Peristenus rubricollis (Thomson), 1973

Goulet, Henri & Mason, Peter G., 2006, Review of the Nearctic species of Leiophron and Peristenus (Hymenoptera Braconidae: Euphorinae) parasitizing Lygus (Hemiptera: Miridae: Mirini:), Zootaxa 1323 (1), pp. 1-118 : 37-41

Peristenus rubricollis (Thomson)

( Figs. 9 habitus, 20, 21, 23, 24, 29, 30, 46, Tables 7 and 8)

Euphorus rubricollis Thomson, 1891: 1749 . Type locality: Sweden, Gualof. Lectotype, male (Zoological Institute, Lund, Sweden) not seen, designated by Loan (1974b) and labelled: “Glf. [= Gualof]; rubricollis (handwritten by Thomson).

Leiophron rubricollis ; Shenefelt, 1969: 46.

Peristenus rubricollis ; Loan and Bilewicz­Pawinska, 1973: 274.

Peristenus conradi Marsh, 1992: 484 . Type locality: United States, Delaware, Newark. Holotype, female ( USNM) . Holotype reared from a nymph of Adelphocoris lineolatus , collected in May 27, 1988, and emerged in March 22, 1989. NEW SYNONYM.

Diagnosis. Mesoscutum densely punctate, without occipital carina in upper third of head, metacoxa light reddish brown to brown, and flagellum 21–24 flagellomeres in females and 20–24 in males.

Description. FEMALE. Colour. Body coloured as follows: head dark brown or black

except for light reddish brown clypeus and face ( Fig. 20 ) and reddish brown spot behind eye in dorsal 0.3 (spot almost extended to occipital carina) ( Figs. 23 , 30 ); mesosoma dark brown or black ( Fig. 46 ). Legs and palpi straw coloured except for brown tarsomere 5 and light reddish brown to dark brown metacoxa ( Fig. 46 ). Flagellum straw coloured at base shifting to reddish brown in apical 0.3–0.6. Stigma brown except straw coloured in basal third (as in Figs. 57 , 59, 60 ).

Structure. Flagellum with 21–24 flagellomeres (respectively 11%, 43%, 35% and 11% of 84 specimens) and flagellomeres enlarged in apical 0.5. Length of gena behind eye 0.90–1.05 times as long as length of eye. Height of eye 1.2–1.3 times as long as minimum distance between inner eye margins. Maximum width of head behind eyes subequal (0.93–0.97) to maximum head width at eye level. Occipital carina absent in dorsal third or at most suggested by transverse sculpture. Metasomal tergum 1 with lateral edges clearly convergent (posterior margin 2.0–2.3 times as wide as narrowest width near base) and elongate (medial length of tergum 1.6–1.9 times maximum width at posterior end). Radial cell 0.5–0.9 as long as stigma width. Forewing vein r lacking (vein RS at junction with vein r straight or angular), and basal cell almost completely densely pubescent and about as densely pubescent as 1 st discal cell.

Sculpture. Punctures on vertex, frons and mesoscutum about 15–25 µm in diameter (similar to diameter of ommatidia). Punctures 40–80 µm apart on vertex and 15–25 µm apart on frons, 25–75 µm apart on mesoscutum. Punctures on mesopleuron densely punctate but smooth anteriorly. Clypeus glabrous or with few setae except for row of long setae along anterior margin. Metasomal tergum 1 with about 10–12 longitudinal ridges, these commonly anastomosing on disc and forming a puncture­like sculpture.

MALE. Colour. Body colour pattern distinctly paler than in female, with clypeus and face light reddish brown, and rest of head reddish brown except for black stripe from antennal sockets to occipital carina and on medial portion of occiput ( Figs. 21, 24 , 29 ). Prothorax and most of mesothorax reddish brown.

Structure. Flagellum with 20–24 flagellomeres (respectively 7%, 49%, 33%, 7% and 4% of 81 specimens) and flagellomeres narrow in apical 0.5. Height of eye 0.88–1.0 times as long as minimum distance between inner eye margins. Otherwise structure and sculpture as in female.

Taxonomic notes. In North America, P. conradi was considered as specifically distinct from P. rubricollis because the North American population is parthenogenetic; only a few males are known. Are the two species specifically distinct?

