¹Programa de Ciencias y Medio Ambiente. Universidad Intercultural del Estado de Guerrero. México.

The diversity of parasitic species and their hosts was estimated on the campus of the Universidad Intercultural del Estado de Guerrero (Intercultural University of the State of Guerrero, UIEG). Through surveys of different vegetation fragments, parasitic plants were visually identified, and their abundance, height above ground (m), and diameter (cm) were recorded. The latter measurement was categorized into three groups: small (1 to 15 cm), medium (16 to 30 cm), and large (31 to 60 cm or more). The normal diameter (Nd), total height (Th), and crown diameter (Cd) of the hosts were recorded. Samples of the parasitic and host species were collected for taxonomic identification. Species accumulation curves were constructed to estimate sampling effort using the EstimateS v.9.1 software. Alpha diversity (Shannon-Wiener -H’-, Simpson, and effective species number) was evaluated. In addition, the mensuration variables were correlated with the abundance of parasitic plant taxa. Seventy-nine hosts from eight taxa belonging to six families (Fagaceae, Clethraceae, Cupressaceae, Betulaceae, Solanaceae and Asteraceae) were recorded. Five parasitic species from four families (Santalaceae, Bromeliaceae, Loranthaceae, and Convolvulaceae) were identified. The diversity of parasite species found in this study is low (H'=1.25, five sp.) and represents 12.5 % of the richness cited for the state of Guerrero.

Keywords: Abundance, diversity, host, mistletoe, Struthanthus interruptus (Kunth) G. Don, mensuration variables.

Se estimó la diversidad de especies parásitas y sus hospederos en el campus de la Universidad Intercultural del Estado de Guerrero (UIEG). A través de recorridos en diferentes fragmentos de vegetación, se reconocieron visualmente a las plantas parásitas y se registró su abundancia, altura sobre el suelo (m) y diámetro (cm). Este último fue categorizado en tres grupos: pequeño (de 1 a 15 cm), mediano (de 16 a 30 cm) y grande (de 31 a 60 cm o más). De los hospederos se registró el diámetro normal (Dn), la altura total (At) y el diámetro de copa (Dc). Se recolectaron muestras de las especies parásitas y hospederas para su identificación taxonómica. Se construyeron curvas de acumulación de especies para estimar el esfuerzo de muestreo mediante el programa EstimateS v.9.1. Se evaluó la diversidad alfa (Shannon-Wiener -H’-, Simpson y el número efectivo de especies). Además, se hizo la correlación de las variables dasométricas con la abundancia de los taxa de plantas parásitas. Se registraron 79 hospederos de ocho taxones, pertenecientes a seis familias (Fagaceae, Clethraceae, Cupressaceae, Betulaceae, Solanaceae y Asteraceae). Se identificaron cinco especies parásitas de cuatro familias (Santalaceae, Bromeliaceae, Loranthaceae y Convolvulaceae). La diversidad de especies parásitas registrada en este trabajo es baja (H’=1.25, cinco sp.) y representa 12.5 % de la riqueza citada para el estado de Guerrero.

Palabras clave: Abundancia, diversidad, hospedero, muérdago, Struthanthus interruptus (Kunth) G. Don, variables dasométricas.

Forests are nature's most diverse ecosystems and provide a wide range of economic, social, environmental, and cultural goods and services to the human population (Armenteras & Rodríguez-Eraso, 2014). However, disturbances affect their structure and, consequently, their ecological functions. In addition, they are vulnerable to attack by certain pest plants such as mistletoe, which, despite possessing photosensitive pigments, have developed parasitic habits, making them partially or totally dependent on their host (Queijeiro-Bolaños & Cano-Santana, 2015). Some epiphytes, when they grow excessively, can limit sunlight penetration and create unfavorable conditions for host trees (Valenzuela-Núñez et al., 2021). Because of this, they have been called “structural parasites” (Benzing, 1979). These organisms have long been of public concern, as they cause damage to forest, fruit, and ornamental species, resulting in significant economic losses (Sánchez-Martínez & Reséndiz-Martínez, 2021). Furthermore, their distribution throughout all environments represents one of the main threats within forests, as they cause low productivity of wood and other products (Asiaín et al., 2008).

In the state of Guerrero, parasitic plants are widely distributed, and during the period 2012-2020 affected an area of 6 729 ha, where the main harmful species were Phoradendron velutinum (DC.) Nutt., Cladocolea sp., Psittacanthus calyculatus G. Don, P. schiedeanus (Cham. & Schltdl.) G. Don, and Tillandsia recurvata (L.) L.; moreover, the entity is classified as high risk (Comisión Nacional Forestal [Conafor], 2021).

