Biogeographical Patterns of Herbivore Arthropods Associated with Chenopodium quinoa Grown along the Latitudinal Gradient of Chile

Identifying the particular guilds of herbivore arthropods that affect the production of crops is key to developing sustainable pest-management strategies; however, there is incomplete information about the identity of herbivore arthropods that could potentially damage the production of both highland and lowland quinoa landraces grown in Chile. By both reviewing the literature and conducting field collections across a large latitudinal gradient, we generated an updated list of 43 herbivore arthropods associated with quinoa production in Chile. In general, most species are polyphagous feeders, and only seven are specialists. The number and identity of species varied in relation with the latitude, such that four distinctive assemblages of herbivores were identified, each containing 32, 27, 34, and 22 species between latitudes 18–26, 26–32, 32–40, and 40–44° S, respectively. The most northern production area (18–26° S) is affected by nine unique species, including the major quinoa pest Eurysacca quinoae Povolný (Lepidoptera: Gelechiidae). Similarly, the central area (32–40° S) contains four unique species, including Eurysacca media Povolný (Lepidoptera: Gelechiidae) and Orthotylus flavosparsus (Sahlberg) (Hemiptera: Miridae). The particular species assemblages described here will help further development of local pest-management practices.


Introduction
Quinoa (Chenopodium quinoa Willd.) is an annual plant mainly grown to obtain grains for human consumption. The interest in cultivating this crop has increased in recent years due to its high nutritional value and its tolerance to soil salinity and drought stress [1][2][3]. Quinoa is cultivated over a wide variety of environments in South America, extending from the high altitudes (>3500 m above sea level (m.a.s.l.)) of the Andean Altiplano areas of Bolivia, Chile, and Perú, to the lowland/coastal areas of Chile and Perú [4,5]. Two distinctive quinoa ecotypes are cultivated in Chile, the salares and the coastal ecotypes [4]. Plants belonging to the salares ecotype grow in the northern region of Chile (18-29 • S), which is separated from the central and southern regions (33-43 • S) by the Atacama Desert and is agroecologically more similar to the Altiplanos of Perú and Bolivia. In the central and southern production regions, the coastal ecotype of quinoa is produced along with many other agricultural vegetables, crops, and fruit trees. Regarding the distribution of quinoa cultivation in Chile, the northern zone (17-26 • S) accounted for 31%, the central zone (29)(30)(31)(32)(33)(34)(35)(36) • S) accounted for 64%, and the southernmost zone (37-44 • S) accounted for 5% of total production during the years 2015-2016 [6].
Understanding the herbivore communities is essential to developing sustainable insect pest management strategies in quinoa production; however, specific studies reporting insect species that feed on quinoa in Chile are scarce and incomplete. For instance, the general compendium of insect pests of economic importance in Chile published by Artigas [10] reported only five insect species that use quinoa as a host plant. A few years later, Lamborot et al. [11] reported five Lepidoptera species found in quinoa grown in central Chile. Later, another compendium of arthropod species found in Chilean agricultural plants reported only eight taxa [12]. Finally, Logarzo et al. [13] reported the finding of one leafhopper species on quinoa in the Chilean Altiplano area. Clearly, this is a low number of species when compared with the potential 78 arthropod taxa reported by Cruces et al. [5] in a recent compilation of quinoa pests that included: 29 species of Lepidoptera, 22 Hemiptera, 16 Coleoptera, 4 Orthoptera, 3 Thysanoptera, 3 Diptera, and 1 Acari.
Because many insect species previously reported to feed on quinoa in other countries are also present in Chile, we decided to review and update this information. The underlying hypothesis is that it will be possible to identify distinct clusters of herbivore arthropods along the latitudinal gradient where quinoas are cultivated in Chile. In addition, we expected to identify latitudinal patterns in host range use, feeding habit, and geographical origin of these arthropods. Hence, the objective of this work was to generate an updated list of arthropod species associated with quinoa production in Chile by both reviewing the literature and conducting field collections on quinoa fields across a latitudinal gradient in a variety of agroecosystems. To further characterize the community of herbivores, species were classified according to their geographical origin and host-range use (i.e., generalist or specialist).
In the central area (Metropolitana and O'Higgins areas), specimens collected included: Achyra similalis, Agrotis ipsilon, Aphis craccivora, Copitarsia spp., Epitrix sp., Feltia subterranea, Frankliniella occidentalis, Liorhyssus lineatoventris, Liriomyza huidobrensis, Macrosiphum euphorbiae, Myzus persicae, Orthotylus flavosparsus, Tetranychus urticae, and Trichoplusia ni. Among these species, a complex of chinch bugs (L. lineatoventris and O. flavosparsus), Copitarsia spp., and L. huidobrensis were more frequently collected. Our results also provide new information for the distribution range of O. flavosparsus, as it was known to be present in Chile [22], but no information on its distribution range and host use had been reported. In turn, the southernmost area of Ancud is characterized by the presence of fewer herbivore species. Here, we only collected Copitarsia spp. and M. euphorbiae. While only a few specimens of M. euphorbiae were detected, Copitarsia caterpillars were found more often but still in low numbers.
Regarding the total number of species expected to affect quinoa in Chile, we found that species assemblages varied in relation to the geographical region. Cluster analysis identified four groups with a percentage of similarity higher than 80% within each cluster (  (Table 2). Interestingly, both Cluster 1 and 3 included unique species. Cluster 1 is defined by nine species that are uniquely found in the northernmost region, which is closest to the borders with Perú and Bolivia. This is the case for Agrotis experta (Walker) In general, most species that feed on quinoa in Chile have a wide range of host use, given that 33 of them are polyphagous (77%) and only 7 are specialists (16%) ( Table 1). When their geographical distribution is analyzed as a variable, the proportion of specialist herbivores ranges between 5 and 15% between parallels 18 and 39 • S, with the lowest proportion in the southernmost area delimited by parallels 40-44 • S (Figure 2). The distribution of the specialist herbivores Eurysacca quinoae, E. media, Coleophora versurella, and Heterotrioza chenopodii (Reuter) (Hemiptera: Triozidae) highly influenced this pattern due to their absence in the southern latitudes of Chile.  Table 2.   Table 2.

