Cockroach pollination ensures sexual reproduction in the non-photosynthetic plant Balanophora tobiracola.

Abstract

While Coleoptera, Diptera, Hymenoptera, and Lepidoptera have traditionally been recognized as key pollinators, recent studies suggest that other insect groups, such as Blattodea (cockroaches), may also play a significant role. However, direct evidence of fruit set resulting from cockroach pollination remains limited, even in plants presumed to rely on this mode of pollination. This study investigated the breeding system of the non-photosynthetic plant Balanophora tobiracola on Yakushima Island, Japan, with a particular focus on the potential occurrence of agamospermy. Additionally, the research rigorously evaluates the pollination effectiveness of cockroaches and ants in B. tobiracola by assessing reproductive success exclusively through their visits. Pollination experiments revealed high fruit set even under emasculation, indicating that agamospermy ensures seed production. However, B. tobiracola still relies heavily on pollinator activity for sexual reproduction. Ants and cockroaches were identified as effective pollinators, whereas contributions of pyralid moths, crane flies, and nitidulid beetles-whose larvae consume B. tobiracola infructescences-were negligible. Notably, a single visit from certain cockroach species significantly enhanced pollination. The above findings demonstrate that B. tobiracola is effectively pollinated by cockroaches and ants. Combining unusual pollinators with agamospermy likely facilitates the reproductive success of B. tobiracola in dense forest understories where typical pollinators, like bees, are scarce. Our results underscore the need to reassess the role of agamospermy as reproductive assurance and the significance of cockroaches and ants as pollinators, particularly for plants in shaded understory habitats.