Asian Citrus Psyllid Populations Research Articles

Topping sweet orange trees as Diaphorina citri bait on the farm edge for huanglongbing management: Opportunities and limitations

Flush shoots of citrus have an important role in huanglongbing (HLB) epidemiology, as the insect vector of HLB, the Asian citrus psyllid (ACP), prefers them for feeding and reproduction. Additionally, ACP's acquisition and transmission of HLB bacteria mainly occurs in these flushes. As pruning stimulates sprouting, we hypothesized that periodically topping sweet orange trees on the orchard's edge (from 0 to 100 m) would attract ACPs from external areas to these flush shoots as bait, instead of ACPs dispersing throughout the orchard. Hence, it would direct HLB management on this edge width. For that, topped trees (TT) were compared to non-topped trees (NTT) located on the orchard's edge, with only NTT after edges (from 100 to 200 m). Vegetative growth, flushing frequency, ACP population, spray coverage, HLB incidence, fruit yield, and quality of Hamlin and Valencia Americana sweet orange trees were evaluated in commercial orchards over three growing seasons. Topping was performed frequently (every 30–45 d) on alternate rows to stimulate the year-round presence of shoot flushes within the orchard's edge. Insecticides were sprayed monthly to control ACP. Topping reduced tree height and canopy volume by 24 % and 20 % on average. Topped trees presented, on average, 3-fold more flush shoots than NTT over time. On Hamlin blocks, ACP numbers and cumulative HLB incidence were 70 % and 90 % higher, respectively, in TT compared to NTT. However, no consistent differences were observed for the Valencia Americana orchard. Moreover, ACP abundance and HLB incidence were similar after the edge regardless of topping. In the edge areas, although tree yield was reduced (∼65 % on average) on TT compared to NTT, topping significantly enhanced external fruit quality. This treatment increased fruit size and weight and promoted intense yellow coloration. Topping increased spray coverage at the top of Hamlin trees by 1.5-fold compared to control. Frequent topping as bait for ACP poses significant risks if the ACP population is not rigorously controlled, potentially leading to further reductions in yield from edge trees.

Comparison of Insecticide Sprays in Alternate Rows and in All Rows on Asian Citrus Psyllid Control and Huanglongbing Progress in Sweet Orange Orchards.

One strategy to reduce huanglongbing (HLB) is controlling its insect vector, the Asian citrus psyllid (ACP) Diaphorina citri, by preventive insecticide sprays. The recommendation is to spray insecticide in all rows (conventional spray [CONV]), but some growers empirically spray in alternate rows (ALT) to increase the spray frequency without increasing the operating cost. Therefore, this work compared the effect of ALT with CONV on the ACP population and HLB incidence. The spray deposition (amount of metallic copper per leaf area), coverage (percentage of water-sensitive paper area covered by spray), and efficacy (ACP mortality) of each treatment were also evaluated on both sides of the trees. Two field trials were performed: Trial #1 compared ALT every 7 days (ALT7) with CONV every 14 days (CONV14), and trial #2 compared different spray frequencies of ALT with CONV every 7 days (CONV7). In trial #1, no differences were observed in the ACP population or HLB progress between ALT7 and CONV14 after 5 years. In trial #2, ALT7 presented the highest percentage of ACP and cumulative HLB incidence than CONV7 and ALT every 3 to 4 days, after 2 years. Hence, when the frequency of ALT was half the frequency of CONV, similar results were observed. Spray deposition, coverage, and efficacy were similar between tree sides in CONV, but they were uneven in ALT, resulting in higher values on the tree side that directly received the spray. Insecticide spray should be performed with the frequency enough to keep new shoots protected during their growth.

Genetic diversity and population structure of the Asian citrus psyllid in China.

