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A new species of a gregarious Meteorus wasp (Braconidae) constructs an unusual cocoon mass. Meteorus restionis sp. n. is described and distinguished from similar species. Cocoons of Meteorus restionis are dark-brown, ovoid, and they are attached perpendicularly by their posterior end along a long, suspended cable. The cable is formed by intertwined, independent threads which are glued together at irregular intervals along its length, suggesting a certain degree of cooperation or at least tolerance among larvae during the construction of the cable. Intertwining and gluing the individual threads in a single cable presumably gives it a greater resistance against wind and other environmental stress. Prior to emergence the wasp cuts a neat, circular cap at the anterior end of its cocoon, and the cap remains attached by some threads to the rest of the cocoon.
cocoon traits, gregarious species, sex ratio
The purpose of this paper is to describe a new species of the genus Meteorus and its uniquely-formed cocoons, recently discovered and observed on the campus of the Universidad de Costa Rica.
Meteorus wasps are koinobiont endoparasitoids primarily of larvae in several Lepidoptera families and, less commonly, of Coleoptera larvae, but no species of Meteorus attack both groups (
Larvae of Meteorus species range from solitary to highly gregarious (
Once emerged from an exophytic caterpillar, the Meteorus larva moves a short distance from the host and begins the construction of its cocoon on a leaf or twig (
Color and shape of cocoons vary across Meteorus
species. Their color ranges from pale-brown to nearly black and their
shape is generally ovoid with either a blunt or a nipple-like anterior
end (
We (ET and GB) collected two groups of cocoons on the Campus de la Universidad de Costa Rica, San Jose province, Costa Rica (9°54'N, 84°03'W;
elevation 1200 m). The campus is located on the western region of the
Central Valley where the mean annual precipitation is 1900 mm and the
mean annual temperature 20°C, with a dry season from December through
March (
Distance between most cocoons of one group was measured: the first basal 14 cocoons, 13 in the middle section of the cable, and the 13 most distal cocoons. Some of these cocoons were photographed under the dissecting microscope using a digital camera Nikon Coolpix 4500, and then individually measured using the program Image Tool v. 3.0. We additionally quantified the weight supported by all threads together (a cable with a length of 7.5 cm) produced by all larvae in the second group. One extreme of the cable was held with a clip and a small plastic container was hung at the other extreme of the cable. Small beads of lead were one by one added into the container and when the cable broke the beads and the container were weighed. Finally small pieces of individual threads that formed part of the cable were cut, mounted on glass slides, and observed and photographed under the compound microscope.
Specimens were sent to SRS and GZJ for description. Morphological terminology and characters used in this description follow
urn:lsid:zoobank.org:act:20E566D9-B21B-4749-8CA0-13D86EC4D2A9
Fig. 1female (point-mounted), COSTA RICA: San José, UCR campus, 1100 m, 1 October 2007, E. Triana and G. Barrantes, emerged from silk cocoons found on Monstera vine growing on Cordia tree surrounded by mowed grass. Deposited in ESUW.
16 females, 6 males, same data as holotype, deposited in ESUW; 5 females, 2 males, same data as holotype, deposited in MZCR.
Mandible strongly twisted, second tooth directly behind first tooth in lateral view; ocelli smaller than OOD, ocello-ocular distance 1.2x ocellar diameter; occipital carina complete; wing membrane clear; vein r ½ length of 3RSa; propodeum areolate-rugose; hind coxa finely rugulose; first metasomal tergite without dorsopes; ventral borders of first tergite joined completely along basal ½ of segment; tergum 2 black laterally, medially with white narrow hourglass-shaped figure.
Meteorus restionis sp. n., lateral view. A Detail of head and anterior mesosoma B Detail of mesosoma showing mesopleuron and sternaulus sculpture C Middle and hind coxa sculpture D Apex of antennal flagellum E Hind tarsal claw with basal lobe; part of ovipositor sheath on left.
Body length = 4.1 mm (Fig. 2A).
