Kollasmosoma sentum van Achterberg & Gomez

Gomez Duran, Jose-Maria & van Achterberg, Cornelis, 2011, Oviposition behaviour of four ant parasitoids (Hymenoptera, Braconidae, Euphorinae, Neoneurini and Ichneumonidae, Hybrizontinae), with the description of three new European species, ZooKeys 125, pp. 59-106 : 68-75

Kollasmosoma sentum van Achterberg & Gomez sp. n. Figs 8-23

Type material.

Holotype, ♀ (RMNH),"Spain, Madrid, Carretera de La Coruña km 7.5, 20.viii.2010, following adult workers of Cataglyphis ibericus , J.M. Gómez Durán, RMNH". Paratypes: 7 ♀ (RMNH (5), RMSEL (1)), topotypic, collected 3.ix. and 13.ix.2010; 1 ♂ (RMS), "(Spain), Granada, Orgiva, 3OS VF68, 500 m, 11241", "Leg. Jose Luis Ruiz de la Cuesta, 6.v.2009, 11241". The only known male paratype of Kollasmosoma platamonense from Spain probably also belongs here.

Oviposition behaviour.

Few observations have been made on the biology of the small Palaeartic parasitoid genus Kollasmosoma van Achterberg & Argaman, 1993. Kollasmosoma platamonense is known to approach the ant Cataglyphis bicolor from behind, briefly contacting its metasoma (R.D. Harkness in Huddleston 1976); van Achterberg and Argaman (1993) reported this species hovering over the nest of Messor semirufus , but no oviposition was observed. Kollasmosoma marikovskii has been reared from Formica pratensis (van Achterberg and Argaman, 1993) and, finally, no information is available on the biology of Kollasmosoma cubiceps (Huddleston). Here we report some observations on oviposition by Kollasmosoma sentum sp. n. in the ant Cataglyphis ibericus (Emery, 1906). 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. The parasitized colony of Cataglyphis ibericus had a polycalic nest with three entrances on the ground, forming a triangle of about 60 cm on each side. This area was visited daily by females of Kollasmosoma sentum during the three weeks of observation. The wasps appeared in groups of 1-3 individuals at any time between 12 PM and 15.30 PM, in the hours of highest temperature (around 35° Celsius). The visits lasted between 30 and 90 minutes. The wasps hovered over the nest entrances or looked for worker ants in the surrounding area when going out to forage or when returning to the nest carrying prey (thus, walking slowly). The wasps’ attacks usually occurred during the brief and characteristic stops of Cataglyphis ants when marching. The wasp was extremely fast, flying at a height of about 1 cm over the ground. In order to observe and record the wasp’s oviposition behaviour, the very speedy workers of Cataglyphis ibericus were kept quiet by means of baits such as Messor barbarus cadavers -a usual prey of this species- and honey (Fig. 15).

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 (Fig. 16). This defensive behaviour is very common and sometimes prevents the wasp from alighting and ovipositing.

Kollasmosoma sentum attacks the ant from behind, and oviposition takes place into both the dorsal and ventral surface of the ant’s metasoma, more rarely into its apex (Movie Kollasmosoma , Appendix II). (On one exceptional occasion, a wasp was observed attacking the ant’s head). In all the cases observed (n= 22) the movements of the wasp’s metasoma during oviposition, and hence the insertion of the ovipositor, followed the direction of the postero-anterior axis of the ant’s metasoma, which suggests that the ovipositor may be inserted through an intersegmental membrane. Basically, two alighting strategies have been observed for achieving the postero-anterior insertion of the ovipositor; strategies that depend on the flight direction of the wasp’s attack and on the inclination of the ant’s metasoma, this last varying from an horizontal position to a vertical one, perpendicular to the ground surface and distinctive for the genus Cataglyphis .

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 (Fig. 17).

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 (Fig. 18 and the first two sequences of Movie Kollasmosoma ). After grasping the ant’s metasoma with the tarsi, and being perpendicularly aligned with respect to it, the wasp starts a 180° rotation around its longitudinal axis. At the same time, the wasp rotates vertically, approaching the metasoma. As a result of both rotational movements, the wasp alights downwards, allowing it to insert the ovipositor following the direction of the postero-anterior axis of the ant’s metasoma.

It is interesting that during the rotation movements of the wasp, its fore tarsi (Fig. 19) keep permanent contact with the ant’s metasoma. To achieve rotation around its longitudinal axis (without lifting the legs off), the tarsi are placed slightly separated, one over the other, on the ventral surface of the ant’s metasoma (Figs 20 and 21). If the right tarsus is placed over the left one, the wasp rotates counter clockwise; if the left tarsus is placed over the right one, the rotation is clockwise. This longitudinal disposition of the wasp’s tarsi on the ant’s metasoma is, therefore, a behavioural adaptation to enable the necessary rotation of the body before oviposition.

