Specialization for Tachinid Fly Pollination in the Phenologically Divergent Varieties of the Orchid Neotinea ustulata

Abstract

Despite increased focus on elucidating the various reproductive strategies employed by orchids, we still have only a rather limited understanding of deceptive pollination systems that are not bee- or wasp-mediated. In Europe, the orchid Neotinea ustulata has been known to consist of two phenologically divergent varieties, neither of which provide rewards to its pollinators. However, detailed studies of their reproductive biology have been lacking. Our study aimed to characterize and understand the floral traits (i.e., morphology, color, and scent chemistry) and reproductive biology of N. ustulata. We found that the two varieties differ in all their floral traits; furthermore, while Neotinea ustulata var. ustulata appears to be pollinated by both bees (e.g., Anthophora, Bombus) and flies (e.g., Dilophus, Tachina), var. aestivalis is pollinated almost entirely by flies (i.e., Nowickia, Tachina). Tachinids were also found to be much more effective than bees in removing pollinaria, and we show experimentally that they use the characteristic dark inflorescence top as a cue for approaching inflorescences. Our results thus suggest that while both N. ustulata varieties rely on tachinids for pollination, they differ in their degree of specialization. Further studies are, however, needed to fully understand the reproductive strategy of N. ustulata varieties.

Plant Attractants and Rewards for Pollinators: Their Significant to Successful Crop Pollination

“…Flower mimicry is a very diverse phenomenon, including Batesian mimicry, in which an unrewarding flower mimics a rewarding one, and Mullerian mimicry or signal normalization, in which two distinct rewarding flowers display similar signals [79,80]. The deception system has developed in different flowering plants families where about one-third of the species in the Orchidaceae family are well known to deceive their pollinators [80][81][82].…”

The genome sequence of Tachina fera Linnaeus, 1761, a tachinid fly

“…The parasitic nature of Tachinid species such as T. fera mean they are important, but underappreciated, regulators of insect herbivory in our ecosystem (Stireman et al, 2006), as well as playing important roles in pollination (e.g. Martel et al, 2021). The chromosome-level genome assembly presented here is, to our knowledge, the first high-quality resource developed for a Tachinid and represents a key step in understanding the complex ecology of these beautiful and spiky flies.…”

The evolution of tachinid pollination in Neotinea ustulata is related to floral cuticular composition and the combined high relative production of (Z)‐11‐C23/C25enes

“…aestivalis and var. ustulata ; Vöth, 1984; Martel et al, 2021). For instance, N. ustulata is pollinated by bees, beetles, and flies (Vöth, 1984; Mrkvicka, 1991; Martel et al, 2021), but tachinid flies are the most efficient pollinators and the ones attracted by the modified inflorescence dark top, which is unique among Orchidinae (except for O. purpurea Huds.).…”

“…ustulata ; Vöth, 1984; Martel et al, 2021). For instance, N. ustulata is pollinated by bees, beetles, and flies (Vöth, 1984; Mrkvicka, 1991; Martel et al, 2021), but tachinid flies are the most efficient pollinators and the ones attracted by the modified inflorescence dark top, which is unique among Orchidinae (except for O. purpurea Huds.). Bees, beetles, and some flies land on open flowers of N. ustulata and pollinate them when trying to reach the nectarless flower spur; however, tachinid flies land on the inflorescence dark top and inspect it to then also visit the open flowers seeking nectar (Martel et al, 2021).…”

“…For instance, N. ustulata is pollinated by bees, beetles, and flies (Vöth, 1984; Mrkvicka, 1991; Martel et al, 2021), but tachinid flies are the most efficient pollinators and the ones attracted by the modified inflorescence dark top, which is unique among Orchidinae (except for O. purpurea Huds.). Bees, beetles, and some flies land on open flowers of N. ustulata and pollinate them when trying to reach the nectarless flower spur; however, tachinid flies land on the inflorescence dark top and inspect it to then also visit the open flowers seeking nectar (Martel et al, 2021). Although tachinid males and females have been recorded pollinating N. ustulata , the overall predominance of males (Martel C et al, unpublished data) may indicate that, in addition to food‐based signals, N. ustulata also exploits gender‐specific signals (e.g., pheromones) (Martel et al, 2021).…”