Abundance and Population Decline Factors of Chrysopid Juveniles in Olive Groves and Adjacent Trees

Numerous species of the family Chrysopidae, commonly found in agroecosystems, whose larvae predate on several pests of economic importance, are regarded as biological control agents. Their abundance and diversity are influenced by vegetation cover, although little is known about the effects of semi-natural habitats on their populations. The objective of this study is to gain a better understanding of the relationship between the trees in semi-natural habitats adjacent to olive groves, juvenile stages of the family Chrysopidae and factors influencing their population decline, which is crucial for an effective habitat management program aimed at conserving these important predators. Using cardboard band traps (eight per tree), the juvenile stages were collected from 25 almond, oak, olive and pine trees over a one-year sampling period. The population decline was caused by parasitoids (26.5%), predators (5.1%) and unknown factors (13.2%). In addition, chrysopids established in olive trees showed the lowest rate of parasitism. We identified ten chrysopid species that emerged from the juveniles collected from almond, oak, olive and pine trees, with a predominance of Pseudomallada prasinus. The chrysopid–parasitoid complex was composed of five species; Baryscapus impeditus (Eulophidae), which was the most abundant, was preferentially associated with Chrysopa pallens, Chrysoperla lucasina and Chrysoperla mediterranea.


Introduction
Of the many families of the Order Neuroptera, Chrysopidae attracted the most attention as compared to Coniopterygidae and Hemerobiidae [1], as numerous species belonging to the Chrysopidae family are regarded as biological control agents given their potential impact on pest populations in crops [2][3][4][5][6]. Larvae are active polyphagous predators of soft-bodied arthropods, such as aphids, whiteflies, thrips and mites, in addition to being widely distributed in agroecosystems [2][3][4][5][6].
Chrysopidae is the second most important family in terms of the number and diversity of species with 1423 valid species belonging to 82 genera [7]. Chrysoperla carnea (Stephens, 1836) sensu lato, which has been reared and released in crops around the world [8][9][10][11], is the species most commonly used in agricultural biological control programs [12]. There is evidence that C. carnea is a complex of at least 21 cryptic species [1,13,14]. Although some species are well defined with respect to morphological characteristics, habitats, courtship songs and molecular techniques, their taxonomy has not been fully relationship between parasitoid and chrysopid assemblages while taking into account the season and tree species (almond, oak, olive and pine) in which the interaction occurred.
The knowledge acquired is a crucial prerequisite for an effective habitat management program aimed at conserving the populations of these important predators.

Area of Study
The study was carried out in the Montes Orientales region, 20 km to the north of the Andalusian province of Granada, which is the fourth largest area devoted to olive grove crops, covering 198,331 hectares (ha) [81]. The landscape in this region is dominated by olive plantations, with patches of semi-natural vegetation mostly composed of P. halepensis, Q. rotundifolia and P. dulcis, in addition to less abundant species, such as Quercus coccifera L. Sampling was carried out in five organic olive farms (Table 1) in conformity with EU legislation [82,83]. All these farms are located at a similar altitude of 800 to 1100 m above sea level, the variety of Olea europaea L. is "Picual" and the plantation schemes are very similar (8 × 8 and 12 × 12 m), with areas ranging from 0.9 to 215 ha. Soil management practices on these farms include the maintenance of spontaneous vegetation cover, which is eliminated by mechanical mowing and/or grazing between April and May. In addition, during the post-harvest period, the soil is fertilized with organic matter, and crushed pruning waste is placed in the rows between crops to create inert cover. The incidence of disease (such as Fusicladium oleagineum) and pests (such as P. oleae and Bactrocera oleae (Gmelin, 1790)) was remedied by timely and targeted treatment (two aimed at diseases and one for pests) using products listed in Annex II of Commission Regulation (EC) no. 889/2008.

