Wasp Wednesday: Wasp vs. Bug

Back when I wrote about the Brown Marmorated Stink Bug, Halyomorpha halys, it was an introduced species from Eurasia that was no more than an indoor nuisance pest in the U.S. in the fall and winter. It has since ballooned into a certifiable agricultural pest in apple and peach orchards, and also vineyards. So panic-stricken are government officials that congress is attempting to pass a $831,000 “farm bill” to find ways of combating the bug. Enter a native wasp, Bicyrtes quadrifasciatus, pictured below.

The wasp is a type of “sand wasp” that preys on true bugs in the order Hemiptera, suborder Heteroptera. Each female wasp digs a burrow in sand, and stocks the cell at the end of the tunnel with paralyzed true bugs that will serve as food for a single larval offspring. Turns out that the Brown Marmorated Stink Bug has become a favorite target of the wasp, which hunts the immature stages of the pest (see figure below).

Alex Surcică has noticed this trend, and wants to document the efficiency of the wasps in controlling the bug. To that end he recently posted this message on his Facebook page:

"Seeking collaborators interested in collecting data on the nest provisioning of the sand wasp, Bicyrtes quadrifasciatus. This solitary (read non-aggressive) wasp occurs throughout North America, east of the Rocky Mountains, and it nests only in sand, along water ways or in sand volleyball courts and kids sandboxes. For making observations, one needs a garden trowel, pen, and notebook. The results of this citizen-science project will be used to assess the role the sand wasp plays in controlling the Brown Marmorated Stink Bug, a multi-million dollar pest. If interested, reply and I will send you more info. Please take an extra moment and share this with your FB friends. Thank you!"

Alex also posted a series of images on his “Bees, Wasps, and Other Beneficials” Facebook page that details how he painstaking excavates Bicyrtes nests to census the number of each prey species taken by the wasp:

“When I'm collecting data on the nest provisioning of the sand wasp, I'm waiting to see a female with her paralyzed prey entering her nest. While she's inside (sometimes can take minutes), I use a twig to mark the nest. I always position the twig three inches to the left of the nest entrance, and at a slight angle that will indicate later on where tunnel was leading to. Once the nest is marked, I search for other nests. Female sand wasps tend to initiate many nests but do not always end up using them. Therefore, I always mark only the nests that had females with prey entering them.”

I heartily applaud Alex for attempting this endeavor; and I encourage my readers to become part of his effort. Bicyrtes quadrifasciatus is common over most of its range, and several females may nest in the same general vicinity. So, once you find one nest, you are likely to find others.

Meanwhile, the U.S. Department of Agriculture is considering importing a parasitic wasp from the geographical area overseas where the stink bug is native. Introductions of parasites as “biocontrols” have not always ended well. There is the risk that the “new” parasite from abroad will find our native, non-pest stink bugs as acceptable a host as the Brown Marmorated Stink Bug. Maybe the native bugs would be even more attractive to the parasite. That kind of scenario has happened before.

I thank Alex Surcică for allowing the use of his images in this post as well. Do check out his “Bees, Wasps, and Other Beneficials” Facebook page for more stunning photos.

Wasp Wednesday: Bicyrtes

Among the most commonly encountered members of the “sand wasp” guild are the eight North American species in the genus Bicyrtes (By-SIR-teez). Two species in particular are widespread in the U.S. and adjacent southern Canada. They are much more sedate and easier to approach than most other members of the subfamily Bembecinae (family Crabronidae), and their predatory habits earn them some respect as well.

Female Bicyrtes actively hunt the nymphs of stink bugs in the family Pentatomidae as food for their larval offspring. The next time your child turns up their nose at Brussels sprouts, let them know it could be a lot worse. Actually, the accepted prey of these wasps includes equally odorous leaf-footed bugs (Coreidae), and shield bugs (Scutellaridae) and assassin bugs (Reduviidae) have also been recorded.

Wasps that burrow in the soil are termed “fossorial,” and a female Bicyrtes is an excellent digger. She can nest in soil of a more coarse texture than most other sand wasps. I imaged this Bicyrtes quadrifasciata excavating a nest in South Deerfield, Massachusetts in fairly rocky soil on the site of a former pickle factory, long since razed but with pavement fragments and pebbles in abundance.

While many sand wasps nest in dense aggregations of dozens (if not hundreds) of individual females, I find that Bicyrtes tends to be more of a loner. The wasp uses a “tarsal rake” of spines on the segments of her front tarsi (“feet”) to tunnel about 15-20 cm down into the soil at a shallow angle. Depending on the species the burrow terminates in a single cell, or several cells branching from the main tunnel. She closes the burrow while she goes off hunting prey.

When returning from a successful hunt, the wasp uses subtle landmarks to relocate her hidden nest. Meanwhile, we can’t remember where we parked the car.

Most sand wasps practice “progressive provisioning,” feeding their larval offspring as they grow, but Bicyrtes stockpiles prey, laying an egg on the first victim to go into a given underground cell. Once she completes a nest, she sets out to repeat the process, having cached enough food ahead of time that she needn’t hang around to spoon feed her children.

Both male and female Bicyrtes are very fond of nectar, and become distracted enough at flowers that they can be closely approached. Look for them on the blooms of Dogbane (and the related Indian Hemp) as well as milkweeds, white sweet clover, wild carrot (Queen Anne’s Lace), and a variety of other weeds.

Bicyrtes can easily be told from similar wasps by the very boxy appearance of the back of the thorax. The angular hind corners of the thorax are often white. Plus, if you are able to get close enough to see that character, you are looking at something other than sand wasps like Bembix and Steniolia that stick around for about a millisecond before zipping off to parts unknown.

I leave you with a parting shot of a female Bicyrtes from Bentsen Rio Grande Valley State Park in Mission, Texas that I have yet to identify to species. Maybe one of you can solve the mystery. In any event, keep an eye out for these wonderful wasps that stick it to our stink bug foes.

Sources: Evans, Howard E. 1966. The Comparative Ethology and Evolution of the Sand Wasps. Cambridge, Massachusetts: Harvard University Press. 526 pp.
Krombein, Karl V. et al. 1979. Catalog of Hymenoptera in America North of Mexico. Washington, DC: Smithsonian Institution Press. Vol. 2, pp 1199-2209.