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20: The Family Tetranychidae Donnadieu

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20   The Family Tetranychidae Donnadieu

The opisthosoma bears up to 14 pairs of dorsal setae, which are named according to the standard notation proposed by Grandjean (1939c). Commonly, only the setae of segments

C (c1–3), D (d1–3), E (e1–3), F (f1–2) and H (h1–3) are evident as

The bodies of the Tetranychidae are soft and more or less ovoid dorsal setae. Except for the setae h2–3, the opisthosomal setae or round. The body is from 350 to 1000 μm long, variously col- are generally similar to one another and also to the prodorsals; oured (red, orange, green or yellow), and consists of a gnatho- they can be finely barbulate, pointed, setiform, clavate, spatusoma and idiosoma. The dorsal disjugal and the ventral sejugal late or lanceolate, and all or partially set on tubercles. The sutures divide the idiosoma into an anterior propodosoma and ­integument is commonly similar to that of the prodorsum. The a posterior hysterosoma. The dorsal surface of the body con- opisthosomal ventral region of the female has one pair of sists of the prodorsum, corresponding to the anterodorsal part aggenital setae (ag), the genital opening, two pairs of lateral genital of the propodosoma, and the opisthosoma, i.e. the hysterosoma setae (g1–2), and the anal opening, with 1–3 pairs of pseudanal setae without legs III and IV (Fig. 2.9D).

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8: Mites as Biocontrol Agents of Weeds

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8  Mites as Biocontrol Agents of Weeds

Weeds compete in agriculture in various ways. They may d

­ irectly affect the management of cultivated plants and reduce the yield, or act in other ways, such as by limiting the utilization of land for grazing. Weeds can be indigenous, exotic or cryptogenic

(neither demonstrably native nor introduced) (Carlton, 1996).

Herbicides comprise about 50% of all the agrochemicals sold worldwide (Woodburn, 1995), which compares with 30% for insecticides. The biological control of weeds could represent a desirable solution to this problem, and the use of arthropods to accomplish this was proposed in the 1830s (Goeden, 1988).

The strategy is to employ natural enemies to reduce the density of weeds to an acceptable level (Van Driesche et al., 2008). This type of control is usually applied against invasive weeds and requires the importation of natural enemies from their areas of origin. These natural enemies are herbivores (mites, insects, etc.) and must not damage other (accompanying) plant species.

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12: The Family Histiostomatidae Berlese

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12  The Family Histiostomatidae Berlese

Morphological Characteristics, Systematics and Bio-ecology

The body of mites of the family Histiostomatidae is large and not dorsoventrally flattened. The gnathosoma is strongly modi­ fied and adapted to feed on minute particles in suspension. The chelicerae are laterally compressed, not chelate, with the digi­ tus fixus comb like and equipped with many fine teeth. The digitus mobilis is short, fused to the base of the digitus fixus, and with few short distal teeth. The palpi have a freely movable and flattened distal segment, with long tarsal solenidion and eupathididal setae (Figs 12.1C and 12.4B). The prodorsum has four pairs of setae (ve, vi, sce, sci) and the hysterosoma ten pairs of dorsal setae (c1, c2, c3, d1, d2, e1, e2, f2, h1, h2); one pair of setae

(h3) is commonly set ventrally. The opisthonotal glands are commonly located between setae e1 and e2. The bursa copulatrix is set between the setae h1 (Fig. 12.1A). The genital valves of the female are fused to the body medially, and form a transverse oviporus; the genital papillae of both sexes are often seen as large rings on the ventral surface and are not closely associated; the posterior pair is set on the ventral opisthosoma (Figs 12.1B and 12.2A) (Hughes, 1976; O’Connor, 2009).

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22: The Family Tarsonemidae Canestrini et Fanzago

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22  The Family Tarsonemidae Canestrini et Fanzago

Morphological Characteristics,

Systematics and Bio-ecology

The Tarsonemidae are small mites, from 100 to 300 μm long, translucent, pale or whitish, but with their colour influenced by the food they ingest. These phytophagous species may appear greenish, depending on the green leaves that they have attacked.

They are usually dimorphic, with the males different from the females in size and morphological characteristics. The body of the female is usually ovoid, and sometimes elongate, such as in

Steneotarsonemus spp., while the male is smaller than the female and has a characteristic subterminal ‘genital capsule’ and a strong leg IV, particularly conformed and with a single claw.

The body consists of a gnathosoma, prodorsum and opisthosoma (Fig. 22.1). The gnathosoma includes parts, such as the stylophore, palpi, infracapitulum and chelicerae (Fig. 2.7G).

The stylophore is derived from the merged bases of the chelicerae and, integrated with the infracapitulum, forms the gnathosomal capsule. The palpi are 2-articulate and usually closely appressed, and the chelicerae are retractable and of different lengths in different species, with the movable digit as a fine stylet. The prodorsum of the female has a sclerotized dorsal shield that is variously ornate, one pair of stigmata, two pairs of setae (v1, sc2), one pair of bothridia supporting the pseudostigmatic organs and one pair of pits (v2) (Figs 2.17A, 22.1). The prodorsal shield of the male has vertical (v1, v2) and scapular setae

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18: The Family Diptilomiopidae Keifer

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18  The Family Diptilomiopidae Keifer

Morphological Characteristics,

Systematics and Bio-ecology

The morphological characteristics of the family Dipti­ lomiopidae are similar to those of the Eriophyidae. The pro­ dorsal shield has two or no setae, the scapular setae (sc) are present or absent, and the unpaired setae vi and ve are largely absent. The gnathosoma is sharply bent towards the base, with cheliceral stylets folded in the same way and long oral stylets. The opisthosoma frequently lacks the setae c1; the re­ maining setae are present, or sometimes any one of the setae c2 or d or setae h1 are absent. The chaetotaxy of the coxal plate is complete, plate I is sometimes without the setae 1b and rarely with the setae 1a. The leg chetotaxy is complete but may be missing the basiventral femoral setae I and II, the antaxial genual seta of genu II, the paraxial tibial seta of tibia

I and both the paraxial and fastigial tarsal setae (ft ¢) or the paraxial and unguinal tarsal setae (u¢) of legs I and II; the tibia I lacks a solenidion; the tarsal empodium may be thick and is commonly divided. The genital coverflap sometimes has one or two rows of ridges and spots or semilunar granules.

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