Collection of Samples
To collect the juvenile stages of chrysopids (larvae and prepupae/pupae), eight corrugated cardboard band traps (10 × 17.5 cm) were placed in a total of 100 trees (25 trees per species): O. europaea (olive), Q. rotundifolia (oak), P. dulcis (almond) and P. halepensis (pine), whose distribution in the sampling sites depended on their availability in the study area (Table 1). The band traps were installed on different branches located 160-170 cm from the ground taking into account the four cardinal directions (two band traps per direction). The 800 band traps were changed each month between June 2016 and May 2017 (a total of 12 sampling events) on the same 100 trees (identified by number).
In the laboratory, the juvenile stages-larvae, "open cocoons", with one or more apertures caused by the emergence of chrysopid or parasitoid adults and predators feeding on juveniles, as well as "closed cocoons", with no apertures and containing a chrysopid larva-were individually labelled and kept in Petri dishes (55 mm in diameter) for observation and monitoring. The trash-bearing juveniles (with exogenous material on their backs) and naked juveniles (with no exogenous material) were also quantified. The larval instars and "closed cocoons" were kept in an incubation chamber (Fitoclima S600 PLH; Aralab, Rio de Mouro, Portugal) in order to monitor their development at a temperature of 25 ± 1 • C, a humidity of 50%-60% and a photoperiod of 16:8 (Light:Dark) hours.
The individual larvae were fed ad libitum with Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs (EphestiaTop; Biotop; Livron-sur-Drôme; France) to facilitate the completion of their biological cycle up to the adult stage and taxonomic identification.
The juveniles that failed to reach the adult stage were inspected under a stereomicroscope (Nikon SMZ 800; Nikon, Tokyo, Japan) in order to ascertain whether death was due to parasitoids or unknown factors. Additionally, we determined whether the aperture in the "open cocoons" was caused by the emergence of an adult chrysopid, a parasitoid or by the feeding of predators. In parasitized cocoons, the number of emerged adult parasitoids, as well as the number and average diameter of exit apertures were quantified ( Figure 1). In the laboratory, the juvenile stages-larvae, "open cocoons", with one or more apertures caused by the emergence of chrysopid or parasitoid adults and predators feeding on juveniles, as well as "closed cocoons", with no apertures and containing a chrysopid larva-were individually labelled and kept in Petri dishes (55 mm in diameter) for observation and monitoring. The trashbearing juveniles (with exogenous material on their backs) and naked juveniles (with no exogenous material) were also quantified. The larval instars and "closed cocoons" were kept in an incubation chamber (Fitoclima S600 PLH; Aralab, Rio de Mouro, Portugal) in order to monitor their development at a temperature of 25 ± 1 °C, a humidity of 50%-60% and a photoperiod of 16:8 (Light:Dark) hours.
The individual larvae were fed ad libitum with Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs (EphestiaTop; Biotop; Livron-sur-Drôme; France) to facilitate the completion of their biological cycle up to the adult stage and taxonomic identification.
The juveniles that failed to reach the adult stage were inspected under a stereomicroscope (Nikon SMZ 800; Nikon, Tokyo, Japan) in order to ascertain whether death was due to parasitoids or unknown factors. Additionally, we determined whether the aperture in the "open cocoons" was caused by the emergence of an adult chrysopid, a parasitoid or by the feeding of predators. In parasitized cocoons, the number of emerged adult parasitoids, as well as the number and average diameter of exit apertures were quantified ( Figure 1). The adult chrysopids that emerged in the laboratory were identified taxonomically up to species level according to the Monserrat key [1]. The emerged adult parasitoids in the laboratory were identified up to species level with the aid of taxonomists with specialist knowledge of the different families (see acknowledgements), the Plant Protection Group collection at the Estación Experimental del Zaidín (EEZ) and the Goulet and Huber key [84].