Morphologically, all character states mentioned for P. conradi (e.g., generally darker colour pattern, forewing vein RS angular at junction with stigma, and notauli weakly indicated) fall within the range of variation of P. rubricollis , and statistical parameters are similar except that those of P. conradi show generally shorter linear measurements.

Biologically, both populations are univoltine on the first nymphal generation of Adelphocoris and Lygus , have a marked preference for Adelphocoris nymphs, and require

3–4 weeks (on average 23 days for P. conradi , and 30.8 days (SD 7.5 days based on 59 specimens) for P. rubricollis in southern Germany) to emerge after being warmed up to 20ºC. This is significantly longer than less than 2 weeks with typical univoltine Peristenus species associated with the first generation of Lygus nymphs.

However, the lack of structural differences is not proof enough to consider the two populations as conspecific.

In North America, W. H. Day (pers. com.) showed differences in number of days elapsed between diapause termination and adult emergence. Specimens of P. conradi and the European P. rubricollis emerged on average after 23 days from Adelphocoris . European P. rubricollis emerge after a markedly longer period when reared from Lygus . He concluded that the biology of P. conradi is different from that of the bisexual P. rubricollis as shown by the markedly greater number of days elapsed to emergence when Lygus nymphs are the hosts. Is the difference in emergence periods related to host size? Adults of P. conradi are quite clearly smaller than typical P. rubricollis . Perhaps larvae of P. rubricollis find it more stressful developing in smaller Lygus nymphs.

The flagellomere frequency distribution is also affected by host. Based on European specimens of P. rubricollis , the frequency distribution of the number of flagellomeres is highest at 22 in females and 21 in males for specimens reared from Lygus whereas this number is highest at 23 in females and 22 in males for specimens reared from Adelphocoris nymphs. In North America, almost all studied specimens of P. conradi were reared from A. lineolatus . Despite a large host, most North American females of this species have 22 flagellomeres.

What would happen if adults of P. conradi were exposed to males of P. rubricollis? Would the progeny simply reintegrate into the P. rubricollis gene pool? What type of progeny would unmated females of P. rubricollis produce in the absence of males? We consider that the P. conradi – P. rubricollis problem is not satisfactorily resolved. W. Day (pers. com.) tested for Wolbachia . There was no evidence of its presence, though it was found in P. digoneutis .

Day et al. (1998) discussed several examples of species with identical morphology that are bisexual in Europe and parthenogenetic in North America. The North American species were considered specifically distinct from their European population. There are also examples of other species that are bisexual in Europe, but parthenogenetic in North America and are considered conspecific (e.g., Dolerus nitens Zaddack ( Hymenoptera : Tenthredinidae ) (Goulet 1983) and Eupelmus vesicularis (Retzius) ( Hymenoptera : Eupelmidae ) ( Gibson 1990)). At present, it is best to consider P. conradi as conspecific with P.rubricollis .

Adults of P. rubricollis have been confused with those of P. digoneutis Loan ( Loan 1973) . Loan (1973) segregated the two species on colour pattern and number of flagellomeres. In addition, adults of the two species differ in their preferred hosts (though both are associated with Lygus ) and their life cycle. A summary of measurements differing between P. rubricollis and P. digoneutis is given in Table 7 (for North American females) and Table 8 (for European males and females).

Adults of P. rubricollis differ from those of P.relictus by puncture development on the mesoscutum (as in Fig. 43 ), face colour ( Figs. 20, 21 ), the spot development behind eye of females, and the head colour pattern of males, and the leg colour ( Figs. 9 , 46 ). A summary of measurement differences between P. rubricollis and P. relictus is given in Table 7 (for North American females) and Table 8 (for European males and females).

Host and biological notes. In North America and in Europe, P. rubricollis has been reared from species in two genera of Mirini , mainly nymphs of Adelphocoris seticormis (Fabricius) and Adelphocoris sp. , and occasionally from those of Lygus rugulipennis and Lygus spp. In North America, this species has been reared from nymphs of Adelphocoris lineolatus and Lygus lineolaris . Adults occur from May to early July in North America (a few specimens were reared from nymphs of the second generation of Adelphocoris sp. in central Europe) with peak of abundance in early June. In North America, this is a univoltine species and in Europe it is almost completely univoltine. Loan and Bilewicz­ Pawinska (1973) published the biology of this species.

