New fossil Stylops (Strepsiptera: Stylopidae) from Dominican amber

SYSTEMATICS, MORPHOLOGY AND PHYSIOLOGY

New fossil Stylops (Strepsiptera: Stylopidae) from Dominican amber

Marcos Kogan^I; George Poinar Jr^II

^IIntegrated Plant Protection Center and Dept of Horticulture. Oregon State Univ, Corvallis, Oregon, 97331, USA; [e-mail]

^IIDept of Zoology. Oregon State Univ, Corvallis, Oregon, 97331, USA; [e-mail]

ABSTRACT

Description of a new species of the genus Stylops from Dominican amber expands the number of families of this order represented by fossils of the mid-Eocene in the Neotropical region. The specimen described herein is reasonably well preserved, except for the tip of the abdomen that hampered observation of the aedeagus. The specimen fits definition of the comtemporary genus Stylops and differs from a related species, Jantarostylops kinzelbachi Kulicka, from Baltic amber, by the larger number of ommatidia, relative proportion of antennal segments, and venation of hind wings. The specimen differs from other contemporary species of Nearctic Stylops in, among other characters, the smaller size, sub-costa detached from costa and maxillary structure. Discovery of this fossil species of Stylops provides evidence of a possibly more temperate climate in the Antilles, since most contemporary species of the genus occur predominantly in the temperate zones of the Nearctic, Palearctic, and Oriental regions. All known species of the genus parasitize bees of the genus Andrena ( sensu lato). Existence of a fossil andrenid, Protandrena eickworti Rozen Jr, of the same Dominican amber, offers evidence of a potential host for this new species of Stylops.

Key words: Fossil insect, Neotropical Strepsiptera, Jantarostylops, Protandrena

For a relatively rare group of insects, Strepsiptera are well represented in the Dominican amber (Table 1). The first species described from that Neotropical amber, based on a single specimen, was the Elenchidae, Protelencholax schleei Kinzelbach. A new species of Myrmecolacidae, Myrmecolax glaesi Kinzelbach, was described and two specimens are known to exist (Pohl & Kinzelbach 1995). In their review of fossil Strepsiptera, Kinzelbach & Pohl (1994) reported having examined four specimens of Myrmecolacidae that seemed to be very close to the complex defined by Stichotrema beckeri (Oliveira & Kogan 1959). The complex includes S. trilobulata (Brailowski), and S. aff. beckeri Kinzelbach. In addition they described S. dominicanum Kinzelbach & Pohl and Bohartilla joachimscheveni Kinzelbach & Pohl. Another closely related species was described the year before as B. kinzelbachi Kathirithambi & Grimaldi. A second specimen included in the Kathirithamby & Grimaldi (1993) paper, was found to be closely related to the contemporary species B. megalognatha Kinzelbach. Poinar & Poinar (1999) illustrated a species of Caenocholax (Myrmecolacidae) possibly close, if not identical, to the contemporary C. fenyesi Pierce. Grimaldi et al (2005) reported much older Strepsiptera from Cretaceous amber including a probable strepsipteran triungulinid from Manitoba, Canada.

Poinar (2004) offered fossil evidence of parasitism by Strepsiptera in the form of a male puparium in a halictid bee (Hymenoptera: Halictidae) and a female cephalothorax and male puparium in planthoppers of two families: Delphacidae and Achilidae (Homoptera: Fulgoroidea), in 15-45 million year old Dominican amber. The halictid bee, Augochloropsis sp., contained an empty male puparium. The achilid planthopper contained two male puparia, one of them empty. The delphacid had two female cephalothoraces and 25 first stage larvae observed on the ventral side of the host's abdomen. Based on these finds, which include the first fossil record of Strepsiptera larvae associated with a host insect, it was possible to establish a minimum age for parasitism of halictid bees and planthoppers by Strepsiptera.

