Diversinervus, Silvestri, 1915

Noyes, John Stuart, 2023, ENCYRTIDAE OF COSTA RICA (HYMENOPTERA: CHALCIDOIDEA), 4 Subfamily Encyrtinae: tribes Arrhenophagini, Habrolepidini, Cerapterocerini, Cheiloneurini, Trechnitini, Cercobelini, Polaszekiini, Protyndarichoidini, Gahaniellini and Syrphophagini (part), mainly primary parasitoids and hyperparasitoids of Coccoidea and Psylloidea (Hemiptera), Taxonomic Monographs on Neotropical Hymenoptera (Oxford, England) 2 (11), pp. 1-921 : 490-492

Genus DIVERSINERVUS Silvestri

Diversinervus Silvestri, 1915:301-304 . Type species: Diversinervus elegans Silvestri , by original designation and monotypy.

Cheiloneuroides Girault, 1915a:96 . Type species: Cheiloneuroides bicristatus Giraulr , by original designation and monotypy. Synonymy with Diversinervus by Girault (1917a:37).

Female. Length about 1.0- 2.1mm.

Body largely brownish yellow to orange, with some distinctly metallic or dusky areas, sometimes mostly dark brown and metallic; gaster dark brown, syntergum often orange; mesoscutum in posterior 0.25X or so with a dark, metallic band that contrasts with the orange anterior part; legs mostly white to pale orange with some dark brown areas; fore wing mainly infuscate from level of proximal part of parastigma to apex, infuscation slightly stronger in middle of wing.

Head at least about 4X as wide as frontovertex, in profile dorsally hardly convex from occipital margin to transfacial ridge, usually sharply bent at about 70° at transfacial carina and from there virtually straight to mouth margin; occipital margin sharp, weakly carinate; area adjacent to eye margin between posterior ocellus and occipital margin with an oval, shiny bottomed depression; eye clothed with conspicuous setae, each about as long as diameter of facet; facial depression usually dorsally sharply delimited by a strong, curved transfacial ridge, in some species facial depression delimited by a more rounded ledge; malar sulcus absent; antenna with scape broadened and flattened, about 2-3.5X as long as broad, pedicel and flagellum subcylindrical, funicle segments subequal in length but distinctly broader distally, club clearly broader than F1, with a slight, oblique apical truncation; mandible with three acute teeth, upper tooth sometimes rounded; palp formula 4-3.

Mesoscutum usually with a distinct tuft of setae in middle (Fig. 1233); notaular lines absent; scutellum with a distinct subapical tuft of setae; sculpture on mesoscutum and scutellum similar, finely striate to longitudinally elongate reticulate arranged in more or less concentric whorls around an imbricate reticulate area in middle, posterior part of scutellum generally with some shallower imbricate-reticulate sculpture; mid tibia with a subbasal external carina in proximal half; fore wing fully developed or strongly reduced and hardly reaching second gastral tergite; fully developed fore wing about 2.7-3.0X as long as broad with apices of postmarginal and stigmal veins connected by a naked, hyaline streak, submarginal vein with parastigma (Fig. 1232) strongly downcurved and clearly expanded towards proximal end of parastigma, marginal vein about 4-8X as long as broad, up to 2X as long as stigmal vein and up to 3X as long as postmarginal vein, basal cell and costal cell often more or less naked, filum spinosum present, composed of about 5 modified setae; axillae moderately raised above level of scutellum.

Gaster with hypopygium reaching about half way along gaster; ovipositor longer than mid tibia, slightly exserted; gonostylus free.

Male. length about 0.8-1.3mm.

Body generally dark brown with a slight metallic sheen, head occasionally completely or partially yellow; fore wing hyaline; legs mostly white to pale yellow; head about 2X as wide as frontovertex and without a transfacial carina; antenna with 6 funicle segments, all longer than broad and clothed with whorls of long setae, the longest of which are about as 5-6X as long as diameter of segments; clava entire and slightly shorter than F5 and F6 combined; sculpture of mesoscutum mainly imbricate-reticulate but very slightly longitudinally elongate anteriorly, scutellum with similar sculpture to that of female; fore wing with marginal vein about 2.5X as long as broad, subequal to stigmal vein which is clearly shorter than postmarginal vein; phallobase with parameres short, digiti each about 2X as long as broad and with a single apical tooth; aedeagus about 0.4X as long as mid tibia, slender but very slightly broadened subapically with apex rounded.

