We found no evidence for host-ant-mediated oviposition in M. alcon. The results demonstrate that oviposition choice is not influenced by the presence of host ants, but that developmental stage and position within a plant of a flower bud are good predictors of oviposition choice.
Our results are consistent with the findings of Thomas & Elmes (2001)
that plant development rather than host-ant presence influences the butterflies’ oviposition choice, but differ in preferred bud size found for G. scabra
. In their study, small buds attracted most eggs, while in ours large buds were favoured. This may reflect differences in the phenology of G. scabra
, which has dense growth. Large buds provide a larger surface area and are more exposed than small buds, which are rather inaccessible. In G. pneumonanthe
, where bud size was more consistent within plants, the apical buds were most attractive to the butterflies, supporting the finding of Nowicki et al. (2005)
that exposed plants are the most attractive for M. alcon
Contrary to the study of van Dyck et al. (2000)
, who found a positive correlation between host-ant presence and egg numbers early in the flight season, which subsequently disappeared, we found no significant change in oviposition choice over time.
The absence of host-ant-dependent oviposition by M. alcon
may reflect either an absence of selection for the use of ant cues, or selection against their use by Maculinea
. Among the former class of explanations is the possible lack of suitable host ant recognition cues. Even though butterflies are very efficient in detecting odours (Hansson 1995
), it is possible that they simply do not encounter suitable cues from their host-ants. For example, ant trail pheromones have been considered the most likely oviposition cues (Henning 1983
), but are mainly short-lived volatile compounds (Vander Meer & Alonso 1998
), which may not be encountered by ovipositing females since the main foraging periods of Myrmica
(morning and evening; Thomas 2002
) are temporally separated from those when most oviposition takes place (mid-day and afternoon; M. A. Fürst 2006–2008, personal observations). Another possible constraint is the limited oviposition time available to Maculinea
females in the field (Kőrösi et al. 2008
), which may make delays in oviposition choice based on ant discrimination costly.
Alternatively, it is possible that ant-dependent oviposition has not been selected because more effective exploitation of the host ants by more effective oviposition strategies may lead to overexploitation of the host ant population and therefore to increased extinction risk.
Our study has clear implications for the conservation of endangered Maculinea species. Lack of ant-dependent oviposition means that active management of sites to increase the overlap of food plant and host ant distributions is required, as the butterflies cannot be relied upon to find their own host ants when rare.