Zethus ceylonicus de Saussure 1867

Zethus (Zethus) ceylonicus Saussure

This rather uncommon wasp, 13–19 mm in length, occurs mostly in Dry Zone localities, but we collected it once in the Wet Zone as well. It was taken from near sea level to an altitude of 610 m in areas with an average annual rainfall ranging from 1500 to 2032 mm. Our records from Sri Lanka are as follows.

Trincomalee District: Amarivayal

Matale District: Kibissa near Sigiriya

Kandy District: Udawattakele Sanctuary

Monaragala District: 6 km NE of Buttala and Angunakolapelessa

NEST ARCHITECTURE.—The wasp nests in abandoned borings of beetle larvae in twigs or exposed roots. P.B. Karunaratne collected a female on 20 March 1976 at Amarivayal. She was beginning a nest in a longitudinal tunnel tightly packed with powdery frass in a dead twig 15 mm in diameter. The wasp was captured when she emerged from a hole in the side of the twig. She had excavated a cavity about 25 mm long in the frass-filled tunnel that ran in both directions from the entrance hole.

I collected another female on 19 June 1978 at Angunakolapelessa. She was hovering at the underside of a dead exposed tree root on the edge of a dry stream bed. She alighted twice on a chimney composed of the tips of plant stems bearing tiny leaves up to 10 mm long. The trumpet-shaped chimney was 15 mm long, flared outward to about 20 mm diameter from a base about 10 mm in diameter and was lined with dried resin. At the base was an oval hole in the root, 9×6 mm, leading inward for 22 mm to a longitudinal boring 50 mm long, 12 mm wide, and 6 mm high. This tunnel contained a linear series of three cells each about 15 mm long. The partitions capping the cells were 1–2 mm thick and composed of bits of leaf gummed together. The cell walls were not lined with leaves or dried resin. The innermost cell was empty but there was a thin layer of leaf bits gummed together at the inner end of the boring. The middle and outermost cells each held a colored pupa almost ready to eclose with the head end directed toward the entrance, a male in the middle and a female in the outermost. There was a thin partition of bits of leaf gummed together capping an empty vestibular cell 5 mm long at the juncture of the entrance tunnel and the longitudinal boring. The nest was probably in an old buprestid tunnel for I found a live buprestid larva in a similar burrow elsewhere in the root.