Cerchysiella raddeii Yang, 2013

Yang, Zhong-qi, Tang, Hua, Wang, Xiao-yi, Wei, Jian-rong & Zhao, Hai-bing, 2013, A new species of Cerchysiella (Hymenoptera: Encyrtidae) parasitic in larva of chestnut trunk borer (Coleoptera: Cerambycidae) from China with notes on its biology, Journal of Natural History (J. Nat. Hist.) 47 (3 - 4), pp. 129-138 : 131-136

Cerchysiella raddeii Yang sp. nov.

( Figures 1 and 2 )

Female

Holotype. Body length 2.1 mm. Body dark brown except gastral tergites brown, face and scutellum with blue-green metallic lustre, but lustre much stronger on scutellum. Antenna with scape and pedicel testaceous, except scape more or less fuscous over basal two-thirds dorsally; flagellum fuscous except third segment of clava fulvous. Setae on head, antenna and mesosoma dark. Coxae concolorous with body; femora fuscous except apex of profemora and mesofemora as well as base of metafemora more or less fulvous; protibiae and mesotibiae and all tarsi fulvous, metatibia fuscous with apical quarter concolorous with tarsi; apical segment of all tarsi dark brown. Wings hyaline, venation brownish-testaceous; setae and pilosity on wing disc infuscate.

Head ( Figures 1 A–D, 2D,E) somewhat prognathous, in dorsal view as wide as mesoscutum and about 2.6 times as wide as long; vertex moderately convex; POL 4.8 times OOL; OOL as long as posterior OD; temple ( Figure 1C ) about 0.28 times as long as eye length, distance from posterior ocellus to occipital margin about the same as longest diameter of posterior ocellus, the margin abrupt but not forming an occipital carina. Eye with obvious dense pilosity; 1.3 times as high as wide; separated by 1.9 times their maximum height and with inner orbits slightly convergent ventrally. Malar sulcus superficial but traceable and slightly curved; malar space 0.5 times eye height. Head in frontal view subquadrate ( Figure 1D ), about 1.25 times as wide as high; toruli obviously below level of lower ocular line, with ventral margins very close to clypeus apical margin, separated from it by 0.56 times their length, and distance between toruli 2.14 times their own width; scrobes shallow and extending upwards convergently, about as long as torulus width; upper face evenly convex, with superficial raised reticulation. Head with sparse setae, but more obvious and denser on lower than upper face, and with a line of about seven small and shallow piliferous punctures close to and along inner orbit. Clypeus crescentic with anterior margin 0.4 times as wide as mouth cavity, and sloped downwards at about 65 ◦ angle relative to lower face, its ventral margin rather deeply emarginate and its arched dorsal margin a little above ventral line of toruli; with about six setae in a transverse line on median area. Cheeks buccate, mouth cavity very wide, about 0.65 times width of head. Antenna ( Figure 1F ) with scape 0.74 times as long as eye height, about 3.9 times as long as wide, dilated and flattened dorsally, with dorsal surface reticulate and setose; combined length of pedicel plus flagellum about equal to head width (0.96 times); flagellum gradually clavate, with first claval segment widest; relative length: width of pedicel, funicle 1, 2, 3, 4, 5, 6 and clava 1, 2, 3 as follows: 18: 10, 11: 11, 11: 13; 10: 14, 10: 16, 10: 17, 12: 18, 13: 22, 13: 20, 11: 17; apex of third claval segment with oblique area of micropilosity.

