Moths and Bees Steal Nectar From Rare Orchids, Researchers Say

One reason Western prairie fringed orchids (Platanthera praeclara) are one hte decline in North Dakota may be due to sneaky romaing hawk moths and bumble bees and a little feeding technique they're using that scientists call "nectar larceny," which is when they remove nectar without providing critical pollination services. Understanding how "nectar larceny," works could help conservations protect rare orchid populations which are listed as a threatened species. 

To better understand nectar larceny, researchers set up net and light traps over the orchids and captured various species of hawk moths and bumble bees, according to a news release.

Among the specimens collected were two hawk moth species, Manduca quinquemaculata and Agrius cingulate. Both of these species are not common in North Dakota and were found to have tongues more than twice the length of the orchid spurs. This means that they could reach deep into the nectar-filled sacs from farther distances, without pollinating the plant. 

Researchers also captured eight bumble bee species. Some of the bees had mouthparts that enable them to cut through the side of a flower's spur without having to be covered in pollen. Since the researchers also found holes and slits in the spurs of many orchids, they concluded the bees were making off with the nectar without pollinating the plants and ultimately killing the plants.

"Plant conservation scientists spend most of their time thinking about factors that directly impact rare plants," Marion Harris, a professor at North Dakota State University and one of the study's authors, said in the release. "Typically, this factor is habitat loss. But for plants that require pollinators for reproduction, you can increase the habitat of the rare plant all you want but fail to save the plant if you ignore the needs of the plant's pollinators. Hawk moth pollinators need larval host plants and nectar for adult reproductive activities. They presumably pay less attention to plants that lack nectar because of nectar robbery or thievery and are harmed by failure to find nectar."

Researchers also noted that it is not uncommon to see hawk moths far from their southern U.S. habitats. However, they are still unsure why these moths have ended up farther north. If this migration becomes a trend, orchids could face increased devastation.

"We propose that nectar larceny will negatively impact the orchid if it occurs at higher levels each year (in the case of robbery) or starts occurring every year due to increased northward migration of long-tongued hawk moths that typically live in the south (in the case of thievery)," Harris added.

This research coincides with previous rare orchid declines that occurred in areas where two additional long-tongued hawk moths normally breed. However, this correlation requires further research. Researchers also noted they plan to test the effects of nectar larceny over different flower populations. From this, they can determine if orchids tolerate, or even benefit from, small amounts of nectar being stolen. 

The study was recently published in the Annals of the Entomological Society of America. 

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