Introduced Hawk Moth Pollinating Prairie Orchid
In the video above, a Spurge hawk moth (Hyles euphorbiae (L.)) visits the threatened Western prairie fringed orchid (Platanthera praeclara). This moth species is native to Europe and was intentionally introduced to North America (Montana and North Dakota) in the 1960s as a biological control species for Leafy spurge (Euphorbia esula L.), an invasive weed that was unintentionally introduced to the United States in the early 1800s. The larval stage of the moth feeds on leafy spurge. The spurge moth was first recorded in southeastern North Dakota (the location of one of the three remaining metapopulations of the orchid) in 2000 and since then has boosted pollination rates for the orchid, which appears to have relatively small numbers of native pollinators. During the video the moth is seen visiting flowers to feed on nectar. The moth uses its 30-40 mm long tongue (proboscis) to search for and feed on nectar. During these visits, pollen sacs of the orchid sometimes attach to the moth’s compound eyes (listen for comments indicating when this happens) and are held on a stalk in front of the moth’s head. Pollen contacts the stigma of the flowers subsequently visited for nectar. (Video by Kristina Fox, NDSU Master’s student.)
Native Hawk Moth Pollinating Prairie Orchid
In the video above, a Hermit sphinx hawk moth (Lintneria eremitus (Hübner)) visits flowers in the orchid inflorescence to feed on nectar (12 microliters) in the 50 mm long spur. When the moth feeds, its large compound eyes contact the flower’s sticky pads (viscidium) that attach to a pollen sac (pollinium). When the moth departs, the pollen sac also departs and takes up a position directly in front of the moth’s head. When the moth next visits a flower, pollen falls on the stigma. The result is an orchid seed capsule that can contain up to 20,000 tiny seeds (3.5 microns length). Moths have been found with up to 8 pollinaria attached to a compound eye. (Video by Kristina Fox, NDSU Master’s student.)
Reorientation of orchid pollen sac on head of hawk moth
In the videos of introduced and native hawk moths you have seen moths picking up pollen during visits to the western prairie fringed orchid. What you cannot see is that the pollen is enclosed in a membranous sac (the pollinium) that is attached to a stalk (the caudicle), which itself ends in a sticky pad (the viscidium). This entire structure (the pollinarium) attaches to the compound eye of the hawk moth when the sticky pad adheres to the eye’s convex surface. As the moth flies away from the flower, the pollen sac is pulled out of its pocket (the anther sac), which normally protects it, and the entire structure (the pollinarium) is removed from the flower. As shown in the video, the pollen sac, the yellow-orange structure on a stalk, takes up a position to the side of the moth’s head. However, as the stalk bearing the pollen sac twists over a period of 10-20 seconds, the pollen sac moves closer to the central axis of the moth's head, a better location for depositing pollen on the stigma of the next flower that is visited by the moth. Note that the moth in the video is lying on its back so that you can see its proboscis, which is curled up. The proboscis is extended when the moth is searching for or feeding on nectar. You also can see the moth’s two antennae and one of its compound eyes, which is black and located between the antenna and the proboscis. The pollen sac is attached to the compound eye that cannot be seen.