The psyllid fauna (Hemiptera: Psylloidea) of vegetable fields in Brazil

ABSTRACT Some psyllids transmit 'Candidatus Liberibacter solanacearum' (Lso), the causal agent of devastating plant diseases of cultivated Solanaceae and Apiaceae. The recent detection of Bactericera cockerelli and Lso in Ecuador seriously threatens these crops in South America. There, neither the role of native psyllids in the Lso epidemiology nor the psyllid fauna of vegetables are known. With the aim to identify potential vectors and risk scenarios for the spread of Lso in South America, a survey of the psyllid fauna of Solanaceae and Apiaceae crops and associated weeds was conducted in Brazil. Samples were taken at 29 localities in four states. A total of 2857 specimens were sampled, representing at least 37 species of 23 genera and seven families. The most frequent species on carrot, chilli pepper and potato were Russelliana solanicola, R. capsici and Isogonoceraia divergipennis, respectively. Immatures of R. capsici were found on chilli pepper and of R. solanicola on carrot and potato, confirming these plants as hosts. The two psyllid species have been suspected previously to transmit plant pathogens of unknown identity. Russelliana solanicola is one of the few polyphagous species. Here the species is reported for the first time from carrot. Recent collections in Rio Grande do Sul suggest that Solanum laxum represents the original host of R. capsici, which subsequently shifted to chilli pepper. Both, adaptation to agricultural crops and the possibility of ability to transmit pathogens, make the two Russelliana species dangerous potential vectors of Lso and other plant pathogens in South America.


Introduction
Jumping plant-lice or psyllids (Hemiptera: Psylloidea) are small phloemsucking insects.Most of the approximately 4000 described species are highly host specific with only a few exceptions (Burckhardt et al., 2014;Ouvrard et al., 2015).While immatures can complete their development usually only on one or a few closely related plant species (=host plants), adults, which are always winged and therefore more mobile, can be encountered often also on non-hosts, called overwintering, shelter, food, or casual plants depending on the situation (Burckhardt et al., 2014).Some psyllids are economically important pests in agriculture, forestry and horticulture.The damage to plants can be direct or indirect.The most devastating damage is inflicted by those species that transmit plant pathogens (Burckhardt, 1994;Hodkinson, 2009;Queiroz et al., 2012) Over the last decades, some psyllid species have emerged as major pests of vegetables, mainly as vectors of 'Candidatus Liberibacter solanacearum' (Lso), the putative etiological agent of potato zebra chip and other disorders in Solanaceae and Apiaceae.The tomato-potato psyllid, Bactericera cockerelli (Šulc), one of the few polyphagous psyllid species (Burckhardt and Lauterer, 1997;Serbina et al., 2015), is notorious as a vector of Lso infecting potatoes and other Solanaceae in North and Central America as well as in New Zealand (Liefting et al., 2009;Munyaneza, 2012).Recently, B. cockerelli and later Lso also were detected in South America (Castillo Carrillo et al., 2019;Caicedo et al., 2020).Bactericera trigonica Hodkinson and Dyspersa apicalis (Foerster) (=Trioza apicalis) transmit other haplotypes of Lso to carrots and other members of Apiaceae in Europe and the Mediterranean including the Canary Islands (Munyaneza et al., 2010;Alfaro-Fernández et al., 2012;Tahzima et al., 2014;Teresani et al., 2014;Mawassi et al., 2018).Furthermore, Bactericera nigricornis currently found in Europe and Asia has shown to be capable of transmiting Lso to potato and carrots (Moreno et al., 2021).