Statistical Analysis
All analyses were carried out using R software version 3.5.0 [85]. Statistical analysis began with data exploration [86]. We explored the total abundance of the juvenile stages collected in four categories (adult, parasitized, and predated chrysopids; unknown factors) in the tree species sampled throughout the study period. For data presentation purposes, the study period was simplified by The adult chrysopids that emerged in the laboratory were identified taxonomically up to species level according to the Monserrat key [1]. The emerged adult parasitoids in the laboratory were identified up to species level with the aid of taxonomists with specialist knowledge of the different families (see acknowledgements), the Plant Protection Group collection at the Estación Experimental del Zaidín (EEZ) and the Goulet and Huber key [84].

Statistical Analysis
All analyses were carried out using R software version 3.5.0 [85]. Statistical analysis began with data exploration [86]. We explored the total abundance of the juvenile stages collected in four categories (adult, parasitized, and predated chrysopids; unknown factors) in the tree species sampled throughout the study period. For data presentation purposes, the study period was simplified by grouping the sampling dates by season: Summer (June, July and August), autumn (September, October and November), winter (December, January and February) and spring (March, April and May). Juveniles (from larvae and "open or closed cocoons"), which produced an adult chrysopid and emerged either in the laboratory or in the field, were categorized under the heading "adult chrysopids". A similar system was used for parasitoids from juveniles, which were grouped under the heading "parasitized chrysopids". Death of juveniles caused by other population decline factors were classified as "unknown factors". Finally, "open cocoons" with apertures due to attacks by predators, were defined as "predated chrysopids".
We then analysed the total abundance of juvenile stages collected from each tree species sampled using a generalized linear mixed model (GLMM) with a negative binomial distribution (Equations (1)-(3)) and a log link function (Equation (4)) in relation to tree species, site and month sampled as fixed factors and the identification of the individual tree as the random factor (Equations (4) and (5)) using the "lme4" software package [87]: Log(µ ij ) = tree species ij + site ij + month sampled ij + a j (4) a j~N (0, σ 2 individual tree) We then calculated the rate of parasitism per tree (%) expressed as the number of juvenile stages affected by parasitism in each tree divided by the total number of juvenile stages collected from each tree multiplied by 100. The rate of parasitism was analysed with the aid of the GLMM with a binomial distribution (Equation (6)) and a logit link function (Equation (7)) using tree species, site and month sampled as fixed factors and the identification of the individual tree as the random factor (Equations (7) and (8)). The "lme4" software package was used for this analysis [87]: a j~N (0, σ 2 individual tree) The models were constructed and selected according to Akaike Information Criteria (AIC) [88]. We also analysed the model residuals and checked for uniformity using the "DHARMa" software package [89]. The multiple comparisons in each model (chrysopid abundance and parasitism rate) for the tree species, site and month sampled variables were checked with the aid of the post-hoc Tukey test using the "multcomp" software package [90].
The data for juveniles categorized as "unknown factors", "predated chrysopids" and "adult chrysopids" were analysed by applying the Kruskal-Wallis test with a Bonferroni adjustment with the aid of the "agricolae" software package [91].
In addition, we calculated the parasitism rate according to the trash-bearing and naked juveniles collected. The rate of parasitism was analysed by applying the Kruskal-Wallis test with a Bonferroni adjustment with the aid of the "agricolae" software package [91].
We employed redundancy analysis (RDA) to determine whether a relationship exists between the composition of chrysopid and parasitoid species and environmental variables (tree species and season). The results were presented using a tri-plot correlation with the aid of the "vegan" software package [92].

Analysis of Collected Cocoons
We separated the "open cocoons" from "closed cocoons". "Open cocoons" were classified as "adult chrysopids" (Figure 1a) which emerged from a single circular orifice with a regular border and an average diameter of 1.65 ± 0.01 mm (n = 5 cocoon apertures). Parasitized juveniles were classified as "parasitized chrysopids" (Figure 1b-d) which emerged through one, two or three regular or irregular circular apertures with a diameter ranging from 0.4 to 1.7 mm (n = 15 cocoon apertures), with the remains of the juvenile host still inside the cocoon. "Open cocoons" were also classified as "predated chrysopids", with one or two even or uneven circular apertures with an average diameter of 1.7 ± 0.07 mm (n = 5 cocoon apertures) ( Figure 1e) to feed on juvenile stages, without remains of the juvenile host inside the cocoon. "Closed cocoons" contained prepupa or pupa which could emerge as "adult chrysopids", could have become "parasitized chrysopids" or may not have emerged at all and died due to "unknown factors".
