Enemies of Mason Bees

Introduction

Mason bees (Osmia species) are common residents of bee hotels and are used for pollination in some commercial agricultural operations, such as apples and other tree fruit. They nest in pre-existing cavities, which they partition into individual cells using mud. These cells are provisioned with pollen and nectar for young bee larvae to eat. These pollen provisions, as well as the bee larvae themselves, attract parasites and other enemies that feed on the provisions or attack the larvae. Natural enemies can severely impact the survival rates of managed mason bees. Further, it is unknown to what extent these enemies spill out from managed mason bees and if they impact natural bee populations in the surrounding landscape. There are a number of groups that attack mason bees, including mites, various parasitic wasps and flies, fungi, and even birds. Being able to recognize mason bee enemies is the first step in mitigating their impact.

Arthropod enemies

Chaetodactylus mites

Order: Sarcoptiformes

Family: Chaetodactylidae

Genus: Chaetodactylus

Chaetodactylus mites are commonly called hairy-footed mites, hairy-fingered mites, or pollen mites (Figure 1). The mites are white to yellow to red in color and tiny: adults are 0.01 inches (0.5 mm) long, while immatures are even smaller, so early instars may be difficult to distinguish from pollen grains in an Osmia nest. They are often the most important pest of agriculturally-managed mason bees in North America and around the world.

Twenty-four Chaetodactylus species are described worldwide, of which ten occur in North America and three occur or are likely to occur in Pennsylvania. All but one Chaetodactylus species are associated with bees in the family Megachilidae. Many parasitize Lithurgus, Hoplitis, and other non-economic megachilid species but C. hirashimai and C. nipponicus (Japan), C. osmiae and C. zachvatkini (Europe), and C. krombeini (North America) are important pests of managed Osmia used for pollination services.

Hairy-footed mites are kleptoparasites. In most cases, they feed on the pollen provision and cause the bee larva to starve, but in some cases may feed on the larva directly. Multiple generations can occur per year, so a single female mite may give rise to thousands of descendants in a season. The mites cannot break through the mud nest partitions, so must wait for bees further back in the nest to emerge and chew through the mud (Figure 2). When this happens, nymphal mites will climb onto the bee and ride on it until it starts its own nest. Although they do not directly attack or feed on adult bees, the presence of too many phoretic nymphs on a bee can hinder its ability to fly. In extreme cases, over 1,500 of these mites have been found on a single O. cornifrons female (Figures 3, 4).

If all of the bees in a nest die, hairy-footed mites can produce a non-phoretic nymph (Figure 5). This stage is immobile and sack-like, with highly reduced legs and other body parts. While they cannot move, these non-phoretic nymphs can persist for years, waiting for a new generation of mason bees to open up and reuse the nest, after which they awaken, molt, and start the cycle again.

Chaetodactylus mites are a major source of mason bee mortality. In Japan, C. nipponicus can cause up to 80% of managed mason bee mortality and annual yield losses of 30% when not treated, while in southern Europe C. osmiae are the second major cause of Osmia death along with Houdini flies. In North America, C. krombeini can cause up to 50% losses of mason bee offspring.

Monodontomerus wasps

Order: Hymenoptera (wasps, bees, ants, and kin)

Family: Torymidae

Genus: Monodontomerus

Monodontomerus are small (4–5 mm, 0.2 inches), dark metallic green wasps with a sculptured exoskeleton. Females have a laterally compressed abdomen and a long external ovipositor (Figure 6). The hind femora have a prominent tooth on the underside near the apical end.

Monodontomerus includes twenty-five species in North America. Different species have been recorded from various caterpillars, fly larvae, sawfly larvae, and nests of solitary bees and wasps. In North America, 12 species are known to attack Megachilidae, of which eight are recorded from Osmia nests specifically. Of those, M. montivagus and M. obscurus are recorded from Pennsylvania, while M. aeneus and M. mandibularis are reported from neighboring states and likely occur here. The non-native M. japonica may occur in the state as well.

Female wasps enter incompletely sealed Osmia nests, sting a bee larva to paralyze it, and then lay their eggs between the larva and the cell wall. Female wasps can also insert the ovipositor through thin mud caps or paper or cardboard nest tubes less than 1 mm (0.04 inches) thick (Figure 7). There are typically around 10, but up to 50 wasp larvae per cell. The Monodontomerus larvae consume the bee larva and then pupate before emerging up to a month later (Figure 8). Because of their fast development, multiple generations of Monodontomerus can occur per year. Monodontomerus overwinter as nearly mature larvae.