The Asian citrus psyllid (ACP) is the main vector of Citrus Huanglongbing, the most damaging citrus disease, causing significant financial losses in the citrus industry. Global warming has expanded the habitat of this pest, allowing it to continue its northward migration to China. Population genetic information of ACP is fundamentally essential for species management. This study investigated the genetic diversity and population structure of Chinese ACP using the mitochondrial cytochrome oxidase subunit I gene by dataset comprised 721 sequences from 27 geographic sites in China. Low haplotype diversity (0.323 ± 0.022) and low nucleotide diversity (0.00071 ± 0.00007) were observed in the entire population, which may indicate recent founder events. Twenty-three haplotypes were identified and clustered into 2 haplogroups: haplogroup I and haplogroup II. Haplogroup II included only 2 unique haplotypes, which occurred exclusively in the Southwest China ACP population. Genetic differentiation analyses were also indicative of Southwest China population was significantly differentiated from the remaining populations. Demographic history analysis showed that ACP population in China has experienced demographic expansion. Our results provided a better understanding of the genetic distribution patterns and structures of ACP populations in China.

Ineffectiveness of applying additional insecticide sprays at the border of the citrus block for the control of Huanglongbing.

Huanglongbing (HLB), mainly associated with the bacterium 'Candidatus Liberibacter asiaticus', is a devastating disease that causes negative impacts on citrus yield and fruit quality. One of the main HLB control measures is based on preventive insecticide sprays, aiming to control its vector, the Asian citrus psyllid (ACP) Diaphorina citri. In blocks on the orchard's periphery, the ACP population is more concentrated in trees closer to the block's edge and gradually decreasing towards its interior. This spread pattern of ACP has motivated growers to perform, empirically based, additional insecticide applications at the border of the block ('AB'), as an additional measure to spraying insecticides in the entire block ('EB'). Hence, this work aimed (i) to evaluate the coverage and efficiency of AB, comparing tree canopy volume, and planting direction; and (ii) to compare ACP population and HLB incidence between blocks treated under EB, and blocks that received 'EB + AB'. Regardless of the operational situation, as the distance increased from the orchard's edge (0m) to the interior, spray coverage exponentially decayed from an average of 21% to less than 1% of coverage, and ACP mortality exponentially decayed from 83% to 7%. In general, the spray coverage and ACP mortality were suitable only for the tree canopy face directly sprayed at the orchard's edge (0m). After 5.5 years, a higher ACP population and number of symptomatic trees were detected in 'EB + AB'. As the 'EB + AB' had no effect in reducing ACP population, or HLB incidence, this additional spraying had no benefit in HLB management. © 2022 Society of Chemical Industry.

Analysis of Citrus Tristeza Virus Incidences within Asian Citrus Psyllid (Diaphorina citri) Populations in Florida via High-Throughput Sequencing.

Simple SummaryThe iconic citrus crop of Florida is suffering from an incurable disease called Huanglongbing (HLB), or citrus greening. HLB is caused by a bacterium Candidatus Liberibacter asiaticus (CLas), which is efficiently vectored by a small insect, the Asian citrus psyllid (ACP). To control the spread of CLas and ultimately HLB, citrus growers primarily depend on environmentally harmful insecticides against the ACP, which can induce insecticide resistance. An alternative, biological approach involves insect-specific viruses (ISVs) of the ACP for future exploitation to exclusively target this insect pest. To identify these ISVs, we have subjected ACPs to high-throughput sequencing, a powerful sequencing technology. This current study follows an initial detection of citrus tristeza virus (CTV) amongst the viruses detected in the ACP during HTS and continues to show the persistent and diverse presence of CTV in Florida ACPs across subsequent years. We suggest that the ACP may be utilized as a tool or lens of CTV presence throughout Florida citrus groves.The destructive citrus disease, Huanglongbing (HLB) or citrus greening, continues to devastate Florida’s citrus industry. A hemipteran insect, the Asian citrus psyllid (ACP), disperses Candidatus Liberibacter asiaticus, one of the putative bacterial pathogens of HLB. This study builds upon ongoing research utilizing high-throughput sequencing to analyze the virome of ACP populations collected from citrus groves throughout Florida. Following the widespread detection of sequences aligning to the genome of citrus tristeza virus (CTV) across consecutive years in the Florida ACP virome, we continued to detect a pervasive amount of CTV in Florida ACPs during subsequent years. Simultaneously, we also detected mixed infections of CTV strains in pooled ACPs from different Florida regions. Predating the HLB epidemic, CTV has been present in Florida for many years and our results confirm its widespread and diverse persistence in Florida citrus groves through a unique lens, the ACP. CTV presence in the ACP likely results from feeding on CTV-infected citrus trees in Florida citrus groves, which may help to understand an overlapping presence of CTV and HLB, both endemic citrus pathosystems in the state, and their role in future integrated pest management strategies.

