Chigger Mite (Acari: Trombiculidae) Survey of Rodents in Shandong Province, Northern China.

Chigger mites are parasites of rodents and other vertebrates, invertebrates, and other arthropods, and are the only vectors of scrub typhus, in addition to other zoonoses. Therefore, investigating their distribution, diversity, and seasonal abundance is important for public health. Rodent surveillance was conducted at 6 districts in Shandong Province, northern China (114-112°E, 34-38°N), from January to December 2011. Overall, 225/286 (78.7%) rodents captured were infested with chigger mites. A total of 451 chigger mites were identified as belonging to 5 most commonly collected species and 3 genera in 1 family. Leptotrombidium scutellare and Leptotrombidium intermedia were the most commonly collected chigger mites. L. scutellare (66.2%, 36.7%, and 49.0%) was the most frequently collected chigger mite from Apodemus agrarius, Rattus norvegicus, and Microtus fortis, respectively, whereas L. intermedia (61.5% and 63.2%) was the most frequently collected chigger mite from Cricetulus triton and Mus musculus, respectively. This study demonstrated a relatively high prevalence of chigger mites that varied seasonally in Shandong Province, China.

[Study on biological characteristics of cypermethrin-resistant and -susceptible strains of Aedes albopictus at different temperatures].

OBJECTIVE: To study the biological characteristics of cypermethrin-resistance strain and -susceptible strain of Aedes albopictus under different controlled temperatures in the laboratory. METHODS: The two strains were raised at three different temperatures, 20, 25 degrees C and 28 degrees C respectively, and the biological characteristics of the two mosquito strains, such as reproduction, development and life expectancy, were observed and recorded in the laboratory. RESULTS: The life expectancy of both strains became shorter as the temperature raised, and the resistant strain(69.37% ± 0.01%, 77.04% ± 0.07%) lived shorter than the susceptible strain(85.24% ± 0.03%, 88.23% ± 0.05%)in average. Under 25 degrees C, the hatching rate of resistant strain decreased by 25.88%, and the pupation rate decreased by 11.18%. In the three temperatures, all the life expectancy expanded as the temperature went up, the periods for the susceptible strain were 19.75 ± 0.10, 23.65 ± 0.07 d and 25.08 ± 0.08 d under 28, 25 degrees C and 20 degrees C. While life expectancy for the resistant strain decreased to 17.21 ± 0.09, 20.95 ± 0.09, 22.58 ± 0.10 d. Under the same temperature, the development timing of the resistance strain was longer than that of the susceptible strain, and the period was the longest under 28 degrees C (156.2 h, 137.1 h). In the three temperatures, all the development periods expanded as the temperature went up, the susceptible and resistant larvae developed 137.1 d and 163.3 d, 247.7 d and 156.2 d, 182.3 d and 263.2 d under 28, 25 degrees C and 20 degrees C. The differences show statistic significance (P < 0.05). CONCLUSION: The resistance of A. albopictus to cypermethrin results in the decrease of adaptability to the environment change and the disadvantage of reproduction at different temperatures.