Spathius ochus Nixon, 1943

Cao, Liang Ming, Achterberg, Cornelis van, Tang, Yan Long, Yang, Zhong Qi, Wang, Xiao Yi & Cao, Tian Wen, 2020, Redescriptions of two parasitoids, Metapelma beijingense Yang (Hymenoptera, Eupelmidae) and Spathius ochus Nixon (Hymenoptera, Braconidae), parasitizing Coraebus cavifrons Descarpentries & Villiers (Coleoptera, Buprestidae) in China with keys to genera or species groups, ZooKeys 926, pp. 53-72 : 53

Spathius ochus Nixon, 1943 Figures 6 , 7 , 8

Spathius ochus Nixon 1943: 372; Chao 1957: 13; Shenefelt and Marsh 1976: 1410; Chao 1978: 180; Chen and Shi 2004: 150; Yuet al. 2012; Tang et al. 2015: 79.

Material.

71♀♀, 5♂♂, China, Guizhou Province, Zunyi City, 27°41'54.91"N, 106°54'40.29"E, collected 10.v.2015 pupae from carcass of Coraebus cavifrons Descarpentries & Villiers under bark of dead Symplocos stellaris Brand, emerged into adults 15-20.v.2015, Tang Yan Long.

Redescription.

Female. Body length 4.1-4.6 mm (Fig. 6A ), forewing length 3.1-3.2 mm.

Color. Body generally brown (Fig. 6A ). Head yellowish brown, basal half of antenna yellow, its apical half brown; pronotum, mesoscutum, propodeum, petiole and legs (except tarsi) dark brown; scutellum, axilla, metanotum, mesosternum, metasoma except first tergite, and telotarsus black; basal half of basitarsus white, and remainder of tarsus yellow. Fore wing distinctly infuscate, with several subhyaline spots and strips, apical 2/3 pterostigma dark brown, veins brown; hind wing subhyaline. Ovipositor sheath pale brown in basal 3/5, yellow in next 1/5 and dark 1/5 apically.

Head. Median length 0.8 × of its width in dorsal view; with transverse striae. Length between posterior margin of lateral ocellus and occipital carina 1/2 of length of head in dorsal view; occipital carina distinct, median portion concave, reversed V-shaped; length of eye: length of temple in dorsal view = 11: 14 (Fig. 6B ); eyes rather large (Fig. 7A ); OOL: OD: POL = 3: 2: 1.Width of head 1.2 × height in anterior view and width of face 1.1 × height of eye; clypeus with transverse thin carina, face covered with sparse white setae; malar space 0.4 × height of eye; height of clypeus 0.4 × its width, exterior margin of clypeus slightly concave; length of maxillary palp 0.6 × head width, 1.5 × height of eye and 3.2 × length of malar space; hypoclypeal depression deeply concave (Fig. 6C ); antennae 36-segmented, scape 1/3 length of first flagellar segment, and 0.65 × its maximum width; first flagellar segment 7.5 × its maximum width, 1.3 × as long as second segment; last antennal segment acute (Fig. 6D ).

Mesosoma. Length of mesosoma 2.4-4.0 × its height in lateral view; pronotal keel fine, weak, with fine posterior branches, mesoscutum distinctly roundly elevated above pronotum. In dorsal view pronotum with parallel longitudinal carina bilaterally, median length of mesoscutum equal to its maximum width; mesoscutum finely granulate; notauli deep and middle of mesoscutum with two parallel longitudinal carinae, between with six transverse carinae. Anterior 1/3 of mesopleuron near pronotum and tegula with short rugae and white setae, posterior 2/3 with scaly sculpture. Scutellum apical 2/3 of scutellum finely granulate; scutellar sulcus 0.3 × as long as scutellum, with 7-9 longitudinal carinae and separated small depressions. Metanotum narrow, medially concave, with 9 or 10 longitudinal carinae, propodeum weakly oblique posteriorly, 1.2 × longer than its apical width, 0.5 × petiole, medio-longitudinal carina bifurcates at basal 1/3 of propodeum, posterior half of propodeum with irregular carinae (Figs 6E , 7B ).