Color (Fig. 2A). Body mostly yellowish brown except head orange, compound eye silver, and other parts of body with dark contrasting markings as follows: flagellum and pedicel dark brown; scape and pedicel orangish brown infused with dark brown; ocellar triangle black; dorsal margin of pronotum with black band; lateral lobes of mesonotum and scutellum dark brown to black; mesonotum medially and scutellar disc yellow; metanotum and propodeum black; apical ½ of hind coxa dark brown to black; hind femur apically, hind tibia, and hind tarsi dark brown; wing membrane clear; wing venation and pterostigma dark brown; metasomal tergites 1–3 black dorsally except petiole yellowish white basally in dorsal view, petiole entirely white ventrally, and tergum 2 medially with white narrow hourglass-shaped figure; ovipositor and sheaths dark brown.
Head (Figs 1 and 2B). Antenna with 32 flagellomeres; flagellar length/width ratios as follows: F1 = 3.5; F2 = 3.3; F3 = 3.2; F28 = 2.5; F29 = 2.5; F30 = 2.5; F31 = 2.5; F32 (apical flagellomere) = 4.0; tip of apical flagellomere acutely pointed; head 1.2× wider than high, head height 1.4× eye height; eye small but protuberant, slightly converging ventrally in anterior view; maximum face width 1.1× minimum face width; minimum face width 1.5× clypeus width; malar space length 1.1× mandible width basally; ocelli smaller than OOD, ocello-ocular distance 1.6× ocellar diameter; lower margin of clypeus with fine rugulose wrinkles; mandible strongly twisted; occipital carina complete; vertex, in dorsal view, descending vertically behind lateral ocelli.
Mesosoma. Notauli rugulose, not distinct, and mesonotal lobes not well-defined; scutellar furrow with 1 median carina; mesopleuron polished, punctate; sternaulus weakly rugulose, broad but not long; propodeum areolate-rugose, median depression absent.
Legs. Hind coxa dull, weakly rugulose; larger hind tibial spur about 0.4x as long as hind basitarsus length; tarsal claw with a small blunt basal tooth, strongly curved.
Wings. Forewing length 3.9 mm; vein m-cu amtefurcal; second submarginal cell of forewing slightly narrowed anteriorly; vein r 0.5× length of 3RSa.
Metasoma. first metasomal tergite without dorsopes; ventral borders of first tergite joined completely along basal ½ of segment; first tergite dorsally longitudinally costate on apical half beyond spiracles, costae slightly convergent posteriorly; ovipositor short, thick at base, 1.6× longer than first tergite.
Other females as in holotype except body length 3.9–4.2 mm; forewing length 3.9–4.0 mm; antennae with 31–32 flagellomeres.
Similar to females except body length 3.9–4.0 mm. Antenna with 31–33 flagellomeres. Body color is similar to females except the white medial pattern on tergum 2 is broader and more variable in shape.
Specimens of Meteorus restionis sp. n. were identified by SRS using the key to Costa Rican Meteorus species by
Female Meteorus restionis. A Pattern of coloration B Head details.
The specific epithet is from the Latin restionis, meaning “rope-maker” as a reference to the cocoon-forming behaviour of this Meteorus species.
All the type specimens were reared from gregarious cocoons collected on campus of the University of Costa Rica, Montes de Oca, San Pedro, San José in Costa Rica. This is the only location where the species has been found, although the associated plants are widespread.
Both groups the cocoons were suspended from a single cable (Fig. 3A), whose entire lengths were 72 cm and 63.5 cm respectively. This cable was formed by individual threads that twisted on each other and intertwined like a rope. In both cases the independent threads were attached to the lower surface of a leaf of a fruit salad vine plant (Monstera deliciosa, Araceae) and they intertwined, forming a single cable, about 5 cm beneath the leaf surface. Both fruit salad vine plants climbed trunks of Cordia eriostigma trees (Boraginaceae) which were separated by 5 m. One of the cables branched off at 12.5 cm from the end, i.e. dividing the main cable in two; one branch having 19 and the second 11 cocoons. The cable of the other group did not branch and had 49 cocoons. No sign of the possible host larva was found in either case. The cocoons in both cases were grouped at the last section of the suspended cable (14 and 17 cm respectively), and the distance between contiguous cocoons varied from 29 to 0 mm (0 mm when two cocoons were opposite to each other at the same level of the cable). The distance between cocoons decreased toward the tip of the cable (basal section: mean = 26.83 mm, SD = 35.49 mm, N = 14; middle section: mean = 1.65 mm, SD = 2.21 mm, N = 13; distal section: mean = 1.58 mm, SD = 2.21 mm, N = 13).