Assessment of Variation in Feeding Behavior by Color Morph in the Asian citrus Psyllid (Diaphorina citri)

The Asian citrus psyllid (ACP) Diaphorina citri (Hemiptera:Liviidae), vector of huanglongbing disease, displays a high degree of color polyphenism. In the adult stage, ACP exhibits abdominal colors that can be separated into three color groupings: blue-green, grey-brown and orange-yellow. Color morphology has been shown to influence important and energetically costly psyllid life traits including reproduction, dispersion, immune defense and resistance to insecticides. Despite this, it remains unclear how color morphology is correlated with feeding behavior. Understanding variation in feeding behavior of the ACP color morphs is critical to better understanding how ACP populations utilize host-plants and to assess potential risk for transmission of the causal agent of huanglongbing disease. We compared the feeding behavior of the three ACP color morphs by using electropenetrography (EPG). We did not detect differences in the feeding behavior activities at phloem or xylem tissues when comparing the three-color morphs. Furthermore, there were no differences in feeding behavioral parameters before reaching phloem or xylem tissues. Our results suggest energy requirements are similar between color morphs and feeding behavior parameters associated with CLas transmission are potentially similar between color morphs.

White and red-dyed kaolin particle films reduce Asian citrus psyllid populations, delay huanglongbing infection, and increase citrus growth

Florida citrus production has declined severely due to huanglongbing (HLB; “citrus greening disease”) caused by Candidatus Liberibacter asiaticus (CLas), a phloem-limited bacterium transmitted by the Asian citrus psyllid (ACP; Diaphorina citri Kuwayama). Kaolin particle films are a tool used to repel insect pests and improve growth. The film covers the natural color of the leaves, which attracts ACP. Kaolin, naturally white in color, has been found to reduce ACP in citrus plantings. Previous research suggests adding a red dye might lead to further ACP reductions by reducing ultraviolet and blue light that attract ACP. We implemented a field experiment to test the effects of white and red-dyed particle films on ACP pressure, CLas infection, and citrus growth over the course of a two-year field study. In this study, white and red-dyed kaolin particle films were applied in young, non-bearing ‘Hamlin’ sweet orange (Citrus x sinensis) trees. The white and red-dyed kaolin treatments reduced ACP pressure and delayed HLB infection, and the red-dyed kaolin particle film was more effective in reducing ACP and in delaying CLas infection. Trees in both the white and red kaolin treatments had greater relative growth rate of trunk cross-sectional area (TCSA) than controls. This effect was observed regardless of CLas infection. Both particle film treatments resulted in greater final TCSA. Our results suggest particle films are an effective alternative to insecticide-based management of ACP and have the added benefit of increasing citrus tree growth under HLB pressure.

Modeling and dynamics of physiological and behavioral resistance of Asian citrus psyllid

The Asian citrus psyllid (ACP) survival in the presence of contact insecticides may be through physiological adaptations or by behaviorally avoiding. Curiously, although the first alternative is the object of frequent attention, the second was often neglected, but both may lead to insecticide resistance. In this paper, we characterize the growth dynamics of ACP population using a novel impulsive differential equation model to account for the effect of physiological and behavioral resistance, and investigate the threshold conditions for the extinction of ACP population. Furthermore, we discuss the optimal switching methods for insecticides based on two different criteria. Our numerical result suggests that ignoring both resistances or behavioral resistance would underestimate the transmission risk of Huanglongbing, whereas only considering behavioral resistance leads to an overestimation.

