Hybrizon buccatus (de Brebisson , 1825)

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 : 86-89

Hybrizon buccatus (de Brebisson, 1825) Figs 7278

Paxylomma buccata de Brébisson, 1825: 23 (type lost).

Oviposition behaviour.

Donisthorpe and Wilkinson (1930) found naked pupae of Hybrizon buccatus among the cocoons of the ant Lasius alienus , and concluded that Hybrizon buccatus is likely to be parasitoid of adult ants, as are the wasps of the genus Elasmosoma . Although authors such as Watanabe (1984) and Marsh (1989) suggested that Hybrizon species may be endoparasitoids of ant larvae, the adult-parasitism hypothesis has remained, being included in general revisions dealing with ants ( Hölldobler and Wilson 1990; Schmid-Hempel 1998). Here we report larval-parasitism of Hybrizon buccatus of the ant Lasius grandis Forel, 1909.

The observations were made in Almazán (Soria, Spain) during July and August, 2010, on a permanent vertical trail of Lasius grandis , situated on a wall 60 cm high. The ants walked up and down, day and night, between two nest entrances of the same colony, one placed in the base and the other at the top of the wall (Fig. 73).

During the 3 weeks of observations, especially between 5-8 PM, one or two females of Hybrizon buccatus could be seen hovering over the trail, at 1 cm or less from the ants, usually in the lower part of the trail (less than 15 cm from the base). They could remain almost stationary in the air for more than 5 minutes. Even in the absence of ants on the trail for a period of time, specimens of Hybrizon buccatus found the precise location of the trail and stayed hovering over it. Location of the trail may involve olfactory or visual clues or both. After a long set of video recording, and hundreds of workers passing through the trail, no oviposition of the wasp could be observed on adult ants. Sometimes the wasp followed and approached an ant with a very quick movement, even touching the ant metasoma with its fore legs, but without oviposition (Fig. 74). This rapid approaching behaviour must be the one referred to Giraud (1857) and Donisthorpe (1910), respectively, as “pounces” and “striking” at the ants, behaviour that led Donisthorpe and Wilkinson 1930) to conclude adult-parasitism for Hybrizon buccatus .

The analyse of video frames revealed oviposition of Hybrizon buccatus into the final instar larvae of Lasius grandis while being transported by worker ants. Two cases were recorded, one with the worker going upward, and the other with the worker going downward (Movie Hybrizon , Appendix IV). In the first case (Fig. 75) the wasp grasped the larva with its fore legs and placed its body in a vertical position over the adult ant. When the metasoma began to bend toward the larva, the middle legs seized the adult ant’s head, and the wings were folded until oviposition finished. Throughout the process the hind legs remained in the air. The whole behaviour, comprising the grasping of the larva and the insertion of the ovipositor, until flying off, lasted 0.40 seconds.

In the second case (Fig. 76), contact of the fore legs with the larva can be seen, while the ovipositor is exserted. The middle legs are probably used to grasp the larva during the bending of the metasoma and oviposition. Again, the hind legs hang in the air. The whole behaviour lasted 0.58 seconds.

Specimens of Hybrizon buccatus twice ignored smaller larvae transported by workers of Lasius grandis (Fig. 77), which may indicate that only final instar larvae are selected for oviposition.

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 Hybrizon buccatus was hovering near a nest of Lasius grandis located at the base of an Atlas cedar tree ( Cedrus atlantica ). First, the wasp held the apex of a grass stem with its fore legs, and then grabbed it with all legs, bending the metasoma and folding the wings (last sequence of Movie Hybrizon and Fig. 78). The frame analysis revealed the movement of the apex of the wasp metasoma touching the stem. The whole behaviour lasted 0.30 seconds.