Resolving the Taxonomic Status of Potential Biocontrol Agents Belonging to the Neglected Genus Lipolexis Förster (Hymenoptera, Braconidae, Aphidiinae) with Descriptions of Six New Species †

Simple Summary Lipolexis is small but widely distributed genus across Europe and Asia. Nevertheless, its taxonomic distinctiveness was subsequently questioned by some authors who considered it as a synonym of the genus Diaeretus. Although Lipolexis is widely distributed and one species (Lipolexis oregmae Gahan) is an important biological control agent, the last taxonomic study on it was conducted more than 50 years ago. Our study employs an integrative approach (morphology and molecular analysis (COI barcode region)), to examine Lipolexis specimens that were sampled worldwide, including specimens from BOLD database. It led to the description of six new species. Each of the new species possesses clear morphological characters that distinguishes it from its congeners. Our findings suggest that two groups can be differentiated within the genus—oregmae and gracilis. Furthermore, we present a key for the identification to all known Lipolexis species of the world. Abstract Lipolexis is a small genus in the subfamily Aphidiinae represented by one species in Europe (Lipolexis gracilis Förster) and by four in Asia (Lipolexis wuyiensis Chen, L. oregmae Gahan, L. myzakkaiae Pramanik and Raychaudhuri and L. pseudoscutellaris Pramanik and Raychaudhuri). Although L. oregmae is employed in biological control programs against pest aphids, the last morphological study on the genus was completed over 50 years ago. This study employs an integrative approach (morphology and molecular analysis (COI barcode region)), to examine Lipolexis specimens that were sampled worldwide, including specimens from BOLD database. These results establish that two currently recognized species of Lipolexis (L. gracilis, L. oregmae) are actually a species complex and also reveal phylogenetic relationships within the genus. Six new species are described and a global key for the identification of Lipolexis species is provided.

The five sequences initially assigned to L. oregmae were separated into two distinct clades with an average genetic distance of 19.9%. A haplotype network supported the presence of two species (L. oregmae, Lipolexis bengalensis sp. n) with high sequence divergence (77 mutational steps) at COI (Figure 2).
Insects 2020, 11, x 2 of 33 following array: parasitoid/country of origin/aphid and plant host (if available)/BOLD, GenBank or private code. Green branches represent L. oregmae lineage, black L. gracilis.
The five sequences initially assigned to L. oregmae were separated into two distinct clades with an average genetic distance of 19.9%. A haplotype network supported the presence of two species (L. oregmae, Lipolexis bengalensis sp. n) with high sequence divergence (77 mutational steps) at COI (Figure 2). The 58 sequences recovered from members of L. gracilis group included 26 haplotypes that fell into two main groups ("group 1" and "group 2") ( Figure 1) with the average sequence divergence of 11.4%. The first group included European specimens which were separated into two clusters with an average COI distance of 7.3% (L. gracilis s.s., Lipolexis labialis sp. n.). The second group included three clades: the first represented by a single specimen from China (Lipolexis takadai sp. n.) with an average genetic distance of 4.5% and 7.2%, from the other two clades. The second clade (Lipolexis pelopsi sp. n.) included six individuals from the Mediterranean, while the third included specimens from the Middle East, the Orient, and Spain. The average evolutionary divergence between the Mediterranean and the third clade was 8%. The Middle East and Oriental region clade, which also contained several specimens from Spain, was further separated into two clades (Lipolexis pakistanicus sp. n. and Lipolexis peregrinus sp. n.) with mean distance of 2.2%. The 26 haplotypes of L. gracilis s.l. (Figure 3) were separated into six distinct groups that corresponded to the named clades shown in the phylogenetic tree.
Morphological analysis of the Lipolexis specimens in each clade revealed diagnostic differences supporting the recognition of six new species which is in concordance with the phylogenetic results. The balance of the Results section describes the new taxa and redescribes L. gracilis and L. oregmae. Figure 2. Haplotype network of COI sequences obtained from specimens in the L. oregmae group. The circle size indicates the number of specimens with a particular haplotype; each black dot represents a nucleotide substitution.