Figure 2.
Latitudinal patterns of host range, feeding habit, and geographical origin of arthropod species that feed on quinoa in each latitudinal cluster of species.

Discussion
This is the first study to compile a list of arthropods that feed on quinoa in C which will help quinoa growers and future insect-plant interaction research. Until study, only 10 insect species had been reported as quinoa feeders within the Chilean ritory. Specifically, the general compendium of insect pests of economic importanc The feeding habit of the arthropod species that attack quinoa in Chile is mostly dominated by chewing and piercing-sucking insects. The relative proportion of chewing insects ranges between 44 and 60%, and that of piercing-sucking hemipterans between 28 and 41%, depending on the geographical area ( Figure 2). Only three species puncture plant cells, including two thrips (F. occidentalis and Thrips tabaci Lindeman) and the two-spotted spider mite (T. urticae). The leafminer L. huidobrensis was the only species identified with this strict feeding habit, which is distributed across the entire Chilean territory (Table 1). Eurysacca species were classified as chewer insects, although it has been reported that they have a leaf-mining habit during the early stages of larval development [7].
Regarding the geographical origin of the 43 arthropod species reported to feed on quinoa in Chile (Table 1), 30 species are native to the New World, while only 2 are Palearctic, and 1 comes from the Indo-Malayan realm. Interestingly, Oncopeltus miles (Blanchard) (Hemiptera: Lygaeidae) is the only native species reported to feed on quinoa in Chile [10]. In turn, 10 species have an uncertain geographical origin, as these are cosmopolitan agricultural pests (Table 1).

