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Research Project
PREVENTING HLB EPIDEMICS FOR ENSURING CITRUS SURVIVAL IN EUROPE
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Host plant preference of Trioza erytreae on lemon and bitter orange plants
Publication . Benhadi-Marín, Jacinto; Garzo, Elisa; Moreno, Aránzazu; Pereira, J.A.; Fereres, Alberto
Trioza erytreae, the African citrus psyllid, is a vector of Candidatus Liberibacter spp., the causal agent of the citrus greening
disease or Huanglongbing (HLB). The spread of the vector throughout the Iberian Peninsula has been continuous since its
introduction in mainland Spain in 2014. The patterns of host preference and feeding behaviour largely depend on olfactory
cues. Understanding these patterns is crucial to prevent further dispersion and develop management measures against the
pest. In this work, a series of settlement, olfactometric, probing, and feeding experiments were conducted to assess the host
preference of T. erytreae for lemon or bitter orange plants. The settlement experiment provided evidence on the preference
of both sexes of T. erytreae for lemon plants, whereas males did not show any significant choice pattern in the case of the
olfactometric assays. Forty EPG variables were analysed to describe and compare the probing and feeding behaviour of T.
erytreae on lemon and bitter orange plants. The EPG variables indicated that T. erytreae has some difficulties in accepting
the phloem of bitter orange plants. This suggests that lemon plants would be a better source for the acquisition of Candidatus
Liberibacter asiaticus (CLas) by T. erytreae since the psyllid spends much longer periods feeding from the phloem on
lemon than on bitter orange.
Web architecture affects the functional response of the space web-builder Kochiura aulica against Trioza erytreae in the laboratory
Publication . Félix-Oliveira, Diogo; Pereira, J.A.; Benhadi-Marín, Jacinto
The “citrus greening disease” or huanglongbing (HLB) is caused by the Gram-negative
bacteria Candidatus Liberibacter spp. One vector of HLB, the African citrus psyllid Trioza erytreae
(del Guercio, 1918), was recorded for the first time in 2014, in mainland Spain, and since then, it has
spread throughout the Iberian Peninsula. Spiders could be natural enemies of T. erytreae. In this work,
we assessed the potential of a model spider species, selected according to the most abundant guild
in the field, as a natural enemy of T. erytreae. Theridiidae was the most successful family, capturing
adults of T. erytreae in the field. Kochiura aulica (Theridiidae) was selected as a model for functional
response assays in the laboratory. The effect of web-building plasticity on the functional response of
K. aulica was investigated using two types of arena. The spiders developed tubular-like or branch-like
webs according to the spatial constraints. The web architecture significantly shifted the trapping
efficiency of K. aulica. Functional responses for tubular and branch webs were both Type-II, but
more psyllid prey were captured and killed in the tubular webs than in branch webs. In addition,
significantly more psyllids survived in branch-like webs. Our results suggest that web architecture
is a key factor driving the number of captured adults of the psyllid. Space web builders could be
successful natural enemies of T. erytreae, although further research is needed to clarify the influence
of web-building plasticity on the functional response and trapping efficiency of spiders.
Spatial distribution pattern and infestation rates of Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) in lemon orchards in the Northern Portugal
Publication . Costa, Jaciley Bragança; Rodrigues, Isabel; Pereira, J.A.
The citrus leaf miner, Phyllocnistis citrella, poses a significant threat to citrus fruit cultivation
worldwide, with its detrimental impact on citrus orchards well-documented. Direct damage
caused by its larvae creating galleries in the leaves, along with increasing the plants'
susceptibility to citrus canker disease, makes it essential to understand the infestation dynamics
of this pest and develop effective management strategies. The main goals of this study were to
evaluate the population fluctuations of adult males of P. citrella in a young lemon orchard in
the parish of Ribela, Vila Nova de Famalicão, from May to December 2023, and to evaluate
the infestation rate of P. citrella larvae in the same orchard from March to December 2023. The
first aims to analyse the population dynamics of adults and develop a sampling methodology
that, with minimal effort, provides accurate estimates of population density, and the second to
evaluate the infestation rate. In the first study, Delta-type traps with sexual pheromones were
utilized to capture males weekly, and thus infer the population levels of the pest. In the analysis
of the results, the spatial distribution was determined using negative binomial tests, Iwao's
method, Lloyd's indices and Taylor's power law, and the determination of the minimum number
of observations necessary for a correct estimate of the population with a minimum sampling
effort. In the second study, lemon tree shoots were randomly collected, which were examined
in the laboratory by dividing leaves with a length of less than 3 cm and leaves with a longer
length of 3 cm to identify the presence of eggs, larvae, pupae and galleries of P. citrella. The
results indicate that the distribution of adults of the citrus leaf miner has an aggregate behavior
obtained by the aggregation indices evaluated. In the determination of the minimum number of
traps for an adequate estimate of the population, values between 2 and 5 traps per homogeneous
area of the plot were obtained, with the lower values for high population levels and the higher
values when the populations are lower. In the second study, the results show that there are
different stages of insect development simultaneously in the field, as long as there is vegetation
growth, and highlight the urgent need for a more detailed understanding of the dynamics of P.