Figure 7. A female Monodontomerus ovipositing through a paper tube. Photograph by Trevor Sless via iNaturalist, used under a CC BY-NC 4.0 license.

Microdontomerus wasps

Order: Hymenoptera (wasps, bees, ants, and kin)

Family: Torymidae

Genus: Microdontomerus

Microdontomerus are similar in appearance to Monodontomerus but lack a large tooth on the hind femora. Otherwise, wasps in these genera look similar and are unlikely to be distinguished except by experts.

Microdontomerus includes 19 described species in North America. Most species are found in Western North America. Different Microdontomerus species have been recorded to attack caterpillars, beetle larvae, gall wasp larvae, or are hyperparasitoids (parasitoids that attack other parasitoids) of other parasitic wasp and fly larvae. Three species have been recorded from the nests of Megachilidae and one species, Microdontomerus parkeri, has been recorded from the nests of Osmia in particular. Microdontomerus parkeri is known from the Southwestern United States and does not occur in Pennsylvania.

Mellitobia wasps

Order: Hymenoptera (wasps, bees, ants, and kin)

Family: Eulophidae

Genus: Mellitobia

Mellitobia are tiny (0.5–1 mm, 0.02–0.04 inches) black or dark-colored wasps, usually with lighter-colored legs (Figures 9, 10). The antennae are elbowed. The head is compressed so that it looks long and thin from the side but round and wide from the front. Female wasps can either be macropterous (having full-sized, functional wings) or brachypterous (having small, non-functional wings), depending on how many eggs were laid on a host larva. Males are light-colored, blind, and nearly wingless, with large antennae. Males mate with their sisters and never leave the host cell, so are only seen if infested bee nests are removed and reared.

Mellitobia includes 7 species in the United States. All species apparently parasitize pupae and pre-pupae of a broad range of insect hosts, including various flies, beetles, moths, and social and solitary wasps and bees. Major outbreaks of Mellitobia have killed hundreds of thousands of alfalfa leafcutter bees (Megachile rotundata) in Utah since 2015. The Minnesota Bee Atlas project reported that Mellitobia were the most common and abundant parasitoids in bee blocks and attacked potter wasps, sphecid wasps, leafcutter bees, and mason bees. Melliobia are not a major pest of commercial Osmia in Pennsylvania but may be present in mixed-species bee hotels. 

Female wasps sting a host pupa or prepupa to paralyze it, usually within 48 hours of finding a suitable host (Figure 11). If a host is not available, or if it is still small and developing, a female Mellitobia can wait up to 60 days for it to grow and mature before stinging it and laying eggs. Multiple clutches of eggs (4–12) are laid per host, so dozens of tiny, white larvae may develop on a single host. Development from egg to adult can be as short as 9 days but typically takes around 20 days, so multiple generations can occur per year. Mellitobia typically overwinter as larvae, and occasionally pupae, in host cells.  Hundreds of wasps may emerge from a single larva.

Leucospis wasps

Order: Hymenoptera (wasps, bees, ants, and kin)

Family: Leucopsidae

Genus: Leucospis

Leucospis are medium-sized (10 mm, 0.4 inches) wasps with a sculptured exoskeleton. Five Leucospis species occur in the United States and Canada. Leucospis affinis, the most widespread, commonly encountered, and economically important species, is yellow and black. Other species are also yellow and black or red and black wasps. Females of most species have a laterally compressed abdomen and a long ovipositor that arches over the back of the abdomen. The hind femora are enlarged (in some species dramatically so) and have 5–8 teeth. The hind tibiae are curved. The wings fold longitudinally to mimic various paper wasps and yellow jackets (Figure 12).

Leucospis affinis occurs throughout the United States, including Pennsylvania (Figure 12). They have been reported to parasitize various resin, leafcutter, and mason bees (family Megachilidae), including Osmia, as well as potter wasp nests. They have been observed around but not reared from horn-faced bee (Osmia cornifrons) nests in Pennsylvania, so are unlikely to be a pest of this species. They appear to be attracted to the aggregation pheromone found in the cocoons. However, they may attack other species that are found in mixed-species bee hotels and a long ovipositor can reportedly bore through an inch or more of wood (Figure 13).

