Corresponding author: Cornelis van Achterberg (
Academic editor: Michael Sharkey
The oviposition behaviour of four ant parasitoids was observed and filmed for the first time. The movies are available from YouTube (search for
In Europe the members of the small tribe
As far as the scanty biological information allows a conclusion, the
The scanty biological information indicates that
For the identification of the tribe
The small subfamily
Until now the biology of
Females of
Elasmosoma
Oviposition of
The observations were made in Almazán (Soria, Spain) in August, 2010 on a warm and calm day between 12.26 PM and 13.38 PM. A group of 30 to 40 of
The wasp attacks always come from behind, paralleling their longitudinal axis to those of the ants. When they are less than 1 cm from an ant they dart forward and the fore legs contact the dorsal surface of the metasoma first. Meanwhile the hind legs, arranged in curved shape, are situated to brace the apex of the metasoma (
Contact with the fore legs is usually followed by hitting of the parasitoid’s head on the host’s metasoma. At this moment the middle and hind legs grasp the metasoma and the wasp folds its wings. The site chosen by the wasp for the initial hit of the fore legs, or the head, is usually the posterior margin of the first gastral segment (T1;
When the hit occurs at the posterior margin of the second or third gastral segments, the wasp climbs onto the metasoma, changing its position to reach the posterior margin of the first gastral segment (
This locational preference for alighting may be visually stimulated by the differentiated border of the posterior margin of the first gastral segment, enhanced by the characteristic dark stripe behind it. The frame analysis in the film clip suggests that the wasp’s head hits the posterior margin of T1 with the mandibles opened, and that a slight deformation of the suture between T1 and T2 is produced. Presumably, the modified structure of the T1-T2 suture is used by the wasp to secure its grasp. The tarsal modifications of
This arrangement of the legs facilitates the appropriate position of the wasp’s metasoma in order to insert the ovipositor into the posterior area of the last metasomal segment, between the pygidium and the hypopygium, probably through the anus.
The precise moment of ovipositor insertion could be detected by the conspicuous downward-movement of the apex of the wasp’s metasoma (
Oviposition attempts sometimes failed due to strong movements of the ant’s metasoma, to strikes by the ant’s legs, or because of defective alighting by the wasp (
Two sequences of a female of
Arrangement of the legs of
Insertion of the ovipositor by
Two sequences of failed attacks by
1 | Scapus longer than pedicellus, somewhat longer than wide ( |
|
– | Scapus (excluding radix) shorter than pedicellus, wider than long ( |
2 |
2 | Dorsal face of propodeum distinctly longer than metanotum, similar to posterior face ( |
|
– | Dorsal face of propodeum about as long as metanotum or shorter ( |
3 |
3 | Outer spur of hind tibia of female enlarged and apically obtuse ( |
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– | Outer spur of hind tibia of female normal and apically acute ( |
Holotype, ♀ (RMNH),“Spain, Madrid, Carretera de La Coruña km 7.5, 20.viii.2010, following adult workers of
Few observations have been made on the biology of the small Palaeartic parasitoid genus
When the wasp approaches, the ant is often aware of its presence, aggressively turning around with opened mandibles, or extending the hind or middle legs to hit the wasp even if it comes from behind (
1) Horizontal alighting: the wasp follows an ant with its metasoma in, or near, a horizontal position, approaches it from behind, in the direction of the longitudinal axis of the ant, and extends the fore legs until grasping the dorsal metasomal surface with its tarsi. With this grasp the wasp jumps over the ant’s metasoma, lays down the middle and hind legs, and folds its wings before starting to oviposit (
2) Vertical alighting: the wasp follows an ant having its metasoma arranged in vertical position, or forming an angle bigger than 45 degrees with the ground surface. It approaches the ant from behind, sometimes following a direction deviating from the longitudinal axis of the ant, and extends its fore legs until grasping the ventral metasomal surface with the tarsi. Now, with this grasp, the wasp accomplishes two kinds of rotational movements, which vary according to both the flight direction of the wasp and the inclination of the ant’s metasoma. An example of this surprising pirouette, that fully involves the two rotations, occurs when the wasp, in horizontal flight, approaches an ant’s metasoma placed in a vertical position (
It is interesting that during the rotation movements of the wasp, its fore tarsi (
The rapid insertion of the ovipositor follows a uniform behavioural pattern. When alighting, the wasp grasps the ant’s metasoma with its three pairs of legs and folds its wings. Immediately, the wasp moves gradually backwards toward a perpendicular position with respect to the metasoma surface, the apex of its metasoma remaining over the ant’s metasoma. A good example is offered during horizontal alighting (
Regarding the oviposition behaviour of
The whole oviposition behaviour of
Outer spur of hind tibia of female normal and apically acute (
Holotype, ♀, length of body 2.0 mm, of fore wing 1.4 mm.
