The influence of larval age and ant number on myrmecophilous interactions of the African grass blue butterfly, Zizeeria knysna (Lepidoptera: Lycaenidae)

Interactions between myrmecophilous Zizeeria knysna larvae and Lasius flavus ants were quantitatively studied in laboratory experiments.Larvae delivered secretions from their dorsal nectar organ (DNO) more frequently in the initial 3-minute interval of an interaction than later on.Tentacle eversions were likewise more common at the beginning of interactions.Non-feeding prepupal larvae secreted significantly more droplets than feeding fourth instars.Actual tending levels differed between larvae tested with 5 (2.6-3. 1 ants per larva) or 15 ants (5.3 ants/larva), respectively.Secretion rates increased with tending level (5-ant trials: feeding L4 larvae 5.5 DNO droplets/h, prepupae 16.4 droplets/h; 15-ant trials: feeding L4 9.5 droplets/h, prepupae 25.5 droplets/h).Secretion droplets averaged 0.2 mm in diameter (volume 0.004 pi).From these data, a model is developed to estimate lifetime DNO secretion amounts of individual larvae.Estimates range from 1. 3-4.7 pi per larva in 5 d, representing approximately 0.2-0.7 mg carbohydrates with a physiological energy equivalent of 3.4-12 J. Hence, Z. knysna larvae provide only a marginal food reward for attendant ants, suggesting that myrmecophily is a lowcost life-history strategy in that butterfly species.