Citri Populations Research Articles

Occurrence and unlimited spread of Diaphorina citri Kuwayama (Hemiptera: Liviidae) in Tanzania: A potential economic threat to the citrus industry

Citrus production is a cornerstone of Tanzania's agricultural sector, supporting economic development and food security. However, the industry faces a critical threat from the Asian citrus psyllid (Diaphorina citri Kuwayama), the primary vector of the destructive Huanglongbing (HLB) disease. This study investigates the distribution, abundance, and environmental drivers of D. citri and the African citrus triozid (Trioza erytreae) in major citrus-growing regions of Tanzania. Surveys conducted between March and May 2023 revealed the presence of D. citri in the Tanga and Morogoro regions, including the first documented occurrence in the Tanga region. Conversely, T. erytrae was confined to the Arusha region. Altitude emerged as a significant factor influencing psyllid abundance. D. citri populations decreased with increasing altitude, while T. erytrae exhibited the opposite trend. Temperature also showed correlations with psyllid populations, though additional research is needed to fully elucidate these relationships. Citrus variety significantly influenced D. citri abundance, with Late Valencia (Kitenesi) being the most susceptible. Importantly, several varieties showed no presence of D. citri, offering potential sources of resistance. The intensity of new flush growth was strongly correlated with psyllid abundance. These findings highlight the urgent need for region-specific and altitude-tailored citrus pest management strategies. The identification of potentially HLB-resistant citrus varieties provides a promising avenue for breeding programs. This research offers critical insights to protect Tanzania's citrus industry and ensure the sustainable production of this vital economic crop. Keywords: Citrus, Citrus greening, Diaphorina citri Kuwayama, Huanglongbing, Trioza erytreae, Distribution, Altitude, Tanzania

The beta pore-forming bacterial pesticidal protein Tpp78Aa1 is toxic to the Asian citrus psyllid vector of the citrus greening bacterium

The Asian citrus psyllid (ACP) Diaphorina citri transmits the causative agent of huanglongbing, or citrus greening disease, that has decimated global citrus production. Pesticidal proteins derived from bacteria such as Bacillus thuringiensis (Bt) can provide effective and environmentally friendly alternatives for management of D. citri, but few with sufficient toxicity to D. citri have been identified. Here, we report on the toxicity of 14 Bt-derived pesticidal proteins from five different structural groups against D. citri. These proteins were selected based on previously reported toxicity to other hemipteran species and on pesticidal protein availability. Most of the proteins were expressed in Escherichia coli and purified from inclusion bodies or His-tag affinity purification, while App6Aa2 was expressed in Bt and purified from spore/crystal mixtures. Pesticidal proteins were initially screened by feeding psyllids on a single dose, and lethal concentration (LC50) then determined for proteins with significantly greater mortality than the buffer control. The impact of CLas infection of D. citri on toxicity was assessed for selected proteins via topical feeding. The Bt protein Tpp78Aa1 was toxic to D. citri adults with an LC50 of approximately 204 µg/mL. Nymphs were more susceptible to Tpp78Aa1 than adults but no significant difference in susceptibility was observed between healthy and CLas-infected nymphs or adults. Tpp78Aa1 and other reported D. citri-active proteins may provide valuable tools for suppression of D. citri populations.

Climate change mitigation and seasonal infestation patterns of citrus psyllid Diaphorina citri: implications for managing huanglongbing (HLB) disease in tangerine citrus

The citrus psyllid, Diaphorina citri, is a recognized vector of the devastating Huanglongbing (HLB) disease in citrus plants, posing a significant threat to global citrus production. As climate change continues to influence agroecological conditions, comprehending the population dynamics of this vector is imperative for effective disease management. This study delved into the relationship between climate variations and D. citri infestation patterns in tangerine citrus orchards from January to December 2018. Leveraging a dataset of 12 monthly observation sets, we comprehensively analyzed the abundance of the citrus psyllid population. Our investigation unveiled a clear association between climate variability and the incidence of citrus psyllid infestations and HLB occurrences. Importantly, our findings revealed that D. citri infestations were confined to the budding phase. Contrary to expectations, rainfall and temperature did not correlate positively with the development of the D. citri population or the prevalence of HLB disease in tangerine citrus. These results suggest other factors significantly affect HLB spread, impacting disease management. Further research is needed to identify and understand these factors, providing valuable insights for mitigating climate change’s impact on citrus cultivation.