In this paper we describe a first species of Stylops from Dominican amber. The identification of a stylopid in this amber inclusion is of interest because, up until now, fossil records from this neotropical region have been restricted to the Myrmecolacidae, Elenchidae and Bohartillidae. This relatively limited representation of the other Strepsiptera families led Kinzelbach & Pohl (1994) to question whether it was "only by chance that neither the widespread Stylopidae and Halictophagidae nor the tropical Corioxenidae have been found in amber inclusions". With this finding we may answer with a cautious 'yes' to their question. The chance for an adult male strepsipteran to be caught in the resin of the Hymenaea protera Poinar tree probably was not very great so it is not surprising that we still have an incomplete record of all the extant Strepsiptera families in the fossil record. It seems, however, reasonable to assume that the presently recognized families of the order already were established by the mid-Eocene and discovery of representatives of the other families may be a matter of time and more diligent search in the most promising Dominican amber mines (Poinar & Poinar 1999).

Material and Methods

The amber piece was polished and prepared using standard procedures (Poinar & Poinar 1999, cf. pp. 189191). The specimen was examined under a Leica-Wild M32 stereo- microscope and a Leica DME compound microscope, both capable of receiving a Spot Insight, model 3.2.0 digital camera. To minimize diffraction, the specimen was immersed in vegetable oil for microscopic observation of more inconspicuous morphological features. Black and white prints of the digital photos were retouched by hand when necessary to enhance visualization of details; the retouched figures were rescanned to produce digital images. Some images were enhanced by removing unwanted background using Photoshop tools.

Genus Stylops Kirby

Type species: Stylops melitae Kirby, 1802: 112

Synonymy after Kinzelbach (1971) and Luna de Carvalho (1972):

Triungulinus Dufour, 1828: 63

Katastylops Pierce, 1918: 455

Neostylops Pierce, 1918: 455

Prostylops Pierce, 1918: 455

Afrostylops Fox & Fox, 1967: 754 (pro parte)

At least 114 species have been described so far in the genus Stylops, making it probably the most numerous of the Strepsiptera. All described species are parasitic of Andrena ( sensu latu) (Hymenoptera: Andrenidae), a group of solitary bees with a predominant temperate zone distribution.

The males of the genus are characterized by six-segmented antennae with flabellum extended from the 3^rd segment at least to the base of 6^th; eyes usually with more than 20 small, round ommatidia; mandibles slender, lanceolate; maxillary palpi robust generally bisegmented; tarsi four-segmented with first segment sub-equal to or longer than any of the distal three segments; postlumbium oval or semi-circular; aedeagus 'pick-axe' shaped with main stem often sinuous with a mild angular protrusion on the external margin; hind wings with R₂ and R₃ well developed and longer than half the length of R₄. The known Nearctic species of Stylops of which male specimens have been described are listed in Table 2.

Stylops neotropicallis sp.n. (Figs 1-12)

 

Type material: Holotype - Male specimen designated D-1-11 in the George Poinar Collection, Corvallis, Oregon, USA. The specimen is almost perfectly set in an oboval amber piece (Fig 1) about 26 mm x 15 mm, and 4 mm at the thickest point. The specimen is set near the edge of the amber piece, with most anatomical features apparent, except for the tip of the abdomen with the aedeagus blocked from view by a refractive flaw in otherwise generally well structured amber. The strepsipteran specimen has a 3.62 mm wing span and the body is 1.52 mm long from tip of head to tip of last discernible abdominal sclerite (Figs 2-3).

Description: Head - Eyes protruded from narrow occipital lateral plates, with at least 30 discernible small ommatidia (Fig 4). Width at edges of eyes 590 µm. Clypeus not distinguished dorsally; post-frons rounded frontad, 230 µm at widest line. Antennae 6-segmented (Fig 5). Length of antennal segments: I - 32.2 µm, II - 55.8 µm, III (base) - 41.2 µm, IV - 148.7 µm, V - 95.7 µm, VI - 276.5 µm. Flabelum of segment III hidden in dorsal view; length at 160 µm (probably under-estimated due to distortion in ventral view); barely reaching base of segment VI; width of flabellum not greater than that of segment VI. Mandible (Figs 6-7) lanceolate, 145 µm long, pointed at tip, arising from "socket-like" structure near frontal margin of head and extending forward (partially prognathe). Maxillary palp robust, longer than mandible, bisegmented, arising from socket-like structure; distal segment (maxillary palp) almost as thick at base as basal segment (stype+cardo), about 1/3 as long (Figs 8-9).