The 58 sequences recovered from members of L. gracilis group included 26 haplotypes that fell into two main groups ("group 1" and "group 2") ( Figure 1) with the average sequence divergence of 11.4%. The first group included European specimens which were separated into two clusters with an average COI distance of 7.3% (L. gracilis s.s., Lipolexis labialis sp. n.). The second group included three clades: the first represented by a single specimen from China (Lipolexis takadai sp. n.) with an average genetic distance of 4.5% and 7.2%, from the other two clades. The second clade (Lipolexis pelopsi sp. n.) included six individuals from the Mediterranean, while the third included specimens from the Middle East, the Orient, and Spain. The average evolutionary divergence between the Mediterranean and the third clade was 8%. The Middle East and Oriental region clade, which also contained several specimens from Spain, was further separated into two clades (Lipolexis pakistanicus sp. n. and Lipolexis peregrinus sp. n.) with mean distance of 2.2%. The 26 haplotypes of L. gracilis s.l. (Figure 3) were separated into six distinct groups that corresponded to the named clades shown in the phylogenetic tree.
Insects 2020, 11, x 2 of 33 following array: parasitoid/country of origin/aphid and plant host (if available)/BOLD, GenBank or private code. Green branches represent L. oregmae lineage, black L. gracilis.
The five sequences initially assigned to L. oregmae were separated into two distinct clades with an average genetic distance of 19.9%. A haplotype network supported the presence of two species (L. oregmae, Lipolexis bengalensis sp. n) with high sequence divergence (77 mutational steps) at COI ( Figure 2). The circle size indicates the number of specimens with a particular haplotype; each black dot represents a nucleotide substitution.
The 58 sequences recovered from members of L. gracilis group included 26 haplotypes that fell into two main groups ("group 1" and "group 2") ( Figure 1) with the average sequence divergence of 11.4%. The first group included European specimens which were separated into two clusters with an average COI distance of 7.3% (L. gracilis s.s., Lipolexis labialis sp. n.). The second group included three clades: the first represented by a single specimen from China (Lipolexis takadai sp. n.) with an average genetic distance of 4.5% and 7.2%, from the other two clades. The second clade (Lipolexis pelopsi sp. n.) included six individuals from the Mediterranean, while the third included specimens from the Middle East, the Orient, and Spain. The average evolutionary divergence between the Mediterranean and the third clade was 8%. The Middle East and Oriental region clade, which also contained several specimens from Spain, was further separated into two clades (Lipolexis pakistanicus sp. n. and Lipolexis peregrinus sp. n.) with mean distance of 2.2%. The 26 haplotypes of L. gracilis s.l. (Figure 3) were separated into six distinct groups that corresponded to the named clades shown in the phylogenetic tree.
Morphological analysis of the Lipolexis specimens in each clade revealed diagnostic differences supporting the recognition of six new species which is in concordance with the phylogenetic results. The balance of the Results section describes the new taxa and redescribes L. gracilis and L. oregmae.  Morphological analysis of the Lipolexis specimens in each clade revealed diagnostic differences supporting the recognition of six new species which is in concordance with the phylogenetic results. The balance of the Results section describes the new taxa and redescribes L. gracilis and L. oregmae.
Mesosoma. Mesoscutum ( Figure 4C) smooth, covering pronotum above; notaulices distinct in very short ascedent portion of anterolateral margin, effaced dorsally, with a series of 6-7 long setae along the latero-dorsal part of mesoscutum, almost reaching to scutellum. Scutellum nearly triangular, bearing 2 long setae on lateral margins. Propodeum ( Figure 4D) clearly areolated, with a wide central areola, with pronounced oblique antero-central carinae extending to the spriracles. External and dentiparal areolae of propodeum with 5-6 and 1-2 long setae in each side, respectively. Forewing ( Figure 4G) densely pubescent, marginal setae longer than the surface setae; venation hyaline; pterostigma triangular, 2.3× as long as wide and equal to R1 vein; vein r and RS long, reaching near the apex of the wing.