citrella infestation. The present work highlights the need for a more in-depth study on the
dynamics of the pest in the region, and the importance of monitoring the populations to support
decision-making and intervention at appropriate times, thus reducing the damage that P. citrella
may cause.
Potential areas of spread of Trioza erytreae over mainland Portugal and Spain
Publication . Benhadi-Marín, Jacinto; Fereres, Alberto; Pereira, J.A.
Trioza erytreae is one natural psyllid vector of Candidatus liberibacter, the causal agent of the citrus greening disease (HLB). Since its introduction in 2014 into the Iberian Peninsula, T. erytreae was able to spread continuously toward southern coastal regions of Portugal and northern coastal regions of the Cantabric sea in Spain. Identifying key areas of potential colonization by the psyllid vector is crucial to anticipate derived problems of establishing the disease. This work aimed to find potential areas that could be colonized by T. erytreae throughout the Iberian Peninsula using 1 km spatial data resolution, a physical barrier, long-distance dispersal events (LDEs), and 30 years of simulation. The bioclimatic suitability of Citrus spp. was used as a surrogate of its spatial distribution and a measure of habitat invasibility. Two localities, one in Portugal and one in Spain, were considered as initial points of the spread of T. erytreae. Four spread scenarios were initially simulated, corresponding to very low, low, medium, and high spread. An altitude of 400 m was included in the model as a physical barrier, and cells up to 500 km apart were allowed to be colonized due to LDEs. In this work, three key risk areas were identified, the citrus-growing areas of Setúbal (Portugal) and Huelva (Spain), and the potential corridors that may connect Guipúzcoa, where T. erytreae is already present, with the Ebro valley (Spain). Future modeling and simulation studies should include biological constraints such as the effect of parasitoids on the population of T. erytreae (e.g., Tamarixia dryi) and other barriers or corridors.
Design and characterization of molecular markers for the detection of predation of Trioza erytreae
Publication . Moudjeber, Rym; Baptista, Paula; Ramos, Vítor Manuel Capela
Trioza erytreae (Hemiptera, Psylloidea) is an important citrus pest being also one of the vectors of Candidatus Liberibacter spp., the causal bacterial agents of citrus HUANGLONGBING (greening) disease, deemed as the most devastating disease for citrus crops. In 2014, T. erytreae was detected in NW Iberian Peninsula, being the first detection of the pest in continental Europe. The spreading of T. erytreae towards Iberian Peninsula is being fast, threatening the citrus production in Europe. Due to the progressively strict EU policies on pesticides, their harmful effects and not successful eradication of T. erytreae attempts, the use of insecticides is regarded as impracticable. Thus, biocontrol using natural enemies is seen as an environmentally sound and effective approach to limited this pest. Hence, the main goal of this work was to develop PCR- based diagnostic methods that can detect for the presence of DNA from T. erytreae in the gut of arthropod predators. Fifteen T. erytreae species-specific primer sets targeting the mitochondrial COI, SSU and LSU regions were designed and tested for their specificity and sensitivity against phylogenetically-related psyllids. Among the 15 primers sets tested, two targeting the COI gene (T3F - T2R) and the rrnL gene (LSU_F2LSU_R1) showed to be highly specific and sensitive to detected T. erytreae DNA, inclusively when mixed at equal ratios with DNA of closely-related taxa of Trioza. The small size of the fragment amplified by these two primer sets (199 bp and 291 bp, for T3F - T2R and LSU_F2-LSU_R1, respectively), suggested their suitability to detected fragmented T. erytreae DNA in the gut of potential predators. Despite these promising results, the feasibility of these primer sets to recognize predators collected in natural settings must be validated in future works.
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Funding agency
European Commission
Funding programme
H2020
Funding Award Number
817526