g setae (g 1 sensu Gonzalez-Rodriguez 1963), and the equal lengths of the other setae ag 1 , ps 1 , ps 2 and ps 3 (g 2 , g 3 , g 4 , pg 1 , Fig. 8, Gonzalez-Rodriguez 1963) is very different to the situation found in A. aimogastaensis, where these setae are equal in size and shape; but setae ps 3 (g 4 sensu Gonzalez-Rodriguez 1963) is completely different to the other setae, both in shape and length. Finally, another important character is the post-ocular body (pob) and the microsculpture around this zone. The pob in A. aimogastaensis is triangular with rounded extremities, and the microsculpture around this zone is smooth to fine integumental striations; in A. collyerae the pob is round and the surrounding microsculpture is a thin-walled network or reticulate.
Shape: ovoid ( Figures 1A,B). Colour: variable. Specimens observed in reflected light: orange-yellow, slightly shiny or white. We studied specimens of different colors and all were female.
Integument: (Figures 1A,B; 2A,D,E) Microsculpture complicated, varying according to body region. Propodosomal plate (P) polyhedral reticulate pattern: tiny accentuated polyhedral reticulated pattern, extending behind vi setal insertion and paraxially to ve and sce setal insertion, and paraxial to eye (eye) and post ocular body (pob). Near the eye and post ocular body and antiaxially to the ve and sce setal insertion smooth (Figs 2A,D). Existing paraxially to eye and pob, very fine integumental striae.
Dorsal region ( Figure 1A). Propodosomal plate (P) trapezoidal, with three pairs of setae: vi situated close to the anterior margin of plate; ve situated slightly anteriorly and paraxially to the eye and the postocular body (pob); sce, situated posteriorly and antiaxially to pob. All setae situated on very small protuberances.
Observation of eye and the postocular body (pob) (not shown on Fig.1A) is complex, because on mites not cleared the eye and the pob can both be observed, but in cleared animals only the eye is visible. Position of ve setae complicating observation in optical microscopy. SEM permits observation of the eye in dorsal view ( Fig.2A,D) as a smooth structure, ovoid and convex in lateral view; length: 9.55 (9.48-9.56) ; width: 6.28 (6.26-6.29) . The pob has a more or less triangular shape with rounded extremities ( Fig.2A, D); 5.81(5.79-5.83) in length and 5.34 (5.32-5.37) in width; a series of longitudinally aligned slightly rounded-convex elevations (r.c.e) present, joined by thread-like strands. In recently mounted specimens (observed in optical microscopy), the pob presenting small red-yellow spots, disappearing quickly; possibly these spots are the r.c.e observed in SEM.
Metapodosomal plate (M) hexagonal to polyhedral. Dorsocentral setae: insertions c 1 and e 1 situated on the same longitudinal level; d 1 insertion situated antiaxially to c 1 and e 1 insertion level. Dorsolateral setae: d 2 insertion situated externally and close to plate margin, posteriorly to c 1 insertion level but anteriorly to d 1 insertion level; e 2 situated slightly paraxially to the d 2 insertion level and posteriorly and antiaxially to d 1 insertion level (Fig. 1A). Intercalary plates (I) ovoid, situated near the body margin (Fig. 1A); f 1 setal insertion situated paraxially to e 2 insertion level and antiaxally to e 1 insertion level.
Legs ( Figure 4A-D). All legs with ambulacrum, composed of two claws with small tooth, and an empodium with three pairs of capitate fan-shaped raylets (resembling leaves of Ginkgo biloba tree) (Fig. 3B).
Remarks. The post ocular body, delimited by red-yellow spots, is clearly visible in fresh recently prepared specimens, but these spots disappear quickly making it difficult to view; this situation is similar to observations made on Hydrozetes lemnae (Oribatida, Hydrozetidae) and at the base of the ultrastructural studies of secondary eye Fernandez 1988, 1990a,b).
Our observations on cuticular components of the genital chamber using optical microscopy must be indicated as relative, and we stress that their value for taxonomic studies is limited as their main significance is only to confirm adulthood [as indicated by Summers and Ehara (1965)].

Problems with Olive orchards in Argentina related to eriophyid mites and their predator Agistemus aimogastaensis sp. n.
The Olive industry in Argentina is significant, with several provinces such as Mendoza, San Juan, San Luis, La Rioja and Catamarca producing olive fruit and their derivatives, though levels of production may vary. Olive production plays a very important socioeconomic role as principal provider of employment in La Rioja and Catamarca Provinces.
In olive orchards eriophyid mites are considered a secondary pest (International Olive Council 2007;Spooner et al. 2007) relating to young trees, and a problem in greenhouses or in zones with high humidity and temperature (Spooner et al. 2007). Regrettably, in Argentina, this problem has high incidence and produces large losses in olive industry yield, reaching up to 20%.
The predominant species of eriophyid mites found in Catamarca and La Rioja Provinces on Olea europaea (variety Arauco) are Aceria oleae and Oxycemus maxwelli. Of these two, A. olea is predominant with a maximum on leaves and fruit in April and November. These two eriophyid mites cause a significant impact on regional economies due to significant fruit and leaf malformations ( Figure 5).
The predator Agistemus aimogastaensis was found in these two provinces in large numbers, principally in relation to the population level of eriophyid mites.
The possibility exists of using this predator as biological control measure of problematic eriophyid mites. Our laboratory observations show that A. aimogastaensis is a voracious predator, principally on A. olea. All ontogenetic stages prey on the mites. Several studies on different predation aspects are being conducted.