Ants and lycaenid butterflies have evolved a mutualistic relationship, where ants feed on carbohydrate-rich secretions from butterfly larvae and in return provide protective or physiological benefits to the butterfly. Invasive species are becoming increasingly more prevalent in native habitats and may negatively impact these butterflies, either directly by predation or indirectly by disrupting the existing ant-larval interactions. The Miami blue butterfly (Cyclargus thomasi bethunebakeri) is a federally endangered butterfly found only in the Florida Keys and has a mutualistic relationship with ants. Frequency of ant tending by carpenter ants (Camponotus floridanus) increases adult female size and fitness. In order to study the protective benefits ants may provide to the Miami blue against insect predators, we conducted a causal experiment using a common lepidopteran predator: spined soldier bug (Podisus maculiventris). We also evaluated predation rates on Miami blue life stages from two invasive ants: Pseudomyrmex gracilis and Solenopsis invicta. Timed observational trials were conducted in outdoor enclosures on potted host plants and video cameras captured interactions. Ant interactions and behavior type were categorized using an ethogram and a three-way contingency was used to assess how behavior benefits protection (Ant Species X Butterfly Life Stage X Behavior). A life table determined which life stage has the highest probability of being predated.
Results/Conclusions
Frequency of ant tending by C. floridanus was consistent in the presence and absence of Podisus maculiventris. In the presence of P. maculiventris, C. floridanus aggressively defended fourth and fifth instar larvae by chasing the predator off the host plant. Both C. floridanus and S. invicta ignored Miami blue eggs on host plants, but P. gracilis was removed and predated the eggs in the majority of trials. Difference in survivorship life stages was significant: eggs and early instar larvae had a higher probability (65%) of being predated since these life stages are not tended as frequently. Mortality of Miami blue larvae was 3-5 times higher in the absence of C. floridanus, suggesting that these tending ants can be effective in protecting later instar larvae against hemipteran predators. These results are critical for successful organism reintroductions and conservation efforts for the Miami blue butterfly, especially during a critical time as species interactions are changing in this vulnerable habitat.