Abstract
BackgroundThe survival of overwintering ticks, is critical for their subsequent population dynamics in the spring, and consequent transmission of tick-borne diseases. Survival is largely influenced by the severity of the winter temperatures and their degree of cold hardiness at the overwintering stage. The bush tick Haemaphysalis longicornis, is widely distributed in China, and can transmit various pathogens that pose serious medical/veterinary problems. In the present study we investigated the effect of low temperature stress to tick survival, super-cooling point and body content of water, glycerol and total protein.MethodsAfter various temperature acclimations, the super-cooling point was measured by Ni/CrNi-thermocouples with a precision temperature recorder. Water content was determined from weight loss of the sample exposed to 60°C for 48 h. Glycerol content was determined using Free Glycerol Reagent as directed by the manufacturer, and total protein was determined using the Bradford assay.ResultsThe 50% mortality temperatures for the adults and nymphs were -13.7°C and -15.2°C, respectively; and the discriminating temperatures for the adults and nymphs were -16.0°C and -17.0°C, respectively. The super-cooling points of the adults and nymphs were -19.0°C and -22.7°C, respectively. The water content of adult H. longicornis decreased substantially after acclimation at 0°C for 10 d, whereas the nymphs decreased after acclimation at 0°C for 20 d, and the glycerol and proteins of both nymphs and adults were significantly increased (p < 0.01) when stressed at 0°C for 10 d.ConclusionsIn H. longicornis, low temperature stress can enhance its cold hardiness and trigger appropriate responses, including reducing water content, and increasing glycerol and total protein content.
Highlights
The survival of overwintering ticks, is critical for their subsequent population dynamics in the spring, and consequent transmission of tick-borne diseases
Collection and rearing of ticks All ticks used in this study originated from adult H. longicornis collected from vegetation by blanket dragging in Xiaowutai National Nature Reserve Area (39°50′ to 40°07′N, 114°47′ to 115°30′E) of Hebei province, north China
Low temperature survival of unfed nymphs and adults To determine the temperature resulting in 50% mortality (LT50) and the discriminating temperature, which is important for testing the response of the rapid cold acclimation [26] of the unfed nymphal and adult H. longicornis, the survival of the ticks following a brief period of acclimation (2 h) was recorded and calculated as follows
Summary
The survival of overwintering ticks, is critical for their subsequent population dynamics in the spring, and consequent transmission of tick-borne diseases. Survival is largely influenced by the severity of the winter temperatures and their degree of cold hardiness at the overwintering stage. As obligate blood sucking ectoparasites of terrestrial vertebrates, are widely distributed capacity and cold hardiness of ticks [11,12,13,14] demonstrating that most ticks if not all, were as freeze-intolerant as many other arachnids. They did show a high potential super-cooling, irrespective of their geographical origin [12]. Little is known about the physiological responses, and biochemical changes in unfed H. longicornis when exposed to low temperatures in winter
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