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 (Fig. 22): the body of the wasp goes back tending to the vertical position. Before reaching the vertical, the apex of the wasp’s metasoma moves down, presumably inserting the ovipositor into the ant’s metasoma. At the vertical position, the apex of the wasp’s metasoma presses down on the ant’s metasoma, completely attaching to it. The wasp continues leaning backwards some way beyond the vertical and, finally, takes flight backwards.

Regarding the oviposition behaviour of Kollasmosoma sentum sp. n., the probable function of the ventral spine, peculiar to this species, located on the fifth sternite (anterior to the hypopygium; Fig. 23) needs mention. Since the rapid insertion of the ovipositor occurs when the wasp is in or near a perpendicular position with respect to the surface of the ant’s metasoma (most likely with the fore legs detached from it), the ventral spine could serve to fix the wasp’s position and act as a supporting point for the oviposition movements of the wasp’s metasoma.

The whole oviposition behaviour of Kollasmosoma sentum sp. n. (comprising the grasping of the ant by the wasp and the insertion of the ovipositor, until flight; Fig. 79) lasted a mean of 0.052 seconds (95% confidence interval: 0.047-0.057; N = 19; SE = 0.002), with a median of 0.050 seconds (interquartile range: 0.047-0.057).

Diagnosis.

Outer spur of hind tibia of female normal and apically acute (Fig. 13); fifth metasomal sternite of female with an apical spine (Figs 14, 23); face strongly convex (Fig. 9); height of eye about 3.6 times width of temple in lateral view (Fig. 9); dorsal face of propodeum shorter than metanotum (Fig. 10); pedicellus of female distinctly protruding (Fig. 11); fore tarsus of female about 1.9 times as long as middle tarsus.

Description.

Holotype, ♀, length of body 2.0 mm, of fore wing 1.4 mm.

Head. Length of third segment of antenna 0.5 times fourth segment, length of third, fourth and penultimate segments 0.5, 0.8 and 1.0 times their width, respectively, and basal segments with distinct setae; pedicellus distinctly protruding and larger than scapus; face strongly convex and densely setose (Fig. 9), without facial tubercles and bristles; length of eye 2.4 times temple in dorsal view; height of eye about 3.6 times width of temple in lateral view (Fig. 9); vertex superficially granulate and having a satin sheen; temples roundly narrowed behind eyes; OOL:diameter of ocellus:POL = 5:4:20; length of malar space 0.05 times height of eye, eye nearly touching base of mandible.

Mesosoma. Length of mesosoma 1.1 times its height; mesoscutum evenly granulate; scutellum granulate and distinctly convex; precoxal sulcus absent; mesopleuron superficially granulate, but speculum shiny and largely smooth; mesosternal sulcus narrow and micro-crenulate; metanotum without a median carina and longer than dorsal face of propodeum; propodeum finely rugulose, dorsal face much shorter than posterior face, with satin sheen, without a median carina and no medial areola and its spiracle small and far in front of middle of propodeum.

Wings. Fore wing: parastigma comparatively large (Fig. 8); vein SR distinctly pigmented; basal half of wing much less densely setose than its distal half. Hind wing: wing membrane sparsely setose basally.

Legs. Hind coxa partly superficially micro-granulate, nearly smooth and with satin sheen; fore coxa nearly flat ventrally; all tarsal claws slender and simple; length of femur, tibia and basitarsus of hind leg 2.9, 4.5 and 4.0 times their width, respectively; fore femur moderately curved in dorsal view, compressed and apically without tooth; fore tibia without protuberances and evenly densely setose, its length 6.3 times its maximum width in lateral view; fore tarsus 1.9 times as long as middle tarsus and 1.6 times as long as fore tibia; fore tibial spur slightly curved and 0.7 times as long as fore basitarsus and 0.4 times fore tibia (Fig. 12); spurs of hind tibia acute apically, their length 1.1 and 1.0 times hind basitarsus.

Metasoma. Length of first tergite 0.6 times its apical width, its surface with satin sheen, granulate, basally and medially flat, and its spiracles not protruding and near apex of tergite; second and third tergites superficially granulate; second metasomal suture obsolescent; remainder of metasoma largely smooth and depressed; fifth sternite with a large and acute apical spine (Fig. 14); setae of metasoma spread and short; second tergite with sharp lateral crease; length of ovipositor sheath 0.05 times fore wing.

Colour. Black; face, clypeus, labrum, malar space, frons antero-laterally and medially, palpi, propleuron, tegula, wings basally, fore and middle legs white; scapus and pedicellus, and hind leg ivory, but hind tarsus dorsally infuscate; pronotal side with brown patch; veins brown; remainder of antenna, humeral plate largely, metasoma laterally, parastigma and pterostigma largely dark brown; wing membrane subhyaline.

Variation. Length of body 1.8-2.1 mm, of fore wing 1.1-1.4 mm, all females have 12 antennal segments; pronotal side may be largely brown.

Etymology.

From “sentus” (Latin for "thorny, spiny"), because of the unique thorn-like spine of the fifth sternite of the female.