Host-pathogen interaction between Asian citrus psyllid and entomopathogenic fungus (Cordyceps fumosorosea) is regulated by modulations in gene expression, enzymatic activity and HLB-bacterial population of the host

The host-pathogen interaction has been explored by several investigations, but the impact of fungal pathogens against insect resistance is still ambiguous. Therefore, we assessed the enzymatic activity and defense-related gene expression of Asian citrus psyllid (ACP) nymphal and adult populations on Huanglongbing-diseased citrus plants under the attack of Cordyceps fumosorosea. Overall, five enzymes viz. superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione S-transferase (GST), carboxylesterase (CarE), and four genes, namely SOD, 16S, CYP4C68, CYP4BD1, were selected for respective observations from ACP populations. Enzymatic activity of four enzymes (SOD, POD, GST, CarE) was significantly decreased after 5-days post-treatment (dpt) and 3-dpt fungal exposure in fungal treated ACP adult and nymphal populations, respectively, whereas the activity of CAT was boosted substantially post-treatment time schedule. Besides, we recorded drastic fluctuations in the expression of CYP4 genes among fungal treated ACP populations. After 24 hours post-treatment (hpt), expression of both CYP4 genes was boosted in fungal treated populations than controlled populations (adult and nymph). After 3-dpt, however, the expression of CYP4 genes was declined in the given populations. Likewise, fungal attack deteriorated the resistance of adult and nymphal of ACP population, as SOD expression was down-regulated in fungal-treated adult and nymphs after 5-dpt and 3-dpt exposure, respectively. Moreover, bacterial expression via the 16S gene was significantly increased in fungal-treated adult and nymphal ACP populations with increasing post-treatment time. Overall, our data illustrate that the fungal application disrupted the insect defense system. The expression of these genes and enzymes suppress the immune function of adult and nymphal ACP populations. As it is reported first time that the applications of C. fumosorosea against ACP reduce insect resistance by interfering with the CYP4 and SOD system. Therefore, we propose new strategies to discover the role of certain toxic compounds from fungus, which can reduce insect resistance, focusing on resistance-related genes and enzymes.

Impacts of invasive ant-hemipteran interaction, edge effects and habitat complexities on the spatial distribution of ants in citrus orchards

The Argentine ant, Linepithema humile, is an invasive ant species well established throughout subtropical climates in the United States. The Argentine ant disrupts natural ecosystems by displacing native ant species and associating with phloem-feeding insects, which they protect from natural enemies in exchange for honeydew excreted by the phloem-feeders. Thus, interactions between these ants and phloem-feeders can be an issue of critical importance in agroecosystems. In this study, we aimed to determine whether the presence or absence of another invasive pest, Asian Citrus psyllid (ACP), Diaphorina citri, adjacent habitat types, and edge complexity impact the species richness, activity, and distribution of ants including the Argentine ant within citrus groves in southern California. When ACP were present and edge complexity was higher, ant activity rates were higher, yet we observed a decline in total ant species richness. Surrounding habitat type had no effect on ant activity or total ant species richness. Understanding the spatial patterns of both the Argentine ant and ACP can aid future management practices for controlling both Argentine ants and Asian citrus psyllid populations.

Symbiotic Fungus Affected the Asian Citrus Psyllid (ACP) Resistance to Imidacloprid and Thiamethoxam.

The Asian citrus psyllid (ACP), Diaphorina citri (Kuwayama) (Hemiptera: Liviidae), is a notorious Rutaceae plant pest. Frequent and extensive use of pesticides has resulted in severe insecticide resistance in ACP populations. Fully understanding the mechanism of ACP resistance to pesticides is vital for us to control or delay the development of resistance. Therefore, we compared the difference in resistance to imidacloprid and thiamethoxam between Hunan (Yongzhou, Chenzhou) and Guangdong (Guangzhou) ACP populations and analyzed the correlations between the resistance level and genes and symbiotic fungi. The results showed that the resistance of the Guangdong ACP population to imidacloprid and thiamethoxam was lower than that of Hunan ACP population, and the relative expression of genes associated with P450 mono-oxygenase and acetylcholinesterase was significantly lower in the Guangdong ACP population than in Hunan ACP population. The differences of mean relative abundances of four symbiotic bacteria among three populations were marginally significant; however, the mean relative abundance of 16 fungi among three populations was significantly different, and positive linear correlations were observed between the resistance level and two fungi (Aspergillus niger and Aureobasidium pullulans) and two genes (CYP4C70 and CYP4DB1). Negative correlations were only observed between the resistance level and two fungi (Golubevia pallescens and Acremonium sclerotigenum). Moreover, four fungi were unique to the Chenzhou population which was the highest resistance to imidacloprid and thiamethoxam. These findings suggested the P450 mono-oxygenase and symbiotic fungi together affected ACP resistance to imidacloprid and thiamethoxam. In the future, we may use environmental G. pallescens and A. sclerotigenum to control or delay ACP resistance.