The psyllid fauna (Hemiptera: Psylloidea) of vegetable fields in Brazil Taciana M. de A. Kuhn 1* , Daniel Burckhardt 2 , Dalva L. Queiroz 3 , Carlos A. Antolínez 4 , Gabriela R. Teresani 5 , João R. S. Lopes 1  1 Universidade de São Paulo, Escola Superior de Agricultura Luiz de Queiroz, Departamento de Entomologia e Acarologia, Piracicaba, SP, Brasil. 2 Naturhistorisches Museum, Basel, Switzerland.  Embrapa Florestas, Colombo, PR, Brasil.  Universidad de Santander, Facultad de Ciencias Exactas, Naturales y Agropecuarias, Bucaramanga, Colombia. 5Instituto Agronômico de Campinas, Fazenda Santa Elisa, Campinas, SP, Brasil.A B S T R A C T Some psyllids transmit 'Candidatus Liberibacter solanacearum' (Lso), the causal agent of devastating plant diseases of cultivated Solanaceae and Apiaceae.The recent detection of Bactericera cockerelli and Lso in Ecuador seriously threatens these crops in South America.There, neither the role of native psyllids in the Lso epidemiology nor the psyllid fauna of vegetables are known.With the aim to identify potential vectors and risk scenarios for the spread of Lso in South America, a survey of the psyllid fauna of Solanaceae and Apiaceae crops and associated weeds was conducted in Brazil.Samples were taken at 29 localities in four states.A total of 2857 specimens were sampled, representing at least 37 species of 23 genera and seven families.The most frequent species on carrot, chilli pepper and potato were Russelliana solanicola, R. capsici and Isogonoceraia divergipennis, respectively.Immatures of R. capsici were found on chilli pepper and of R. solanicola on carrot and potato, confirming these plants as hosts.The two psyllid species have been suspected previously to transmit plant pathogens of unknown identity.Russelliana solanicola is one of the few polyphagous species.Here the species is reported for the first time from carrot.Recent collections in Rio Grande do Sul suggest that Solanum laxum represents the original host of R. capsici, which subsequently shifted to chilli pepper.Both, adaptation to agricultural crops and the possibility of ability to transmit pathogens, make the two Russelliana species dangerous potential vectors of Lso and other plant pathogens in South America.
Bactericera cockerelli and Lso, which were recently discovered in Ecuador, represent a serious threat to the potato industry in South America (Castillo Carrillo et al., 2019;Caicedo et al., 2020).Recently the vector was also reported from Colombia and Peru but not Lso (ICA, 2021;SENASA, 2021).In the west Palaearctic, Lso infects other crops such as carrot and celery transmitted by native psyllids.This may happen also in South America.From South America, two Russelliana species, viz.R. capsici Burckhardt and R. solanicola Tuthill, are suspected to vector plant pathogens.Russelliana capsici (Figs 1A, B) was reported from Argentina (Buenos Aires, Entre Ríos) and Brazil (Minas Gerais, Pananá, Santa Catarina, São Paulo) associated with witches' brooms on chilli pepper.It is suspected that the witches' brooms are caused by a Candidatus Liberibacter or Phytoplasma species (Burckhardt et al., 2012).Russelliana solanicola (Figs 1C, D) was reported as pest on potato and as vector of an unidentified pathogen causing 'Potato Yellows' (Tuthill, 1959;Chávez et al., 2003;Salazar, 2006).It is known from Argentina, Bolivia, Brazil, Chile, Peru and Uruguay (Serbina and Burckhardt, 2017) and represents another one of the few polyphagous psyllid species, associated with several families of eudicots (clade Caryophyllales + asterids) (Serbina et al., 2015).
As these plant pathogens are often controlled via their vectors, a better knowledge of the psyllid fauna of vegetable crops in South America is imperative and a matter of urgency.From Brazil, only 165 species of Psylloidea have been reported, of an estimated 1000 species that potentially occur there (Burckhardt and Queiroz, 2012, 2020, 2023).Similarly, there is a general lack of information on the psyllid fauna of vegetable crops in Brazil, making predictions about potential psyllid vectors of Lso difficult or even impossible.For closing this gap, a survey was conducted, sampling psyllids in vegetable fields in 16 important production areas in the Center-South region of Brazil with the aim to identify potential vector species of Lso and other phloem restricted plant pathogens.

