From The Xerces Society for Invertebrate Conservation
Whether you wake to find mist hanging in damp hollows, snow draping the last of your tomato vines, or sunshine glinting off a warm sea, there is one thing that unites us all this month: pumpkins. With Halloween quickly followed by Thanksgiving, pumpkins seem to define this season. We make family trips in a quest for the perfect jack-o’-lantern, dress up in pumpkin costumes to go trick or treating, decorate our homes with them, and slice them up to make pies, bread, and soup.
Pumpkins are native to Central America and the desert Southwest. The pumpkin we typically carve or cook is a species called Cucurbita pepo, although there are four species of Cucurbita that include cultivars called pumpkins. With corn and beans, pumpkins and other squash form the “three sisters,” a staple part of Native American agriculture. Because of this, pumpkins spread to new areas of North America, including New England, where Native tribes introduced the early Pilgrims to pumpkins. This was fortunate for the settlers, as pumpkins helped them fend off starvation during their first winters.
The squash bee (Peponapis pruinosa) relies on pumpkins for survival, and seems to have followed pumpkins across the continent. The bee is a specialist forager and will only collect pollen from squash flowers. Females often nest in the ground around the base of pumpkin plants, and males take shelter in flowers overnight. Because of this, it must once have been limited to areas in which pumpkins are native.
Yet today the squash bee has expanded its range, adapting to dramatically different climates and environments, and is found as far south as Florida and north as Ontario. These bees can often be found in home gardens, and will even colonize newly created community gardens amid the tall buildings and parking lots of a city, witness to their amazing ability to follow squash plants!
Although squash bees depend on pumpkin plants, it is not a one-way relationship. Squash bees are highly efficient pollinators of pumpkin flowers. Pumpkin flowers open at dawn, a period of the day that can be too dark or too cold for most bees to be active. The squash bee, however, is adapted to fly in these conditions. It is an early riser, and will often be up half an hour before dawn, the perfect time to visit squash flowers. The bees also have widely spaced hairs in their pollen brush (a patch of hairs for carrying pollen), an adaptation to cope with pumpkin flowers’ large pollen grains.
Squash bees are not the only bees that pollinate pumpkins, which is fortunate for those of us living in the few areas these bees haven’t yet reached. There are four other species of Peponapis and a few species in the closely related genus Xenoglossa, which are also squash specialists. None of these are as abundant or widespread as the squash bee, nor as adept at moving into new areas.
Bumble bees, including the common eastern (Bombus impatiens) and the two-spotted (Bombus bimaculatus), also are regular visitors, as is the long-horned bee Melissodes bimaculata, which is often seen on pumpkins in gardens of the eastern U.S. In addition, many farmers rent honey bees (Apis mellifera) to pollinate fields of pumpkins. This range of pollinators ensures the sustainability of North American pumpkin crops and our access to the perfect Halloween pumpkin.
The Xerces Society is a nonprofit organization that protects wildlife through the conservation of invertebrates and their habitat. For more information visit www.xerces.org.