DISTRIBUTION. Mainly Afrotropics and southern Asia to Australia, although a species which may be cervantesi (Girault) was recently found in a greenhouse in Canada (S. Marshall, pers. comm.) and D. elegans Silvestri has been introduced into North America and Europe and is newly recorded from Costa Rica (see below).

HOSTS.Recorded as primary parasitoids of soft scales ( Hemiptera : Coccidae ) (for a comprehensive list see Rosen & Alon, 1983).

BIOCONTROL. Three or four species of Diversinervus species have been introduced into various countries for the control of soft scale pests with varying degrees of success. In 1937, Diversinervus smithi Compere, 1940 was imported into California ( USA) from South Africa for the control of Parasaissetia nigra (Nietner) but did not become established (Bartlett in Clausen, 1978). In 1976-1977, Diversinervus cervantesi (Girault, 1933) was imported into Israel from South Africa for the control of Saissetiae oleae (Olivier) and became established. At about the same time an unidentified species of Diversinervus was imported for use against Ceroplastes sp. but not released (Argov & Rössler, 1988). Diversinervus nr stramineus Compere was released in Australia (Queensland and New South Wales) from Kenya in 1999 for the control of Coccus viridis (Green) and quickly became established and contributed towards the successful control of the pest (Smith et al., 2004). The most frequently used species, D. elegans , has been used in several different European countries, the USA and Australia for the control of several soft scale pests with little success (see below).

COMMENTS. Diversinervus is probably most easily confused with Cheiloneurus Westwood and Anisophleps Fidalgo , species of all three genera having a subcylindrical flagellum, a generally largely infuscate fore wing with the apices of the postmarginal vein and stigmal vein connected by a naked, hyaline streak, tuft of setae at the apex of the scutellum and hypopygium not reaching the apex of the gaster. It is important to be able to separate Diversinervus and Anisophleps from Cheiloneurus reliably because it is likely that all species of Cheiloneurus are hyperparasitoids of scale insects whilst those of Diversinervus and Anisophleps are primary parasitoids. This would have important implications for any use in biological control introductions. The most reliable character by which to separate Diversinervus and Anisophleps from Cheiloneurus is the fore wing venation. In fully winged species of Cheiloneurus the postmarginal and stigmal veins are very short in relation to the marginal vein, in most cases the marginal vein is more than 1.5X as long as the stigmal vein and at least 3X as long as the postmarginal vein whilst in fully winged species of Diversinervus and in Anisophleps the marginal vein is usually not longer than the either the stigmal vein or the postmarginal vein. Separation of brachypterous specimens is more difficult, but in all Diversinervus and Anisophleps the sculpture of the mesoscutum always has a tendency to form whorls around a central imbricate reticulate area. These whorls may be in the form of striate sculpture through lineolate-reticulate to imbricate sculpture but always in the posterior part of the mesoscutum the direction of the sculpture merges rather than diverges as in Cheiloneurus . Unfortunately, this difference may be difficult to appreciate where the sculpture of the mesoscutum is shallow or not well-defined. In addition Cheiloneurus never has a tuft of setae on the mesoscutum or clearly differentiated, scattered scale like setae anteriorly on the mesoscutum whereas in most species of Diversinervus there is a clear tuft of setae in the middle of the mesoscutum or scattered scale-like setae on the anterior part of the mesoscutum. In addition, in Diversinervus , the infuscation of the fore wing always extends to the apex of the wing, whereas in the majority of species of Cheiloneurus the apex frequently has a distinct hyaline area. Females of Diversinervus can be distinguished from those Anisophleps by the presence, in the latter, of a darker, curved, subapical band delimiting the distal part of the infuscate area of the fore wing with the apex of the wing being hyaline and by the shape of the anterior margin of the transfacial carina in dorsal view. In Diversinervus the transfacial carina is roundly convex in dorsal view, whereas in Anisophleps it is strongly medially invaginate.

See also comments under Ludesia (p. 179).

IDENTIFICATION. 12 species known: Prinsloo, 1985 (key to 7 southern African species); Hayat, 2006 (key and review of 4 Indian species); Rosen & Alon, 1983 (catalogue of 10 species).