Feeding behavior and hormoligosis associated with imidacloprid resistance in Asian citrus psyllid, Diaphorina citri.

Imidacloprid is a neonicotinoid insecticide used for managing the Asian citrus psyllid, Diaphorina citri Kuwayama, which serves as vector of phytopathogens causing citrus greening. However, development of resistance to neonicotinoids among populations of D. citri has coincided with occasional control failures in the field. The objectives of this research were to (1) survey current levels of imidacloprid resistance in Florida citrus; (2) compare feeding behavior between imidacloprid-resistant and susceptible D. citri using electrical penetration graph recordings, and (3) investigate the possible amplification of insecticide hormoligosis associated with resistance. Field surveys confirmed that the susceptibility of D. citri populations to imidacloprid has decreased in commercial Florida citrus groves compared with a laboratory-susceptible population. Following 12 generations of selection, resistance to imidacloprid increased by 438 fold compared with the susceptible strain. Imidacloprid-susceptible D. citri feeding on citrus exhibited significantly more bouts associated with intercellular pathway (C), phloem penetration (D), phloem salivation (E1), and nonprobing (Np) activities than imidacloprid-resistant counterparts. However, there were no differences observed in the frequency or duration of phloem ingestion or xylem feeding between susceptible and resistant D. citri. There was no statistical difference in fecundity between resistant and susceptible strains. However, the fecundity of imidacloprid-susceptible female D. citri treated with a sublethal concentration of imidacloprid (LC25) increased significantly compared with controls, while such hormoligosis was less pronounced among imidacloprid-resistant psyllids. Our results suggest that imidacloprid-resistant psyllids may cease feeding sooner than susceptible counterparts following sublethal exposure to this insecticide, indicative of a behavioral resistance mechanism.

Candidatus Kirkpatrickella diaphorinae gen. nov., sp. nov., an uncultured endosymbiont identified in a population of Diaphorina citri from Hawaii

Diaphorina citri is the hemipteran pest and vector of a devastating bacterial pathogen of citrus worldwide. In addition to the two core bacterial endosymbionts of D. citri, Candidatus Carsonella ruddii and Candidatus Profftella armatura, the genome of a novel endosymbiont and as of yet undescribed microbe was discovered in a Hawaiian D. citri population through deep sequencing of multiple D. citri populations. Found to be closely related to the genus Asaia in the family Acetobacteraceae by 16S rRNA gene sequence analysis, it forms a sister clade along with other insect-associated 16S rRNA gene sequences from uncultured bacterium found associated with Aedes koreicus and Sogatella furcifera. Multilocus sequence analysis confirmed the phylogenetic placement sister to the Asaia clade. Despite the culturable Asaia clade being the closest phylogenetic neighbour, attempts to culture this newly identified bacterial endosymbiont were unsuccessful. On the basis of these distinct genetic differences, the novel endosymbiont is proposed to be classified into a candidate genus and species ‘Candidatus Kirkpatrickella diaphorinae’. The full genome was deposited in GenBank (accession number CP107052; prokaryotic 16S rRNA OP600170).

Gene silencing of cathepsins B and L using CTV-based, plant-mediated RNAi interferes with ovarial development in Asian citrus psyllid (ACP), Diaphorina citri.