Mesosoma ( Figures 1A,B , 2D,E ) about 1.25 times as long as wide; in lateral view moderately depressed; mesoscutum and scutellum planate and almost at the same level. Pronotum short, sloping steeply in front and without pronotal carina; dorsum reticulate and covered with dense, moderately stout setae; collar slightly narrower than mesoscutum (0.86 times) and only about 0.11 times length of mesoscutum. Mesoscutum 1.46 times as wide as long without notaular lines, evenly and slightly convex, and covered with dense setae; dorsum superficially and delicately reticulate. Axillae triangular, width 2.16 times lateral length, surface with very fine, superficial reticulation; anteromedial angles close but not touching. Scutellum as long as wide and about as long as mesoscutum; dorsum fairly flat, with about 12 evenly distributed setae except bare mediolongitudinally, and sunken and with a pair of setae within posterior two-fifths. Metanotum with dorsellum concealed under marginal rim of scutellum, but lateral panel well developed, its lateral length 0.22 times length of scutellum, and with conspicuous oblique striations medially downwards. Propodeum very short, appearing as a transverse strip and concealed under apex of scutellum medially, with marginal rim of scutellum extending beyond posterior margin of propodeum so in dorsal view visible only laterally, with exposed lateral regions even narrower than lateral panel of metanotum; propodeum posteriorly descending steeply and truncate without hind rim along posterior margin; with dense, fine transverse striations dorsally; spiracle large, located at lateral–posterior corner of propodeum, the distance to anterior margin of propodeum less than its own length; callus with relatively short setae. Fore wing ( Figure 1G ) 2.5 times as long as wide, greatly exceeding apex of metasoma when directed posteriorly ( Figure 2D ); costal cell with a line of setae close to anterior margin within distal half, lower surface with three complete lines of setae; basal cell with a line of about nine to eleven setae close to submarginal vein and with six to nine setae forming basal setal line; filum spinosum short and directed towards junction of marginal vein and parastigma, consisting of a line of six to seven pegs, and clearly converging with the distinctive line of long setae (about nine) on the proximal margin of linea calva; submarginal vein plus parastigma with 11–13 bristles; wing disc densely setose beyond filum spinosum and oblique bare strip paralleling filum spinosum; submarginal vein including parastigma 7.2 times length of marginal vein; marginal vein 0.7 times as long as stigmal vein and 1.5 times length of postmarginal vein; stigmal vein about 2.3 times as long as postmarginal vein, and 0.86 times as long as combined length of marginal and postmarginal veins; stigma small and subquadrate. Hind wing 3.5 times as long as wide; densely setose. Mesopleuron well developed and moderately convex, evenly covered with delicate, superficial reticulations. Legs ( Figure 2 A–E) with all coxae and femora densely, but superficially reticulate; profemur 1.26 times as long as protibia; mesofemur 0.91 times as long as mesotibia and the mesotibia 1.5 times as long as protarsus; mesotibia with a row of six apical pegs, and with very long tibial spur equal in length to basitarsus; mesotarsi 1–4 ventrally with different numbers of pegs and stout setae on each tarsomere: basitarsus having 10 pegs in arrangement of two lines, one complete line with seven pegs nearby outer margin and another line with three pegs only in apical third of length running parallel, second tarsus having four pegs arranged in a curved line, third and fourth tarsi having three pegs in arrangement of oblique line respectively; metacoxa well developed, cordiform, 1.23 times as wide as long; metafemur and metatibia stout, 2.6 and 5.4 times as long as wide, respectively; metatibia with two apical spurs, the outer spur 0.5 times as long as the longer inner spur.

Metasoma in dorsal view elliptical ( Figure 1B ), about 1.44 times as long as wide, about 0.86 times as wide as mesoscutum, and as long as mesosoma (in natural, airdried specimens, metasoma severely collapsed with dorsum deeply sunken except for tergite 1, its width about 0.82 times length of mesoscutum and its length 1.58 times its width); cercus located at about basal third, with three long bristles; all tergites shiny without reticulation except last tergite with very dense, tiny punctures; tergites bare except basal tergite with three to four short setae laterally and with relatively dense setae behind spiracle; in lateral view apex of metasoma truncate ( Figure 1A ) with hypopygium extending to about same level as last tergite, and with triangular, densely setose ovipositor sheath exposed between them ( Figure 1A ); hypopygium ventrally with conspicuous setae, its posterior margin deeply excised medially, in ventral view appearing as a subcircular hollow ( Figure 2E ).

Male ( Figure 1E )

Length 1.9 mm. Similar in colour and structure to female except for antenna. Scape conspicuously dilated and appearing flattened apically, about 2.2 times as long as wide, and 0.58 times as long as eye height; pedicel short, its length only 0.6 times length of funicle 1; combined length of pedicel plus flagellum 1.18 times head width; flagellum light yellow with very long setae, the setae dorsally on funicle 1–5 more than 2.0 times as long as width of funicular; funicle 1 the longest segment, about 1.45 times as long as funicle 2, funicles 2–6 all the same length; clava two-segmented, about as long as distal two funicle segments combined.

