Simulation of developmental rate and temperature trend, and assessement of resistance risk to pyridaben of Tetranychus truncatus Ehara

In recent years, Tetranychus truncatus Ehara has become one of the main pests in Hexi area of Gansu Province, for which pyridaben was widely used due to its special physiological mechanism and broad-spectrum efficiency. However, T. truncatus has developed resistance to the sole application of pyridaben for a long perod of time. The aim of this paper was to verify the effect of temperature on risk development rate of resistant and susceptible populations of Tetranychus truncatus Ehara. Then based on the results of resistance selection, the study evaluated the resistance risk of T. truncatus to pyridaben. To do this, the relationship between development rate and temperature was analyzed using the Wang-Lan-Ding model at six temperatures (16 ℃, 20 ℃, 24 ℃, 28 ℃, 32 ℃ and 36 ℃). The realized heritability (h²) of T. truncatus was estimated and the resistance risk of T. truncates to pyridaben under different resistance selection pressure predicted on the basis of resistance breeding and selection in the laboratory. Then threshold trait analysis was done in quantitative genetics to provide a theoretical support for the application of pyridaben and comprehensive control of T. truncatus. The results showed that based on the fitted Wang-Lan-Ding models, the minimum and maximum boundary temperatures of susceptible populations were 10.05 ℃ and 39.24 ℃, whereas that of the resistant populations were 13.45 ℃ and 41.89 ℃, respectively. The fitted models also showed that the maximum boundary temperature of resistant populations was significantly greater than that of susceptible populations. This implied that resistant populations had much stronger suitability to extreme temperatures than susceptible populations. The realized heritability (h²) of T. truncatus resistance to pyridaben was 0.11, and h² for the first period and mid-term selection experiment (0.12 and 0.18, respectively) was higher than that for the later period (0.08), but h² (0.14) sharply increased at terminal stage. Under laboratory conditions with h² = 0.11, developing a 10-fold increase of resistance to pyridaben required 1023 generations under selection pressure (mortality) of 50%90%. Under field conditions (h² = 0.05), it required 2146 generations to develop the same resistance level．The results suggested that T. truncatus had resistance risk to pyridaben. However, when pyridaben was applied under rotation with other insecticides without cross-resistance and reduced selection pressure, the resistance development rate of T. truncatus delayed.