Material examined and range. About 388 adults were studied including, 228 from Europe and 160 (2♂, 96♀, 62♂ / ♀) from North America. We have included W. H. Day published records as “( WHD)” with no reference to the number of specimens ( Day et al. 1998, 2000). Most of these specimens were seen and they were all correctly identified. Several attempts at establishing this species were made between 1978 and 1990. By 1988, it was certainly established at Newark, Delaware. Day et al. (1992, 1998, 2000) summarized the history of introduction into North America and its subsequent expansion. The species has been encountered between northern Delaware and southern Quebec ( Day et al. 2000; Broadbent et al. 1999).

CANADA. QC: near St. Constant (2♀) . USA. DE: New Castle Co., Newark (2♂, 73♀, 51; CNCI, USNM, USDA) . NJ: Blairstown (7♀, 1; USDA) ; Mt Holly (9♂, 8♂ / ♀; USDA) ; Rancocas (2♀, 2; USDA) ; Newton (1♀); Burlington Co., near Juliustown ( WHD) ; Cumberland Co., Carmel (1♀; USDA) ; Gloucester Co., near Harrisonville ( WHD) ; Middlesex Co., near Cranbury ( WHD) ; Monmouth Co., near Marlboro ( WHD) ; Salem Co., near Cohansey ( WHD) . NY: Dutchess Co., Hyde Park ( WHD) ; Ulster Co., High Falls (1♀; USDA) ; Ulster Co., Wallkill ( WHD) .

Peristenus pallipes complex. The following nine species of Peristenus on Lygus are native and part of a difficult species complex known from temperate and boreal regions of the Holarctic region. The complex is so diverse that most of its species are difficult to characterize as they could hardly be recognized on structures alone. Without detailed biological data from known hosts most of these species could not have been recognized.

Adults have a complete or almost complete occipital carina dorsally ( Fig. 33 ), which distinguishes them from the three introduced species. They also are densely punctate on the frons, and over all or most of the median lobes of the mesocutum. The flagellum is dark brown to black at least in its apical third, and it consists of 17 or more flagellomeres in females and 20 or more flagellomeres in males.

The nine species are divided into two groups based on puncture development on the frons, colour pattern of the metatibia, length of the flagellum, and minimum distance between eyes.

Peristenus dayi group. This group consists of two species, P. braunae and P. dayi . Punctures are large and dense on the vertex between inner eye margin and lateral ocellus ( Fig. 26 ). The metatibia is straw coloured or pale reddish brown and is at most darkened in apical 0.2–0.3, and metatarsomere 1 is straw coloured ( Fig. 11 ). In females, the length of the flagellum relative to maximum width of head between the outer eye margins is above 2.78, and the height of the eye relative to minimum distance between the inner eye margins is below 1.23 in almost all specimens (Tables 9 and 10) ( Fig. 17 ).

Figures

FIGURES 6–12. 6–9. Habitus with frontal view of head. Codes: “a” clypeal colour; “c” metacoxal colour; “f” metafemoral colour; “g” facial colour; “h” genal spot. 10–12. Lateral view of metatibia.

FIGURES 13–24. 13–22. Frontal view of head. Code: “a” ventral edge of clypeus. 23–24. Dorsal view of head.

FIGURES 25–36. 25–27. Dorsal view of head with insert to show sculpture. 28–31. Lateral view of head. 32–33. Posteroir view of head. Code: “a” dorsal end of occipital carina. 34. lateral view of antenna. 35–36. Last five flagellomeres in lateral view.

FIGURE 37–49. 37. Lateral view of antenna. 38–39. Last six flagellomeres in lateral view. 40–44. Dorsal view of mesosoma. 45–49. Lateral view of mesosoma.

FIGURES 50–58. 50–52. Forewing. 53–54. Basal and subbasal cells of forewing. 55–58. Radial cell and stigma of forewing.

FIGURES 59–66. 59–63. Radial cell and stigma of forewing. 64. Hind wing. 65–66. Basal and subbasal cells of hind wing.