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a vector of the bacteria Candidatus Liberibacter americanus (CLam) and Candidatus Liberibacter asiaticus (CLas), which are phloem-restricted and associated with the most important and destructive worldwide citrus disease, Huanglongbing (HLB). Currently, no cure for HLB has been described. Therefore, measures have focused on reducing D. citri populations. In these insects, cathepsin B (DCcathB) and L (DCcathL) enzymes play an important role in digestion, and are involved in embryogenesis, immune defense, and ecdysis. In this study, we used a CTV-based vector to deliver dsRNA (CTV-dsRNA) into Citrus macrophylla plants targeting DCcathB and DCcathL genes in D. citri that fed on the phloem of these CTV-RNAi infected plants. Subsequently, we evaluated expression of DCcathB and DCcathL genes as well as the Vitellogenin (Vg) gene by RT-qPCR in D. citri fed on CTV-dsRNA occurring in plant phloem. It was found that a defective phenotype in D. citri females as a result of knockdown of DCcathB and DCcathL genes mediated by CTV dsRNA. These results showed that Psyllids fed on plants treated with the CTV-dsRNA exhibited downregulation of the Vg gene, one of the most important genes associated with embryogenic and female development, which was associated with dsRNA-mediated silencing of the two cathepsin genes. Based on our findings, a CTV-based strategy for delivering RNAi via plants that targets DCcathB and DCcathL genes may represent a suitable avenue for development of dsRNA-based tools to manage D. citri that limits the spread of HLB.

Field evaluation of different eco-friendly alternative control methods against Panonychus citri [Acari: Tetranychidae] spider mite and its predators in citrus orchards

Abstract Biotic stress caused by pests on citrus trees has become a major problem for ecologists around the world, hence the need to develop ecological approaches to surmount this stress. To evaluate the effectiveness of diverse control methods on the pest Panonychus citri and its predators, Euseius stipulatus, Phytoseiulus persimilis, and Typhlodromus sp. Different treatments were applied in orchards planted by Citrus clementina in the Gharb area of Morocco (T0 = treated by water only, T1 = spirodiclofen (the molecular formula is C21H24Cl2O4). 0.5 L/ha, T2 = 5% black soap 125 L/ha, Its ingredients are: argan oil, olive oil, black olive, salt, water, vegetable potash, without chemicals. T3 = mixture of two detergents; Oni product is composed of the following ingredients (sodium C12-13 parenth sulfate, and sodium C14-17 alkyl sec sulfonate) and Tide product with the following ingredients (sodium C10-16 alkylbenzene sulfonate, propylene glycol and sodium borate). Results obtained during the follow-up period showed that the black soap, spirodiclofen, and two detergent treatments provided a decrease in the P. citri population in comparison with plot treated by water during the whole monitoring period. We found 5,044 mobile forms of P. citri in the plot treated by water only, 1,544 forms in the plot treated with spirodiclofen, 3,002 forms in the plot treated with black soap, and 1,567 mobile forms in the plot treated with two detergents. This study demonstrated that all three treatments had a negative effect on the predators that survived in comparison to the control (T0), while the negative impact of spirodiclofen on beneficial phytoseiid mites was greater than that of black soap and detergents. However, the increase in temperature according to the follow-up weeks showed a significant effect on the evolution of the density of the studied mites. Unfortunately, the chemical products like spirodiclofen used against various citrus pests are considered toxic to phytoseiids and to the agro-ecosystem in general. This comparison aims to detect the effectiveness of black soap and mixtures of two detergents on P. citri and their impacts on its predators: E. stipulatus, P. persimilis, and Typhlodromus sp. to replace the use of pesticides by these alternative methods, which remain effective and environmentally friendly.

Bacterial Pesticidal Protein Mpp51Aa1 Delivered via Transgenic Citrus Severely Impacts the Fecundity of Asian Citrus Psyllid, Diaphorina citri.

