Mimetic host shifts in a social parasite of ants: Caterpillar survivors in Myrmica nests

Host specificity was measured by comparing the proportion of caterpillars that were adopted into different Myrmica nests with the proportion that survived to adulthood or pupation. Data were obtained from one population for 4 years near Przemy-l, s.e. Poland. The proportion of larvae adopted was estimated by baiting for ants beneath stratified random samples of gentians and by counting the number of eggs on each plant. Previous work had shown there was no difference in egg or larval survival on gentians growing in different ant territories, nor in the ratio of larvae retrieved from beneath plants by different ant species: the first Myrmica worker to encounter a larva retrieved it, and where two species overlapped there was no bias in retrieval towards one species. The distribution of the egg population on gentians is therefore an accurate surrogate for the distribution of the final instar population entering nests of each Myrmica species. Adult estimates of M. rebeli were obtained by recording eclosing individuals along stratified transects across sites, and identifying the nest after confirming that it contained an empty pupal case. Additional data were obtained by excavating all Myrmica nests near gentians along stratified transects that had supported known densities of eggs the previous year, and counting the pupae they contained. No mortality has been recorded in pupae in Myrmica cells before eclosion.