Material and methods
From 2014 to 2016, vegetable fields at 87 localities were studied, and psyllids were found at 29 localities in 16 municipalities and four states of the Center-South region of Brazil (Table 1, Supplementary Material).The samples were taken using direct (visual inspection of plant, sweep net or beating tray) and indirect methods (yellow tray water trap).
For the visual inspection, 5-10 plants per species were examined for approximately one minute in each sampled area, counting the number of adult psyllids and checking for the presence or absence of immatures.With the sweep net and beating tray, 10 samples were taken consisting of 10 sweeps and four beats, respectively.In most localities, sampling using direct methods was performed on a single date, except for Piracicaba where samples were taken at nine dates (Supplementary Material).The psyllids were collected with an entomological aspirator and placed in vials with 70% ethanol for preservation.Eleven crop species and five weed species were examined (Table 2).The plant species varied according to their availability at different localities and sampling dates.Weeds, when present in pure clusters in or adjacent to the field, were sampled with a sweep net.
Each two yellow tray water traps were installed at approximately 60 cm above ground at three municipalities and four at one municipality (Table 1, asterisk).They were filled with 500 ml water and 3 ml of liquid detergent.The insects were collected every seven days during the sampling period, which varied between the locality (Supplementary Material): Campinas, SP (15 weeks), Maria da Fé, MG (9 weeks), Perdizes, MG (13 weeks) and Piracicaba, SP (8 weeks).The insects were sifted, manually sorted and preserved in 70% ethanol.
The nomenclature of psyllids follows Ouvrard (2022) and that of the plants the World Flora Online (WFO, 2022).The classification of psyllids is that of Burckhardt and Queiroz (2023).

Results
During the survey, 2857 specimens (2818 adults and 39 immatures) were collected, representing at least 37 species of 23 genera and six families (Table 3).Of these, specimens representing 23 species could be identified to species, and the remainder only to genus or species group.These latter 14+ species represent undescribed species (e.g.Mitrapsylla) or species complexes (e.g.Euceropsylla), and describing and revising these is beyond the scope of the present study.The Brazilian psyllid fauna is poorly known and perhaps only 10% of the existing species are described (Burckhardt and Queiroz, 2012, 2020, 2023).Overall, the most frequent species were R. solanicola, Isogonoceraia divergipennis White and Hodkinson and R. capsici with 73%, 10% and 3%, respectively, of the total number of adult specimens collected (Tables 4 and 5).None of the currently known vectors of Lso, e.g.Bactericera species, were present in our collections, but two species were found that are suspected to vector plant pathogens, i.e.R. capsici and R. solanicola (Burckhardt et al., 2012;Serbina et al., 2015).
With direct methods, 2344 total adult specimens were found: 2269 on crop plants and 75 on weeds (Table 4).On carrot, of the 2065 total specimens, 1965 were R. solanicola, 68 were Mitrapsylla spp., 25 were I. divergipennis and the seven remaining specimens belonged to five other species.On chilli pepper, of the 107 total specimens, 98 were R. capsici, four were R. solanicola, two were I. divergipennis, and the remaining three specimens belonged to three other species.Of the 92 specimens collected from potato 77 were I. divergipennis, eight were R. solanicola and the remaining seven belonged to six other species.Among the weeds, only Parthenium hysterophorus L. yielded a high number of psyllids: 70 specimens of R. solanicola.No psyllids were collected on bell pepper (Capsicum annuum L.), cabbage (Brassica oleracea var.capitata L.), celery (Apium graveolens L.) and tomato (Solanum lycopersicum L.).A few single psyllids were found on tobacco (Nicotiana tabacum L.), parsley [Petroselinum crispum (Mill).Fuss], African or Ethiopian eggplant (Solanum aethiopicum Jacq.), and eggplant (Solanum melongena L.) among the crop plants, and Amaranthus spp.L., Bidens pilosa L., Melampodium perfoliatum (Cav.)Kunth and Solanum americanum Mill.among the weeds (Table 4).