A total of 1345 juvenile stages of chrysopids were collected between June 2016 and May 2017, over half of which (741 juveniles; n = 1200 trees sampled) completed their development to adulthood in the laboratory or in the field. The other juveniles (604 juveniles; n = 1200 trees sampled) failed to reach adulthood due to the action of parasitoids (357 juveniles; n = 1200 trees sampled), predators (69 juveniles; n = 1200 trees sampled) and unknown factors (178 juveniles; n = 1200 trees sampled) ( Table 2).
With regard to the temporal evolution of the parasitism rate, juvenile chrysopids collected in almond trees were found to be affected by parasitism between the months of July and September, reaching a maximum of 34.8% in August. A similar tendency was detected in pine trees, with a maximum of 26.5% recorded in August. On the other hand, juvenile chrysopids in olive and oak trees were affected by parasitism virtually throughout the whole period of the study, with oak trees displaying a maximum rate of 28% in January (Figure 2).
With regard to the temporal evolution of the parasitism rate, juvenile chrysopids collected in almond trees were found to be affected by parasitism between the months of July and September, reaching a maximum of 34.8% in August. A similar tendency was detected in pine trees, with a maximum of 26.5% recorded in August. On the other hand, juvenile chrysopids in olive and oak trees were affected by parasitism virtually throughout the whole period of the study, with oak trees displaying a maximum rate of 28% in January (Figure 2). With respect to the sites sampled, the average rate of parasitism was found to be significantly higher in the Los Almendros farm (12.24 ± 2%; n = 216 trees sampled) as compared to the Norberto farm (8.49 ± 1.23%; n = 336 trees sampled), although differences in relation to the other farms (Píñar (right), La Pedriza and Píñar (left)) or with respect to inter-farm rates were not significant ( Table 3,  Table S2).
A With respect to the sites sampled, the average rate of parasitism was found to be significantly higher in the Los Almendros farm (12.24 ± 2%; n = 216 trees sampled) as compared to the Norberto farm (8.49 ± 1.23%; n = 336 trees sampled), although differences in relation to the other farms (Píñar (right), La Pedriza and Píñar (left)) or with respect to inter-farm rates were not significant ( Table 3,  Table S2). Table 4. Abundance (mean ± SE) of chrysopid species that emerged in laboratory from chrysopid juveniles collected from almond, oak, olive and pine trees by season. On the other hand, the parasitism rate of naked juveniles (5.08 ± 0.55%; 287 juveniles; n = 1200 trees sampled) was significantly higher than that for trash-bearing juveniles (3.69 ± 0.51%; 70 juveniles; n = 1200 trees sampled) (Kruskal-Wallis χ 2 = 11.64, d.f. = 1, p < 0.001).
