Rates of oviposition and some other aspects of reproductive behaviour in Tholymis tillarga (Fabricius) in Kenya (Anisoptera: Libellulidae)

During April, 1984, T. tillarga were observed to be highly active at Hunter’s Lodge, Kenya, from 0.6:20 to 07:00 (sunrise: 06:28) and from 16:30 to 18:45 h (sunset:18:32 h). At other times they were probably resting in dense vegetation. In the evening, males flew continuously within limited areas along the water margin, never perching but hovering with increasing frequency as the light intensity diminished. Hovers were made over green leaves of Typha, Cyperus and Sparganium which were floating horizontally at the water surface, and onto which females oviposited epiphytically. A female oviposited by making a series of downwards swoops onto a leaf; when guarded by a male she remained ovipositing onto the same leaf, making a swoop every 1.32 ± 0.36 s (s.d), but when unguarded she visited a succession of different leaves, making a swoop every 2.06 ± 1,03 s (s.d.). Many eggs were eaten by fish soon after being laid, but this ceased once they had become firmly stuck to a leaf. The frequent switching between leaves by unguarded females may have helped to reduce egg predation. Guarded females did not switch between leaves, possibly because of the risk of being lost by their guards particularly in dim light. Eggs were laid in discrete batches of about 9, each egg being orientated in the batch with its anterior pole facing outwards. The eggs were covered in a thick network of spumaline which stuck them firmly to the leaf but allowed contact between the water and the chorion. The female is equipped with an egg basket, a structure on the 9th abdominal sternite in which eggs are probably stacked and orientated prior to each downward swoop. It is estimated that at 28-30° C eggs were laid at 405 min'1 when the female was guarded, and at 261 min'1 when not guarded. About 44-66 batcnes comprised a clutch, and thus 400-600 eggs could be laid in one bout of oviposition.