The presence of immature psyllids is important to determine whether a particular plant constitutes a host (Burckhardt et al., 2014) or if the presence of the psyllid is just accidental.In our survey, all samples of Russelliana capsici, which always included some immatures (not shown in tables), were collected exclusively on chilli pepper, varieties 'biquinho', 'bode' and 'malagueta'.Similarly, the majority of specimens of R. solanicola were collected on carrot, on which we found also immatures (Supplementary Material).A single immature of R. solanicola was found on potato (Supplementary Material).
Yellow tray water traps were set up in fields of carrot, African eggplant, eggplant and potato (Table 5).The two psyllid species, which were represented by immatures in the direct collection methods, were not (Russelliana capsici) or only poorly (R. solanicola) represented in the traps.The most frequent species was Isogonoceraia divergipennis present in all traps but most numerous in fields of African eggplant.Two other psyllids, Heteropsylla caldwelli Burckhardt and Paracarsidara sp. had large numbers mostly in potato.The other species were represented in smaller numbers.
With both direct and indirect collecting methods, the largest numbers of individuals were found in late spring and early summer (September and October), particularly Russelliana solanicola on carrot in São José do Rio Pardo in 2015 (1872 individuals: 1861 adults and 11 immatures) and Isogonoceraia divergipennis on carrot and potato in Casa Branca in 2015 (99 adults, no immatures).

Discussion
At least 37 species were collected, of which only two develop on the studied vegetables: Russelliana capsici on chilli pepper and R. solanicola on carrot and potato.Chilli pepper, carrot and potato are, hence, confirmed host plants of the two species.Hosts of the other psyllids belong, as far as known, to the Fabaceae (over 15 species), Anacardiaceae, Asteraceae, Myrtaceae (each three species) and six other families with one or two species each (Table 1).Apart from the two Russelliana species, all psyllids were collected on non-host plants.An example to illustrate this is I. divergipennis, the second most abundant species in our study.The species is monophagous on Caesalpinia pluviosa (Burckhardt and Queiroz, 2012), a widely planted ornamental and shade tree (Lorenzi, 1992).It was found on carrot, chilli pepper, potato and tobacco, in addition to traps in all four crops.Since no immatures were found, its occurrence on potato (27% of the collections of this species) and other crops is accidental.Similar observations were made in European vegetable fields.In a study on Swiss carrot psyllids, 41 species (corresponding to over a quarter of the known Swiss psyllid fauna) were trapped, and only four of them develop on carrots (Burckhardt and Freuler, 2000).In Spain, representatives of seven psyllid genera (Arytainilla, Bactericera, Blastopsylla, Cacopsylla, Ctenarytaina, Spanioza and Trioza) have been found associated with carrot and potato (Antolínez et al., 2019), but only two Bactericera species actually develop on the crops: B. nigricornis (Foerster) on carrot and potato (Antolínez et al., 2019;Moreno et al., 2021); and B. trigonica Hodkinson on carrot and celery (Antolínez et al., 2017).
The species composition varied considerably from one locality to another, but no geographic patterns could be detected.The localities that were sampled with traps that were deployed for a longer period of time usually, but not always, had more diverse samples: Perdizes (11 weeks): 20 spp., Maria da Fé (6 weeks): 14 spp., Piracicaba (7 weeks): 12 spp.and Campinas (16 weeks): 4 spp.All of the 23 species that were identified to species have been reported previously from Brazil (Burckhardt andQueiroz, 2012, 2020).Sixteen of them represent native species that are widely distributed on hosts that often grow on the edges of fields.