The Asian citrus psyllid (ACP) Diaphorina citri vectors the causative agent of citrus greening disease that has the capacity to decimate citrus production. As an alternative and more sustainable approach to manage D. citri than repeated application of chemical insecticides, we investigated the potential use of the bacteria-derived pesticidal protein, Mpp51Aa1, when delivered by transgenic Citrus sinensis cv. Valencia sweet orange or Citrus paradisi cv. Duncan grapefruit. Following confirmation of transcription and translation of mpp51aa1 by transgenic plants, no impact of Mpp51Aa1 expression was seen on D. citri host plant choice between transgenic and control Duncan grapefruit plants. A slight but significant drop in survival of adult psyllids fed on these transgenic plants was noted relative to those fed on control plants. In line with this result, damage to the gut epithelium consistent with that caused by pore-forming proteins was only observed in a minority of adult D. citri fed on the transgenic Duncan grapefruit. However, greater impacts were observed on nymphs than on adults, with a 40% drop in the survival of nymphs fed on transgenic Duncan grapefruit relative to those fed on control plants. For Valencia sweet orange, a 70% decrease in the number of eggs laid by adult D. citri on transgenic plants was noted relative to those on control plants, with a 90% drop in emergence of progeny. These impacts that contrast with those associated with other bacterial pesticidal proteins and the potential for use of Mpp51Aa1-expressing transgenic plants for suppression of D. citri populations are discussed. IMPORTANCE Pesticidal proteins derived from bacteria such as Bacillus thuringiensis are valuable tools for management of agricultural insect pests and provide a sustainable alternative to the application of chemical insecticides. However, relatively few bacterial pesticidal proteins have been used for suppression of hemipteran or sap-sucking insects such as the Asian citrus psyllid, Diaphorina citri. This insect is particularly important as the vector of the causative agent of citrus greening, or huanglongbing disease, which severely impacts global citrus production. In this study, we investigated the potential of transgenic citrus plants that produce the pesticidal protein Mpp51Aa1. While adult psyllid mortality on transgenic plants was modest, the reduced number of eggs laid by exposed adults and the decreased survival of progeny was such that psyllid populations dropped by more than 90%. These results provide valuable insight for potential deployment of Mpp51Aa1 in combination with other control agents for the management of D. citri.

Influence of ‘Candidatus Liberibacter asiaticus’ infection on the susceptibility of Asian citrus psyllid, Diaphorina citri to Bacillus thuringiensis pesticidal proteins, Mpp51Aa1 and Cry1Ba1

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) transmits the Gram-negative bacterium ‘Candidatus Liberibacter asiaticus’ that causes citrus greening disease. While chemical control has been the main management strategy for limiting D. citri, the widespread usage of chemical sprays has decreased the susceptibility of D. citri to most insecticides. Pesticidal proteins produced by the bacterium Bacillus thuringiensis (Bt) are active against a wide variety of insects and provide a more sustainable approach to insect control. Herein, we investigated the impact of ‘Ca. L. asiaticus’ infection of D. citri on the toxicity of two Bt proteins (Mpp51Aa1 and Cry1Ba1). Proteins were delivered to healthy and ‘Ca. L. asiaticus’-infected D. citri via topical feeding application. The LC50 values of Mpp51Aa1 and Cry1Ba1 were calculated for both nymphs and adults. Additionally, we evaluated the effect of each protein on the survival probability and life span of healthy and ‘Ca. L. asiaticus’-infected D. citri. The LC50 values indicated that adults and nymphs were more susceptible to Mpp51Aa1 than to Cry1Ba1 in both healthy and ‘Ca. L. asiaticus’-infected D. citri. ‘Ca. L. asiaticus’-infected adults and nymphs were more susceptible to Mpp51Aa1 and Cry1Ba1 than healthy insects, and nymphs were more susceptible to Mpp51Aa1 and Cry1Ba1 than adults. Moreover, we found that Mpp51Aa1 had a greater impact than Cry1Ba1 on the survival and lifespan of adults, and ‘Ca. L. asiaticus’-infected insects were more affected by these pesticidal proteins than healthy adults. These results have important implications for the use of pesticidal proteins in D. citri management in Florida and elsewhere given the widespread presence of ‘Ca. L. asiaticus’ in the D. citri population. In this era of eco-friendly control strategies, Bt-derived pesticidal proteins provide a promising avenue to reducing the application of chemical insecticides for D. citri management.