Metasoma. Petiole ( Figure 4E) long and slender, slightly widened at apex and narrow posteriorly; its length 2.6-2.9× as long as wide at spiracles; petiole is dorsally smooth, but it bears crenulated longitudinal carinae along the sides, a feature typical for the oregmae group, and two long setae near the base of petiole at each side. Ovipositor sheath long ( Figure 4F), wide at base and curved downwards, bearing scattered very long setae in the middle portion; distally dilated slightly. Length of ovipositor sheath 2.5-2.8× as long as maximum width at base and 7.3-7.6× as long as minimum width at tip. Second valvulae with a convex dorsal outline, second valvifer narrow, widened at the joint in point with ovipositor sheath.
Mesosoma. Mesoscutum ( Figure 5C) smooth, covering pronotum above; notaulices distinct in very short ascendant portion of anterolateral margin, effaced dorsally, with a series of 8-10 long setae along the latero-dorsal part of mesoscutum. Scutellum nearly triangular, bearing 2-3 long setae on lateral margins. Propodeum ( Figure 5D) areolated, with a wide central areola, sometimes with no clear anterior carinae. External and dentiparal areolae of propodeum with 2-3 and 1 long setae in each side, respectively. Central areola with rugosities. Forewing ( Figure 5G) densely pubescent, marginal setae longer than the surface setae; pterostigma triangular, 2.5-2.9× as long as wide and subequal to R1 vein (proportion between pterostigma length and R1 vein length 0.9-1.1); vein r and RS long, reaching near the apex of the wing.
Metasoma. Petiole ( Figure 5E) long and slender, slightly widened at apex; its length 2.7-3.2× as long as wide at the weak prominent spiracles; a pair of central carinae, distinctly prominent along dorsal surface of the petiole, diverging toward base. Ovipositor sheath strong, long and slightly curved ( Figure 5F), dilated at the apex. Length of ovipositor sheath 2.5× as long as wide at the base, and approx. 10× as long as tip.
Metasoma. Petiole ( Figure 6E) long and slender, slightly widened at apex; its length 2.8× as long as wide at spiracles, with prominent central carina. Ovipositor sheath ( Figure 6G) long and slender, strongly curved downwards, wide at base, narrowing in the last third and slightly wider at the tip. Length to width ratio of the ovipositor sheath is 2.7 at the widest site, and 10 at the tip.
Body length: 1.5-1.8 mm.  Mesosoma. Mesoscutum ( Figure 8C) smooth, covering pronotum above; notaulices distinct in very short ascedent portion of anterolateral margin, effaced dorsally, with a series of 6-7 long setae Mesosoma. Mesoscutum ( Figure 7C) smooth, covering pronotum above; notaulices distinct in very short ascedent portion of anterolateral margin, effaced dorsally, with a series of 6 to 10 long setae along the latero-dorsal parts of mesoscutum, reaching to scutellum. Specimens collected in Greece possess densely pubescent mesoscutum with 18 to 20 setae. Scutellum nearly triangular, bearing 5-6 setae on lateral margins. Propodeum ( Figure 7D) areolated, with a wide central areola, sometimes with undefined upper carinae. External and dentiparal areolae of propodeum with 5-6 and 0-1 long setae in each side, respectively. Forewing ( Figure 7G) densely pubescent, marginal setae long and longer than the surface setae; venation reduced; pterostigma triangular, 2.3-2.6× as long as wide and subequal to R1 vein; vein r and RS long, reaching near to the apex of the wing.
Metasoma. Petiole ( Figure 7E) long and slender, slightly widened at apex; its length 2.4-2.6× as long as wide at spiracles, slightly prominent in lateral margin; a pair of central carinae short, prominent along dorsal surface of the petiole; Ovipositor sheath narrow and curved downwards ( Figure 7F), dilated at the apex, bearing 3 large long setae in the middle portion. Ovipositor 3.1× as long as wide at the widest part and 9.1× as long as wide at the tip.
Distribution. Mediterranean distribution, recorded from Bosnia and Herzegovina, Montenegro and Greece.