The other seven species are associated with crops; three species are native (the two Russelliana spp.and Mastigimas anjosi Burckhardt et al. on Cedrela and Toona), and four are adventive (Blastopsylla occidentalis Taylor, Ctenarytaina spatulata Taylor and Glycaspis brimblecombei Moore on eucalypts, as well as Diaphorina citri Kuwayama on Citrus and other rutaceous hosts).
We found the highest number of psyllids in late spring and early summer (September and October), which is consistent with other studies in Brazil.In citrus orchards in the State of São Paulo, the highest density of D. citri was observed in the same months (Yamamoto et al., 2001).A study on population fluctuations of the guava psyllid Triozoida limbata (Enderlein) showed that the species is present during the whole year, but with a peak in October (Dalberto et al., 2004).The large number of psyllids collected during spring indicates, in addition to population peaks, the increase in the movement of adult psyllids at this time of year, probably in search of suitable mates and hosts.In our study, this could explain the large numbers of adults of some species on the crops despite the fact that they do not develop on these plants (e.g.species of the genera Heteropsylla, Mitrapsylla, Paracarsidara or Platycorypha).
There were significant differences between direct and indirect sampling methods.The yellow trays yielded a larger species diversity, however, the most abundant species in the yellow trays were not the most common species observed directly on the plants.The most abundant species on carrot (R. solanicola) and potato (I.divergipennis) by direct collection methods were not the most collected in the yellow trays in these two crops.Since, yellow trays are not neutral traps and may attract insects different from the ones than land on a given crop (Hall et al., 2007), it is highly likely that several species collected in yellow trays in our work are migrant insects, which do not develop on the crop.
Russelliana capsici has been recorded from Argentina (Buenos Aires, Entre Ríos) and Brazil (MG, SC, SP) (Burckhardt et al., 2012).In the present study we collected the species in MG and SP and we examined additional material from Goiás, Mato Grosso do Sul, Rio de Janeiro and  (Knapp, 2013).
On the other hand, chilli pepper is suspected to originate from tropical northern Amazonia (Pickersgill, 1971).Judging from the presumed native distribution of the two plants it seems more likely that S. laxum is the original host plant of R. capsici and chilli pepper constitutes a more recently acquired host.Shifts from native to introduced plants (but not necessarily the closest relatives) seem to turn the psyllids into invasive pests, as in Diaphorina citri (shift from Murraya koenigii (L.) Spreng.(=Bergera koenigii L.) to Citrus) or M. anjosi (shift from Cedrela to Toona) (Hollis, 1987;Burckhardt et al., 2011) Russelliana solanicola is one of the few polyphagous psyllid species.It has been reported from plants in the Amaranthaceae, Asteraceae, Escalloniaceae and Solanaceae (Serbina et al., 2015;Serbina and Burckhardt, 2017).Here we report it for the first time from Apiaceae (carrot) which belongs to the same clade (asterid II) as Asteraceae and Escalloniaceae.Of all specimens of this species collected in our study, 96% were captured directly on carrot, at different locations in GO, MG and SP.Russelliana solanicola is widely distributed in subtropical and temperate South America and was reported as a pest of potato in Chile and Peru (Serbina et al., 2015).Interestingly, in our study R. solanicola was rare on this crop with only eight adults and one immature.The reason for this discrepancy is unknown, but it may be influenced by different environmental conditions or different host races.A similar case is known from another potato psyllid, Bactericera nigricornis.It is considered a severe pest of potato in Iran (Fathi, 2011) but was found only in very low numbers in Spain without any eggs or immatures (Antolínez et al., 2019).In our study, we collected a large number of R. solanicola on the weed Parthenium hysterophorus L. This weed is a confirmed host of R. solanicola (Serbina et al., 2015).