Group and shape of cocoons of Meteorus restionis. A Distal section of a hanging cable showing 20 of the 49 cocoons in the group. Note the nearly perpendicular position of the cocoons relative to the cable B Individual cocoon; note the lack of the nipple-like anterior end typical in cocoons of other species C Detail of the anterior end showing its shape and the very fine cut produced for the wasp inside prior to its emergence.
The cocoons were dark-brown and had an ovoid shape. The posterior end was wider than the anterior end which was blunt, rather than ending with a nipple-like final portion as the cocoons of some other species (Figs 3B–C). All cocoons were attached nearly perpendicularly by the posterior extreme to the suspended cable, rather than to an individual thread (Figs 3A, 4A–B). Prior to emergence the wasps cut a neat, circular cap at the anterior end of the cocoon, and the cap remained attached by some threads to the rest of the cocoon (Fig. 5A). Inside the cap there was a yellow soft-pad against which the head of the pupating wasp “rested” inside the cocoon (Fig. 5A–B).
Cocoons attached by the posterior end to the cable. A A circle of relatively thick threads secure the cocoon to the cable B Cocoon attached to the cable.
Cap of the cocoon and pupating wasp. A The cap finely cut by the wasp hangs from a few threads to the rest of the cocoon. The bottom of the cap is covered by a soft yellowish pad B Position of the pupating wasp inside the cocoon; the top of the wasp’s head rests on the pad.
The cable was very resistant to breaking. One of the cables resisted a weight of 44.17 g before breaking. What looked like a single thread, constructed possibly by an individual larva, consisted of two relatively thick threads when observed under the compound microscope and each of these threads were formed by multiple very thin fibrils (Figs 6A–B). Additionally, the fibrils and threads were glued together and at irregular intervals along the cable with large clogs of a resin-like substance that bound several threads together (Fig. 6C).
Details of the threads and resin-like clog. A A pair of relatively thick threads, possibly produced by a single larva, glued together B The threads consist of a large number of fibrils C Clog of a resin-like substance. Clogs bind together threads along the cable.
All but one wasp emerged from the first group of cocoons collected (cocoons of the other group were empty). Within this group 22 wasps were females and eight were males. This sex ratio significantly differed from a 1:1 proportion (p = 0.011, Binomial test). Pupae were not hyperparasitized; the only wasp that did not emerge was completely developed and the cause of its failure to emerge was unknown.
The cocoons of Meteorus restionis sp. n. differ in several respects from those described for other species (
The construction of such a cable seems to require that
all larvae begin to construct the cocoon approximately at the same time,
that each larva somehow twists its individual long thread with other
larvae’s threads, and glue its thread at irregular intervals with some
other threads. Hence, twisting the threads and gluing them together
indicate some degree of cooperation, or at least some degree of
tolerance, that results in the construction of a single cable, more
resistant to environmental stress. Both tolerance and some degree of
cooperation, which not always include coordinated actions (see
Gluing and binding the threads to form a cable and
attaching each individual cocoon to this cable, rather than to each
individual thread, presumably gives the cocoon additional resistance
against wind, rain, other environmental stress, and against possible
impacts of flying animals. It is also possible that long threads give
better protection against ants or other crawling predators (
Internally, cocoons of Meteorus restionis look very similar to those of other species (
The biology of Meteorus restionis
brings further information to the understanding of the evolution of the
apparent cooperative behavior associated to the construction of complex
cocoons in the genus Meteorus.
However, only a phylogenetic analysis will provide the opportunity to
understand the evolution of cooperative behavior within this
cosmopolitan genus (
We thank Zhaojie Zhang, of the UW Microscopy Core Facility, for assistance with scanning electron microscopy. We also thank Gavin Broad and Mark Shaw for their comments that improved the final version of this paper. Financial support was provided by the Vicerrectoría de Investigación, Universidad de Costa Rica, and in part by McIntire-Stennis project No. WYO-362-02, Braconid Wasps in Forest Ecosystems.