Baryscapus impeditus was the most numerous species (903 individuals from 84 parasitized juveniles). The number of parasitoids per parasitized juvenile ranged from one to 30 (10.75 ± 0.65; n = 84 parasitized juveniles), which emerged through one, two or three unevenly edged circular apertures with an average diameter of 0.42 ± 0.02 mm (n = 5 cocoon apertures) (Figure 1c). Helorus ruficornis was the second most abundant species (64 individuals from 64 parasitized chrysopids). A single parasitoid emerged from each cocoon through a single helicoidal-shaped aperture with a clearly defined edge and an average diameter of 1.72 ± 0.04 mm (n = 5 cocoon apertures) (Figure 1b). With respect to Isodromus puncticeps (52 individuals from 12 parasitized chrysopids), the number of individuals per parasitized chrysopid, which emerged, through a single unevenly edged circular aperture with an average diameter of 0.77 ± 0.04 mm (n = 5 cocoon apertures), ranged from one to ten (4.33 ± 0.85; n = 12 parasitized juveniles) (Figure 1d). The following species were much less abundant: Nine Gelis iliciola and five Perilampus minutalis individuals emerged through an unevenly edged aperture with a diameter of 1.11 ± 0.05 mm (n = 5 cocoon apertures) and 1.58 ± 0.26 mm (n = 5 cocoon apertures), respectively; in both species, each parasitoid emerged from a single parasitized juvenile. Table 5. Abundance of juvenile chrysopids parasitized (mean ± SE) by the parasitoid species complex in almond, oak, olive and pine trees by season.

Season
Tree Species

Multivariate Analysis of the Relationship between Parasitoid and Chrysopid Species, Tree Species and Season
Using RDA analysis, we determined that tree species and season accounted for 14.1% of the variation in the parasitoid and chrysopid community. The first two RDA axes accounted for 79% of this variation and adjusted R 2 for 12.8%, suggesting that other variables were not captured by the model.
The RDA correlation tri-plot ( Figure 3) showed that three groups of species were positively inter-correlated. The first group was composed of three chrysopids (C. baetica, P. flavifrons and P. picteti) and one parasitoid (H. ruficornis). The abundance of C. baetica reached maximum levels in oak trees in autumn, with a similar pattern being observed for P. flavifrons and P. picteti only in spring, while the parasitoid H. ruficornis recorded maximum abundance in oak trees in all seasons (Tables 4 and 5).
The second group was composed of three chrysopids (C. pallens, C. lucasina and C. mediterranea) collected in spring and summer and two parasitoids (B. impeditus and I. puncticeps) (Figure 3). C. lucasina appeared in spring in almond trees and then spread to the four tree species, while C. pallens was only detected in almond trees and C. mediterranea reached maximum abundance in pine trees in summer (Tables 4 and 5). B. impeditus was mainly observed in almond trees and dispersed to pine trees in summer, though with a lower level of abundance, while the other parasitoid species I. puncticeps appeared in spring in almond and pine trees and had a preference for almond trees in summer (Tables 4  and 5).
The third group is composed of C. pallida, R. almerai, C. mutata, P. prasinus and the parasitoid P. minutalis. R. almerai only appeared in olive trees in spring and summer, while C. pallida was reported in olive trees throughout the year, reaching maximum levels in almond trees in summer. C. mutata was mainly recorded in summer and autumn. Finally, P. prasinus, though collected from olive and almond trees throughout the year, reached maximum abundance in olive trees in autumn, with the parasitoid P. minutalis showing a similar pattern (Tables 4 and 5).

Discussion
This study provides an insight into the abundance of chrysopid populations in olive groves, as well as almond, oak and pine trees adjacent to the crop, in addition to population decline factors. Juvenile stages of chrysopids were more abundant in almond, oak and olive trees than in pine trees. We found that parasitoids and chrysopids shared a similar temporal pattern in our study area. Additionally, the period of parasitoid incidence was found to extend beyond the April to November period previously reported [78,93]. We observed that parasitoid abundance was highest in the

Discussion
This study provides an insight into the abundance of chrysopid populations in olive groves, as well as almond, oak and pine trees adjacent to the crop, in addition to population decline factors. Juvenile stages of chrysopids were more abundant in almond, oak and olive trees than in pine trees. We found that parasitoids and chrysopids shared a similar temporal pattern in our study area. Additionally, the period of parasitoid incidence was found to extend beyond the April to November period previously reported [78,93]. We observed that parasitoid abundance was highest in the summer months in olive trees, which is in line with the findings of Neuenschwander and Michelakis [80] and Campos [78].
