Notes on the life history of Sancassania boharti (Acari: Acaridae) and its relationship to the alkali bee, Nomia melanderi (Hymenoptera: Halictidae).

S. boharti is a mite associate of the alkali bee only in Fremont County, Wyoming. Its life stages are typical of acarid mites. Duration of all life stages, mean female life span, and mean fecundity at 3 temperatures are given. Large mite colonies were sup ported on sick or decaying bee larvae or on moldy pollen. Small colonies were occasionally found with healthy bee larvae. Hypopi moulted to tritonymphs within 30 hours and to adults less than 77 hours after food exposure. Large mite populations build up swiftly, then crash, leaving only hypopi. Mites were comparatively rare on healthy tenerals or pupae in cells and much more common on bees captured in flight. Males carried larger mite populations than females. S. boharti was the most important necrophage of diseased bees at the Fremont County sites. Its role as a vector of bee disease is discussed. Studies of the natural history of many species of aculeate Hymenoptera show them to be closely interrelated with nidicolous mites belonging to several, diverse families. The Hymenoptera offer these nidicoles an organized and stable habitat with respect to food, shelter, and substrate and, at the same time, opportunity for efficient dispersal. The mites are most often saprophages which subsist on a variety of organic debris, including dead host larvae, the bodies or fragments of arthropods stored as provisions, feces, cast skins, pollen, etc. A number may be facultative or obligate cleptoparasites (Horstia, Lackerbaueria, Vespacarus, Trochometrid ium, Chaetodactylus). Some are fungivores, and some are parasites, many of the latter appearing to be benign and causing no significant increase in host mortality. Still others (e.g., Macrocheles, Rhodacacarus, Ereynetes) are predators of worms, other mites, or (probably) various small insects such as psocids and Collembola, also found in the cells. Krombein (1962, 1967) and Mostafa (1970) summarize much of the existing information concerning life histories of mites associated with those Hymenoptera nesting in wood. Cross and Bohart (1969, 1978) and Eickwort (in Woodring, 1973; Eickwort, 1979; Rack and Eickwort, 1979) have studied several acarine associates of halictine bees. Most Acari associated with Hymenoptera are adapted in some fashion for phoresy, perhaps the most efficient method available to small organisms to dis perse into microniches essentially identical to those of their parents. Adaptations must be behavioral and morphological (e.g., mechanisms which maximize at taching and clinging capabilities and minimize dehydration) and also develop mental, at least insofar as to permit synchronization of the phoretic stage with the emerging adult host (Krombein, 1967). Sancassania (=Caloglyphus) boharti (Cross, 1968) is a rhizoglyphine mite be longing to the Family Acaridae, most of whose members possess a highly spe 1 Department of Biology, The University of Alabama, Tuscaloosa, Alabama 35487. 2 Department of Biology, Utah State University, Logan, Utah 84322. Accepted for publication 24 October 1989. This content downloaded from 157.55.39.157 on Fri, 08 Jul 2016 05:09:16 UTC All use subject to http://about.jstor.org/terms 604 JOURNAL OF THE KANSAS ENTOMOLOGICAL SOCIETY cialized phoretic second nymphal instar ("deutonymph," intercalary stage", "hyp opus") which may or may not be mandatory in the life cycle. The alkali bee, Nomia melanderi Ckll., is a solitary, gregariously nesting halic tine bee found, sometimes in immense numbers, in suitably moist, fine-particled, alkaline soil throughout the Great Basin. Because of its importance as a pollinator, chiefly of alfalfa, it has been studied intensively, and its bionomics are relatively well known (Bohart and Cross, 1955; Stephen, 1959; Stephen and Evans, 1960; Frick, 1960; Stephen, 1965). In 1955-1956 and 1965-1966, we studied alkali bees at various nesting sites in Utah, Wyoming, and Idaho (Cross and Bohart, 1969). Despite the wide geo graphic range of the bee, S. boharti was an associate only in nesting sites near Shoshoni, Wyoming, and was particularly numerous in an artificial site created in 1954-1955 in an initial effort to establish bee populations in desired localities near seed fields. Bee mortality, particularly of overwintered prepupae, pupae, and unemerged tenerals, was unusually high in the Shoshoni area, and S. boharti commonly infested cells containing the decaying bees. This paper presents details of the life history of S. boharti and some aspects of its relationship to the alkali bee. Life tables for this species will be published elsewhere. Materials and Methods Observations were made from bees and cells at nesting sites near Shoshoni and Pavillion, Fremont County, Wyoming, in 1955-1956 and 1964-1966, and from cells dug at the Shoshoni sites and transported to the laboratory. Data on fecundity, oviposition period, and duration of stages were obtained in the laboratory. Mites were easily reared in disposable polystyrene zipper boxes partly filled with damp plaster of Paris-charcoal (Lipovsky, 1953), utilizing granulated baker's yeast as food. Rearing dishes were held in constant temperature chambers at 20?, 23?, and 26?, ? 