Type material

Holotype. ♀, China: Jixing Forest Farm, Jile Village , Meihekou City , Jilin Province, emerged 1 July 2005 from larva of Massicus raddei collected on 16 May 2005 and reared in laboratory.

Paratypes. 160♀ and 40♂ with same data as holotype ; 160♀ and 40♂, 28 June 2005, reared from larva of same host from same locality .

Distribution

China: Northeastern China, including Jilin, Liaoning and Helongjiang provinces, as well as Inner Mongolia. The species may eventually be found throughout China where its host, the oak longhorn beetle, M. raddei occurs.

Etymology

The species epithet is derived from the species name of its host, Massicus raddei .

Diagnosis

We have compared the new species with original descriptions of all other described species of the genus, and found that the new species is different from all other species in the genus with the following characters: 1) female body length 2.1 mm (others less than 1.6 mm); 2) female antenna with funicle 1 as long as wide and funicles 2–4 notably wider than long ( Figure 1F ), combining male funicles 1–5 each with very long setae and the setae dorsally more than 2.0 times as long as width of its own funicle segment ( Figure 1E ). The characters above are particularly similar to the Japanese species Cerchysiella togashii Tachikawa 1988 , which is also a parasitoid of cerambycid species ( Mesosa longipennis Bates ), but can be distinguished from it by: 1) female length 2.1 mm (the latter 1.4 mm); 2) female temple 0.28 times as long as eye length (the latter temple not developed); 3) female with pedicel 0.7–0.8 times as long as combined length of funicle 1 plus 2 (the latter with pedicel as long as both funicular segments combined) and all funicle segments much longer than in the latter, particularly funicle 1 as long as wide (the latter with funicle 1 much wider than long); 4) male with funicle 1 1.5 times as long as funicle 2 and each of the other funicular segments (the latter male with funicle 1 as long as funicle 2 or other funicular segments).

Biological observations

Cerchysiella raddeii Yang sp. nov. is a gregarious koinobiont endoparasitoid inside the larva of M. raddei . A total of 209 mature larvae of the longhorn beetle were collected on 16 May 2005 from four split oak tree trunks from the type locality and reared as described in the Material and methods section. All the longhorn beetle larvae were active and fed normally in the beginning, but after 2 weeks, 14 larvae ceased feeding, their colour changed from milk-white to grey-yellow, and they died ( Figure 3A ), after which the larval body gradually became red and hardened ( Figure 3B ). Adult wasps emerged from these 14 host larvae between June 26 and July 1 ( Figure 3C ), indicating a parasitism rate of 6.7% from our rearing. All the wasps from a single larva emerged within about 1.5 hours from only three to six holes that were chewed in the mummy body wall by the first group of females to emerge. The contents and organs of the host larvae were consumed by the parasitoids ( Figure 3D ). The number of wasps and the female: male sex ratio of the emerged wasps from 11 host larvae were counted and calculated ( Table 1 ). The wasps that emerged from the other three host larvae were used for biological control tests, so were not counted.

Cerchysiella raddeii appears to have the characteristics of an excellent biological control agent for suppression of the longhorn beetle M. raddei because of a relatively high parasitism rate, the large number of individuals reared from a single host larva (average 1083.82), and the high female: male sex ratio (9.67: 1, df = 1,20, F = 183.89, P <0.0001) ( Table 1 ).

Figures

Figure 1. Cerchysiella raddeii Yang, sp.nov. (A) Female, lateral view; (B) female, dorsal view; (C) female, head, dorsal view; (D) female, head, frontal view; (E) male, antenna; (F) female, antenna; (G) female, forewing.

Figure 2. Cerchysiella raddeii Yang, sp.nov., female. (A–C) Legs, except coxae, (A) fore leg, (B) middle leg, (C) hind leg; (D) newly emerged adults; (E) ventral view.

Figure 3. Mature larva of Massicus raddei parasitized by Cerchysiella raddeii Yang, sp.nov. (A) Newly dead larva; (B) dead larva after becoming hard and reddish; (C) wasps emerging from a parasitized larva; (D) opened mummy of larva with internal organs consumed by the larvae of Cerchysiella raddeii.