Bee Mites : Acari : Acariformes : Trombidiformes : Pyemotidae : Pyemotes
Pyemotes herfsi (Oudemans, 1936)
Pediculouides Herfsi Oudemans, 1936: 397, Figs 1-2.
Pyemotes herfsi: Cross & Moser, 1975: 723; Cross at al., 1981: 182 (included in key); Dinabandhoo and Dogra, 1982: 29
Pyemotes zwoelferi Krczal, 1963 (synonymized by Cross at al., 1981)
Hosts. Many insect species from different orders, including Apis cerana Fabricius, 1793. Type host - Tineola bisselliella (Hummel, 1823) (as Sitotroga biselliella Hum.)
Distribution. Holarctic and Oriental regions (Oudemans, 1936; Dinabandhoo and Dogra 1980; Broce, 2006; Marutani et al., 1992). (type locality - Gemany: Leverkusen)
Biology. This mite parasitizes a variety of insect hosts, including bees. Dinabandhoo and Dogra (1980) report that colonies of Apis cerana infested by Pyemotes herfsi in Kulu, India show symptoms of restlessness or lethargy and do not produce brood. The infested colonies were recovered by fumigating them with dichlorvos. Pyemotes herfsi causes high incidences of red, itching, and painful welts on people in the midwestern United States, where the mite is normally preying on gall-making midge larvae on oak leaves (Broce, 2006).
The below account on biology is based on Herfs (1926) and Cross (1965).
Both males and females pass through all immature stages while still within the enormously distended, globular opisthosoma of the mother mite, and are born as adults. Most males are born during the first half of the birth period and normally are present only in small numbers (three to five percent of the total number of offspring at 25°C). They seldom leave the body of the mother and are parasitic upon it. At 25°C, males of P. herfsi removed from the maternal "opisthosomal globe" died 16 to 25 hours after removal, presumably from starvation, and if placed on the bodies of normal, healthy hosts did not feed. Males are usually found resting quietly on the opisthosoma of the mother, for the most part near the vulva. They may assist in the birth of the females by grasping the latter with the hind legs and pulling, shifting the grasp, pulling again, etc. This aid is not necessary since birth of the females continues smoothly in the absence of males although taking slightly longer (average birth time of females of P. herfsi with males, 171 seconds, average time without males, 217 seconds). As soon the newly born female completely leaves the birth canal, the male initiates copulation. In he grasps the female and adjusts, with the assistance of the hind legs, her body until contact is made. This entire process of adjustment and mating may take 10 minutes or more, although actual copulation probably lasts only 20 to 30 seconds.
Males of P. herfsi normally assist only in the birth of the females, paying no attention to emerging males. They likewise ignore mated females, although one or more males may attempt to disrupt pairsin copulo. Early in the birth period of the mother, only a single P. herfsi male is usually found on the opisthosoma but as this period progresses, several may be present. Shortly (within 10 minutes) after being mated, the young female leaves the body of the mother and seeks food. If, however, males are lacking on the maternal hysterosoma, young females do not leave but remain resting upon the latter for some time awaiting the birth of a male. Only after a full day or longer do they leave.
Unmated females seemingly suffer a high mortality, only about 10 percent of those in experimental cultures surviving to produce offspring. Such females are arrhenotokous, producing only males. The total number of offspring produced compares favorably with that of mated females of the same size. According to both Krczal and Herfs, young females die of starvation within 48 hours of their birth if food is not found. This statement makes dispersion and perhaps overwintering difficult to explain since it is obviously the young females which must disperse. Herfs found that young females unable to find a host would sometimes return to the mother and feed in the manner of the male on the parent's hysterosoma. Rarely this filial parasitism became permanent and ended with the death of the mother and the production of offspring by the daughter. More commonly it was quite transitory and resulted in no visible harm to the mother while seemingly providing the daughter with enough food to prevent at least immediate starvation.