Host. Species in the genus Aphis L. Etymology. Lipolexis pelopsi sp. n. takes its name after Pelops, mythological king of Peloponnese region, which is the area of the first collected specimens. Diagnosis. Lipolexis pakistanicus sp. n. belongs to "gracilis" group and shares the same number of maxillary (three) and labial palpomeres (one) as L. peregrinus sp. n. and L. takadai sp. n. However, it has a more elongate pterostigma than these species (2.9 length to width ratio in L. pakistanicus sp. n., vs. 2.6-2.7 and 2.4-2.7 in L. takadai sp.n. and L. peregrinus sp. n., respectively) ( Figure 8).  Mesosoma. Mesoscutum ( Figure 8C) smooth, covering pronotum above; notaulices distinct in very short ascedent portion of anterolateral margin, effaced dorsally, with a series of 6-7 long setae along the latero-dorsal part of mesoscutum, reaching to scutellum. Scutellum nearly triangular, slightly crenulated along lateral margins, bearing 2-3 long setae on lateral margins. Propodeum ( Figure 8D) clearly areolated, with a wide central areola, oblique antero-central carinae extending to the spriracles. External and dentiparal areolae of propodeum with 3-4 and without long setae in each side, respectively. Forewing ( Figure 8G) densely pubescent, marginal setae longer than the surface setae; venation reduced; pterostigma triangular, 2.9× as long as wide and little shorter than R1 vein (proportion between pterostigma length and R1 vein length 0.90); vein r and RS long, reaching near to the apex of the wing.
Metasoma. Petiole ( Figure 8E) slightly widened at apex; its length 2.7× as long as wide at spiracles, prominent in lateral margin; dorsally smooth but it bears short and strong mediodorsal carina with two short longitudinal carinae diverging along the sides to the posterior part of petiole. Petiole bears two very long setae along both sides near base. Ovipositor sheath ( Figure 8F) long, wide at base, curved downwards, with no visible setae; distally more dilated than in other species, upper part of the ovipositor sheath more sclerotized along the whole length. Length of ovipositor sheath 2.56× as long as wide at base and 6.5× as long as minimum width at tip. Diagnosis. Lipolexis peregrinus sp. n. belongs to "gracilis" group and possesses three maxillar palpomeres and one labial palpomere as L. takadai sp. n. and L. pakistanicus sp. n. However, it clearly differs from both species by having shorter F1 (proportions between length and maximum width at middle of F1 in L. peregrinus sp. n., 3.4-3.8 vs. 4.75 in L. takadai sp. n. and 4.25 in L. pakistanicus sp. n., respectively) and more elongated petiole (proportion between length and width of petiole at spiracles in L. peregrinus sp. n., 3.1-3.3 vs. 2.8 in L. takadai sp. n. and 2.7 in L. pakistanicus sp. n., respectively (Figure 9). Insects 2020, 11, x 15 of 33 Head ( Figure 10B) transverse, wider than mesosoma at tegulae, with sparse long setae. Eyes large, oval, laterally prominent. Face uniformly pubescent with moderately long setae. Clypeus protrudent with 7-9 long setae. Tentorial index 0.25-0.40. Malar space equal to 0.10-0.15× as long as longitudinal eye diameter. Mandible bidentate, with 6-9 long setae on outer surface. Maxillary palps with four palpomeres. Labial palps with one palpomere. Antenna 12-segmented ( Figure 10A), Mesosoma. Mesoscutum ( Figure 9C) smooth, covering pronotum above; notaulices distinct in very short ascedent portion of anterolateral margin, effaced dorsally. Mesoscutum sparsely setous with a 5-7 long setae along the latero-dorsal parts. Scutellum nearly triangular, bearing 1-3 long setae on lateral margins. Propodeum ( Figure 9D) areolated, with a wide central areola, oblique antero-central carinae clearly extending to the spriracles. External and dentiparal areolae of propodeum with 3-5 and 0-1 long setae on each side, respectively. Forewing ( Figure 9G) densely pubescent with setae longer than the ones on surface; pterostigma triangular, 2.4-2.7× as long as wide and shorter than R1 vein (proportion between pterostigma length and R1 vein length 0.90); vein r and RS long, reaching near the apex of the wing.