Ecological Aspects of the Vector-Borne Bacterial Disease, Citrus Greening (Huanglongbing): Dispersal and Host Use by Asian Citrus Psyllid, Diaphorina Citri Kuwayama.

Determining the influence of abiotic and biotic factors on pest dispersal behavior is a critical component of integrated pest management. The behavioral and physiological traits of movement of the Asian Citrus Psyllid (ACP), Diaphorina citri Kuwayama, has received significant attention. Field and laboratory experiments have explored the physiological capabilities of ACP dispersal, as well as, the abiotic and biotic drivers that initiate movement behavior. Abiotic factors such as temperature, barometric pressure, humidity, landscape, and orchard architecture, as well as, biotic factors including mating status, pathogen infection, and morphotype have been investigated in great detail. The current review focuses on dispersal of ACP with the goal of synthesizing current knowledge to suggest management tactics. Overall, vision serves as the primary modality for host finding in ACP. Current data suggest that ACP populations increase more within uniform landscapes of seedling trees, as compared to mature orchards with randomly interspersed young seedlings. The data also suggest that establishment and conservation of visual and physical barriers might be beneficial to protect orchards from ACP. Management of ACP must take into account large-area cooperation, orchard border surveillance and treatment, removal of non-crop habitat, and an understanding that immigration can occur from distances of several kilometers.

Reproductive performance among color morphs of Diaphorina citri Kuwayama, vector of citrus greening pathogens

Diaphorina citri Kuwayama, commonly known as Asian citrus psyllid (ACP), transmits the bacterium Candidatus Liberibacter asiaticus (CLas), one of the causative agents of Huanglongbing (HLB) to citrus trees. Within ACP populations, three adult abdominal color polymorphisms: gray/brown, blue/green, and orange/yellow have been described. Despite the economic importance of this insect, the molecular mechanisms governing reproduction and vitellogenesis are not well understood. The current results describe the expression patterns of VgA1-like and Kr-h1, ovary morphology, and oviposition behavior in two different ACP morphotypes. Our results showed that VgA1-like exhibited female sex-specific expression, was upregulated more in blue/green than gray/brown females, and increased in expression with age only in blue/green morphs. The transcription factor Kr-h1, associated with reproduction in some insect species, was expressed in both sexes, was upregulated in 1 and 7 days old blue/green compared to gray/brown females, and exhibited reduced expression by 14 days of age in both morphotypes. Our results demonstrated an association between VgA1-like expression, oocyte development, and the blue green abdominal color of D. citri, which were linked to higher reproductive output than observed in gray/brown females. Overall, this study described the importance of the genes VgA1-like and Kr-h1 in D. citri vitellogenesis, and explained the mechanisms underlying differential reproductive performance among D. citri abdominal color morphs.

Automated vision-based system for monitoring Asian citrus psyllid in orchards utilizing artificial intelligence

Specialty crop growers face challenges from numerous diseases and pests. For example, the Asian citrus psyllid (ACP) is a key pest of citrus due to its role as vector of huanglongbing (HLB) (greening disease). There is no known cure for HLB, but vector management is critical, both for slowing spread and attenuating symptoms in infected trees. Therefore, monitoring ACP population, as well as other pest populations, is an essential management component for timing and assessment of control actions. Manual crop scouting is often labor intensive and time consuming. In this work, an automated system was developed and evaluated utilizing machine vision and artificial intelligence to monitor ACP in groves. This system comprised a tapping mechanism to collect insects from the tree’s branches and a board with a grid of cameras for image acquisition. A software was developed using two convolutional neural-networks to accurately detect and distinguish psyllids from other insects and debris fallen from the tree. A GPS was utilized to automatically record individual tree position to facilitate data assessment on large groves. A precision and recall of 80% and 95%, respectively, was obtained on detecting ACPs on a sample of 90 young citrus trees. The system proved a great potential to automate scouting procedures in citrus and to be extended to other crop insects.

