(Beyond Pesticides, August 2, 2017). August’s PolliNATION Pollinator of the Month is the Pollen Wasp! Pollen wasps, of the small subfamily Masarinae are the only “vegetarian” wasp in the family Vespidae., They feed solely on nectar and pollen, unlike their more aggressive Vespid wasp cousins. There are 300 species of pollen wasp from 14 genera spread across the globe, however, in the U.S., all 14 species of pollen wasps originate from the genus Pseudomasaris.
Pollen wasps are found throughout the world, though they tend to concentrate in arid areas of southern Africa, and North and South America. They are not documented in the tropics or in Antarctica. In the United States, they can be found from Washington to as far south as New Mexico, and as far east as Nebraska. They are solitary pollinators who make their nests out of mud, often attached to branches, rocks, or hanging off ledges.
Diet and Pollination
Pollen wasps differ from their omnivorous Vespid wasp relatives by rearing their young on nectar and pollen, rather than other insects. They are the only Vespid species which do so. Their nests, made up of a mixture of soil and nectar, are usually comprised of 4-10 parallel cells that hold an egg, nectar, and a small pollen patty. Pollen wasps then seal their nests with mud. Before emerging, newborn larvae consume the stored food, pupate, and break then through the mud seal as adults.
Pollen wasps are known to specialize in foraging on very specific flowers, including beardtongues, borage, and tansies, though there are also reports of the insects feeding on mallows and marigolds. These wasp pollinators have long proboscis that allow them to reach nectar in their preferred flowers species. Most bees will use corbicula, or “pollen baskets,” a small indent surrounded by hairs on their back legs, to secure collected pollen before bringing it back to a nest or hive. However, pollen wasps do not have corbicula, but instead exclusively collect pollen in their crop –an expanded portion of the pollen wasp’s digestive track that can be used to temporarily store pollen and nectar, and which they will subsequently use to feed their young.
Pollen wasps are generally striped with colors that may include red, brown, black, white, and yellow. Pseudomasaris species in the United States are often mistaken for yellow jackets, as they both share the same striped yellow and black pattern across the top of their abdomen. However, the major distinguishing characteristic between the two wasps are is the shape of their antennae. While the yellow jacket’s antennae stick straight out, the pollen wasp’s antennae is clubbed at the end. In contrast to the mud nests of the pollen wasp, a yellow jacket nest is made of paper and grows to thousands of cells by late summer.
There is no reported explanation in current scientific literature for the similarity in appearance between pollen wasps and yellow jackets. However, it may be a form of Batestian mimicry, whereby the relatively docile pollen wasp invokes the warning signals of the more aggressive yellow jacket. While the pollen wasps rarely sting, they are capable of doing so. Unlike honey bees and like their closer wasp relatives, their stinger is not barbed, allowing the insect to sting multiple times.
Ecological Role and Threats to Existence
Pollen wasps can play an important role in pollinating certain flowers. For instance, the United States Forest Service (USFS) notes that the pollen wasp species Pseudomasaris vespoides specializes in pollinating beardtongue. It has been observed pollinating the blowout beardtongue, an endangered flowering plant limited in range to nine counties in Nebraska and one location in Wyoming. A number of additional rare beardtongue species rely on P. vespoides pollination, giving the insect an important role in maintaining ecological diversity in the Western U.S.
As the National Research Council (NRC) noted in its 2007 report on the status of pollinators in North America, data on the prevalence and distribution of Pseudomasaris species is sparse. For example, P. micheneri has only been observed in the Inyo Mountains of California, and that research was conducted as far back as the 1940s. Another species, P. macswaini, is suspected of having a very limited distribution in California and may be at risk, according to NRC.
How to Protect the Species
One of the most important actions one can take to protect pollen wasps is eliminating the use of pesticides that can harm these unique insects. Neonicotinoids, once applied, will make their way into a plant’s vascular system, and express itself in pollen and nectar, putting pollen wasps at risk. Other insecticides, like synthetic pyrethroids, are acutely toxic to many non-target pollinators, and may leave harmful residue on plants and their flowers once applied. Since there is little data on the range and distribution of pollen wasps, encouraging public land managers to forgo the use of insecticides and herbicides in natural areas can make an important impact on the availability and quality of forage for pollen wasps.
Although there is insufficient data on pollen wasp flower preferences, and one cannot guarantee the strain of beardtongue planted, for instance, will be attractive to pollen wasps, establishing a diversity of flowers in one’s garden will foster a diversity of pollinators. In addition to beardtongues, residents within pollen wasp range can try to attract these insects by planting water leaf species, borage, and tansies. Lastly, use careful judgement before swatting at lone yellow jackets, or going after their nests, as they may be easily mistaken pollen wasps.
BugGuide.net. 2005. Subfamily Masarinae- Pollen Wasps. http://bugguide.net/node/view/22272
Eaton, Eric. 2011. Wasp Wednesday: Pollen Wasp. http://bugeric.blogspot.com/2011/11/wasp-wednesday-pollen-wasp.html
Encyclopedia of Life. N.D. Pollen Wasps. http://eol.org/pages/5243/details
National Research Council. 2007. Status of Pollinators in North America. https://www.nap.edu/catalog/11761/status-of-pollinators-in-north-america
United States Forest Service. N.D. Pollen Wasps. https://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/masarines.shtml
Xerces Society. 2011. Attracting Native Pollinators. https://books.google.com/books?id=ry243ZLP2OAC&printsec=frontcover#v=onepage&q&f=false