1?C. Mean values for duration of immature stages and for female longevity are taken from Legg (1970), and are based on a large number of specimens examined at regular 8 hour intervals. Females were always paired with 2-3 males in obtaining fecundity data. Results and Discussion life cycle: Stages in the life cycle of S. boharti are typical of astigmatid mites. In sequence, they are: egg, larva, protonymph, deutonymph, tritonymph, and adult, the deutonymph being facultative. All stages are found together, and in cultures, all were noted to feed on the yeast provided, except for the deutonymph, as noted below. egg: The elliptical, pearly-translucent, sticky eggs are scattered about the cell, chiefly on the food and cell wall. Females in culture appeared to oviposit indis criminately, i.e., egg numbers at any spot were correlated with time spent at that spot. Mean hatching time (to nearest hour) was 48 hours at 26?C, 80 hr at 23?C, and 105 hr at 20?C (N = approx. 200). larvae: The tiny six-legged larvae moulted to the protonymph in an average of 36 hr at 26?C, 37 hr at 23?C, and 53 hr at 20?C. protonymph: Mean duration of this stage was 19 hr at 26?C, 23 hr at 23?C, and 31 hr at 20?C. This content downloaded from 157.55.39.157 on Fri, 08 Jul 2016 05:09:16 UTC All use subject to http://about.jstor.org/terms VOLUME 63, NUMBER 4 605 deutonymph: Under favorable environmental conditions, this form is omitted from the life cycle, protonymphs moulting directly to tritonymphs. Its appearance signals environmental degradation, especially food shortage. It is the overwin tering form of the mite in alkali bee cells. Unlike deutonymphs of many astigmatid mites, those of S. boharti are able to walk smoothly and quickly and are the most peripatetic stage in the entire life cycle. Together with their flattened shape, this mobility presumably enables them to traverse the rather loose mud plug with which the mother bee closes each cell, thus to enter or leave cells with minimum difficulty. Under laboratory conditions, we noted deutonymphs to moult to tritonymphs within 36 hr in the presence of suitable food, while a control group from the same series of bee cells remained active but untransformed after 2 months. Poe (1966) found S. boharti hypopi to transform into tritonymphs in the presence of the odor of food alone, and Cutcher and Woodring (1969) postulated effects of osmotic pressure derived from varying concentrations of ammonium salts, food, or culture debris to affect deutonymphal transformation to the tritonymph in this species. External and internal morphology of the hypopus of S. boharti has been studied in detail by Woodring and Carter (1974). tritonymph: Mean duration of this stage was 20 hr at 26?C, 60 hr at 23?C, and 54 hr at 20?C. adult: Tritonymphs moult to adult males and females (Fig. 1). The former are polymorphic, one form exhibiting hypertrophied and structurally modified legs III. Mean developmental time, egg to adult, was 135 hr (5.6 days) at 26?C, 200 hr (8.3 days) at 23?C, and 231 hr (9.6 days) at 20?C. Mean adult life span for female mites was 12.6 days at 26C? (n = 20), 12.8 days at 23?C (n = 22), and 22.3 days at 20?C (n = 25). Mean fecundity for mites at 20?C was 558.1 eggs/female (n = 29), and 476.6 eggs/female at 23?C (n = 18). Fecundity was not measured at 26?C. Newly emerged females were usually mated within 5 minutes of eclosion, and oviposition began in approximately 30 hr at 23?C. Mating occurred intermittently throughout the life of the female and appeared to be necessary for her to sustain maximum fecundity. Unmated females were usually sterile. However, in a small percentage of cases, arrhenotokous parthenogenesis was noted to occur. Sex ratios were obtained by rearing a total of 1081 adults from eggs and 229 adults from hypopi at the above 3 temperatures. In no case did ratios differ materially from an expectation of 0.5. Pooled data yielded 649 males and 661 females for a ratio of 0.495/0.505 (Chi-square = 0.723, n.s., with respect to deviations from 0.5). Heterogeneity Chi-square was non-significant.