Threshold Temperatures and Thermal Requirements of Psyllaphycus diaphorinae (Hymenoptera: Encyrtidae), a Hyperparasitoid of Diaphorencyrtus aligarhensis (Hymenoptera: Encyrtidae) and Tamarixia radiata (Hymenoptera: Eulophidae)

The temperature-driven development rates and longevity times of Psyllaphycus diaphorinae Hayat (Hymenoptera: Encyrtidae), a hyperaparasitoid of Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) and Diaphorencyrtus aligarhensis (Shafee, Alam & Agarwal) (Hymenoptera: Encyrtidae), 2 primary parasitoids of Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), were quantified. Development times and longevity were investigated at 6 average daily temperatures (15, 18, 20, 25, and 32 °C) that either were constant or fluctuated over 24 h. Thermal performance curves for egg-to-adult development of P. diaphorinae reared on D. aligarhensis were characterized using 1 linear and 2 nonlinear degree-d models (i.e., Ratkowsky and Performance-2). Daily thermal fluctuations had significant effects on development rates and longevity of P. diaphorinae adults. Psyllaphycus diaphorinae reared under fluctuating profiles completed development more slowly (20, 25, and 32 °C), and survived longer (18–32 °C) than those reared under constant profiles with equivalent mean temperatures. In addition, P. diaphorinae emerged from fluctuating but not constant profiles at 15 °C. Estimates of thermal constants (i.e., degree-d to complete development) predicted by the linear model were 36% lower for the constant temperature regimen than the fluctuating temperature regimen. Nonlinear and linear model estimations of the theoretical lower and upper thermal thresholds ranged between –3.7 to 11.9 °C and 33.7 to 34 °C, respectively. The development rate of male and female P. diaphorinae was most favorable at 30 °C. These results demonstrate the significant effects of average temperatures and daily temperature variations on P. diaphorinae life history.