Phoretic deutonymphs of the mite Chaetodactylus krombeini dispersing on the orchard mason bee, Osmia lignaria, Michigan
Fig. 1. Phoretic deutonymphs of the mite Chaetodactylus krombeini dispersing on the orchard mason bee, Osmia lignaria, Michigan. Click here to enlarge Mite Chaetodactylus krombeini (Chaetodactylidae)
Fig. 2. Chaetodactylus krombeini Click here to enlarge
Bee Mites : Acari : Acariformes : Sarcoptiformes : Chaetodactylidae : Chaetodactylus

Chaetodactylus krombeini Baker, 1962

Chaetodactylus krombeini Baker, 1962a: 229, Figs 1-24 (holotype HDN (no. 2815), paratypes (10 HDNs, 3Ls, 45 PNs, 33 inert HDNs, 2TNs, 5 males, 6 females) in USNM).
Chaetodactylus (Spinodactylus) krombeini: Fain, 1981: 2 (as tentative junior synonym of Chaetodactylus claviger)
Chaetodactylus osmiae non Dufour, 1839: Krantz, 1978: 419, Figs. 211-1, 121-2 (species authorship attributed to Dujardin).
Chaetodactylus (Spinodactylus) claviger non Oudemans, 1928: Fain, 1981: 2 (part.).
Chaetodactylus krambeini Abou Senna, 1997: 677 (lapsus)
[see Klimov and OConnor, 2008 for complete synonymy]

Material (show database records) (USA). 5HDN's - USA: Arizona, Cochise Co., 5mi W Portal, ex Osmia ribifloris on mesosoma , 15 Feb 1961, M. A. Cazier, AMNH, BMOC 04-0508-020; 5HDN's - Cochise Co., Ash Spring, 7mi SW Portal, 6400 ft., ex Osmia ribifloris over body, 31 Mar 1965, B. & C. Durden, AMNH, BMOC 04-0508-022; 5 HDNs - California, Napa Co., Angwin, ex Osmia ribifloris biedermannii (pronotum and propodeum), 15 Feb 1966, L. Eighme, USNM, BMOC 96-0510-103; 7 HDNs - Placer Co., Applegate, ex O. ribifloris (1st metasomal tergite), 22 Feb 1966, T.Griswold, USNM, BMOC 96-0510-104; 1 HDN - Idaho, Franklin Co., Cub River Canyon, ex male of O. bucephala on Thermopsis montana Nutt. (Fabales: Fabaceae), 1 Jun 1948, G.E. Bohart, USNM, BMOC 96-0510-144; 5 HDNs - Maryland, Prince George's Co., Beltsville, ex O. bucephala propodeum, 25 Apr 1978, F.D. Parker, USNM, BMOC 96-0510-145; 10 HDNs - Michigan, Livingston Co., E.S. George Reserve, ex O. lignaria mesosoma, 4 May 1972, T. Green, UMMZ, BMOC 91-1015-001; 20 HDNs - same locality and host, 25 Apr 1978, F.C. Evans, UMMZ, BMOC 91-1015-002; 11 HDN - Nevada, Elko Co., Lamoille Canyon, Ruby Mts., Elev. 9200', ex O. grindeliae (propodeum), 19 Jul 1975, T.L. Griswold, USNM, BMOC 96-0510-137; 3 HDNs - same locality and host, (propodeum), 19 Jul 1975, T. Griswold, USNM, BMOC 96-0510-138; 7 HDNs - Nye Co., Mt. Spring Pass, ex O. ribifloris (1st metasomal tergite) on Berberis (Ranunculales: Berberidaceae), 4 May 1963, G.E. Bohart, USNM, BMOC 96-0510-093; 1 larva, 2 protonymphs, 10 females - New York, Onondaga Co., Syracuse, ex O. lignaria nest, no date, M. O'Brien #0.22, BMOC 79-0312-001; 1 larva, 2 protonymphs, 7 tritonymphs, 4 females, 3 males - same data, BMOC 79-0312-002; 7 HDNs - Tompkins Co., Ithaca, ex male of O. lignaria, 30 Apr 1975, S. Jaronski, BMOC 75-0507-001; 2 HDNs - Ohio: Franklin Co., Worthington, ex Osmia chalybea over body, 17 May 1902, J. G. S. OSU OSUC 0065892, BMOC 03-1106-009; 19 HDNs - Licking Co., ex Osmia lignaria on pronotum, 10 May 1936, R. C. Osburn OSU OSUC 0066019, BMOC 03-1106-010; 1 HDN - Columbus, ex Osmia simillima on scutellum, May, Jas. S. Hine OSU OSUC 0066098 BMOC 03-1106-013; 5 HDNs - Oregon, Benton Co., Corvallis, ex O. lignaria propinqua (propodeum), 1 Apr 1957, R.F. Koontz, USNM, BMOC 96-0510-101; 3 HDNs - Benton Co., Corvallis, holes in fence post, 47-6186, ex O. nigrifrons, 17 Apr 1947, L. Wallace, USNM, BMOC 96-0510-146; 8 HDNs - Utah, Cache Co., Logan, USAC Campus, ex O. lignaria propinqua (propodeum) on Prunus armeniaca L. (Rosales: Rosaceae), 27 Apr 1948, G.E. Bohart, USNM, BMOC 96-0510-100; 3+6 HDNs - Cache Co., Cowley Canyon, ex O. montana (metasomal tergites I-II + propodeum), 13 May 1989, W.J. Hanson, USNM, BMOC 96-0510-122; 6 HDNs - Cache Co., W. Hodges Canyon, Malaise Trap, ex O. bucephala (propodeum), 13-20 June 1980, T.Griswold, USNM, BMOC 96-0510-143; 2 HDNs - Cache Co., Birch Canyon [label reads: Birch Creek Canyon], ex O. californica (pronotum), 23 May 1982, TL/RT Griswold, USNM, BMOC 96-0510-110; 6 HDNs - Cache Co., Logan Canyon, Tony Groove, ex O. lignaria propinqua (propodeum) on Salix (Salicales: Salicaceae), 20 May 1948, G.E. Bohart, USNM, BMOC 96-0510-102; 6 HDNs - Washington Co., Pintura, ex O. ribifloris (propodeum) on Rhus ovata S. Wats. (Sapindales: Anacardiaceae), 12 Apr 1970, G.E. Bohart, USNM, BMOC 96-0510-094; 1 HDN, 1 larva - Weber Co., S Monte Cristo Peak [label reads "S Monte Cristo"], ex O. montana (1st metasomal tergite), 23 Jun 1973, G.F. Knowlton, USNM, BMOC 96-0510-120; 6 females, 5 males, 3 HDNs, 2 tritonymphs, 1 protonymph, 3 larvae - Washington, King Co., Bothell, O. lignaria nest, 17 Jun 1998, E.A. Sugden, UMMZ BMOC 98-1202-001. Voucher specimens in AMNH, OSAL, UMMZ, UNAM, USNM.