Discussion
This is the first study to compile a list of arthropods that feed on quinoa in Chile, which will help quinoa growers and future insect-plant interaction research. Until this study, only 10 insect species had been reported as quinoa feeders within the Chilean territory. Specifically, the general compendium of insect pests of economic importance in Chile reported one aphid (Smynthurodes betae Westwood (Hemiptera: Aphididae)), one chinchbug (O. miles), and three Lepidoptera species (Helicoverpa zea (Boddie), Rachiplusia nu Guenée, and S. recurvalis) [10]. Another study that focused on caterpillars reported five Lepidoptera species found in quinoa in central Chile, including E. media, Copitarsia turbata (Herrich-Schäffer), R. nu, C. versurella, and A. similalis [11]. The most recent compendium of arthropod species found in Chilean agricultural plants reported a total of 8 taxa, including Copitarsia sp., H. zea, O. miles, R. nu, Sigelgaita chilensis Heinrich, S. betae, S. recurvalis, and Tapajosa sp. [12]. However, we found a few incorrect species names and host use attributions in Klein-Koch and Waterhouse [12] and made appropriate corrections to construct Table 1. Specifically, Sigelgaita chilensis Heinrich does not feed on quinoa [10]; thus, it was not included here. Additionally, Klein-Koch and Waterhouse [12] lists Tapajosa sp. as a quinoa feeder, but as stated by Logarzo et al. [13], Tapajosa sp. was identified later as A. centrolinea. Finally, there is uncertainty about the identity of the species reported as C. turbata [11] because there is considerable confusion among Copitarsia species in South American literature [34]. Therefore, all individuals identified as Copitarsia during the conduction of this study are reported here as Copitarsia spp. and were saved for further taxonomic analysis.
Most species that feed on quinoa are chewing stages belonging to Lepidoptera and a few species of Coleoptera and Orthoptera, followed by piercing-sucking Hemiptera. Insects with a chewing feeding habit feed on leaves, inflorescences, and developing grains. Flower-and seed-feeding insects, such as Gelechiidae and Noctuidae, often cause serious damage to quinoa production [5,7,16]. Piercing-sucking hemipterans, such as Aphididae and Cicadellidae, feed on phloem/xylem sap extracted from leaves, stems, and inflorescences, while chinch bugs in Heteroptera may also feed on immature grains [15]. In contrast, Thysanoptera species can puncture and extract cell contents of leaves, buds, inflorescences, and pollen. Agromyzidae species use a different feeding strategy, as the larvae of L. huidobrensis construct feeding galleries in the leaves of quinoa, and adult females puncture the leaves with their ovipositor to feed on cell content [5]. The larvae of a few species feed underground, such as Epitrix and those belonging to Anthomyiidae [5,18].
Although a variety of insects feed on quinoa, some are rarely seen in the field [9]. Additionally, only a few species are commonly observed in high population numbers, thereby causing concerns to growers about potential yield losses [5,7,9]. Typically, Eurysacca melanocampta (Meyrick) and E. quinoae are frequently cited as the most significant quinoa pests in Perú and Bolivia [5,7]. Nonetheless, the geographical location of quinoa production has been shown to influence species richness and its abundance, even within the same country. In a recent study conducted in two lowland sites (La Molina and Majes) and one highland site (San Lorenzo) of Perú, Cruces et al. [9] detected higher populations of M. euphorbiae, E. melanocampta, and L. huidobrensis in La Molina, as well as of F. occidentalis in the locality of Majes; only E. melanocampta was a major pest in San Lorenzo. Concordantly, we identified four distinct groups of species associated with quinoa along a latitudinal gradient of Chile (Table 2). Nine unique insect species feed on quinoa in the northern territory (Cluster 1), including A. experta, A. centrolinea, C. includens, E. quinoae, Pseudomeloe sp., S. frugiperda, S. ochrea, S. recurvalis, and T. rubricollis. This geographic area is close to the borders with Perú and Bolivia, and it is geographically isolated from the central and southern quinoa production areas by the Atacama Desert. Indeed, many of these species are also reported from the Altiplano areas of Bolivia and Perú [5]. During our observations in the quinoas grown in the altiplano area of Ancovinto, we found relatively high numbers of E. quinoae, H. atacamae, H. gelotopoeon, and Copitarsia sp. larvae feeding on leaves, flowers, and developing grains, as well as occasional clusters of the aphid A. craccivora during grain development, but otherwise, other species were uncommon.
Coastal ecotypes grown at higher latitudes are potentially affected by a distinct assemblage of insect species. Particularly, the central region (Cluster 3) concentrates the highest number of species, with unique species including E. media, Epitrix sp., O. flavosparsus, and C. versurella. Nonetheless, not all the species present in this area have been signified as major pests in other lowland areas of quinoa production [9]. Indeed, during our field studies, we only observed population outbreaks of Copitarsia sp., L. lineatoventris, and O. flavosparsus, as well as occasional infestations with A. craccivora and L. huidobrensis. In the southernmost production area (Cluster 4), the number of herbivorous arthropod species is the lowest, therefore representing potential advantages for the sustainable production of quinoa at higher latitudes.
Most species potentially found on quinoa in Chile show a wide range of host use. Generalist herbivores are often major pests in other agricultural crops, and therefore, they could potentially colonize quinoas grown near vegetables and other crop species as quinoa production areas diversify outside the highlands of the Andes. This has been reported in Perú, where lowland quinoas are negatively affected by polyphagous feeders such as F. occidentalis, M. euphorbiae, and L. huidobrensis [9]. Similarly, several polyphagous insect species negatively affect quinoas in other countries, such as Argentina [15], the United States [18], and Italy [42][43][44]. Interestingly, many of these generalist feeders are also cosmopolitan invasive pests that represent potential pest problems in other areas of the world where quinoa production is expanding. In these sites, quinoa plants were scouted by whole-plant visual inspections, plant beating, and using a sweeping net. Similar sampling efforts were devoted to each sampling date, which corresponded to 1 h of scouting. Special attention was given to collecting insects that were actively feeding. For inspections, each site was monitored in a random pattern, selecting at least 5 sectors where 5-10 plants were sampled per sector. Plant tissues affected by each species were annotated as leaves, stems, and/or panicles (flowers and/or seeds). Immature stages were brought to the laboratory and reared individually until adult emergence. Identifications of field-collected specimens were conducted on mounted adult specimens and comparing their morphological traits with available taxonomic publications [10,23,27,28,[30][31][32][33][45][46][47], or directly with identified specimens in the Colección Nacional de Insectos, Museo Nacional de Historia Natural, Santiago, Chile (MNNC). Voucher specimens are conserved in the Entomological Collection of the Museo Nacional de Historia Natural, Santiago, Chile and in the Entomological Collection of Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Santiago.

