Pollination by biting midges in Dioscorea tokoro and Vincetoxicum aristolochioides with a secondary contribution of gall midges

Abstract

Although small flies, such as those of the suborder Nematocera, are abundant and well-known flower visitors, their importance as pollinators is not fully appreciated. In this study, we attempted to identify the pollinators of Dioscorea tokoro (Dioscoreaceae) and Vincetoxicum aristolochioides (Apocynaceae). Our working hypothesis was that these species are pollinated by gall midges (Diptera: Cecidomyiidae), because gall midges visited flowers and laid eggs in them during our preliminary observations. Flower visitors were investigated using direct observations, time-lapse photography, and sticky traps installed close to the inflorescences. A supplemental pollination experiment demonstrated that D. tokoro was not wind pollinated. In both plant species, several genera of nocturnal gall midges were the most frequent flower visitors, followed by diurnal biting midges (Diptera: Ceratopogonidae) belonging to the Forcipomyiinae. Less frequent visits by members of the Sciaridae (Diptera) and Lepidoptera also were observed. Examination of body pollen revealed that biting midges carried pollen on several areas of their bodies, but gall midges were infrequent pollen carriers for either plant species. DNA barcoding showed that gall midges carrying pollen differed from those that engaged in oviposition. Our results suggested that the two plant species were primarily pollinated by biting midges with a smaller contribution from gall midges. This study highlights the importance of biting midges as pollinators. Biting midges also pollinate cacao and several wild plant species, and they may potentially also pollinate crops, such as yam, some of which have floral traits similar to those of D. tokoro.