Effects of artificial pollination and herbivore exclusion on the fruit set and seed production of the golden orchid Cephalanthera falcata in Japan

Abstract

The golden orchid Cephalanthera falcata is on the verge of extinction from Japan due to foraging by the agromyzid fly Japanagromyza tokunagai and the decline of pollinator bees. Artificial pollination and bagging treatments that exclude foraging flies are promising conservation measures. I examined the rates of fruit set and ripe seed production resulting from the artificial pollination and bagging of C. falcata at one field site in Fukui Prefecture, Japan. I tested 13 individuals over 3 years from 2021 to 2023, classified into three treatment groups: (1) no artificial pollination + no bagging (8 individuals), (2) artificial pollination + no bagging (3 individuals), and (3) artificial pollination + bagging (2 individuals). Artificial pollination resulted in an average of 4 fruits per individual (range: 1–6 fruits), while untreated plants produced 2.1 fruits on average (range: 1–6 fruits; Wilcoxon’s rank sum test, p = 0.151). Additionally, the mean damage rate per individual, which was calculated as the proportion of fruits damaged by J. tokunagai out of all fruits, was 0% in the bagged group and 100% in the untreated group (Wilcoxon’s rank sum test, p < 0.001). Thus, the bagging of C. falcata produced statistically significant improvements in ripe seed production. However, artificial pollination of C. falcata did not produce statistically significant improvements in fruit set production. My results suggest that fruit set production is not affected by artificial pollination for C. falcata. The damage of C. falcata by J. tokunagai is quite noticeable, with serious implications for the species’ ongoing reproduction and survival.