Effects of artificial pollination and herbivore exclusion on the fruit set and seed production of the rare orchid Calanthe discolor in Hokuriku District, Japan

Abstract

Abstract: The rare orchid Calanthe discolor is on the verge of extirpation 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. We examined the rates of fruit set and ripe seed production resulting from the artificial pollination and bagging of C. discolor at five field sites in Fukui Prefecture, Japan. We tested 24 individuals over 2 years from 2021 to 2022, classified into three treatment groups: 1) no artificial pollination + no bagging (13 individuals), 2) artificial pollination + no bagging (5 individuals), and 3) artificial pollination + bagging (6 individuals). Artificial pollination resulted in an average of 5 fruits per individual (range: 1–9 fruits), while untreated plants produced only 0.2 fruits on average (range: 0–2 fruits; Wilcoxon rank sum test, p < 0.0001). Additionally, the average percentage of each plant damaged by flies such as J. tokunagai was 0% in the bagged group and 56% (range: 0–100%) in the untreated group (Wilcoxon rank sum test, p < 0.01). Thus, both artificial pollination and bagging of C. discolor produced statistically significant improvements in fruit set and ripe seed production. Our results suggest that pollination opportunities are reduced in untreated C. discolor, with serious implications for the species’ ongoing reproduction and survival.