Cold hardiness and biochemical response to low temperature of the unfed bush tick Haemaphysalis longicornis (acari: ixodidae) (Epidemiologic Perspectives & Innovations)

Background: 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. 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. Methods: After 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[degree sign]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. Results: The 50% mortality temperatures for the adults and nymphs were -13.7[degree sign]C and -15.2[degree sign]C, respectively; and the discriminating temperatures for the adults and nymphs were -16.0[degree sign]C and -17.0[degree sign]C, respectively. The super-cooling points of the adults and nymphs were -19.0[degree sign]C and -22.7[degree sign]C, respectively. The water content of adult H. longicornis decreased substantially after acclimation at 0[degree sign]C for 10 d, whereas the nymphs decreased after acclimation at 0[degree sign]C for 20 d, and the glycerol and proteins of both nymphs and adults were significantly increased (p < 0.01) when stressed at 0[degree sign]C for 10 d. Conclusions: In 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.