The four other Leucospis species are restricted to the southern or southeastern United States. Two red and black species and the red and black subspecies of L. affinis are found primarily in Florida, where they form a mimicry complex (Figure 14). Leucospis slossonae have been recorded from the nests of rotund resin bees (Anthidellum species). The hosts of other North American Leucospis are apparently unknown. Given this lack of reports, they likely do not parasitize Osmia or other commercially important species. 

Cuckoo wasps

Order: Hymenoptera (wasps, bees, ants, and kin)

Family: Chrysididae (cuckoo wasps)

Genus: Chrysura

Chrysura are medium-sized (6–12 mm, 0.25–0.5 inches), bright metallic green to blue-green wasps. The exoskeleton is heavily sculptured with pits and the abdomen has three visible segments (Figures 15, 16). The stinger is soft and incapable of stinging.

Forty-seven species of cuckoo wasps have been reported from Pennsylvania. All but one species parasitize the nests of various solitary and social bees and wasps. Three of the forty-seven species are known to parasitize Megachilidae, including Osmia. The most commonly, almost exclusively, encountered species is Chrysura kyrae. Chrysura pacifica has also been reported from the state, but it is easily confused with C. kyrae (differentiating the species requires examination of male genitalia or DNA), so older records may have misreported it. Chrysis cembricola usually parasitize the potter wasp Symmorphus canadensis. A single individual has been reared from a horn-faced bee (O. cornifrons) nest in Pennsylvania. This was likely an accidental parasitism since both S. canadensis and O. cornifrons construct mud nests in pre-existing cavities and tubes. Because other cuckoo wasps parasitize various solitary bees and wasps, other cuckoo wasp species may be found around mixed-species bee hotels (Figure 17).

Female cuckoo wasps enter an Osmia nest while it is still being provisioned and lay a single egg on the provisions. Once the nest is sealed, the wasp hatches and attaches to the bee larva. The Osmia larva continues to feed on the nest provisions and grow as the wasp larva grows with it. Once the Osmia larva matures, it is generally killed and consumed by the wasp larva. However, in some cases it may survive the wasp attack and pupate into an adult bee.

After feeding, the cuckoo wasp larva spins a thin cocoon and matures into an adult, which overwinters in the host nest. There is one generation per year.  The emergence of adult C. kyrae coincides with the spring emergence of adult hornfaced bees in Pennsylvania.

Sapyga wasps

Order: Hymenoptera

Family: Sapygidae

Genus: Sapyga

Sapyga are medium-sized (10–15 mm, 0.4–0.6 inches) black wasps with yellow banding on the abdomen and yellow marks on the thorax. The eyes are deeply notched. The antennae are thick and form a gradual club that is often curved towards the tip.

Eight species of Sapyga occur in the United States and Canada. Two of these, S. centrata and S. louisi, are widespread in the east, including Pennsylvania (Figures 18, 19). Additionally, S. martini occurs across northern North America as far south as New York, so may occur in higher elevation areas of Central Pennsylvania.

All Sapyga species parasitize solitary bees. Both S. centrata and S. martini are recorded from Osmia nests, but parasitism rates can vary by bee species. Over 80% of nests of the native O. pumilia can parasitized by Sapyga, while extensive work with native blue orchard bees (O. lignaria) and introduced hornfaced bee (O. cornifrons) in Pennsylvania has not recorded a single instance of Sapyga parasitism in those species. Sapyga louisi are usually associated with the nests of other Megachilidae (mainly Hoplitis and possibly Megachile), but a single individual was reared from the nest of the invasive mason bee, O. caerulescens.

Sapyga are kleptoparasites. A female wasp will lay one to several eggs in an Osmia nest while the female is away foraging. The first wasp larva to emerge kills the Osmia larva and any of its siblings before consuming the nest provisions. Once mature, the Sapyga larva spins a cocoon and emerges as an adult, which overwinters in the host nest. There is one generation per year.

Houdini fly

Order: Diptera (true flies)

Family: Drosophilidae (vinegar flies)

Species: Cacoxenus indagator

Houdini flies are small (2.5 mm, 0.1 inches) grey flies with red eyes (Figure 20). They are related to and resemble vinegar or fruit flies, which are often associated with over-ripe fruit. Houdini flies are the only drosophilids found in and around Osmia nests.

Houdini flies are native to central and southern Europe but were accidentally introduced into North America, likely through infested Osmia nest material. The earliest records in the United States are from New York in 2011, while the first record in Pennsylvania was in 2019 outside of Philadelphia. Unconfirmed community science records exist on iNaturalist from Massachusetts and Maryland, so this pest may be more widespread in the Northeast than is currently recognized. On the West Coast, Houdini flies have been reported from Oregon, Washington, and British Columbia.