Young females of P. herfsi are stimulated by moving objects soon after leaving the mother, stretching the body toward the source of the stimulus. Such behavior indicates dispersion by phoresy, a phenomenon which has been observed only rarely in Pyemotes despite its widespread occurrence in other members of the family. In view of the fact that young females starve so quickly, the questions of their survival between generations of the host and of overwintering remain essentially unanswered. As mentioned by Krczal, perhaps the phoretic period is ephemeral, serving only to bring the females into fortuitous contact with one of a number of possible hosts. This could explain their rare and sporadic occurrence in the nests of solitary bees and social wasps, hosts in which an overwintering period would be required of the young females. Presumably, such a period would result in their migration or death, thus preserving the host from further attack until the next "accidental" infestation occurred.
Upon finding a host, the young female selects a favorable location and inserts her chelicerae, an action which may elicit striking or curling movements from the host. Within a short time, the host begins to show signs of paralysis, this increasing until the larva is completely incapable of movement. Time elapsed between onset of attack and complete paralysis depends upon the number of punctures made, but generally is two to four hours. The same larva may be attacked by several mites, Herfs having counted a maximum of 178 on a single host. The parasite develops quickly, the opisthosoma increasing in both length and width until the mite assumes a form quite similar to an incandescent light bulb. This stage is usually reached in about 24 hours. Complete development, in which the opisthosoma becomes a huge, turgid sphere may be completed in another 24 hours, although it usually requires seven to eleven days to reach maximum size. At 25° C the average time from initial insertion of the chelicerae to birth of the first offspring is 9.5 days in P. herfsi. The size of the opisthosomal globe is well correlated with the number of offspring produced. In cases of multiple parasitism the size of the opisthosoma will be reduced, and females concerned will produce a relatively small number of offspring, sometimes averaging as low as six or seven. Females ofP. herfsi reared singly produced a maximum of 284 offspring and averaged 128 at 25°C and 150 at room temperature.
The birth period, usually terminated by the death of the female, ranged from 9 to 33 days and averaged 17.3 days. The average life span of the females in Herfs' cultures at 25° C. was 26.8 days as measured from the beginning of feeding to the death of the mite. The average life span of the male is much shorter, since it dies with the mother mite. It was found that longevity of P. herfsi males was also positively correlated with amount of sexual activity. The temperature of the microhabitat was also an important factor affecting both longevity and fecundity of both sexes. Several previous workers have found 25 to 30° C to be optimum and Herfs noted a loss in the ability of the mother to give birth at 35°C.
Control. Colonies of Apis cerana infested by Pyemotes herfsi in India were cured by three treatments of fumigation with dichlorvos (Dinabandhoo & Dogra, 1980).
10 ml of dfchlorvos solution (50 ppm) was applied to a strip of blotting paper stapled to an empty frame. To avoid direct contact by bees, the strip was enveloped by perforated paper. A treatment frame was put into the brood chamber in the spring (3 treatments each of 12 h, at intervals of 2 days) or in the autumn (5 treatments each for 24 h on alternate days). Post-treatment examination revealed that the mite was controlled
following three fumigations. No mites were found on bees examined after treatment. The uptake of dichlorvos by the bees was calculated to be 25G-500 ng per colony (5,000-10,000 bees), whtch is considered a safe level (after Dinabandhoo & Dogra, 1979).
References
Broce, A. B., L. Zurek, J. A. Kalisch, R. Brown, D. L. Keith, D. Gordon, J. Goedeke, C. Welbourn, J. Moser, R. Ochoa, E. Azziz-Baumgartner, F. Yip & J. Weber. 2006. Pyemotes herfsi (Acari: Pyemotidae), a mite new to North America as the cause of bite outbreaks. Journal of Medical Entomology.43: 610-613.
Dinabandhoo, C. L. & G. S. Dogra. 1979. Dichlorvos for the control of acarine disease of Indian honey bee, Apis cerana Fab. Indian Bee Journal.41: 1-6.
Image Gallery
B. OConnor and P. Klimov ©
Created: April 28, 2012
Last modified: 