Impact of different temperatures on survival and energy metabolism in the Asian citrus psyllid, Diaphorina citri Kuwayama.

Temperature influences the life history and metabolic parameters of insects. Asian citrus psyllid (ACP), Diaphorina citri is a tropical and subtropical pest. ACP invaded new regions around the world and threatened the citrus industry as a vector for Huanglongbing (HLB) disease. ACP is widely distributed and can survive high (up to 45 °C) and low temperatures (as low as -6 °C). The precise mechanism of temperature tolerance in ACP is poorly understood. We investigated adult survival, cellular energy balance, gene expression, and nucleotide and sugar-nucleotide changes under the effect of different temperature regimes (0 °C to 45 °C with 5 °C intervals). The optimum temperatures for survival were 20 and 25 °C. Low temperatures of 0 °C and 5 °C caused 50% mortality after 2 and 4 days respectively, while one day at high temperature (40 °C and 45 °C) caused more than 95% mortality. The lowest quantity of ATP (3.69 ± 1.6 ng/insect) and the maximum ATPase enzyme activities (57.43 ± 7.6 µU/insect) were observed at 25 °C. Correlation between ATP quantities and ATPase activity was negative. Gene expression of hsp 70, V-type proton ATPase catalytic subunit A and ATP synthase α subunit matched these results. Twenty-four nucleotides and sugar-nucleotides were quantified using HPLC in ACP adults maintained at low, high, and optimum temperatures. The nucleotide profiles were different among treatments. The ratios between AMP:ATP and ADP:ATP were significantly decreased and positively correlated to adults survival, whereas the adenylate energy charge was increased in response to low and high temperatures. Exploring energy metabolic regulation in relation with adult survival might help in understanding the physiological basis of how ACP tolerates newly invaded regions.

Herbivory by the insect diaphorina citri induces greater change in citrus plant volatile profile than does infection by the bacterium, Candidatus Liberibacter asiaticus.

The volatile organic compound (VOC) profile in plant leaves often changes after biotic and abiotic stresses. Monitoring changes in VOCs in plant leaves could provide valuable information about multitrophic interactions. In the current study, we investigated the effect of Asian citrus psyllid (ACP) infestation, citrus greening pathogen (Candidatus Liberibacter asiaticus [CLas]) infection, and simultaneous attack by ACP and CLas on the VOC content of citrus leaves. Leaf volatiles were extracted using hexane and analyzed with gas chromatography-mass spectrometry (GC-MS). Although ACP is a phloem-sucking insect that causes minimal damage to plant tissues, the relative amount of 21 out of the 27 VOCs increased 2- to 10-fold in ACP-infested plants. The relative amount of d-limonene, ß-phelandrene, citronellal, and undecanal were increased 4- to 20- fold in CLas-infected plants. A principle component analysis (PCA) and cluster analysis (CA) showed that VOC patterns of ACP-infested and CLas-infected plants were different from each other and were also different from the controls, while the VOC pattern of double-attacked plants was more like that of the controls than that of ACP-infested or CLas-infected plants. VOC amounts from leaves were compromised when plants were attacked by ACP and CLas. The results of this study showed that a simple direct extraction of citrus leaf volatiles could be successfully used to discriminate between healthy and CLas-infected plants. Information about the effects of insect and pathogen attack on the VOC content profile of plants might contribute to a better understanding of biotic stress.

Silencing abnormal wing disc gene of the Asian citrus psyllid, Diaphorina citri disrupts adult wing development and increases nymph mortality.

Huanglongbing (HLB) causes considerable economic losses to citrus industries worldwide. Its management depends on controlling of the Asian citrus Psyllid (ACP), the vector of the bacterium, Candidatus Liberibacter asiaticus (CLas), the causal agent of HLB. Silencing genes by RNA interference (RNAi) is a promising tool to explore gene functions as well as control pests. In the current study, abnormal wing disc (awd) gene associated with wing development in insects is used to interfere with the flight of psyllids. Our study showed that transcription of awd is development-dependent and the highest level was found in the last instar (5(th)) of the nymphal stage. Micro-application (topical application) of dsRNA to 5(th) instar of nymphs caused significant nymphal mortality and adult wing-malformation. These adverse effects in ACP were positively correlated with the amounts of dsRNA used. A qRT-PCR analysis confirmed the dsRNA-mediated transcriptional down-regulation of the awd gene. Significant down-regulation was required to induce a wing-malformed phenotype. No effect was found when dsRNA-gfp was used, indicating the specific effect of dsRNA-awd. Our findings suggest a role for awd in ACP wing development and metamorphosis. awd could serve as a potential target for insect management either via direct application of dsRNA or by producing transgenic plants expressing dsRNA-awd. These strategies will help to mitigate HLB by controlling ACP.