Genetic variation and structure of Diaphorina citri (Hemiptera: Liviidae) in populations from México

AbstractThe Asian citrus psyllid, Diaphorina citri Kuwayama, is native to Asia but has recently invaded North America. Asian citrus psyllid is a significant pest of citrus crops by its direct feeding but, more importantly, as the vector of the bacterium ‘Candidatus Liberibacter asiaticus’, which causes Huanglongbing disease. Asian citrus psyllid was first found in México in 2001 and 2002 and, since then, has spread quickly across the country, suggesting rapid adaptation to new environments. Yet, we lack information on the genetic variation and structure that could facilitate or inhibit adaptation. Using six microsatellite markers, we analyzed genetic variation and structure among six localities in México: three in western states near the Pacific coast and two in the Yucatán Peninsula near the Gulf of México. We found low genetic diversity (no more than three alleles per locus) and intermediate differentiation between all populations. Asian citrus psyllid populations clustered into two genetic groups, but, surprisingly, these clusters were present in western populations. The first group included El Arenal, and the second group included Autlán de Navarro, Colima, and Tecomán. Interestingly, both of the Yucatán populations shared variation from the two clusters, suggesting admixture. We infer that reproductive isolation, barriers to gene flow, local selection, and the possibility of multiple invasions have influenced the current genetic structure of Asian citrus psyllid in México.

Uptake of soil-applied thiamethoxam in orange and its effect against Asian citrus psyllid in different seasons.

Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is an important pest of citrus worldwide because it transmits the bacteria causing huanglongbing (HLB). We investigated the effects and persistence of two soil application rates of thiamethoxam on ACP populations in two flushing seasons in the field. Thiamethoxam and clothianidin residues in the fruit were detected to evaluate food safety. Soil application of 50% thiamethoxam water-dispersible granules at concentrations of 4 and 10 g tree-1 significantly decreased ACP populations, and there was a positive correlation between control efficacy and the persistence of thiamethoxam and clothianidin in leaves, providing longer-term protection for up to 90 days in the fall compared with 60 days in the spring. Higher thiamethoxam and clothianidin amounts were observed in new leaves than in old leaves. Thiamethoxam and clothianidin residues at a high rate in fruit were 0.012 and 0.010 mg kg-1 at harvest, respectively, and neither insecticides was detectable at low rates. These results demonstrate that soil-applied thiamethoxam plays a role in defending ACP, and provides an extended period of control efficacy. This knowledge could provide a reference for the control of ACP by soil application of thiamethoxam to reduce HLB spread. © 2018 Society of Chemical Industry.

Effect of Potassium Silicate Application on Populations of Asian Citrus Psyllid in Tahiti Lime

Asian citrus psyllid [ACP (Diaphorina citri)] is one of the most serious threats to the global citrus (Citrus sp.) culture, and management of ACP has depended primarily on the application of chemical insecticides. The expression of resistance mechanisms to herbivory is a key component in integrated pest management in crop production in which silicon (Si) applications can play an important role in plant–insect relationships. The objective of the current study was to evaluate the application of Si to tahiti lime (Citrus latifolia) plants under natural infestations of ACP. Two experiments were conducted using 15-month-old seedlings and 2-year-old trees, respectively. Treatments were 1) foliar Si sprays (potassium silicate) at a dose of 2 mL·L–1, 2) soil Si application at a dose of 1 kg commercial product per plant, 3) combined soil and foliar applications of Si at the doses just listed, and 4) untreated plants (control). The application of Si treatments to both seedlings and trees affected ACP oviposition, causing a reduction of 60%. Applications of Si did not affect the nutritional status (macronutrients and micronutrients) of plants in either test, except that the foliar concentration of Si tended to be greater in the soil and soil + foliar treatments than in the other treatment in both seedlings and trees. Based on these results, we suggest that Si can be added as a component of ACP integrated pest management programs.