Metasoma. Petiole ( Figure 9E) long and slender, slightly widened at apex; length 3.1-3.3× as long as wide at spiracles, slightly prominent at lateral margin; a pair of central carinae, distinctly prominent along dorsal surface of the petiole, merged or separate in anterior part, but diverging toward base; one long seta at the base of each lateral side; spiracular tubercules smooth, positioned beyond the first half of the segment. Ovipositor sheath ( Figure 9F) long, wide at base, curved downwards; distally dilated slightly, upper part of the ovipositor sheath more sclerotized along the whole length. Length of ovipositor sheath 2.8-2.9× as long as maximum width at base and 8.0-9.0× as long as minimum width at tip.
Body length: 1.5-2.0 mm. Coloration: Head light brown. Mouthparts yellow. Scape, pedicel and F1 yellow to light brown, remaining antennal segments brown. Mesosoma and metasoma light brown to brown. Petiole light brown.
Distribution. Europe (Spain and Slovenia) and Oriental region (China and Japan-mined from GenBank, see Table S1 for sample information).
Etymology. Lipolexis peregrinus sp. n. takes its name in regard to its unknown place of origin (latin peregrinus = foreign, from abroad). Material

Female
Diagnosis. Lipolexis gracilis has a petiole with central bifurcating carinae, a feature that positions it within the gracilis species group. It possesses maxillary palps with four palpomeres, labial palps with one palpomere (the same combination as L. pelopsi). However, it differs from the latter by a less pubescent body and elongated petiole (proportions between length and maximum width of petiole at spiracles, 3.0-3.6 in L. gracilis vs. 2.4-2.6 in L. pelopsi sp. n.).
Mesosoma. Mesoscutum ( Figure 10C) smooth, covering pronotum above; notaulices distinct in very short ascedent portion of anterolateral margin, effaced dorsally, with a series of 6-8 long setae along the latero-dorsal part of mesoscutum, reaching to scutellum. Scutellum nearly triangular, bearing 2-3 long setae on lateral margins. Propodeum ( Figure 10D) areolated, with a wide central areola, oblique antero-central carinae extending to the spriracles. External and dentiparal areolae of propodeum with 3-4 and 0-1 long setae in each side, respectively. Forewing ( Figure 10G) densely pubescent, the upper marginal setae slightly longer than the surface setae; venation reduced; pterostigma triangular, 2.3-2.5× as long as wide and equal or subequal to R1 vein (proportion between pterostigma length and R1 vein length 1.0-1.1); vein r and RS long, reaching near to the apex of the wing.
Metasoma. Petiole ( Figure 10E) long and slender, slightly widened at apex; length 2.7-3.2× as long as wide at spiracles, slightly prominent in lateral margin; a pair of central carinae, distinctly prominent along dorsal surface of petiole, merged or separate in anterior part, but diverging toward base; spiracular tubercules smooth, positioned beyond the first half of the segment. Ovipositor sheath ( Figure 10F) long, wide at base, distally dilated slightly and slightly curved downwards. As in all Lipolexis species, the upper part of the ovipositor sheath more sclerotized along the whole length. Length of ovipositor sheath 2.9× as long as maximum width at base and 9.6× as long as minimum width at tip. Body length: 1.5-1.8 mm.
Coloration: Head dark brown, face brown. Mouthparts except tips of mandibles yellow. Scape, pedicel and F1 brown, other segments darker. Pronotum brown; mesoscutum and mesopleuron dark brown. Propodeum brown. Legs light brown, hind femur and tibia slightly darker at the middle. Wings slightly infumated, venation yellowish brown. Petiole brown. Metasoma dorsally dark brown. Ovipositor sheath yellow, dorsally darker.

Lipolexis oregmae (Gahan 1932)
Diaeretus oregmae (Gahan, 1932), Ann Entomol Soc Am, 25, 736-757. Lipolexis scutellaris Mackauer, 1962, Entomophaga, 7, 1, 37-45. Remarks about L. wuyiensis, L. pseudosctullearis and L. myzakkaiae. On the basis of its description, L. wuyiensis is very similar to L. oregmae and it parasitizes Ceratovacuna lanigera Zehntner (=Oregma lanigera), the same aphid host as L. oregmae in the Philippines. Furthermore, apart from the drawing of the petiole of L. myzakkaiae, which does not follow the original description (i.e., two lateral longitudinal wavy branched carinae), both L. myzakkaiae and L. pseudoscutellaris are morphologically similar to L. oregmae. Moreover, it seems that neither species has been mentioned in the scientific literature since their description. In our opinion, all three species are likely to be conspecific with L. oregmae. However, due the absence of type material, the authors refrained from official synonymization.