The presence of "predated chrysopids" and "unknown factors" had a marked seasonal character, with the largest number in both categories recorded in summer, when the environment is less humid and temperatures are higher than in other seasons. This concurs with the results of previous studies which demonstrate that conditions, such as low humidity and high temperatures lead to increased mortality and slower development in the preimaginal stages [35,59,94]. This slower development could also render the juvenile stages more vulnerable to predators.
Overall, we found that mortality caused by parasitism (26.5%) constitutes a major chrysopid population decline factor. Although this is very similar to the level (27.7%) determined by Campos [78] in olive groves in southern Spain, it is quite low compared to the levels (80% and 54.9%, respectively) reported in olive groves by Alrouechdi et al. [50] in France and Neuenschwander and Michelakis [80] in Crete.
With regard to tree species, the parasitism rate per tree in olive trees was very low as compared to previous studies [50,78,80,93] and considerably lower than that in the three arboreal species (almond, oak and pine) studied. This, together with predation and unknown factors, make olive trees the most important arboreal species with regard to the number of viable next-generation adult chrysopids.
The highest rate of parasitism recorded in almond, oak and pine trees could be due to their location in semi-natural areas bordering the crop. The semi-natural habitats and landscape bordering the crop are characterized by greater species richness and parasitoid diversity than other types of habitat such as crop and vegetation cover [95]. Few data are available on the seasonality of parasitism in these trees. However, we demonstrated that the parasitism rate in pine and almond trees is higher in the summer months, which is similar to the pattern found by Judd [58] in pine trees. Oak trees showed a more-or-less constant rate of parasitism throughout the year, which is similar to the rate of close to 15% recorded in other studies [96]. Additionally, oak trees become a parasitoid bank in winter due to their high rate of parasitism. This could have a negative effect on the next chrysopid generation and enable parasitoids to move into olive groves in spring. However, low rates of parasitism in olive trees and high rates in oak trees in spring suggest that parasitoids remain in oak trees. As almond trees have a high rate of parasitism in summer and are a good reservoir of juvenile chrysopids, they could play an important role in increasing chrysopid populations in olive groves in the summer months, when P. oleae are especially harmful to olive trees.
The chrysopid community is composed of ten species in our biotope, with, as already noted in previous studies, P. prasinus and the C. carnea complex accounting for the majority of individuals [21,29,97]. On the other hand, studies focusing on the parasitoid complex of chrysopids have reported that a relationship exists between chrysopid species and their associated parasitoids [45,49,56]. The parasitoid complex is composed of five species: Three primary parasitoids (B. impeditus, H. ruficornis and I. puncticeps), with the highest levels of abundance, and two primary parasitoids, which also could act as hyperparasitoids (G. ilicicola and P. minutalis), with the lowest levels of abundance.
B. impeditus, the most abundant species, affected a large number of chrysopids, mainly juveniles of the species C. mediterranea, C. lucasina and C. pallens, which were collected in almond and pine trees. Our results regarding this parasitoid, which is characterized by gregarious behaviour and emerges from the host through various orifices, corroborate the findings of previous studies [45,50]. Although the period of activity of B. impeditus was similar to that in olive groves in Crete and France, the number of parasitoids per host was larger in our study [47,80].
The second most important parasitoid was H. ruficornis, which is found in Palearctic, Nearctic and Afrotropical regions [98][99][100]. This species has been previously cited in the Iberian Peninsula [101], specifically in olive groves [78,93]. Our findings would appear to contradict those of New [56], who has stated that H. ruficornis is in a minority among species in the chrysopid parasitoid complex in Europe due to competition from other parasitoids for hosts. In our study, the second most abundant parasitoid H. ruficornis, which competed with four parasitoid species, plays a similar role to that observed by New [56]. Although little is known about its biology, H. ruficornis can, in our view, be classified as a solitary parasitoid, as only one parasitoid exits in the host cocoon. This behaviour resembles that of other species of the same genus and concurs with other studies which suggest that all species of the genus Helorus are biologically similar [45,48,51,56,98]. H. ruficornis has also been shown to parasitize species of the genera Chrysoperla, Pseudomallada, Chrysopa, and Nineta [45,46,51,56]. We observed that H. ruficornis parasitizes the juvenile stages of the genera Pseudomallada (P. picteti, P. flavifrons and P. prasinus) and C. baetica which have a preference for oak trees in the Iberian Peninsula [21,102].