From “sentus” (Latin for “thorny, spiny”), because of the unique thorn-like spine of the fifth sternite of the female.
Baits were used to keep the ants quiet
Workers of
Horizontal alighting.
Vertical alighting.
Stereomicroscopic image showing the fore legs of a female of
Arrangement of the fore legs a female
Arrangement of the fore legs of the female of
Oviposition of
1 | Females: third and following antennal segments with short and adpressed setae; fore tibia widened subbasally ( |
2 |
– | Males: third and following antennal segments with medium-sized and erect setae; fore tibia narrow subbasally ( |
7 |
2 | Fore femur straight in dorsal view ( |
|
– | Fore femur curved in dorsal view ( |
3 |
3 | Anterior subbasal tooth of fore tibia minute ( |
4 |
– | Anterior subbasal tooth of fore tibia wide triangular ( |
5 |
4 | Fore tibial spur nearly straight and 0.7–0.8 times as long as fore basitarsus ( |
|
– | Fore tibial spur strongly curved and 0.8–0.9 times as long as fore basitarsus ( |
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5 | Posterior longitudinal carina of fore tibia with a submedial thorn-like protuberance; facial tubercles thick and nearly as long as pedicellus; [fore tibial spur distinctly curved in both sexes]; E Palaearctic (Mongolia) | |
– | Posterior longitudinal carina of fore tibia without a submedial thorn-like protuberance ( |
6 |
6 | Pair of facial bristles minute, 0.2 times as long as pedicellus and distance between bristles about 1.2 times width of scapus ( |
|
– | Pair of facial bristles medium-sized, about as long as pedicellus and distance between bristles about equal to width of scapus ( |
|
7 | Hind femur partly dark brown or black; fore tibial spur strongly curved; [vertex finely granulate; clypeus black]; Mongolia | |
– | Hind femur yellowish-brown or brown, sometimes infuscate basally; fore tibial spur moderately curved or nearly straight ( |
8 |
8 | Length of fore tarsus 1.8–2.0 times fore tibia and tibia widened apically ( |
|
– | Length of fore tarsus 1.2–1.5 times fore tibia and tibia slender apically ( |
(all RMNH unless otherwise indicated) Austria (Aschbach, 1400 m; Bach, Lechtal, 1200 m), Bulgaria (Rogen; h. Teneran; Batak; Smoljanski esera; h. Erqupria; Jemkovo; m. Nektenica; Gababovo (all Rhodopi)), England (RMS: Midhurst Common, W. Sussex, hovering above and swooping down on
One male from Bulgaria (RMNH: H. Ruen, Rhodopi Mts, 29.vii.1969, A. Germanov) belongs to a related species; it has the fore tarsus 1.5 times as long as fore tibia, the fore tibial spur with rather long setae and straight and the vertex granulate.
Netherlands (Meijendel, dunes near The Hague; Rockanje, wet
If the scapus and tegulae of a male are pale yellowish or whitish, the hind coxa largely yellowish-brown and the vertex finely granulate, the specimen may represent the unknown male of
Holotype, ♀ (RMNH),“Slovakia, Predna Hora, n[ea]r Murán, 25.vii-1.viii.2009, 850 m,
Unknown.
Fore tibia of female about 4.8 times as long as wide, slightly narrowed basally, with short carina and below it bristly setose and with a small anterior subbasal tooth (
Holotype, ♀, length of body 3.3 mm, of fore wing 2.2 mm.
4.7 and 7.0 times their width, respectively and basal segments without distinct setae; facial tubercles small and facial bristles 0.4 times as long as pedicellus, distance between bristles about 1.3 times width of scapus (
From “rectus” (Latin for “straight”) and “calcar” (Latin for “spur”), because of the straight spur of the fore tibia.