Houdini flies are kleptoparasites of Osmia. The fly larvae hatch before the bee larvae and consume the pollen reserves (Figure 21). When only two or three fly larvae are in a cell, the bee larvae will often be able to complete development, although the resulting adult is smaller than average. However, when more fly larvae are present (up to 20 in a cell), the pollen reserves are depleted, and the bee larva starves.

After Houdini fly larvae mature, some chew through the mud cell partitions and congregate in the nest "vestibule", where they pupate. Larvae sometimes chew an escape hole in the final cap of the nest before pupating. If a mason bee survives further back in the nest, it chews through the mud partitions as it emerges and allows the flies to escape the nest. However, sometimes the larvae do not chew through all of the mud partitions and no mason bees survive to break through them. When this happens, newly emerged adult Houdini flies press and inflate their still-soft heads against the mud partitions. This creates enough pressure that the flies can eventually break through the mud and leave the nest. Because of this behavior, Houdini flies are named after the famous escape artist Harry Houdini.

Adult Houdini flies emerge about 20 days after mason bees emerge. Female flies congregate around active Osmia nests but are not skittish, so can often be squished by hand or sucked up and removed with an aspirator before they fly away.

In southern Europe, Houdini flies are the most important nest parasites of Osmia. While their impact in North America isn’t yet clear, they may become important pests if they become widely established. 

Fungal enemies

Chalkbrood

The genus Ascosphaera contains 28 fungus species that are only associated with bees. Some species are saprotrophs that live on larval feces, pollen provisions in nests where eggs failed to develop, and other substances in solitary bee nests. Very little is known about these saprotrophs but they do not seem to impact bee health and development. Other species are pathogenic and cause a disease called chalkbrood. Chalkbrood fungi are species-specific, so different fungal species cause chalkbrood in different bee groups, including mason bees (A. torchioi), leafcutter bees (A. larvis and A. aggrerata), and honey bees (A. apis). Chalkbrood is the most important fungal pathogen of mason bees.

The spores of chalkbrood fungi are common in the environment and are picked up by adult bees while foraging at flowers. The adult bees spread the chalkbrood spores to pollen stores while provisioning the nest, which the bee larvae later consume. After the spores enter the larval gut, they begin to compete with the larva for pollen, which causes it to starve. Once the larva is dead, the fungus invades the rest of the body and produces spore-filled asci under the larval exoskeleton. This gives the dead larva a characteristic chalky black, grey, brown, to white discoloration.

Each infected larva can produce millions of chalkbrood spores. When uninfected bees deeper in the nest complete their development, they emerge through the chalkbrood-infected nest cells, pick up the spores, and disperse them back into the environment to start the cycle again.

Vertebrate enemies

Woodpeckers and rodents, including chipmunks, squirrels, and mice, will peck or chew on active mason bee nests during the warm months in order to feed on the larvae (Figure 22). Mice will also attack nests that are stored for the winter.

Control

General measures for many enemies

Mason bee nests and bee hotels that are not cared for by routinely replacing and cleaning nesting materials can be overrun with parasites to the point that they kill more bees than they produce. However, parasitism and predation by many enemies can be reduced or avoided entirely by actively managing bee nests.

Allowing bees to reuse nesting material year after year drastically increases the prevalence of chalkbrood, Chaetodactylus mites, and other parasites. Mason bees will use highly contaminated nests, so the number of bees flying around a nest is not indicative of the prevalence of parasites and fungi. Therefore, avoid pre-made nests where the nesting material can’t be removed and replaced. This includes most commercially available bee hotels. Instead, use pre-made paper tubes and hollow stems (e.g., Phragmites reeds, milkweed, joepye weed, etc), which can be discarded every year (Figure 23). Alternatively, use nest designs that can be deconstructed and cleaned with a bleach solution. If you use nesting material that cannot be easily cleaned using a mild bleach solution or by heat shock over an open flame (e.g., pre-drilled wood logs or bee hotels with nests that cannot be removed), dispose of and replace the material every two or three years.

If you are producing a large number of individuals of a single species or genus (e.g., Osmia for orchard pollination), then opening, inspecting, and cleaning the nests is an excellent, but somewhat labor intensive, way to reduce the number of bees lost to parasitoids.