Thorax - Prothorax extending frontad appearing to intrude between bases of eyes. Mesothorax reduced; front wing narrow at base, club-shaped at tip. Metathorax (Fig 10) with prescutum about as long as scutellum; scutum angularly expanded laterally; postlumbium with frontal and caudal sections rounded and with frontal and caudal lines meeting laterally into a sharp angle. Postnotum about as long as praescutum+scutellum combined. Sternal features of thorax not clearly discernible. Hind wings (Figs 12-13) about 1.85 mm from tip of wing to axillary region; wing venation consisting of C clearly running along 2/3 of front wing margin; an apparent SC running parallel to distal 1/2 of R1; R2 slightly curved, longer than R3; R4 and MA running full distance from axilla to margin of wing; CuA1 fading distally, CuA2 present, CuP and ANL probably hidden by fold of wing (venation nomenclature following Kinzelbach 1971). Legs: femur and tibia of fore-and midlegs short and stout; tarsi sub-equal in length and width, appearing ventrally clad with short pulvillus; coxae of front legs global, robust (Fig 11).

Abdomen - Eight tergites visible dorsally, segments 3-5 with narrow sclerotized band in middle. Terminalia not visible.

Discussion

Table 2 offers a listing of the main male diagnostic characters of the species of Nearctic Stylops in comparison to those of S. neotropicallis sp.n. S. neotropicallis seems to differ from all known Nearctic male Stylops by its smaller size, structure of maxillary palps and mandibles, placement of eyes with base reaching below the front margin of prothorax, and detached SC vein in the hind wing. The impossibility to discern the shape of the aedeagus removes this character from a more complete diagnostic definition. The small size of this species suggests that it may be associated with an andrenid host which is also of a small size. Studies of large series of Coenocholax fenyesi, parasitizing Solenopsis invicta in Texas showed a correspondence of the range of host sizes to male C. fenyesi sizes (Kathirithamby & Johnston 1992). Description of Protandrena eickworti Rozen Jr 1997, a panurgine bee from Dominican amber, provides evidence of a contemporary potential host for S. neotropicallis.

Kulicka (2001) described the genus Jantarostylops for a specimen found in the Baltic amber. The diagnostic characters offered by Kulicka include the following: antennal segments 2-5 structurally similar, lateral process of the 3^rd segment reaching middle of 6^th; eyes with 12-15 ommatidia; hind wings with R₄, R₅ and M₁ veins present. The specimen described here, however, seems to fit within the definition of extant Stylops particularly in the number of ommatidia and the absence of R5 in the hind wings. The current study of this specimen does not warrant erection of a new genus or its inclusion under Jantarostylops. This view, however, may change if further study of the morphology of the species reveals additional distinguishing features from extant Stylops.

The finding of S neotropicallis is of interest not only from the stand point of the fossil record, but also from the aspect of the zoogeography of the genus. The vast majority of the extant Stylops species occur in the temperate zones of the Holoarctic (Paleartic 45.6% of all species and Nearctic 35.1%) and Oriental (19.3%) regions. The present record is the first from the Neotropics, suggesting, perhaps, that the climate in the Antilles in that mid-Eocene period was more temperate than it is today.

Received 24/I/09.

Accepted 30/III/09.

Edited by Roberto A Zucchi

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Publication Dates

• Publication in this collection
  14 May 2010
• Date of issue
  Apr 2010

History

• Received
  24 Jan 2009
• Accepted
  30 Mar 2009