Legs. Fore femur 0.8 × length of tibia and 3.6 × its maximum width, fore tibia 6.5 × longer than wide, outside with a row of spines and apex with comb of spines, ratio of fore tarsal segments I-V = 20: 10: 7: 5: 6; mid femur 0.7 × length of tibia, ratio of mid tarsal segments I-V = 10: 6: 5: 4: 8; hind coxa simple, hind femur 2.5 × longer than wide, 0.7 × as long as hind tibia, ratio of hind tarsal segments I-V =18: 9: 6: 4: 8.

Wings. Forewing 3.5 × its width; pterostigma 3.5 × its maximum width; 1-R1 1.25 × pterostigma, r originate from middle of pterostigma; SR1 7.2 × longer than r, straightly extending to wing margin; r nearly 1/4 of 2-SR, cu-a perpendicular to CU1, m-cu enters second submarginal cell; meeting point of 2-SR, 2-M and 2-SR+M weak, veins reduced; 1-SR+M straight, 1-SR 1/4 length of 1-M; M+CU1 distinctly curved, apical subbasal cell narrow and elongate, r-m unsclerotized, hardly invisible; 3-M and CU1a reaching wing margin. Length of hind wing 4.5 × its width, m-cu and SR pigmented (Fig. 7E ).

Metasoma. First tergite 3.5-3.9 × longer than its maximum apical width in dorsal view, with regular longitudinal carinae; in lateral view first tergite slender and 1.5-1.7 × as long as propodeum, spiracular tubercles located at basal third, laterally with erect white long setae; tergites 2-4 densely granulate; fifth and sixth tergites smooth. Length of visible setose part of ovipositor sheath 0.7-0.8 × length of metasoma, 0.85 × length of fore wing, and 0.6 × length of body (Fig. 7C, D ).

Male. Body length 4.0-4.2 mm, forewing 2.7 mm (Fig. 8 ), otherwise similar to female.

Remarks.

The mesosoma is variably depressed; usually 2.4-2.9 × longer than high, but in some specimens up to 3.7-4.0 ×. Obviously, this character is useless to separate S. tereus Nixon, 1943. Therefore, we agree with Chao (1957) that the latter cannot be separated. Spathius ochus is a gregarious koinobiont ectoparasitoid like most other Spathius , each buprestid larva can feed 3-9 individuals. From one tree 11 borer larvae were parasitized by 42 individuals of S. ochus , together with seven borer larvae were parasitized by M. beijingense and 34 live buprestid pupae, resulting in a parasitism rate of about 21.2% for S. ochus . The sex ratio is about 14:1 (71 females to 5 males).

The very interesting phenomenon of synparasitism ( Tobias 2007) is shown in Figure 2D ; one individual of M. beijingense and four individuals of S. ochus were together parasitizing the same woodborer larva. Likely, these two ectoparasitoid species laid their eggs near the host at about the same time, and the larvae did not start fighting each other because the host was large enough to avoid severe food competition. Of course, this is only circumstantial evidence that is in need of corroboration.

The species is very similar to S. parochus Belokobylskij & Maeto and can be recognized with the key below.

Figures

Figure 2. A A mature pupa of Metapelma beijingense Yang, near the buprestid larva B a new pupa of M. beijingense Yang, with the buprestid larva C empty cocoons of Spathius ochus Nixon D pupa of M. beijingense Yang and cocoons of S. ochus Nixon showing synparasitism.

Figure 6. Spathius ochus Nixon, ♀, China, Guizhou. A Habitus, lateral aspect B head, dorsal aspect C head, anterior aspect D antennae, lateral aspect E mesosoma, dorsal aspect.

Figure 7. Spathius ochus Nixon, ♀, China, Guizhou. A Head, lateral aspect B metasoma, lateral aspect C metasoma, lateral aspect D metasoma, lateral aspect E wings.

Figure 8. Spathius ochus Nixon, ♂, China, Guizhou. A Habitus, dorsal aspect B head and mesosoma, dorsal aspect C head and mesosoma, lateral aspect D metasoma, dorsal aspect.