Ineffectiveness of ants in protecting two sympatric myrmecophilous plants against endophytic beetles

Extrafloral nectarized plants attract ants, which may protect them against herbivory and increase plant fruit set production. In some cases, however, ants are ineffective against herbivores. Such events occur, for instance, when herbivores present adaptations to avoid ant predation. Thus, the outputs of these interactions depend on factors such as ant identity, plant phenology and herbivore features. Here, we investigated the endophytic florivorous beetles' impact on the reproductive success of their host plants, two sympatric Banisteriopsis (Malpighiaceae) species, depending on the action of extrafloral nectaries (EFNs) visiting ants. We experimentally manipulated the presence of ants and herbivores on B. malifolia and B. laevifolia species during their reproductive period to test the effectiveness of ants-EFNs mutualism on plant fruit set production. We performed treatments where three similar inflorescences were selected to be (I) control branch, with no manipulations, (II) beetle-free branch, isolated with textile cover and (III) ant-free branch, isolated at the base with atoxic wax. We hypothesized that endophytic herbivores have a negative impact on the plant reproductive success because they escape the action of ants (biotic defences). As a result, we observed (i) that florivorous Anthonomus beetles have a negative impact on Banisteriopsis reproductive success; (ii) ants fail in protecting plants against floral endophytic beetles; and (iii) most of the results were species-specific. Our results indicate that these systems present very conditional outcomes that depend on the intrinsic factors of each plant species.

Automated summary

This study investigated the impact of endophytic florivorous beetles on the reproductive success of Banisteriopsis plants, and examined the role of ants visiting extrafloral nectaries (EFNs). The results showed that the outcomes of these interactions depend on intrinsic factors of each plant species.