Evaluation of Three Commercial Biopesticides for the Reduction of Diaphorina citri (Hemiptera: Liviidae) Populations

Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is the most serious threat to the global citrus industry, and its management has mainly depended on the application of chemical insecticides. The use of biopesticides can play an important role in regulating this pest. In a first test, two separate experiments were conducted in two different municipalities (Apulo and Jerusalen, Cundinamarca, Colombia) to evaluate the effect of foliar Beauveria bassiana and imidacloprid sprays on ACP populations in 2015 and 2016, respectively. In a second test, two separate tests were carried out in commercial Tahiti lime orchards to evaluate the efficacy of three different commercial biopesticides (Beauveria bassiana and extracts of Sophora sp. and garlic-chili pepper). In test 1, imidacloprid-treated trees showed a reduction (60% and 80%) in cumulative ACP adults in 2016. ACP cumulative nymphs were also diminished by foliar imidacloprid and B. bassiana application, between 40% and 65% in 2015 and 2016, respectively. ACP cumulative eggs showed lower individuals in imidacloprid-treated flushes at 3 and 4 weeks after treatment 9 (WAT) in 2016. In test 2, the results obtained showed ACP adults and eggs unaffected by biopesticide treatments; nymphs were reduced 50% to 75% in trees treated with the three biopesticides in comparison with control trees. All three biopesticides tested can be considered useful tools in integrated pest management (IPM) programs for ACP, since these products reduced immature ACP individuals between 50% and 75% under field conditions.

Detection and biochemical characterization of insecticide resistance in field populations of Asian citrus psyllid in Guangdong of China

The Asian citrus psyllid, Diaphorina citri Kuwayama, is one of the most damaging pests of citrus-producing regions throughout the world. The use of insecticides is the main strategy for controlling psyllid and has increased year by year. In this study, four field populations of D. citri were evaluated for resistance to nine different insecticides using the leaf-dip method. The results showed that the highest level of resistance for D. citri was found in imidacloprid with a resistance ratio of 15.12 in the Zengcheng population compared with the laboratory susceptible population. This was followed by chlorpyriphos (6.47), dinotefuran (6.16), thiamethoxam (6.04), lambda-cyhalothrin (4.78), and bifenthrin (4.16). Piperonyl butoxide (PBO) and triphenyl phosphate (TPP) showed significant synergism on imidacloprid effects in the Zengcheng population (3.84- and 2.46-fold, respectively). Nevertheless, diethyl maleate (DEM) had no synergism on imidacloprid. Biochemical enzyme assays suggested that general esterase, glutathione S-transferase and cytochrome P450 monooxygenase activities were higher in the field-collected populations than in the laboratory susceptible population. However, glutathione S-transferase may play a minor role in the resistance of adult D. citri to insecticides. At the molecular level, resistance of D. citri to imidacloprid is mainly related to the increased expression of CYP4C68 and CYP4G70 (>5-fold).

Host Plant-Mediated Interactions Between 'Candidatus Liberibacter asiaticus' and Its Vector Diaphorina citri Kuwayama (Hemiptera: Liviidae).

The Diaphorina citri Kuwayama (Hemiptera: Liviidae) also known as Asian citrus psyllid transmits 'Candidatus Liberibacter asiaticus' (CLas) associated with the citrus Huanglongbing (HLB). Minimizing Asian citrus psyllid populations is one of the most important methods for HLB control. The development and survival of Asian citrus psyllid were evaluated on CLas+ and CLas- plants of Citrus reticulata Blanco. cv. Mashuiju (Sapindales: Rutaceae) or Citrus sunki Hort. ex Tanaka (Sapindales: Rutaceae) to assess the effects of CLas infection on vector populations. The development times were unaffected between CLas+ and CLas- plants for eggs and first to third instar nymphs but decreased for fourth instars, fifth instars, and total nymphal life on CLas+ plants. The survival rates of eggs and first and second instar nymphs were significantly lower, while those of third to fifth instar nymphs were significantly higher on CLas+ plants. However, overall nymphal survival did not differ between CLas+ and CLas- plants. The pre-oviposition period of Asian citrus psyllid on CLas+ plants decreased, while oviposition period increased, resulting in significantly higher fecundity and population trend index compared with those on CLas- plants, illustrating an overall fitness benefit of CLas infection to Asian citrus psyllid. On the other hand, the longevity and resistance to starvation and lower temperatures of adults from CLas+ plants were significantly lower than those from CLas- plants suggesting that there may be a fitness cost for Asian citrus psyllid on CLas+ plants. The development time of eggs and nymphs and adult longevity were always shorter on C. reticulata regardless of infection status. This knowledge of host plant, pathogen, and vector interactions is useful for developing Asian citrus psyllid-HLB management programs.