Of the two species from the genus Isodromus that parasitize chrysopids [48], we collected I. puncticeps, which is in a minority in the parasitoid complex studied. Although this resembles the pattern observed in Greek olive groves [56,78,80,96], I. puncticeps plays an important role in French olive groves [47,50,103]. With the aid of RDA analysis, although we found a positive relationship between the abundance of B. impeditus and I. puncticeps, given the insufficient number of individuals of the latter, we were unable to shed any light on this relationship. Nevertheless, as previously described by Clancy [45] and Campos [78], we found I. puncticeps to be a gregarious parasitoid.
While the characteristics that enable chrysopids to protect against natural enemies include the use of exogenous trash by juveniles as a defensive shield against predation [72], evidence with regard to parasitism is less clear [49,71,104]. In our study, the rate of parasitism was found to be higher in naked chrysopid species (C. lucasina, C. mediterranea, C. mutata, C. pallida and C. pallens) as compared to trash-bearing species (C. baetica, P. flavifrons, P. picteti, P. prasinus and R. almerai); however Muma [49] found that the rate of parasitism is lower in naked chrysopids than in more abundant trash-bearing chrysopids. Therefore, depending on chrysopid assemblage and abundance, as well as the parasitoid complex associated with each geographical area, rates of parasitism will, in our view, be affected by whether juvenile chrysopids are trash-bearing or naked. However further research is required to cast light on this relationship.

Conclusions
We have demonstrated that chrysopid abundance in almond and oak tree species in the arboreal stratum adjacent to olive groves is comparable to that in olive trees. With regard to population dynamics, the combined effect of three decline factors (parasitism, predation and unknown factors) of chrysopid populations over the short term needs to be taken into account when habitat management is being considered to conserve these populations. Additionally, in the biotope studied, we found that ten chrysopid species use the arboreal stratum to develop their biological cycle, in which P. prasinus is the most abundant species. We also found that three out of the five species in the parasitoid complex of the family Chrysopidae are primary parasitoids, with B. impeditus showing a preference for C. pallens, C. lucasina and C. mediterranea; and H. ruficornis being associated with C. baetica, P. flavifrons and P. picteti, representing the majority of parasitoid species. A knowledge of chrysopid population decline factors in semi-natural habitats could be crucial for an effective habitat management program aimed at conserving and expanding chrysopid populations to boost the presence of chrysopids and the natural pressure on pests and to contribute to olive grove sustainability.
Supplementary Materials: The following are available online at http://www.mdpi.com/2075-4450/10/5/134/s1, Table S1: Multiple comparisons of generalized linear mixed model (GLMM) abundance of juvenile stages of chrysopids in relation to tree species, site and month sampled including estimate, standard error (SE) and p value. Significance codes: *** p < 0.001, ** p < 0.01, * p < 0.05, Table S2: Multiple comparisons of GLMM parasitism in relation to tree species, site and month sampled including estimate, standard error (SE) and p value. Significance codes: *** p < 0.001, ** p < 0.01, * p < 0.05. Author Contributions: M.C. and F.R. obtained funding. M.C., R.A.H. and F.R. conceived and designed the study. R.A.H. and F.R. carried out the sampling, identified the chrysopids and parasitoids and formal analyses. M.G.-S. participated in three monthly sampling and identified parasitoids up to superfamily-family level. R.A.H., M.C. and F.R. wrote, reviewed and edited the manuscript. The manuscript was revised and approved by all the authors.
Funding: This research was funded by the Junta de Andalucía (excellence project P12-AGR-1419).