Agistemus aimogastaensis, Leiva, Sergio, Fernandez, Nestor, Theron, Pieter & Rollard, Christine, 2013

Leiva, Sergio, Fernandez, Nestor, Theron, Pieter & Rollard, Christine, 2013, Agistemus aimogastaensis sp. n. (Acari, Actinedida, Stigmaeidae), a recently discovered predator of eriophyid mites Aceria oleae and Oxycenus maxwelli, in olive orchards in Argentina, ZooKeys 312, pp. 65-78 : 66-72

Agistemus aimogastaensis sp. n.

Etymology.

The specific epithet is dedicated to the city of Aimogasta, La Rioja, Argentina, where the specimens were found.

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.

Diagnosis

(adult female). Propodosomal plate: trapezoidal; ornamented with a faintly accentuated, polyhedral reticulate pattern; eyes clearly visible, ovoid convex, smooth; post ocular body triangular, rounded extremities, with series of longitudinally aligned small round-convex elevations, joined by thread–like strands. Metapodosomal plate hexagonal to polyhedral; ornamented with accentuated transverse polyhedral reticulate pattern. Wide area with fine transverse integumental striae, separating propodosomal and metapodosomal plates. Humeral and intercalar plates marginally. Setaeg, ps1, ps2 Similarly shaped, finely barbate, sharply tipped; ps3 minutely dentate, truncate g, ps1, ps2 larger than ps3 and very different in shape and appearance in optical and SEM. Legs: genua II, III, IVsetal formula 0-0-0; leg IV lacks solenidion. Ambulacra with two claws and empodium with three pairs of bicapitate, fan shaped Y-raylets.

This species most closely resembles Agistemus collyerae Gonzalez-Rodriguez 1963, principally in relation to the setation of leg IV. However Agistemus 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 Agistemus collyerae in relation to the unusual lengths of the ag2 setae (pg2 sensu Gonzalez-Rodriguez 1963) and g setae (g1 sensu Gonzalez-Rodriguez 1963), and the equal lengths of the other setae ag1, ps1, ps2 and ps3 (g2, g3, g4, pg1, Fig. 8, Gonzalez-Rodriguez 1963) is very different to the situation found in Agistemus aimogastaensis , where these setae are equal in size and shape; but setae ps3 (g4 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 Agistemus aimogastaensis is triangular with rounded extremities, and the microsculpture around this zone is smooth to fine integumental striations; in Agistemus collyerae the pob is round and the surrounding microsculpture is a thin-walled network or reticulate.

Description.

Measurements: SEM: 325 (312-351) × 160 (152-173) Light microscopy: 336 (331-339) × 168 (166-174) (n=10).

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.

Metapodosomal (M) plate with polyhedral reticulate pattern, accentuate (Fig. 2D). Humeral plate (H), Intercalary plate (I), and Suranal plate (SA), more or less smooth (Fig. 1A).

Fine integumental striae covering zone between Propodosomal, Metapodosomal, Humeral, Intercalar and Suranal plates (Figs 1A, 2A).

Fine integumental striae covering venter of idiosoma, epimeral zone smooth (Fig. 1B).

Legs: cuticular surface smooth.

Setation. All dorsal setae minutely denticulate and truncate (Fig. 3C, D). Length: vi 12.60 (12.04-13.012); ve 13,78 (13.05-13.92); sce 18.80 (18.78-18.93); c2 20.70 (19.89-21.01; c1 19.5 (19.56-19.80); d1 16.45 (16.43-16.48); e1 18.1 (18.00-18.09); d2 19.33 (19.23-19.92); e2 17.80 (17.77-17.84); f1 17.85 (16.01-17.69); h1 14.20 (14.18-14.24); h2 17.20 (17.16-17.24).

Ventral setae: epimeric smooth (1a, 1b, 1c, 2a, 3a, 3b, 3c, 4a, 4b, 4c); (ag1, ag2) and g, ps1, ps2, finely barbate (Fig. 3E), sharply tipped; ps3 minutely dentate, truncate (Fig. 3F).

Length: ag1 17.61 (17.58-17.66); ag2 17.70 (17.68-17.75); g 17.25 (17.17-17.29); ps1 17.40 (17.38-17.43); ps2 18.20 (18.18-18.24); ps3 17.05 (17.00-17.12).

In optical microscopy the dorsal setae and genital ps3 appear as dark, while epimerics, paragenital and genitals (g, ps1, ps2) appear transparent. Scanning Electron Micrographs depicted in Figure 3.

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.

Propodosomal and metapodosal plates separated by a relatively large expanse of fine integumental striae (Fig. 1A, 2A).

Humeral plate (H) ovoid, situated antiaxially to P-plate and slightly antiaxially to M-plate; setae c2 insertion situated slightly paraxially to d2 insertion level (Fig. 1A).

Metapodosomal plate (M) hexagonal to polyhedral.

Dorsocentral setae: insertions c1 and e1 situated on the same longitudinal level; d1 insertion situated antiaxially to c1 and e1 insertion level. Dorsolateral setae: d2 insertionsituated externally and close to plate margin, posteriorly to c1 insertion level but anteriorly to d1 insertion level; e2 situated slightly paraxially to the d2 insertion level and posteriorly and antiaxially to d1 insertion level (Fig. 1A).

Intercalary plates (I) ovoid, situated near the body margin (Fig. 1A); f1 setal insertion situated paraxially to e2 insertion level and antiaxally to e1 insertion level.

Ventral region. Epimera well defined (Fig. 1B). Setal formulae: 3-1-3-3. Anogenital region clearly discernible. Two pairs of paragenital setae: ag1, ag2; and four pairs of setae: g, and three anal setae ps1, ps2, ps3 (see Setation). g, ps1, ps2 and ps3 differing in shape (See Setation).

Cuticular components of the genital chamber with preatrium (pre), saucer-shaped structure, longitudinal striate and postatrium (post) bilobed; between pre and pos a constriction or waist (w) (Fig. 1D).

Legs (Figure 4 A–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).

Setal formulae (solenidia in parentheses) I (1-4-2(1)-5(1)-11(1)); setae k on genu I; II (1-4-0-5(1)-8(1)); III (1-2-0-5(1)-7(1)); IV (1-2-0-4-7).

Setal formulae of palp (3-1-2-8(1)) (Fig. 1C); tarsus with four eupathidia and solenidion ω; (ul) ζ, sul ζ united in fork, with typical characteristics of Stigmaeidae ( Grandjean 1944). Palp tibial claw present (Fig. 3A).

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( Alberti and 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 socio-economic 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, Aceria oleae 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 Agistemus aimogastaensis is a voracious predator, principally on Aceria oleae . All ontogenetic stages prey on the mites. Several studies on different predation aspects are being conducted.