While the majority of the collected psyllid species does not seem to have any negative impact on the crops, the situation with the two Russelliana species is more serious, as both might be potential vectors of Lso or other plant pathogens.Russelliana capsici apparently shifted within Solanaceae from a native plant to a crop species and may do this again in future.Russelliana solanicola is known to colonize a broad range of crops and weeds.The wide host range shown by R. solanicola represents a serious threat to Solanaceae and Apiaceae crops if there is a Lso introduction in areas where the species is established.Accordingly, special attention should be given to countries such as Peru where R. solanicola and B. cockerelli may co-occur.The possibility exists that R. solanicola could acquire Lso, or that B. cockerelli could acquire the apparent pathogen transmitted by R. solanicola reported by Salazar (2006) and others.Psyllid testing is beyond the scope of this paper; however, we encourage routine monitoring of Lso and other relevant plant pathogens in this psyllid species to confirm its vectorial capacity and also as part of a surveillance strategy to avoid spill over of Lso and other vectored plant pathogens to other countries in the region.

Conclusions
This is the first comprehensive study of the psyllid fauna of vegetable fields in South America.Russeliana capsici was found to be associated with chilli pepper, and R. solanicola was found on carrot and potato.It is important to emphasize that this is the first report of R. solanicola from carrot.The two species develop on these crops, documented by the presence of immatures.The polyphagous R. solanicola also was found in large numbers on Parthenium hysterophorus, a weed that was known previously as a host (Serbina et al., 2015).During the survey, at least 37 additional psyllid species were found.Specimens of 23 of these species could be identified to species, with the remaining 14+ species being undescribed or belonging to genera that are taxonomically poorly known.Most of the species collected are native taxa often associated with Fabaceae, along with several adventive species associated with citrus and eucalypts.Even though some of the species were found in considerable numbers (I.divergipennis, Heteropsylla caldwelli or Paracarsidara sp.) none of these psyllids develop on any of the examined crop species.
Another very important conclusion from our study is that for monitoring psyllid populations in vegetable fields, direct methods, such as visual inspection or the use of a sweep net or beating tray, are much more efficient than yellow tray water traps.The traps collected only six specimens of R. solanicola compared to 98 adults of R capsici and 2050 adults of R. solanicola taken with direct methods.
To date, Lso has not been reported from South America outside of Ecuador (Castillo Carrillo et al., 2019;Caicedo et al., 2020), and it is unknown whether the two native R. capsici and R. solanicola would be capable of transmitting Lso.Salazar (2006) and others reported what they thought to be a virus transmitted by R. solanicola in potatoes in Peru.Moreover, Hansen et al (2022) and Kwak et al. (2021) reported a new Candidatus Liberibacter species associated with R. capsici that may be potentially pathogenic on Capsicum.The role played by weeds as reservoirs for the psyllids and associated plant pathogens is unknown.Future studies should address these aspects along with surveys to observe the spread of B. cockerelli and Lso, as well as plant pathogens associated with native Russelliana species, in South America.

Table 2
Crops and weed species sampled during the collection of psyllid fauna (Hemiptera: Psylloidea) from vegetable fields in Brazil.

Table 3
Psyllids collected during the project with their known host plants and general distribution.Asterisks indicate the assumed host family for psyllid taxa that were not identified to species.

Table 4
Psyllid species and number of individuals collected on vegetable crops (Carrot -Daucus carota L.; Parsley -Petroselinum crispum (Mill.)Fuss;Chilli pepper -Capsicum chinense Jacq.; Tobacco -Nicotiana tabacum L.; African eggplant -Solanum aethiopicum Jacq.; Eggplant -Solanum melongena L.; Potato -Solanum tuberosum L.) and weeds by direct sampling methods.See Supplementary Material for details.Rio Grande do Sul, thus expanding the known range of distribution.In RS we collected seven samples, including one with many immatures, on Solanum laxum (Solanaceae, tribe Solaneae), a new host record, which is within the subfamily Solanoideae only distantly related to Capsicum (tribe Capsiceae).Solanum laxum occurs naturally in southeastern Brazil from MG to RG, to the Río de la Plata in Argentina and Uruguay, and into Paraguay.The plant also is cultivated in temperate and subtropical regions around the world and is often naturalized