Female
Diagnosis. Lipolexis oregmae possesses a petiole that bears lateral longitudinal carinae, which is a morphological character of the oregmae group of species. It differs from the other member of the group, L. bengalensis sp. n. by the number of maxillary palpomeres (three maxillar palpomeres in L. oregmae vs, two in L. bengalensis sp. n.).
Mesosoma. Mesoscutum ( Figure 11C) smooth, covering pronotum above; notaulices distinct in very short ascedent portion of anterolateral margin, effaced dorsally, with a series of 9-10 long setae along the latero-dorsal part of mesoscutum, reaching to scutellum. Scutellum nearly triangular, bearing 2 long setae on lateral margins. Propodeum ( Figure 11D) clearly areolated, with a wide central areola, oblique antero-central carinae extending to the spiracles. External and dentiparal areolae of propodeum with 6-7 and with one long setae on each side, respectively. Forewing ( Figure 11G) densely pubescent, marginal setae longer than the surface setae; venation reduced; pterostigma triangular, 2.2× as long as wide and equal to R1 vein; vein r and RS long, reaching near the apex of the wing.
Metasoma. Petiole ( Figure 11E) long and slender, wide at base, narrowing towards the apex and then slightly widened; length 3.3× as long as wide at spiracles, dorsally smooth, bearing lateral longitudinal carinae. Ovipositor sheath ( Figure 11F) long, wide at base, curved downwards, bearing 3 scattered long setae in the middle portion; distally dilated slightly, upper part of the ovipositor sheath more sclerotized along the whole length. Length of ovipositor sheath 2.8× as long as maximum width at base and 10× as long as minimum width at tip. Body length: 1.5-1.8 mm.

Discussion
Until recently, taxonomists relied on morphological and ecological studies as a basis for describing new species or identifying newly collected specimens. However, easy access to DNA sequence information has now enabled integrative taxonomy which combines morphological/ecological and molecular data to clarify species boundaries. The barcode region of COI is by far the most widely utilized molecular marker used for molecular studies on the subfamily Aphidiinae [30,44,45]. Aside from aiding the identification of the newly collected specimens, this gene region aids the delineation of species boundaries, an approach of particular value for aphidiine genera that are suspected to include cryptic species complexes [46][47][48][49]. Our study reinforced the value of COI as it separated Lipolexis species with high resolution and bootstrap support. The molecular results were concordant with those from morphological study leading to the description of six new species of Lipolexis. Each of these species possessed diagnostic morphological characters which separates it from its congeners which makes the fact that they went unnoticed surprising.
Based on morphological and molecular differences, Lipolexis can be separated into two main groups, i.e., gracilis and oregmae. The average genetic distance between species in these two groups is high, ranging from 21.7% to 23.2%. Furthermore, gracilis and oregmae groups are morphologically distinguished by the differing shape of the petiole: members of the L. gracilis group have a petiole with prominent central carinae, while those in the L. oregmae group have a petiole that is smooth dorsally, but with noticeably crenulated lateral longitudinal carinae. Additionally, members of the gracilis group have a slightly shorter metacarpal vein (R1) than members of the oregmae group (proportion between length of pterostigma and metacarpal vein is 0.90-1.1 in gracilis group versus 0.75-0.90 in oregmae group).
