Trechnites, Thomson, 1876

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 : 567-568

Genus TRECHNITES Thomson

Trechnites Thomson, 1876:118 . Type species: Metallon fuscitarsis Thomson , by subsequent designation of Erdös (1957:56).

Psylledontus Crawford, 1910:88 . Type species: Psylledontus insidiosus Crawford by monotypy and original designation. Synonymy with Trechnites by Ferrière (1961:39).

Metallonella Girault, 1915:77 . Type species: Metallonella australiensis Girault , by original designation. Synonymy with Psylledontus by Girault (1924:4) and synonymy with Trechnites by Ferrière (1961:39).

Female. Overall length about 0.8-1.7mm.

Head and thorax dull, dark brown to largely metallic blue or green.

Head with occipital margin narrowly rounded or sharp, sometimes carinate; eyes distinctly setose, setae about as long a diameter of facet; antenna with scape elongate, subcylindrical to slightly broadened and flattened, pedicel relatively elongate, as long as F1-F2 or sometimes F1-F3 combined; funicle 5-segmented; clava 3-segmented (solid in some extralimital species), usually obliquely truncate at apex with sensory area extending along much of ventral part of apical segment; mandible variable, with three subequal teeth, 2 lower teeth and a truncate upper tooth, 2 teeth and a broad upper truncation, two short teeth and a median truncation or 4 teeth; palp formula 3-3 or 3-2.

Mesoscutum with notaular lines present, partial or complete; fore wing about 2.3-2.4X as long as broad; parastigma not swollen to slightly swollen and weakly triangular; marginal vein punctiform, often not reaching anterior wing margin; postmarginal vein virtually absent; stigmal vein long and forming an angle of about 50° with anterior wing margin; filum spinosum present, composed of 4-8 pegs-like setae; mesopleuron not expanded posteriorly, separated from posterior margin of propodeum by about diameter of spiracle so that propodeum laterally is broadly in contact with hind coxa and clearly separating mesopleuron from base of gaster.

Gaster with apex of syntergum transversely truncate or with a membranous invagination either side of apex; paratergites absent; hypopygium extending at least to level with apex of syntergum, with a short to moderately long mucro (posterior median projection) that encloses ovipositor; gonostylus immovably fused to the relatively broad second valvifer; ovipositor not exserted or hardly exserted.

Male. Length about 0.7-1.3mm.

Similar to female but for solid clava and genitalia; pedicel sometimes strongly swollen; clava solid; genitalia with phallobase about 4X as long as broad; digitus about 3-4.5X as long as broad with 1-3 apical teeth, parameres weakly developed, apical set present; aedeagus 6-9X as long as broad, broadest subapically, about 0.5-0.8X as long as mid tibia.

DISTRIBUTION. Cosmopolitan.

HOSTS. Reliably reported as primary endoparasitoids of nymphs of jumping plant lice ( Hemiptera : Psyllidae , Triozidae ) (see Noyes, 2019). Records of other hosts (Coccoidea and Aphididae ) or as hyperparasitoids require confirmation.

BIOCONTROL. Trechnites insidiosus Crawford (as psyllae Ruschka ) and an unidentified of Trechnites species (possibly sadkai Guerrieri & Noyes, 2009) were released in the western United States of America from Europe, Iran and Afghanistan from 1966-1990 for the control of Cacopsylla pyricola (Förster) ( Hemiptera : Psyllidae ) a major pest of pear. Trechnites insidiosus was already present in North America and therefore data are not available recording the effectiveness of the

introduced parasitoids. The unidentified species from Europe was recovered in Washington state in 1991 and the Afghanistan biotype was recovered a few generations after its release in California in about 1978 ( Unruh et al., 1995). Trechnites insidiosus is currently being tested for mass release or conservation in order to maximise natural control of pear psylla in the Western USA ( Le Goff et al., 2021).

COMMENTS. Species of Trechnites can be separated from all other encyrtid parasitoids of Psylloidea by the 5-segmented funicle in both sexes. In all other genera the funicle is either 6-segmented (e.g., Psyllaephagus , Arianus , Caldencyrtus , Dalek ) or 4-segmented ( Cercobelus ). Trechnites is extremely close to Coccidaphycus Blanchard (1940) and the two should probably be treated synonymously. However, given some very minor morphological differences, I am retaining Coccidaphycus as a valid genus until fresh material can be examined and the true host relationship can be confirmed. The genus differs from Trechnites in having a 4-segmented maxillary palp and tridentate mandibles and is reported to be a parasitoid of Coccoidea. All species currently placed in Trechnites have a 3-segmented maxillary palp. The mandible of Trechnites is variable. Some species, including the type species, have two acute lower teeth and a truncate upper tooth, the majority seem to have short, acute upper and lower teeth and a broadly truncate middle tooth which sometimes is distinctly concave giving the appearance of two middle teeth (i.e., 4-toothed mandible), very few species have 3 fairly even, short or somewhat rounded teeth. However, in Coccidaphycus nigricans Blanchard the mandible appears to have 3, fairly long, very acute teeth ( Blanchard, 1940, Fig. 2c). Crucially, the structure of the hypopygium of Coccidaphycus nigricans Blanchard is not mentioned by Blanchard (1940) or De Santis (1964) and is therefore unknown. This would help determine whether or not to treat the two genera synonymously because the hypopygium of Trechnites is very characteristic in its shape (see Guerrieri & Noyes, 2009). Other characters that have been used to separate the two genera, such as colour, extent of sensory area on apical segment of clava, sculpture of mesoscutum and scutellum and variation in the marginal vein (see Noyes & Hayat, 1984; Guerrieri & Noyes, 2009) are too variable to be reliable. The apparent difference in host relationships may be grounds for maintaining the two genera separately. All species of Trechnites are parasitoids of nymphs of jumping plant lice (Psylloidea) whereas the type series of Coccidaphycus nigricans was reared from a collection of scale insects (Coccoidea). However, there is some doubt that coccid hosts listed by Blanchard (three separate families: Monophlebidae , Kerriidae and Coccidae ) are the true hosts. It seems likely that that the type series (4E and 1G) was reared from a collection of soft scales on their host plant that were placed in a container and not from individual scale insects. It is possible that psyllid nymphs were mixed up with these scale insects and it was from these that the parasitoids actually emerged.

IDENTIFICATION. Worldwide, 34 species known, including 4 species described below as new. For aids to identification see Guerrieri & Noyes, 2009 (revision of 5 European species); Trjapitzin, 1989 (key to 7 Palaearctic species); Prinsloo, 1981 (identification of four Afrotropical species); Ayyamperumal & Manickavasagam, 2018 (key to 11 Indian species); Zu & Li, 2016 (identification of three species from China).