Assessment of Electrostatic Sprayer Against Citrus Psylla <i>Diaphorina citri</i> Kuwayama in Kinnow Mandarin

Field experiments were conducted to evaluate and standardize the efficiency of electrostatic sprayer for checking citrus psylla Diaphorina citri population in kinnow mandarin orchards using the recommended insecticide imidacloprid @ 0.0071% and compared to standard knapsack sprayer and tractor mounted power sprayer. The results revealed that the use of electrostatic sprayer was significantly efficient in reducing >30% spray volume, covered significant more area (4.8-5.6 ha/ day), is labour saving (1 labour per operation) and much effective in reducing D. citri population by >80% after 14 days of spray in kinnow mandarin orchards.

A predatory mite that suppresses Diaphorina citri populations on plants with pollen and oviposition sites

AbstractThe Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the major citrus pest worldwide because it can transmit the bacteria associated with citrus greening disease (huanglongbing, HLB). The most common management strategy of this pest is chemical control, but this often results in pest resistance and threatens the sustainability of the citrus culture. There is therefore need for sustainable control strategies such as biological control. Previous experiments showed that the predatory mite Amblyseius herbicolus Chant (Acari: Phytoseiidae) is able to develop and reproduce on D. citri eggs. Here, we studied the population dynamics of this pest on plants with and without A. herbicolus on isolated orange jasmine plants, Murraya paniculata (L.) Jack (Rutaceae), an important host plant of the pest. Predatory mites were released 1 week before the release of D. citri and were provided with twines with pollen as oviposition sites and food source, respectively, to maintain populations of A. herbicolus in the absence of the pest. Densities of adults and nymphs of D. citri on plants with predators were about 85% lower than on plants without predators, showing that A. herbicolus is a potential biocontrol agent of D. citri. However, the stage structure of the D. citri populations at the end of the experiment did not differ significantly between control plants and plants with predators. This led us to investigate whether the predator attacked other stages besides eggs. Indeed, predators were able to feed and reproduce on first and second instar nymphs of D. citri, but not on instars 3–5. Concluding, the release of A. herbicolus with alternative food and oviposition sites can reduce infestations of D. citri. We suggest that field experiments should be done in areas where HLB occurs to test whether releases of this predator limit the spread of this devastating disease.

IPS (In-Plant System) Delivery of Double-Stranded Vitellogenin and Vitellogenin receptor via Hydroponics for Pest Control in Diaphorina citri Kuwayama (Hemiptera: Psyllidae).

Diaphorina citri, a vector of citrus huanglongbing (HLB) disease, frequently leads to HLB outbreaks and reduces Rutaceae crop production. Recent studies have investigated the effects of RNA interference (RNAi) targeting the Vitellogenin (Vg4) and Vitellogenin receptor (VgR) genes, which are involved in egg formation in this pest, providing a theoretical foundation for developing new strategies to manage D. citri populations. This study presents RNAi methods for Vg4 and VgR gene expression interference and reveals that dsVgR is more effective than dsVg4 against D. citri. We demonstrated that dsVg4 and dsVgR persisted for 3-6 days in Murraya odorifera shoots when delivered via the in-plant system (IPS) and effectively interfered with Vg4 and VgR gene expression. Following Vg4 and VgR gene expression interference, egg length and width in the interference group were significantly smaller than those in the negative control group during the 10-30-day development stages. Additionally, the proportion of mature ovarian eggs in the interference group was significantly lower than that in the negative control group at the 10, 15, 20, 25, and 30-day developmental stages. DsVgR notably suppresses oviposition in D. citri, with fecundity decreasing by 60-70%. These results provide a theoretical basis for controlling D. citri using RNAi to mitigate the spread of HLB disease.