Five new species belonging to the L. gracilis group were discovered in this study: Lipolexis labialis sp. n., L. pelopsi sp. n., L. takadai sp. n., L. pakistanicus sp. n. and L. peregrinus sp. n. Furthermore, within the gracilis group, two additional clusters are formed, one constituted of L. gracilis s. str. and L. labialis sp. n., and the second of the remaining species (L. pelopsi sp. n., L. takadai sp. n., L. pakistanicus sp. n. and L. peregrinus sp. n.) with the average between group distance of 11.4%. Although L. labialis sp. n. is most closely related to L. gracilis (average genetic distance of 7.3%), the two species are readily distinguished by their differing number of labial palpomeres. L. gracilis possesses one labial palpomere while L. labialis sp. n. has two. These two species have overlapping distributions in Europe, but may use different hosts. All reared specimens of L. labialis employed Macrosiphini aphid hosts (Myzus Passerini, Roepkea Hille Ris Lambers) excepting one reared from Anoecia corni (F.). Although L. gracilis has also been reported from Myzus [43,50], in the light of the new species discoveries, it is not clear whether the specimens reared from Myzus are indeed L. gracilis or might be some other Lipolexis species, such as L. labialis sp. n. or L. peregrinus sp. n.
In this phylogenetic analysis, within the second cluster of the gracilis group, L. takadai sp. n. wasrepresented by just a single specimen from China. However, morphological examination of other Lipolexis revealed two specimens from Japan which fully correspond to it. Although molecular data indicate that L. takadai sp. n. is most closely related to L. peregrinus sp. n., L. pakistanicus sp. n. and L. pelopsi sp. n. (3.9%, 4.5%, 6.8% average COI divergence respectively), it possesses several morphological differences from other species of Lipolexis. Although it is only known from China and Japan, its actual distribution may be much broader. Lipolexis takadai sp. n. was reared from Aphis gossypii Glover, a common host for other Lipolexis.
A second species from this cluster, Lipolexis pelopsi sp. n., is most closely related to L. peregrinus sp. n., L. pakistanicus sp. n. and L. takadai sp. n., with 6.9%, 8.6%, 6.8% average COI distance, respectively. It has a Mediterranean distribution as it was reared from aphids collected in Greece, Bosnia and Herzegovina, Croatia, and Montenegro. It is a parasitoid of aphids in the genus Aphis attacking various plant species. Lipolexis pelopsi sp. n. coccurs in this region with L. gracilis and L. labialis sp. n., and also shares an aphid host (Aphis sp.) with L. gracilis. It is characterised by a pubescent body (specimens from Greece possess heavily setose mesoscutum), a feature that distinguishes it from all other species. a recent event. Furthermore, Finlayson [25] stated that the larval morphology of Lipolexis exhibits plesiomorphic morphological characters. One possibility might be that Lipolexis separated early in the evolution of Aphidiinae and acquired adult apomorphic traits independently. Further research is needed in order to try to resolve the complex and poorly investigated position of Lipolexis and its relationships with the other aphidiine members.

Conclusions
Our study revealed six new species of Lipolexis (L. peregrinus sp. n., L. pelopsi sp. n., L. labialis sp. n., L. takadai sp. n., L. pakistanicus sp. n. and L. bengalensis sp. n.). Each of these species possesses clear morphological characters that distinguishes it from its congeners. Moreover, two groups can be differentiated within the genus-oregmae and gracilis. The genetic distances between them are even higher than intrageneric distances within the potentially genus Ephedrus. The oregmae group consists out of L. oregmae and L. bengalensis sp. n. of Oriental origin. The gracilis group of species can be separated into two clades, one consisting of L. gracilis and L. labialis sp. n., and the other of L. peregrinus sp. n., L. takadai sp. n., L. pelopsi sp. n. and L. pakistanicus sp. n. Furthermore, the consistency of number of palpomeres is in concordance with the geographical distribution: the European species (L. gracilis, L. labialis sp. n. and L. pelopsi sp. n.) possess four maxillar palpomeres, while the Oriental ones (L. oregmae, L. takadai, L. bengalensis, L. peregrinus and L. pakistanicus) have three. We provide a key to the world Lipolexis species.
Author Contributions: K.K. and Ž.T. conceived and designed the experiments. Ž.T., A.P., J.Č., K.K., E.R., N.G.K., Y.A., J.A., and P.D.N.H. provided specimens that were used for morphological or molecular analyses. K.K., J.Č., and A.P. carried out laboratory work and data analysis, Ž.T., K.K., and N.G.K. (L. pelopsi sp. n.) provided species descriptions. K.K. and Ž.T. wrote the original draft of the paper. All authors have read and agreed to the published version of the manuscript.