Abstract
Some entomopathogenic fungi species, Isaria fumosorosea, and Hirsutella citriformis were found to be efficient against the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). However, the susceptibility to these fungi increases when the psyllid infected with Candidatus Liberibacter asiaticus (Las), which is transmitted by D. citri and causes citrus greening disease. In this study, we examined the Las‐infected and Las‐uninfected D. citri susceptibility to entomopathogenic fungi at different temperature regimes (5–40°C). When D. citri adults exposed to cold temperature (5°C), they showed less susceptibility to entomopathogenic fungi as compared with control (27°C). Irrespective of infection with Las, a significantly positive correlation was observed between temperature and percentage mortality caused by different isolates of I. fumosorosea, 3A Ifr, 5F Ifr, PS Ifr, and H. citriformis isolates, HC3D and 2H. In contrast, a significantly negative correlation was found between temperature and percentage mortality for 3A Ifr for both Las‐infected and Las‐uninfected psyllids. Detoxification enzymes, Glutathione S‐transferase levels in D. citri showed a negative correlation, whereas cytochrome P450 and general esterase levels were not correlated with changes in temperature. These findings revealed that detoxification enzymes and general esterase levels are not correlated with altered susceptibility to entomopathogenic fungi at the different temperature regimes. Conclusively, temperature fluctuations tested appear to be a significant factor impacting the management strategies of D. citri using entomopathogenic fungi.
Highlights
The Asian citrus psyllid (ACP), Diaphorina citri (Hemiptera: Liviidae), is native to Asia and southeastern Florida and has invaded several regions of the world (Capoor & Viswanath, 1967; Grafton-Cardwell, Stelinski, & Stansly, 2013; Huang, Tsai, & Wang, 1984; Nava et al, 2010; Yan, Zeng, & Zhong, 2015)
The stock populations were maintained for about nine generations prior to experiments on the same host plants kept in mesh cages (50 × 50 × 50 cm) in greenhouse at a temperature of 27 ± 1°C, a photoperiod of 14:10 light/dark (L/D; 14 hr light 6:00–20:00), and 75 ± 5% relative humidity (RH), with no insecticide exposure
The results of the study showed that psyllids exposed to cold stress were more tolerant to entomopathogenic fungi than controls, seems to be possible effects that could be observed during winter compared to summer temperature variations
Summary
The Asian citrus psyllid (ACP), Diaphorina citri (Hemiptera: Liviidae), is native to Asia and southeastern Florida and has invaded several regions of the world (Capoor & Viswanath, 1967; Grafton-Cardwell, Stelinski, & Stansly, 2013; Huang, Tsai, & Wang, 1984; Nava et al, 2010; Yan, Zeng, & Zhong, 2015). Diaphorina citri primarily attacks young flush of citrus trees but can attack stressed citrus trees if the pest population density is high It has become the most important insect pest of citrus in southeastern Florida (Halbert, 1997) and has recently threatened native citrus plants in China (Yan et al, 2015). Many biocontrol agents have been used against D. citri (Khan, Arif, Hoddle, & Hoddle, 2014; Qureshi, Rogers, Hall, & Stansly, 2009) but the most effective agents are entomopathogenic fungi, Isaria fumosorosea Wize (= Paecilomyces fumosoroseus) (Hypocreales: Cordycipitaceae) and Hirsutella citriformis Spear (Hypocreales: Ophiocordycipitaceae) (Avery et al, 2013; Speare 1920). Entomopathogenic fungi applied to these citrus trees, where they infect D. citri nymphs and adults (Avery et al, 2013)
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