WHITE RIVER JUNCTION – As a budding ecologist who grew up in central Texas, I’ve long been an admirer of the Pink Evening Primrose (Oenothera speciosa). I said a mournful goodbye to the delicate wildflowers before my parents moved up to Vermont. After a few months of living here, I was surprised and delighted to learn that the Common Evening Primrose (Oenothera biennis) would show up in midsummer, decorating the hillsides of my new home. This taste of Texas is native to eastern and central North America, where its bright yellow color, four petals, and long stamen make it a common sight during Vermont summers. Primrose is pollinated by multiple moth and bee species where it grows in fields, thickets, and along woodland borders. And though it attracts a plethora of pollinators, two have a specialized relationship with the flower.
Primrose Moth (Schinia florida) in Aitken State Forest, Mendon, Vt.
Among the insects that aid in the pollination of this primrose, none are as well equipped for the task as the Evening Primrose Sweat Bee (Lasioglossum oenotherae). These sweat bees have developed a close relationship with this and other narrow-leafed primroses due to one defining characteristic, the long leg hair of the female worker bees. These large, shiny, black bees’ scopa, the masses of hairs on its legs, have evolved to be maximally efficient at handling evening primrose’s pollen grains, which are held together by sticky threads called viscin. Once caught on the sweat bee’s distinctive leg hair, ropes of primrose pollen can be transported to another flower. Essentially, we can think of the scopa as hooks that transfer chains of pollen among plants as sweat bees collect the pollen to feed to larval young. In this manner, the cycle continues for generations of both plants and insects.
This hairy relationship isn’t Common Evening Primrose’s only specialized plant-insect interaction. The Primrose Moth (Schinia florida) is clad in cute pastel colors that may remind Vermonters and moth lovers alike of the Rosy Maple Moth (Dryocampa rubicunda). Except, rather than a maple tree, this yellow and pink moth uses the Common Evening Primrose flower as a host for its lifecycle.
Unlike the pollinating Primrose Sweat Bee, the Primrose Moth is greedy in its relationship to the evening primrose. The cycle of selfishness starts when an adult moth lays its eggs in the primrose flower. Then, instead of helping the host plant out by pollinating the flower, the larvae munch on the flower buds, damaging the plant’s reproductive organs. However, it’s only when larval populations are especially high that any serious damage is done via herbivory.
After an unfortunate loss for the plant and a nutritious meal for the moth, the former caterpillars emerge from their cocoons as winged adults. At this stage, the moths spend their time hiding in partially closed flower buds during the day, camouflaging into the plant so an onlooker would only see the creamy yellow tips of their wings popping out from the petals. When the sun sets, the flower buds open and the moths come out, ready for a sugary drink. The Primrose Moth has a notably long proboscis (about half of its entire body length!) that they use to drink nectar from the flowers.
The adult moths go on to spend their days drinking nectar through their straw-like tongues. As the flowers begin to wilt, and their sunny yellow fades to a pink color, the Primrose Moth remains camouflaged thanks to its pink fuzz. These pink pastel pests have now taken advantage of the Common Evening Primrose throughout every stage of their lifecycle without providing the benefit of pollination. Despite the hungry caterpillars eating the buds of the plant, this plant-insect interaction continues through generations of both flowers and moths.
Interspecific relationships range across a spectrum from mutually beneficial to mutually harmful. On the positive end of the spectrum, the Common Evening Primrose gets what it needs from the Primrose Sweat Bees’ pollination as the sweat bee harvests pollen and nectar. In a more one-sided specialized relationship, the Primrose Moth gets a camouflaged refuge and food source throughout its life cycle. Together, these relationships and the ones in between make up the complex ecological web present in the natural systems around us.
Gita Yingling is on the staff at the Vermont Center for Ecostudies.
Gita Yingling