Effect of the type of citrus fruit on the biological parameters of Panonychus citri (Acari: Tetranychidae) under laboratory conditions

The citrus red mite, Panonychus citri (McGregor, 1916), is considered a very important pest in most citrus-growing countries. The developmental periods, reproduction rates, and population growth parameters of P. citri were evaluated using the fruit peel under experimental conditions (25 ± 1 °C, 50 ± 5% RH and 14:10 h photoperiod) on five Citrus species: Mexican lime (C. ×aurantiifolia (Christm.) Swingle), grapefruit (C. ×paradisi Macfad.), sweet orange (C. ×sinensis (L.) Osbeck), mandarin (C. reticulata Blanco), and tangelo fruit (C. ×tangelo J.W. Ingram & H.E. Moore). The developmental period of the immature stages of P. citri averaged 26.64, 25.93 and 25.75 d for sweet orange, mandarin, and tangelo fruit, respectively. The adult stage was not achieved in Mexican lime and grapefruit. Immature survival was less than 50% in mandarin and tangelo fruit, in contrast, in sweet orange it was 57%. On average, oviposition was 3.55, 4.95 and 5.00 eggs female-1, on sweet orange, mandarin, and tangelo fruit, respectively. The intrinsic natural growth rate (rm), net reproduction rate (R0), generation time (T), and finite growth rate (λ) of P. citri showed significant differences among the tested species (p < 0.05). The rm and R0 values were 0.005 and 1.209 for sweet orange, 0.026 and 2.474 for mandarin and 0.020 and 2.000 for tangelo fruit. The results indicated that mandarin was the most suitable species for the P. citri population growth, whereas sweet orange was less suitable to proliferate. These differences are important in the integrated management of P. citri on citrus.

Resistance of Panonychus citri (McGregor) (Acari: Tetranychidae) to pyridaben in China: monitoring and fitness costs.

Panonychus citri is a major citrus pest worldwide. The short life cycle and high reproductive potential of P. citri, combined with heavy acaricide use, have led to high levels of resistance to acaricides, posing a threat to global resistance management programs. Here, resistance monitoring was established to determine the pyridaben resistance status of ten P. citri populations in China from 2014 to 2021 using a leaf-dipping assay. Four characterized strains-the susceptible strain (Lab_S), the resistant strain (Pyr_R), as well as the segregated resistant strain (Pyr_Rs) and the segregated susceptible strain (Pyr_Control) derived from the crossing of the Lab_S and Pyr_R strains, were used to evaluate the life-history characteristics using age-stage, two-sex life tables. Most P. citri populations developed high resistance to pyridaben. Resistance levels exceeded 1000-fold in Yuxi, Anyue, Nanning, and Ganzhou populations compared with the Lab_S strain. Compared with Pyr_Control, two key fitness cost criteria, developmental period and fecundity, showed significant differences in Pyr_Rs under consistent conditions. The intrinsic rate of increase, net reproductive rate and gross reproductive rate were lower in the resistant strain compared with the Pyr_Control strain. The Pyr_Rs strain had a lower relative fitness of 0.934 compared with the Pyr_Control. Moreover, the life-history traits and population parameters of the Pyr_R strain also showed significant differences compared with the Lab_S strain. The resistance levels to pyridaben varied greatly among the different P. citri populations and showed regional differences. Substantial fitness costs are associated with pyridaben resistance. This study provides potential implications for developing strategies for resistance management in P. citri. © 2022 Society of Chemical Industry.

Genetic diversity of Diaphorina citri (Hemiptera: Liviidae) unravels phylogeographic structure and invasion history of eastern African populations.

The Asian citrus psyllid (Diaphorina citri Kuwayama) is a key pest of Citrus sp. worldwide, as it acts as a vector for Candidatus Liberibacter asiaticus, the bacterial pathogen that causes citrus Huanglongbing. Diaphorina citri has been reported in Kenya, Tanzania, and more recently in Ethiopia. This study assessed the genetic diversity and phylogeographic structure of the pest to gain insights into the potential sources of its introduction into Africa. Population structure and differentiation of D. citri populations from China, Ethiopia, Kenya, Tanzania, and the USA were assessed using 10 microsatellite loci. Additionally, five new complete mitogenomes of D. citri collected in China, Ethiopia, Kenya, Tanzania, and the USA were analyzed in the context of publicly available sequences. Genotype data grouped the D. citri populations from Kenya and Tanzania in one cluster, and those from Ethiopia formed a separate cluster. The two genetic clusters inferred from genotype data were congruent with mitochondrial sequence data. The mitogenomes from Kenya/Tanzania/China had 99.0% similarity, and the Ethiopia/USA had 99.9% similarity. In conclusion, D. citri populations in eastern Africa have different sources, as the Kenyan and Tanzanian populations probably originated from southeastern Asia, while the Ethiopian population most probably originated from the Americas.

