Transcriptome analysis reveals TOR signalling-mediated plant flush shoots governing Diaphorina citri Kuwayama oviposition.

Asian Citrus Psyllid (ACP), Diaphorina citri, is a key vector transmitting the causative agent of Huanglongbing (HLB) disease. Population growth of ACP is evident after feeding on plant flush shoots, as they only oviposit here. However, the underlying mechanism as to why flush shoots govern oviposition is unclear. This study compares the fecundity and ovarian morphology of ACP between young flush and mature leaves. Furthermore, the transcriptome of mated females infesting Murraya paniculata was analysed. Finally, the gene of the key Target of Rapamycin (TOR) signalling pathway was silenced by RNAi. Results indicated that flush shoot feeding activated the development of the psyllids ovary and therefore induced oviposition. A total of 126 and 2794 differentially expressed genes were detected at 1 and 5 days, respectively, after pest infestation of flush shoots compared to mature leaves. Many genes are involved in protein metabolism, Mitogen-Activated Protein Kinase (MAPK) signalling pathway, hormone synthesis, and TOR signalling pathway: all thought to activate reproduction. Silencing of the positive regulator gene DcRheb in the TOR pathway resulted in lower levels of ecdysone and juvenile hormone and decreased vitellogenin synthesis, further disrupting reproductive ability. This study enhances understanding of the molecular mechanism underlying ACP's reproductive strategy.

Effects of Candidatus Liberibacter asiaticus on the fitness of the vector Diaphorina citri.

AIMS: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama transmits the bacterium 'Candidatus Liberibacter asiaticus' (Las), which causes citrus huanglongbing (HLB) disease. Although many studies have been conducted on the biology of ACP on different host plants, few have taken the plant, Las bacteria and the vector insect within one context to evaluate the effects of Las on the fitness of ACP under field conditions. Understanding the relationship between Las and ACP is critical for both ACP and HLB disease management. METHODS AND RESULTS: We estimated the development and survival of ACP immatures, the longevity and fecundity of ACP female adults in four treatments (Las-positive or -negative ACP on Las-infected and -free citrus plants). Las-positive ACP immatures developed significantly faster on Las-infected citrus than those on Las-free plants. The fecundity and longevity of Las-positive female adults were also greater, or longer on Las-infected citrus shoots, whereas the survival of Las-positive immatures was significantly lower on Las-infected citrus shoots, compared to those that developed on Las-free plants. Similarly, the intrinsic rate of population increase (rm ) was highest (0·1404) when Las-positive ACP fed on Las-infected citrus shoots and the lowest (0·1328) when the Las-negative ACP fed on Las-free citrus shoots. CONCLUSIONS: Both the Las infection in ACP and citrus plants had obvious effects on the biology of ACP. When compared to the Las infection in ACP insects, the Las infection in citrus shoots had a more significant effect on the fitness of ACP. SIGNIFICANCE AND IMPACT OF THE STUDY: To efficiently prevent the occurrence and spread of HLB disease, it is critical to understand the ecological basis of vector outbreaks and disease incidence, especially under field conditions. Thus, this study has increased our understanding of the epidemiology of HLB transmitted by psyllids in nature.

Efficacy of the entomopathogenic nematode, Steinernema feltiae, against sweetpotato whitefly Bemisia tabaci (Homoptera: Aleyrodidae) under laboratory and glasshouse conditions.

The potential of using the entomopathogenic nematode Steinernema feltiae to control the sweetpotato whitefly Bemisia tabaci (Gennadius) has been established in previous laboratory studies. However, laboratory studies can overestimate the level of control achieved by biocontrol agents in the glasshouse. Glasshouse trials are therefore required to confirm laboratory results before full-scale commercial development is considered. Under both controlled laboratory and glasshouse conditions high mortality of second instar B. tabaci (>90% and >80%, respectively) was recorded after application of S. feltiae. The efficacy of the biocontrol agent at various application rates was also investigated, where halving the rate of S. feltiae application caused no significant reduction in B. tabaci mortality on tomato foliage. Steinernema feltiae has shown much potential for incorporation into integrated pest management strategies for the control of B. tabaci.

Effect of temperature and host plant leaf morphology on the efficacy of two entomopathogenic biocontrol agents of Thrips palmi (Thysanoptera: Thripidae).

The efficacy of two entomopathogenic biocontrol agents, Steinernema feltiae (Filipjev) and Verticillium lecanii (Zimmerman) Viégas (reclassified now as Lecanicillium muscarium (Petch) Zare & Gams), against Thrips palmi Karny was investigated. Assessments of the effect of temperature on the efficacy of S. feltiae indicated that higher mortality of T. palmi was recorded at 20 degrees C compared to either 15 or 25 degrees C, whereas significantly higher T. palmi mortality followed application of L. muscarium at 25 degrees C. Testing the control agents efficacy on three host plants; chrysanthemum, sweet pepper and cucumber, under constant temperature and high humidity conditions produced no significant difference in the level of T. palmi larval mortality on each host plant. Incorporating the chemical insecticide imidacloprid with both biological agents in a combined control strategy increased T. palmi juvenile mortality. The potential role of S. feltiae and L. muscarium within integrated pest management programmes for the control of T. palmi is discussed.