COS 117-4 - Using motion-triggered video monitoring to identify Platanthera orchid pollinators and their potential role in hybridization

Background/Question/Methods

Insects provide a valuable ecosystem service through pollination. Through the transfer of pollen, insects may facilitate hybridization between species, barring other methods of reproductive isolation. Numerous orchid species are able to naturally hybridize, despite often having specific pollinators. The Platanthera orchids are widespread across North America, with many hybrids being described. However, little is known about how this occurs. Two species which can grow in sympatry on Vancouver Island, British Columbia (BC), Canada, P. dilatata and P. stricta, have been reported to produce the hybrid P. ^xestesii. While pollinators for these species are unknown in BC, the former species has been reported to be pollinated by Lepidopterans, while the latter is pollinated by various short-tonged insects (e.g., bees and flies). The questions asked by this study were: 1) what insects are pollinating these orchids on Vancouver Island, and do they differ from pollinators reported elsewhere, and 2) are there any shared insect pollinators for these two orchid species which may be facilitating hybridization? These questions were answered using motion-triggered continuous video monitoring during the summer of 2020 in Strathcona Provincial Park on Mt. Washington. Diurnal and nocturnal Raspberry Pi cameras and motherboards were used for these observations.

Results/Conclusions

We recorded 753 videos, with 655 showing insects and 91 showing arachnids. A total four orders, 11 families, 12 genera, and 10 species were identified for the two weeks of observations. Three families were seen removing pollinia from P. dilatata (suggesting pollination): 14 bumblebees (nine B. flavifrons, one B. mixtus, one B. sitkensis, and three unidentified Bombus spp.), a fritillary butterfly (Speyeria hydaspe), and one unidentified noctuid moth. No insects were seen removing pollinia from P. stricta, and only one pterophorid moth was active in the flowers of both species. Our study shows that this method of video observation if effective for identifying and characterising the behaviours of potential pollinators. These findings have implications for the pollination ecology of these Platanthera orchids. The species identified as potential pollinators of P. dilatata had not been reported elsewhere for the orchid, highlighting how pollinators may differ through a species’ range. While no insects were observed pollinating both orchid species, a shared floral visitor was observed. These orchids vary visually (colour and spur length) and chemically (scent production), and it is unknown how they are attracting their pollinators. Shared visitors and pollinia transfer between them may be rare.