Identification. See key. Known from all stages.

Osmia (Osmia) lignaria Say, 1837 (type host)
Osmia (Osmia) lignaria propinqua Cresson, 1864
Osmia (Osmia) ribifloris Cockerell, 1900
Osmia (Osmia) ribifloris biedermannii Michener, 1936
Osmia (Acanthosmioides) nigrifrons Cresson, 1878
Osmia (Centrosmia) bucephala Cresson, 1864
Osmia (Cephalosmia) californica Cresson, 1864
Osmia (Cephalosmia) montana Cresson, 1864
Osmia (Helicosmia) chalybea Smith, 1853
Osmia (Melanosmia) grindeliae Cockerell, 1910
Osmia (Melanosmia) simillima Smith, 1853

Distribution (show map). USA: Arizona, California, Idaho, Maryland (type locality), Michigan, Nevada, New York, Ohio, Oregon, Utah, Washington.

Biology. Chaetodactylus krombeini is primarily associated with the megachilid bee Osmia lignaria. Life cycles of both bee and mite were studied by Krombein (1962). He observed deutonymphs disposed in a random fashion over the bee's body, although the majority were attached to setae on the propodeum or anterior part of the metasoma. One or more of these deutonymphs were observed to crawl off the body of the female bee while she provisioned the cell with pollen and nectar. Presumably they then transformed into tritonymphs. Adult mites of both sexes were present in infested cells 3 to 4 days after the cell was provisioned. In an attempt to explain this phenomenon, Krombein speculates that the phoretic deutonymphs transform into tritonymphs and females, each of which lays a single egg that develops very rapidly into an adult male. This male mates with its mother, or with another female that may be in the same cell, and the female then proceeds to lay fertilized eggs.
Male bees were more commonly infested with phoretic deutonymphs, and also had more mites per bee. This phenomenon is possibly a consequence of the skewed sex ratio and of the prior emergence of male bees in the spring.
Chaetodactylus krombeini may attack and kill the egg or young larva in a newly provisioned cell or in newly infested cells. Occasionally the mites do not kill the host but feed on the provisioned pollen, and the young bee larva is nutritionally deprived (Bosch and Kemp 2001). In this case a smaller than normal adult bee may develop, along with some mites. Ordinarily, the mites are unable to gain access to uninfested cells once the infested cell is capped, and they are confined to the original cell until the partition is broken down the following spring by emergence of an adult bee from one of the earlier constructed cells. Mites frequently move into adjacent cells when partitions break during nest manipulation in managed colonies of Osmia lignaria (Bosch and Kemp 2001).
After killing and feeding on the bee egg or young larva, the female mite deposits her eggs principally on the cell walls beyond the pollen-nectar mass. The eggs hatch in 4 to 5 days into larvae. The larvae feed on nectar from the pollen-nectar mass and transform into protonymphs, which also continue to feed on the nectar. There is some doubt as to what happens next, but it seems probable that the protonymphs occurring early in the season transform directly into tritonymphs, bypassing the deutonymphal stage completely. However, Chaetodactylus deutonymphs were never found in nests early in the spring. The tritonymphs transform into adults, which in turn repeat the cycle, within the infested cell until all the provisioned food has been consumed. The number of generations and duration of breeding is dependent on the volume of the pollen-nectar mass.
Formation of the immobile deutonymph in Chaetodactylus may be due to insufficient food or to decreased humidity caused by the use of all of the nectar, or to a combination of both factors. It is not possible to state what factors determine whether immobile and/or phoretic deutonymphs will develop in an individual nest. Formation of the latter was never observed in the laboratory. In an undisturbed nest, both forms of deutonymphs are probably confined to the originally infested cells because of the presumed inability of the mites to break through the mud partitions separating the cells.