Genetic Modification of Bergera koenigii for Expression of the Bacterial Pesticidal Protein Cry1Ba1.

The curry leaf tree, Bergera koenigii, is highly attractive to the Asian citrus psyllid, Diaphorina citri, which vectors the bacterial causative agent of citrus greening or huanglongbing disease. This disease has decimated citrus production in Florida and in other citrus-producing countries. As D. citri exhibits high affinity for feeding on young leaves of B. koenigii, transgenic B. koenigii expressing bacteria-derived pesticidal proteins such as Cry1Ba1 have potential for D. citri management when planted in or adjacent to citrus groves. Importantly, the plant pathogenic bacterium that causes citrus greening does not replicate in B. koenigii. Transgenic plants of B. koenigii were produced by insertion of the gene encoding the active core of the pesticidal protein Cry1Ba1 derived from Bacillus thuringiensis. The transformation success rate was low relative to that of other citrus, at 0.89%. T-DNA integration into the genome and cry1ba1 transcription in transgenic plants were confirmed. Transgenic plants expressing Cry1Ba1 differed from wild-type plants, differed in photosynthesis parameters and hormone levels in some instances, and a marked delay in wilting of detached leaves. The gut epithelium of D. citri fed on transgenic plants was severely damaged, consistent with Cry1Ba1-mediated pore formation, confirming expression of the pesticidal protein by transgenic B. koenigii. These results demonstrate that transgenic B. koenigii expressing bacteria-derived pesticidal proteins can be produced for potential use as trap plants for suppression of D. citri populations toward protection of citrus groves from citrus greening.

Monitoring of Diaphorina citri populations from Florida reveals reduced susceptibility to cyantraniliprole and thiamethoxam

AbstractThe Asian citrus psyllid, Diaphorina citri, is an important pest that transmits the causal pathogens of huanglongbing (HLB) in citrus. In Florida, HLB threatens citrus production and insecticide overuse for the vector has resulted in evolution of resistance among populations of D. citri to commonly used insecticides. Cyantraniliprole is effective against nymphal and adult D. citri. However, since the introduction of cyantraniliprole use in Florida, observations have suggested that duration of population suppression following foliar sprays against D. citri has decreased from 60 to 28 days during the period between 2012 and 2020. Here, we sampled populations of D. citri from four locations in FL and measured their susceptibility to four insecticides compared with a susceptible laboratory culture. A vial bioassay method was used to measure direct toxicity of insecticides to D. citri. For bifenthrin, cyantraniliprole, dimethoate and thiamethoxam, the resistance ratios of field populations were 6.67–11.33, 3.20–36.37, 12.50–82.50 and 4.60–10.08, respectively. Data suggested that susceptibility levels of D. citri populations to cyantraniliprole have decreased over 10‐fold at three separate citrus growing locations in Florida. Although some shifts in the resistance ratio of cyantraniliprole appear to have occurred since its use began in FL citrus, the resistance ratios are congruent with field observations indicating that D. citri should remain susceptible to label rate applications of this mode of action without control failure. However, our results indicate that sufficient field variation in susceptibility to cyantraniliprole exists among populations of D. citri to justify careful management of this insecticide for prevention of insecticide resistance development.

