title: Effects of high and low temperatures on development time and mortality of house dust mite eggs.
abstract: Hatching of Dermatophagoides pteronyssinus eggs was investigated when exposed to temperatures ranging from -70 to +70°C, at varying degrees of humidity (dry and wet heat, direct sunlight) and lengths of time (seven intervals, ranging from 0.5 to 5 h). Exposure to cold was induced using a domestic refrigerator at 4°C, its freezing compartment at -10°C and a deep freezer at -20, -40 and -70°C. For each time interval, there were three slides containing 30 eggs per slide, except for sunlight (five sets of slides). After treatment, all experimental groups were kept on an open work bench for 15 days of observation at ambient room temperature (ca. 22°C) and ca. 75% relative humidity. Control groups with 10 eggs per slide, in triplicate, followed a similar protocol. An egg was considered hatched if an emerging larva was detected from a cracked shell. Results indicated that at 40°C for both dry and wet heat, approximately 80% of all eggs survived. At direct sunlight and dry heat at 50°C, the thermal death point (TDP) occurred at 3 and 5 h, respectively. At 60 and 70°C both wet and dry heat, TDP occurred almost instantaneously. Under cold conditions, only the deep freezer at -70°C was effective in preventing hatching. It may be concluded that exposure to direct sunlight for 3 h, dry/wet heat of 60 and 70°C for a minimum of 30 min, and -70°C prevent egg hatching. This study may have relevance for mite control procedures.
authors.affiliation: Siriraj Dust Mite Center, Department of Parasitology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand. sivmh@mahidol.ac.th
authors.forename: Vanna
authors.initials: V
authors.lastname: Mahakittikun
authors.forename: John Joseph
authors.initials: JJ
authors.lastname: Boitano
authors.forename: Prapakorn
authors.initials: P
authors.lastname: Ninsanit
authors.forename: Teerapong
authors.initials: T
authors.lastname: Wangapai
authors.forename: Kornraphat
authors.initials: K
authors.lastname: Ralukruedej
mesh_terms: D000818:Animals; D010063:Ovum / Q000254:growth & development*; D039981:Pyroglyphidae / Q000254:growth & development*; D013696:Temperature; D013983:Tick Control