Very early in the spring the phoretic deutonymph presumably attaches to an adult bee as the latter chews its way through the mud seal capping its cell. In an undisturbed nest the mites in the innermost cell or cells would possibly die in situ because of their inability to mount an adult bee. The mites would need to infest some cells in the middle or near the outer end of the nest, so that bees would develop in the innermost cells and provide the necessary vehicle for migration of the mites as the bees chewed their way out of the nest. Mites trapped in the innermost cell might be released by a female bee chewing through the closing partition during her efforts to clean out the debris from an old nest for re-use.
The role of the immobile deutonymph in initiating a new infestation requires additional investigation. Some of the immobile deutonymphs transformed to tritonymphs several days after the bees left the nest in the spring. Theoretically, it would be possible for the immobile deutonymphs to remain in that stage in an old nest for some length of time. If this nest was then re-used by another bee, the capping of cells by that bee would increase the humidity to the point where the heteromorphic deutonymphs could transform into tritonymphs, which would then infest the cells provisioned by that bee.
Obviously, the presence of both immobile and phoretic deutonymphs in a mite species may be of profound evolutionary significance. The phoretic deutonymphs, which attach to the body of the host bee and then drop off in a new nest of that same bee species, insure only the continuation of the same host relationship. But the occurrence of immobile deutonymphs, which remain in the old nest, gives the mite species an opportunity to colonize other species of bees that also nest in abandoned borings.
Parasitism by Ch. krombeini can attain high levels, especially in humid areas of the United States (Bosch & Kemp, 2001).

Control. Inspection of Osmia lignaria nests in semi-translucent paper straws and removal of infested cells is a time-consuming, but effective method to prevent damaging Ch. krombeini infestations in managed colonies. Stripping cocoons out of the nesting materials and managing loose cocoons, instead of whole nests, reduces initial infestation because emerging bees are not forced to walk through infested cells. However, releasing O. lignaria populations as loose cocoons increases dispersal of prenesting females (Bosch and Kemp 2001).
Studies on the Japanese species Chaetodactylus nipponicus, associated with the hornfaced bee, Osmia cornifrons, showed significant reductions of mite infestation in nesting materials treated with endosulfan (60-600 ppm). These same studies indicated that exposure of hornfaced bee nests to high temperatures (e.g., 60 days at 30°C, or three days at 40°C) effectively kills Ch. nipponicus mites without harming hornfaced bees, as long as the bees are in the prepupal stage (Sekita and Yamada 1993, Yamada et al. 1971). Similarly, treating cocoons of O. cornuta and O. rufa during the winter period with a 0.007% solution of endosulfan for a period of 3 min is a very effective method of controlling Ch. osmiae in Europe. It was found that such treatment of cocoons had no negative effect on the bees inside (Krunić et al. 2005). The potential utility of these or similar methods to control Ch. krombeini in Osmia lignaria populations is being tested.

Notes. Specimens from Osmia pumila (8 HDNs, 4 females - USA: New York, mixed sample from 5 localities from Suffolk (4) and Nassau Co. (1), Osmia pumila nest cell V-VI 1998, K. Goodell UMMZ BMOC 98-1110-001) probably belong to a closely related species. In three well mounted females, the dorsal opisthosoma has a pattern of large tubercles (1.9-2.5 in diameter) (versus conical or subconical mammillae (1.5-2.0) in Ch. krombeini) and the outer ridge of the supracoxal sclerite is shorter than tibia II (longer in Ch. krombeini). Deutonymphs from O. pumila do not have any distinct differences from those of Ch. krombeini, but all have slightly thinner s III and longer e1. Since mites from O. pumila originated from mixed samples with small sample size, and all characters of phoretic deutonymphs overlap with Ch. krombeini, we refrain from specifically determining these specimens at this time.

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Bosch, J. & W. P. Kemp. 2001. How to manage the blue orchard bee as an orchard pollinator. Beltsville, MD: Sustainable Agriculture Network. 88 pp.
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Created: Mar 24, 2009
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