Total Number of Expected Species
First, we compiled records of insect and mite species to create a comprehensive list of arthropods reported to feed on quinoa around the world. We used the following scientific articles, books, and technical reports: [5,7,10,11,15,16,18,38,41,48]. Thereafter, this list was checked for the correct use of scientific names and updated. Arthropod species names were checked against currently available records for species present in Chile and updated with the species found in the surveys conducted in this study.
This checklist of arthropods associated with quinoa production in Chile was supplemented with bibliographical information about their geographical distribution in Chile, as well as their feeding habits and host range. Feeding habits were classified according to their mouthparts into chewing, piercing-sucking, cell-puncturing, and leaf-mining habits. Host range use was classified either as generalist or specialist if the species had been reported feeding on several non-related plant genera or only on a few related plant species [49]. Additionally, the species were classified according to their geographical origin into Nearctic (North America), Neotropic (Central and South America), Nearctic-Neotropic (American continent in general), Palearctic (Eurasia), Indo-Malayan (India-Asia), Chile (Native), or as unknown [10,13,20,27,28,50].

Data Analysis
Multivariate cluster analysis was conducted to find associations among species according to their presence/absence within each political region of Chile (latitudinal variables). Data matrix was constructed using the presence or absence (values 1 or 0, respectively) of the 43 arthropod taxa (reported in Table 1)  . Specifically, for the linkage method, the distance between two clusters was calculated with the furthest-neighbor method, which is the maximum distance between variables of one cluster relative to another cluster. Distance between variables was calculated using the correlation method to consider positively correlated data to be closer than negatively correlated data, as it calculates distances between 0 and 1 for positive correlations and values between 1 and 2 for negative correlations. A total of 13 amalgamation steps were considered to create the dendrogram. Similarity levels ranged between 100 (13 clusters) and 91.3% (7 clusters) for the first 7 steps, and between 88.2 to 85.8% for steps 8 (6 clusters) to 10 (4 clusters), after which the similarity dropped below 74%.