Occurrence of house dust mites in central Texas.
D. pteronyssinus has been found in house dust samples from California, Colorado, and Ohio (Arlian et al., 1982; Moyer et al., 1985; Mulla et al., 1975). D. farinae has been identified in house dust samples from California, Colorado, Ohio, Tennessee, and Texas (Arlian et al., 1982; Hall et al., 1971; Moyer et al., 1985; Mulla et al., 1975; Shamiyeh et al., 1971). Although both D. pteronyssinus and D. farinae have been reported in the United States, the former is usually more common in Europe and South America (Cunnington et al., 1987). The Entomological Society of America has approved the names "European house dust mite" for D. pteronyssinus and "American house dust mite" for D. farinae (Wharton, 1976).
In an earlier study, Hall et al. (1971) found D. farinae in dust samples from the Fort Worth-Dallas area in Texas. Although it is probable that house dust mites occur throughout the state, this assumption has not been confirmed by actual collection in the field. The purpose of this study was to determine if Dermatophagoides occurs in central Texas.
Dust samples were collected between 9 June and 28 June 1989 in Bell and Coryell counties using a hand-held rechargeable vacuum (Black and Decker Dustbuster, model 9330) with the internal filter removed. Samples from residential and public buildings were collected by vacuuming an area encompassing half a square yard for two and one-half minutes. Dust was collected in a coffee filter held over the rectangular nozzle of the vacuum by a rubber band. Dust samples were preserved in a solution of 50 percent ethyl alcohol and stored until they could be examined for mites.
Mites were separated from the dust using the method of Furumizo (1973). Each sample was mixed with alcohol, teased apart, seived, and allowed to settle in a graduated cylinder for 24 hours so that the volume of dust could be measured in milliliters. The original sample sizes ranged from 0.2-3.6 milliliters of dust. If the original sample size exceeded one milliliter, it was divided to reduce the amount of time spent searching for mites. Division was accomplished by stirring the sample to suspend the particles and quickly pouring it into a splitter-funnel to minimize bias in obtaining equal fractions. All of the mite counts were reported with respect to one milliliter of dust.
Number of individuals, stage of life-cycle, and species of house dust mite were noted for each sample. Stages in the life cycle of Dermatophagoides include egg, larva, protonymph, tritonymph, and adult. In this study, mites were identified as larva, nymph (including both protonymphs and tritonymphs), adult male and female, or as "unknown" when only a fragment of the exoskeleton was found. Because identification is based on sexually mature mites, the species could be determined only when adults were found. D. farinae was distinguished from D. pteronyssinus by the shape of the distal portion of the bursa copulatrix in the female and the enlarged second pair of legs and length of the hysteronotal shield in the male.
Thirteen (72 percent) of 18 dust samples examined were positive for house dust mites (Table 1). Most mites were found in samples taken from carpets. No trend was apparent between the number of mites found and the use of the location as a private residence or a public facility. The sample with the most mites (160 mites per milliliter) was from a church classroom with short weave carpet. The room was used only one or two times a week by approximately 10 persons. However, for most samples, an association seemed to exist between the number of mites and the extent of human use. Five (38 percent) of the 13 locations where mites were obtained were infested only with D. farinae, five (38 percent) with both species, and two (15 percent) contained D. pteronyssinus alone. One sample (eight percent) contained only a single nymph, thus preventing identification of the species present. Other mites found in this study included unidentified species of Oribatidae, Cunaxidae, Raphignathidae, Acaridae, and Bdellidae.
The findings in this study demonstrate that house dust mites occur in a variety of locations in central Texas. In a previous study of house dust mites in the Forth Worth-Dallas area, only D. farinae was found to be present (Hall et al., 1971). The occurrence of D. pteronyssinus in central Texas represents a new locality record for this species. D. pteronyssinus originally may have become established in this area due to the movement of infested furniture, carpets, and bedding materials between Europe and the Fort Hood military installation in Bell County.
We thank Dr. Dennis Dillin for his help in acquiring special equipment.
TABLE 1. Occurrence of house dust mites. Origin of Species Lifestages dust found L N M F U House (2) D. farinae 0 2 0 3 2 House (2) D. pteronyssinus 0 8 5 12 0 House (2) D. farinae 10 14 3 2 0 House (3) D. farinae (25 percent) 0 3 5 4 0 D. pteronyssinus (75 percent) House (3) None 0 House (4) D. pteronyssinus 0 0 1 0 1 Office (2) None 0 Office (2) D. farinae 0 0 1 0 0 Office (3) D. farinae (50 percent) 0 2 5 1 0 D. pteronyssinus (50 percent) Office hall (2) None 0 Office hall (2) None 0 Church D. farinae (50 percent) 0 4 3 3 1 sanctuary (2) D. pteronyssinus (50 percent) Church D. farinae 0 3 0 2 2 class (2) Church D. farinae 12 57 42 49 0 class (2) School D. farinae (91 percent) 6 29 12 10 1 class (2) D. pteronyssinus (9 percent) Library (3) Unidentified 0 1 0 0 0 Library (3) None 0 Weight D. farinae (62 percent) 2 6 9 4 0 room (2) D. pteronyssinus (39 percent) Origin of Species Total no. No. mites dust found of mites per ml/dust House (2) D. farinae 7 12 House (2) D. pteronyssinus 25 36 House (2) D. farinae 29 32 House (3) D. farinae (25 percent) 12 15 D. pteronyssinus (75 percent) House (3) None 0 0 House (4) D. pteronyssinus 2 3 Office (2) None 0 0 Office (2) D. farinae 1 5 Office (3) D. farinae (50 percent) 8 10 D. pteronyssinus (50 percent) Office hall (2) None 0 0 Office hall (2) None 0 0 Church D. farinae (50 percent) 11 28 sanctuary (2) D. pteronyssinus (50 percent) Church D. farinae 7 9 class (2) Church D. farinae 160 160 class (2) School D. farinae (91 percent) 58 97 class (2) D. pteronyssinus (9 percent) Library (3) Unidentified 1 1 Library (3) None 0 0 Weight D. farinae (62 percent) 21 26 room (2) D. pteronyssinus (39 percent) (1) Number of mites of each stage: L, larvae; N, Nymph; M, Male; F, Female; U, Unknown. (2) Carpeted floor. (3) Hardwood floor. (4) Upholstered furniture.
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SARAH L. OUTHOUSE AND STANLEY D. CASTRO
Department of Biology, University of Mary Hardin-Baylor, Belton, Texas 76513
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|Title Annotation:||GENERAL NOTES|
|Author:||Outhouse, Sarah L.; Castro, Stanley D.|
|Publication:||The Texas Journal of Science|
|Date:||Feb 1, 1990|
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