Bioclimatic Thresholds, Thermal Constants and Survival of Mealybug, <i>Phenacoccus </i><i>solenopsis</i> (Hemiptera: Pseudococcidae) in Response to Constant Temperatures on Hibiscus

Temperature-driven development and survival rates of the mealybug, Phenacoccussolenopsis Tinsley (Hemiptera: Pseudococcidae) were examined at nine constant temperatures (15, 20, 25, 27, 30, 32, 35 and 40°C) on hibiscus (Hibiscusrosa-sinensis L.). Crawlers successfully completed development to adult stage between 15 and 35°C, although their survival was affected at low temperatures. Two linear and four nonlinear models were fitted to describe developmental rates of P. solenopsis as a function of temperature, and for estimating thermal constants and bioclimatic thresholds (lower, optimum and upper temperature thresholds for development: Tmin, Topt and Tmax, respectively). Estimated thresholds between the two linear models were statistically similar. Ikemoto and Takai’s linear model permitted testing the equivalence of lower developmental thresholds for life stages of P. solenopsis reared on two hosts, hibiscus and cotton. Thermal constants required for completion of cumulative development of female and male nymphs and for the whole generation were significantly lower on hibiscus (222.2, 237.0, 308.6 degree-days, respectively) compared to cotton. Three nonlinear models performed better in describing the developmental rate for immature instars and cumulative life stages of female and male and for generation based on goodness-of-fit criteria. The simplified β type distribution function estimated Topt values closer to the observed maximum rates. Thermodynamic SSI model indicated no significant differences in the intrinsic optimum temperature estimates for different geographical populations of P. solenopsis. The estimated bioclimatic thresholds and the observed survival rates of P. solenopsis indicate the species to be high-temperature adaptive, and explained the field abundance of P. solenopsis on its host plants.本研究探究了温度对扶桑绵粉蚧（Phenacoccus solenopsis Tinsley，半翅目Hemiptera: 粉蚧科Pseudococcidae）的发育与存活率的影响，实验在朱槿（Hibiscus rosa-sinensis L.）上设置了9个恒温梯度（15、20、25、27、30、32、35与40℃）。初孵移动若虫（crawler）在15至35℃范围内可顺利发育至成虫，尽管低温会对其存活率产生影响。本研究采用2种线性模型与4种非线性模型拟合扶桑绵粉蚧的发育速率随温度变化的函数关系，用于估算其热常数（thermal constants）与生物气候阈值（bioclimatic thresholds，即发育下限温度Tmin、最适温度Topt与上限温度Tmax）。两种线性模型估算得到的阈值无统计学差异。池本-高井线性模型（Ikemoto and Takai’s linear model）可用于比较扶桑绵粉蚧在朱槿与棉花两种寄主上各虫态的发育下限温度是否等效。雌、雄若虫及整个世代完成累计发育所需的日度（degree-days），在朱槿上分别为222.2、237.0与308.6，显著低于其在棉花上的对应值。基于拟合优度（goodness-of-fit）评价标准，3种非线性模型对未成熟虫态、雌雄成虫的累计生活史阶段以及整个世代的发育速率拟合效果更佳。其中简化β型分布函数（simplified β type distribution function）估算得到的最适温度Topt与观测到的最大发育速率更为接近。热力学SSI模型（Thermodynamic SSI model）显示，扶桑绵粉蚧不同地理种群（geographical populations）的内在最适温度（intrinsic optimum temperature）估算值无显著差异。本研究估算的生物气候阈值与观测到的扶桑绵粉蚧存活率表明，该物种具有高温适应性，这也解释了其在寄主植物上的野外种群发生量。