• Remove finished nests once a week or more frequently. Finished nests can be recognized by the mud or leaf plug at the end of the nest. Do not bend, break, or tilt the nests to avoid disturbing the developing bee larvae. The nests should be stored in an unheated, protected space, such as a garage or shed, in a fine mesh enclosure such as a drawstring organza bag, Bug Dorm or other mesh bug cage, or similar enclosure. The fine mesh will keep parasitoids from accessing the nests. If you have multiple enclosures, keep the nests organized by the date collected.
• After wild bees are done flying (usually in September or October), open the nests and rinse off the bee pupae with water. While you clean the pupae, inspect the nests for mites, parasitoid wasps (many species overwinter as adults so are easily distinguished from bee larvae), and chalkbrood. Dispose of any infestations you find. The cleaned pupae can be set out on a paper towel to air dry.
• Alternatively, you can store finished nests without opening and inspecting them. This may be easier when using hard nest material, such as bamboo, or if you do not have time or the inclination to open and inspect the nests.
• During the winter, store cleaned pupae or completed nests in a cold, protected space that cannot be accessed by mice. This could be inside a refrigerator or in a plastic container in an unheated, protected area (e.g., a garage, shed, or under a porch). If using a plastic container, make sure it has small holes to allow gas exchange and to prevent condensation buildup, which could allow mold to grow.
• In the spring, open the container to allow the bees to escape. Bee stored in the refrigerator over the winter should be removed by mid-March. The container should be blacked out except for the exit hole to enable the bees to easily find the exit. Make sure the hole cannot be accessed by mice.
• Many parasites emerge after their hosts. If you did not open the nests to inspect for parasites and are rearing a single bee species or multiple species and marked the date collected, discard the nests after the bees have emerged in order to eliminate parasites. However, if you are rearing multiple species and the nests are mixed together, do not discard them after some bees have emerged as other species may emerge in subsequent weeks or months.

Specific measures for specific enemies

Chaetodactylus mites can crawl from one infested nest to another within the same bee hotel. One study found that lining nest holes with waxed paper significantly reduced the number of nest cells infested by mites, likely because the waxed paper acted as a physical barrier to prevent mites from moving between nests. The same study also found that more bees were produced in nests lined with waxed paper, probably due to the reduction in mite parasitism.

Monodontomerus are attracted to black lights, so installing a black light over a bowl or pan of soapy water in the storage area of completed nests can capture and kill large numbers of wasps.

Woodpeckers and other birds can be discouraged from attacking nests by installing hardware plastic cloth over the nest entrances. Some experts advise against using chicken wire as the hard metal can damage bee wings, but others have used it successfully. Because these barriers disrupt the flight of incoming bees, they should only be used if absolutely necessary, i.e., after damage has occurred to prevent additional damage. The hardware cloth should be installed 3–4” away from the nest and pulled taught. Any closer and birds may still access the nest, any further will be more disruptive to bee flight.

Additional Resources

For additional information about mason bees and other cavity-nesting pollinators, please refer to the following resources:

Managing a Solitary Bee Hotel

How to Manage a Successful Bee Hotel

Mason Bees in the Home Garden

Orchard Pollination: Solitary (Mason) Bees

Spring Bees: Who Are They and Where Do They Live?

Who are Our Pollinators? 

References 

Anderson, A. R., R. A. Ramirez, J. E. Creech, and T. L. Pitts-Singer. 2023. Life cycle of Melittobia acasta (Hymenoptera: Eulophidae) using Megachile rotundata (Hymenoptera: Megachilidae) as a host. Annals of the Entomological Society of America, 116(4): 207–218. doi.org/10.1093/aesa/saad011

Bissett, J. 1988. Contribution toward a monograph of the genus Ascosphaera. Canadian Journal of Botany-Revue Canadienne De Botanique, 66: 2541–2560.

Bohard, R. M., and L. S. Kimsey. 1982. A synopsis of Chrysididae in America north of Mexico. Memoirs of the American Entomological Institute, 33: 1–266.

Browne, F. B. 1922. On the life-history of Melittobia Acasta Walker; a chalcid parasite of bees and wasps. Parasitology 15(3–4): 349–370 + 1 plate.

Bug Guide. 2021. Monodontomerus. Accessed on 19 June 2024.

Bug Guide. 2023. Leucospis. Accessed on 19 June 2024.

Bug Guide. 2024. Sapyga. Accessed on 19 June 2024.

