The Influence of Temperature Variation on Life History Parameters and Thermal Performance Curves of Tamarixia radiata (Hymenoptera: Eulophidae), a Parasitoid of the Asian Citrus Psyllid (Hemiptera: Liviidae)

Abstract

This study examined the effects of seven constant and fluctuating temperature profiles with corresponding averages of 12 to 38°C on the life history of the Punjab, Pakistan-sourced Tamarixia radiata (Waterston) released in California for biological control of Diaphorina citri Kuwayama. One linear and seven nonlinear regression functions were fit to egg-to-adult development rate data to characterize thermal performance curves. Temperature fluctuations significantly affected both development and longevity of T. radiata. Estimates of degree-days predicted by the linear model were 30% higher for the fluctuating regime than the constant regime. Nonlinear model estimations of theoretical minimum and maximum developmental thresholds were lower for the fluctuating regime when compared to the constant regime. These predictions align with experimental observations. Parasitoids reared under fluctuating profiles at low average temperatures developed faster (15°C) and survived longer (15–20°C) when compared to those reared under constant regimes with corresponding means. In contrast, high average fluctuating temperatures produced parasitoids with an extended developmental period (35°C) and reduced longevity (30–35°C). A meta-analysis of published T. radiata development datasets, together with the results of this study, indicated convergence in degree-days and theoretical minimum developmental thresholds among geographically distinct parasitoid populations. These findings demonstrate the significant effects of temperature on T. radiata life history and have important implications for optimization of mass-rearing and release efforts, improvement of predictions from climate modeling, and comparison of T. radiata population performance across climatic gradients and geographic regions.

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

“…The duration of adult life span of P. diaphorinae increased, however, with decreasing temperature regardless of the temperature regimen, and females lived longer than males on average (Table 4). Interestingly, P. diaphorinae reared under high fluctuating temperatures had greatly reduced longevity in comparison with hyperparasitoids reared under constant temperature counterparts (Table 4), a finding that aligns with the results of previous studies showing a narrow range of thermotolerance for many insect taxa (Neven 2000;Colinet et al 2015;McCalla et al 2019;Milosavljević et al 2019a, c). This is notable, because hyperparasitoids reared under high fluctuating temperature regimens appear to be at risk of accumulation of detrimental effects due to exposure to temperature extremes (Colinet et al 2015), and these may be amplified further by adverse temperature effects on the host upon which they are developing.…”

“…Therefore, fluctuating temperatures allowed successful development of both male and female hyperparasitoids over a wider temperature range (i.e., 15-32 °C), than did constant temperatures (i.e., 18-32 °C). These results support the hypothesis that thermal variation at low average temperatures, above and below the daily thermal mean, allows arthropod development to occur at temperatures outside the limits defined by constant regimens (Jensen 1906; Packard & Packard 1993;Gilbert & Raworth 1996;Kontodimas et al 2004;Hall et al 2011;Colinet et al 2015;McCalla et al 2019;Milosavljević et al 2019a, c).…”

“…1). These results are supported by other studies suggesting that phenology predictions using models fit to constant temperature data could produce unrealistic estimates of generation times for field populations that are exposed to fluctuating temperature cycles (Liu et al 2002;Warren & Anderson 2013;Colinet et al 2015;McCalla et al 2019;Milosavljević et al 2019a, c).…”

“…The theoretical lower thermal thresholds for development of T. radiata and D. aligarhensis, 2 primary parasitoids P. diaphorinae attacks, range from −6 to 12 °C (McCalla et al 2019;Milosavljević et al 2019a). In this study, thermal thresholds, estimated by the linear and 2 nonlinear (i.e., Ratkowsky and Performance-2) models ranged from −4 to 12 °C for P. diaphorinae (Table 3), which falls within the previously reported range for these 2 primary parasitoids of D. citri.…”

“…The coefficient of determination (R 2 ) and its adjusted value (R 2 adj ), although commonly used in the literature to describe the fit of nonlinear models to development data, were not used to assess goodnessof-fit for nonlinear models because they do not describe accurately the validity of a nonlinear fit to data (see Spiess and Neumeyer 2010 for further explanation). Instead, nonlinear model goodness-of-fit was assessed with the residual sum of squares (Shi et al 2015;Ratkowsky & Reddy 2017;McCalla et al 2019;Milosavljević et al 2019a):…”