Holotype, ♀ (RMNH),“Spain, Madrid, Carretera de La Coruña km 7.5, 20.viii.2010, following adult workers of
In recent years the oviposition behaviour of the genus
The observations were made in Madrid (at the enclosed area of the Institute for Agriculture and Food Research and Technology (INIA), Carretera de La Coruña Km 7.5, Spain) during August and September, 2010, in three colonies of
When the ant moves up, the wasp approaches it from behind and waits until the ant’s body is in a vertical position. Then, the wasp head hits the ant’s mesonotum while the fore legs dart forward and brace the mesopleuron. The frame analysis reveals that the tibia are the part of the legs that firmly hold the mesopleuron (
After contact, the wasp’s head is separated from the ant’s body, the wasp’s metasoma is placed vertically and its wings are folded. Then ovipositor insertion begins, during which time the middle legs can be seen to be sometimes holding the posterior part of the ant’s mesosoma (
Oviposition was not always fully successful. Of a total of 25 attempts observed, 17 were completed, 4 were initiated but ended with the wasp and the ant -still joined- falling to the ground, and in the other 4 cases the wasp failed to grasp the ant and flew away immediately. Hence, the grasping of the ant appears to be a critical moment of the oviposition process. Sometimes the wasp’s head hit on the ant’s pronotum instead of its mesonotum, or the wasp attacked an ant that was not in a vertical position. In these circumstances it had more difficulty holding the ant, whose vigorous movements usually resulted in oviposition failure. Other times the first hit of the wasp’s head, together with the strong grasping of its fore legs, caused the ant to detach from the surface and fall down with the wasp.
The whole oviposition behaviour of
On one occasion a strange behaviour was observed. One
The described oviposition behaviour of
Fore tibia of female about 4.0 times as long as wide, distinctly narrowed basally, with long carina and below it a double row of small pegs and with a wide triangular anterior subbasal tooth; mesosoma extensively marked with pale yellowish patches; metasoma brownish-yellow, with first tergite entirely blackish and most tergites basally and apically dark brown, fore femur curved in dorsal view; fore spur nearly straight and robust; facial tubercles small and facial bristles 0.2 times as long as pedicellus, distance between bristles about 1.2 times width of scapus. Runs in the key by
Holotype, ♀, length of body 2.8 mm, of fore wing 1.8 mm.
From “vesculus” (Latin for “weak, little, poor”) because this new species has poorly developed facial bristles.
Female of
Position of wasp’s tibiae (yellow arrow) of three
Two attack sequences of
Insertion of the ovipositor by
For a key to the European species, see
The observations were made in Almazán (Soria, Spain) during July and August, 2010, on a permanent vertical trail of
During the 3 weeks of observations, especially between 5–8 PM, one or two females of
The analyse of video frames revealed oviposition of
In the second case (
Specimens of
An unexplained aberrant behaviour was observed in Madrid (at the enclosed area of the Institute for Agriculture and Food Research and Technology (INIA), Carretera de La Coruña Km 7.5, Spain) in September, 2010, when a female of
Female of
Female of
Oviposition sequence of
The arrow points the exserted ovipositor of the female of
Female of
Aberrant behaviour of a female of
Duration of the oviposition behaviour (comprising the grasping of the ant by the wasp and the insertion of the ovipositor, until taking off) of three neoneurine
From the observations here recorded on the oviposition behaviour of four European ant parasitoid wasps, some general conclusions are offered. The grasping of the ant (or the larva, in the case of
In order to grasp the host, the visual perception of these ant parasitoids seems highly developed, especially considering the extremely short time elapsing during the oviposition sequence (
The location of the oviposition insertion varies in the four species, each presenting particular situations.
Regarding the oviposition behaviour of the three neoneurines, the persistent defensive behaviour displayed by the ants is also significant. The ants are usually aware of the presence of the wasps, to which they turn towards with opened mandibles and sometimes catch them. Oviposition is also frequently impeded by the hits and movements of the ant’s legs.
We wish to thank Kiko Gómez Abal for his help in the determination of the ant species, Luis M. Carrascal for his valuable statistical advise, Dr L.O. Hansen (Oslo) and Dr M. Koponen (Helsinki) for the loan of specimens and Dr M.R. Shaw (Edinburgh) for his comments on the first draft and for the loan of his neoneurine specimens. We thank both reviewers (Prof. Dr M.J. Sharkey and Dr M.R. Shaw) for substantial improving the text.
Movie
Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Movie
Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Movie
Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Movie
Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.