Conrow, R. T., K. M. Zivicki, and G. P. Setliff. 2016. Cuckoo wasps of Pennsylvania (Hymenoptera: Chrysididae). Transactions of the American Entomological Society, 142: 113–129.

Coutin, R., and R. D. de Chenon. 1983. Biologie et comportement de Cacoxenus indagator Loew (Dipt., Drosophilidae) cleptoparasite d'Osmia cornuta Latr. (Hym., Megachilidae). Apidologie, 14(3): 233–240.

Graenicher, S. 1905. On the habits and life-history of Leucospis affinis (Say): A parasite of bees. Bulleting of the Wisconsin Natural History Society, 3–4: 153–159. 

Grissell, E. E. 2000. A revision of New World Monodontomerus Westwood (Hymenoptera: Chalcidoidea: Torymidae). Contributions of the American Entomological Institute, 32(1): 1–90.

Grissell, E. E. 2005. A review of North American species of Microdontomerus Crawford (Torymidae: Hymenoptera). Journal of Hymenoptera Research, 14(1): 22–65.

Holquinn, J. A. 2023. The life history traits and morphology of Chaetodactylus krombeini. M.S. thesis, University of California, Riverside. xii + 108 pp.

Janšta, P., A. Cruaud, G. Delvare, G. Genson, J. Heraty, B. Křížková, and J.-Y. Rasplus. 2018. Torymidae (Hymenoptera, Chalcidoidea) revised: molecular phylogeny, circumscription and reclassification of the family with discussion of its biogeography and evolution of life-history traits. Cladistics, 34: 627–651. doi 10.1111/cla.12228.

Joshi, N. K., K. Nathani, D. J. Biddinger.  2020. Nest modification protect immature stage of the Japanese Orchard Bee (Osmia cornifrons) from invasion of a cleptoparasitic mite pest. Insects, 11(1): 65. doi: 10.3390/insects11010065

Kimsey L. S., and R. M. Bohart. 1990. The chrysidid wasps of the world. Oxford University Press. 652 pp.

Klimov, P. B., and B. M. OConnor. 2008. Morphology, evolution, and host associations of bee-associated mites of the family Chaetodactylidae (Acari: Astimata) with a monographic revision of North American taxa. Misscellaneous Publications, Museum of Zoology, University of Michigan, 199: 1–243.

Krombein, K. V. 1938. Descriptions of four new wasps (Hymenoptera: Sapygidae, Sphecidae). Annals of the Entomological Society of America, 31: 465. DOI: 10.1093/aesa/31.4.467

Krombein, K. V., P. D. Hurd, Jr., D. R. Smith, and B. D. Burks. 1979. Catalog of Hymenoptera in America north of Mexico. Volume 1. Symphyta and Apocrita (Parasitica). Smithsonian Institution Press. 1198 pp.

Krunić, M., L. Stanisavljević, M. Pinzauti, and A. Felicioli. 2005. The accompanying fauna of Osmia cornuta and Osmia rufa and effective measures of protection. Bulletin of Insectology, 58(2): 141–152.

Minnesota Bee Atlas. 2024. Minnesota Bee Atlas. Accessed on 20 June 2024.

O’Connor, B. 2016. North America bee-associated mites. Accessed on 21 June 2024.

PolliNation Podcast. 2020. Episode 154 – Josh Vlach – Invasive pests and pollinators. Accessed on 19 June 2024.

Purrington, C. 2019. Houdini fly. Accessed on 19 June 2024.

Mader, E., M. Spivak, and E. Evans. 2010. Managing alternative pollinators. A handbook for beekeepers, growers, and conservationists. Sustainable Agriculture Research & Education (SARE), College Park, MD. 

Thorp, R. W. 1968. Ecology of a Proteriades and its chrysura parasite, with larval descriptions (Hymenoptera: Megachilidae: Chrysididae). Journal of the Kansas Entomological Society 41: 324–331.

UCD Community. 2023. Universal Chalcidoidea Database Website. Accessed on 19 June 2024.

wallamaloo. 2012. Kleptoparasitic fly? Accessed 19 June 2024.

Washington State Department of Agriculture. 2020. New Pest Alert: Houdini fly (Cacoxenus indagator). Accessed on 19 June 2024.

Wynns, A. A., A. B. Jensen, and J. Eilenberg. 2013. Ascosphaera callicarpa, a new species of bee-loving fungus, with a key to the genus for Europe. PLoS  ONE 8(9); e73419: 1–9. doi: 10.1371/journal.pone.0073419