Effects of Constant and Fluctuating Temperatures on Development Rates and Longevity of Diaphorencyrtus aligarhensis (Hymenoptera: Encyrtidae)

Abstract

The effects of fluctuating and constant temperatures on the development and longevity of Diaphorencyrtus aligarhensis (Shafee, Alam, and Argarwal) (Hymenoptera: Encyrtidae), a parasitoid sourced from Pakistan and released in California for the classical biological control of Diaphorina citri Kuwayama (Hemiptera: Liviidae), were examined. The influence of six fluctuating temperatures that averaged 15, 20, 25, 30, 32, and 35°C, over 24 h on the development times and longevity of male and female D. aligarhensis were quantified and compared to six constant temperatures set at the same average temperatures. The development rates of immature stages of D. aligarhensis as a function of temperature were modeled using one linear and four nonlinear models. Fluctuating temperatures had significant effects on parasitoid development times and longevity which differed across experimental temperatures. Degree-days required for completion of cumulative development of D. aligarhensis were significantly different being 21% lower under fluctuating temperature regimens when compared with constant temperatures. The lower temperature threshold estimates above which development occurred were estimated to be lower under constant than fluctuating temperatures. The estimated values of upper and optimum temperature limits were similar for individuals reared under constant and fluctuating temperatures. Diaphorencyrtus aligarhensis lived longer at constant intermediate temperatures and for shorter times at constant lower temperature extremes when compared with their fluctuating temperature counterparts. Daily thermal fluctuations significantly influenced life history parameters of D. aligarhensis and should be considered when assessing likelihoods of establishment and impacts of this parasitoid on D. citri across diverse citrus-growing climates.

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

“…Results presented here indicate that realistic fluctuating temperature scenarios significantly influenced development rates and longevity of P. diaphorinae, resulting in significant deviations from observations for constant temperature regimens. This finding is in alignment with similar studies on D. aligarhensis (Milosavljević et al 2019a) and T. radiata (McCalla et al 2019), the 2 dominant primary parasitoids that attack D. citri.…”

“…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):…”

“…In quarantine, D. aligarhensis was identified as a preferred host for P. diaphorinae when compared to T. radiata (Bistline-East & Hoddle 2016). The Pakistani population of D. aligarhensis is a bi-parental solitary endoparasitoid that has been mass produced and released in California for classical biological control of D. citri (Milosavljević et al 2017a(Milosavljević et al , 2019a. Diaphorencyrtus aligarhensis parasitizes second through fourth instar D. citri nymphs, and provides additional mortality through host feeding (Rohrig 2010;Rohrig et al 2011;Bistline-East et al 2015;Vankosky & Hoddle 2017a, b).…”

“…Temperature profoundly affects insect growth, population dynamics, and species distributions (Gilbert & Raworth 1996;Obrycki & Kring 1998;Jalali et al 2009;Koda & Nakamura 2010;Marchioro & Forester 2011;Nooten et al 2014;Milosavljević et al 2016Milosavljević et al , 2017bMilosavljević et al , 2019aSchowalter 2016;Damos et al 2018). For poikilotherms, increasing temperature can have significant effects on life history parameters such as development time, lifespan, and reproduction rates (Roy et al 2002;Kontodimas et al 2004Kontodimas et al , 2007Broatch et al 2006;Logan et al 2006;Pilkington & Hoddle 2006a, 2007aZamani et al 2007;Pilkington et al 2014;Luhring & DeLong 2016).…”