Screening commercial entomopathogenic fungi for the management of Diaphorina citri populations in the Lower Rio Grande Valley, Texas, USA

Ten strains of entomopathogenic ascomycete fungi, sourced from commercial formulations of blastopore or conidiospore formulations, were tested in 14 different formulations in a primary acquisition/direct spray bioassay against adult Asian citrus psyllid (Diaphorina citri Kuwayama (Hemiptera: Liviidae)). The Cordyceps (Isaria) javanica Apopka 97-C (conidia) strain was used as the standard. A statistical ranking system was established in which top performing pathogenic strains were selected for further screening and eventual field trials. Modified Potter-type spray towers were utilized to deliver a range of doses of viable spores to adult D. citri in an aqueous spray consistent with the rate of spores per hectare often used in real-world spray applications. Mortality was assessed after a seven-day incubation period under controlled climate conditions reflecting those in the Lower Rio Grande Valley (LRGV) of Texas, USA. Of the 14 preparations, the strains Metarhizium anisopliae E9, C. fumosorosea Ifr9901, Beauveria bassiana ATCC 74040 and ANT-03, M. anisopliae ESALQ1037, and M. robertsii DWR2009, showed greater levels of mortality than the standard, Apopka 97-C, in the laboratory setting. Of those six, two (Ifr9901 and ANT-03) were selected for further evaluation based on efficacy, commercial availability, geographical registration, and market outlook on production.

Trophic relationship between Chrysoperla externa (Neuroptera: Chrysopidae) and Planococcus citri (Hemiptera: Pseudococcidae) associated with rose bushes

This study aimed to determine the consumption of Planococcus citri (Risso, 1813) (Hemiptera: Pseudococcidae) nymphs and the predator:prey ratio required for high predatory efficacy and survival of Chrysoperla externa (Hagen, 1861) (Neuroptera: Chrysopidae) larvae under different densities of prey, reared in rose bushes. Consumption by first-, second-, and third-instar larvae of C. externa was assessed. The predatory efficiency and survival of the predator were calculated for larvae in the second instar under densities of 20, 40, 80, 120, and 160 nymphs of P. citri and predator:prey ratios of 1:5, 1:10, and 1:20. The assessments were performed after 24 and 48 hours of exposure between species. There was increasing consumption throughout the larval development of C. externa. The predator:prey ratios 1:5 and 1:10 were the most efficient for P. citri population reduction, but the 1:5 ratio led to lower survival of larvae than the 1:10 and 1:20 ratios. There was a positive correlation between C. externa larval density and cannibalism (ρ = 0.45) and a negative correlation between predator density and P. citri population density (ρ = -0.81). Third-instar larvae consume more P. citri nymphs than second-instar larvae. Second-instar larvae of this lacewing released at a 1:20 ratio caused total mortality of mealybug nymphs within 48 hours, regardless the density of P. citri, with high larvae survival of C. externa.

Assessment of Two Novel Host-Derived Beauveria bassiana (Hypocreales: Cordycipitaceae) Isolates Against the Citrus Pest, Diaphorina citri (Hemiptera: Liviidae).

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), vectors 'Candidatus Liberibacter spp.', the causative agent of Citrus Greening Disease (CGD) or Huanglongbing (HLB). Managing populations of psyllids in the Lower Rio Grande Valley (LRGV), TX, United States is imperative given a continuous increase in HLB-positive trees. A component of integrated pest management (IPM) program is the use of strains of entomopathogenic fungi for the biological control of D. citri. In an attempt to find endemic strains of entomopathogenic fungi that grow favorably under LRGV environmental conditions and naturally infect D. citri, psyllids were collected from local residential areas, surface sterilized, and plated on a semi-selective agar medium. Collection of over 9,300 samples from 278 sites throughout the LRGV led to the positive identification of two Beauveria bassiana (Balsamo-Crivellii) Vuillemin (Hypocreales: Cordycipitaceae) isolates, ACP18001 and ACP18002. Chi-square analysis of primary and secondary acquisition bioassays revealed that both field isolated strains outperformed Cordyceps (Isaria) fumosorosea (Wize) (Hypocreales: Cordycipitaceae) Apopka97 under both primary (direct spray) and secondary acquisition (adult exposure to sprayed foliage) bioassays with ACP18002 marginally outperforming ACP18001 under secondary acquisition. Slopes of the dose response regression lines for the three fungi were not significantly different. In addition, the thermal profiles for vegetative growth of each isolate indicated that the field isolates grew at higher rates than the standard at higher temperatures. The new isolates may prove to be good candidates for the management of D. citri populations in the LRGV.