Insufficient information on parasitic plants in the Montaña Region limits the planning of strategies for their control. The objective of this study is to evaluate the diversity of aerial parasitic species (on stems, leaves, or flowers) (Nickrent, 2002) and their tree hosts in the campus of the Intercultural University of the State of Guerrero (UIEG), as well as to identify the relationship between the abundance of these pest plants and the mensuration variables of their hosts.

The UIEG campus is located in La Ciénega, in the municipality of Malinaltepec, Guerrero, at kilometer 54 on the Tlapa-Marquelia highway, at 2 061 masl (Figure 1). The climate is temperate subhumid A(C)m and the vegetation corresponds to an oak-pine forest (Instituto Nacional de Estadística y Geografía [Inegi], 2020).

Rectoría = Administrative offices; Almacén = Storeroom; Auditorio = Auditorium; Biblioteca = Library; Laboratorio = Laboratory; Salones = Classrooms; Cancha 1 = Court 1; Comedor = Canteen; Humanidades = Humanities; Viveros = Nursery; Cancha 2 = Court 2.

Figure 1. Geographical location of the community of La Ciénega, Malinaltepec municipality, and of the parasitized hosts within the UIEG campus.

The hosts were selected directly from fragments of original vegetation (oak-pine forest) located on the UIEG campus, through surveys and with the aid of binoculars (model BN131056 Bushnell^®). Trees with deformities, yellowed or wilted leaves caused by parasitic plants and structural parasites were visually identified. The latter belonged to the genus Tillandsia L. (Benzing, 1979), as the hosts had large quantities of them. Once identified, the infested individuals were georeferenced (model GRGPSMAP65S Garmin^® GPS) (Figure 1).

The number of parasites per host was recorded, as well as the diameter in cm (using a model TP50ME Truper^® tape measure), categorized as small (1-15 cm), medium (16-30 cm), and large (31-60 cm or more). In addition, the height (m) above ground level (AHAG), stem, or branch on which they were located was measured using a model 360PC Suunto^® clinometer. The normal diameter (cm) of the hosts was measured with a model 283D Forestry Suppliers^® diameter tape (Mostacedo & Fredericksen, 2000); the total height (m), with a model PM5/360PC Suunto^® clinometer, and the crown diameter (m) with a model TP50ME Truper^® measuring tape, from North to South and West to East, in order to average both measurements and avoid overestimating or underestimating them (Benavides-Meza & Fernández-Grandizo, 2012).

Specimens of the hosts and parasitic plants were collected for taxonomic identification following the method suggested by Lot and Chiang (1986). They were identified using specialized literature (Fonseca & Velázquez, 1998; Martínez-Ambriz, 2020; Pulido-Esparza et al., 2004; Valencia-Ávalos, 2010; Valencia-Ávalos et al., 2002) and the nomenclature was corroborated in the database at The World Flora Online (2025).

Accumulation curves for parasitic species were constructed using each host recorded per species as a sampling unit. To do this, the nonparametric Chao 2 estimator was used in the EstimateS v.9.1 software (Colwell & Elsensohn, 2014). Diversity was estimated using Shannon-Wiener indexes (H'), Simpson dominance (λ), and effective species numbers (⁰D, ¹D, and ²D) (Moreno et al., 2011) (Table 1).

Pi = Relative abundance of species i; nl = Natural logarithm; ^qD = Diversity; q = Diversity order: Total number of species = ⁰D; Number of abundant species = ¹D = e^H’, Number of very abundant species = ²D =

The correlation analysis between the mensuration variables (Th, Cd, and Nd) of the hosts and abundance was performed using the R 4.3.3 software (Barrios, 2024).

The observed species (observed_S) and those calculated with the Chao 2 estimator indicated 100 % of the recorded parasitic taxa; i. e., the sampling effort was representative.

Seventy-nine hosts belonging to six families were identified; of the latter, Fagaceae was the best represented, with three species; while Clethraceae, Cupressaceae, Betulaceae, Solanaceae and Asteraceae had only one species (Table 2).

Table 2. Number of individuals of the host species of parasitic plants recorded at the UIEG campus and their mensuration variables.

Family	Scientific name	Common name	Abundance	Cd	Th	Nd
Fagaceae	Quercus candicans Née	Oak	17	10.5	14.1	37.8
	Quercus martinezii C. H. Mull.	White oak	2	12.9	13.5	47.0
	Quercus scytophylla Liebm.	Red oak	13	9.4	12.5	26.3
Clethraceae	Clethra oleoides L. O. Williams	Aguacatillo	32	6.6	10.5	28.7
Cupressaceae	Hesperocyparis benthamii (Endl.)Bartel	Cypress or white cedar	3	8.5	14.8	35.8
Betulaceae	Alnus acuminata Kunth	Andean alder	8	7.3	13.1	23.2
Solanaceae	Solanum diphyllum L.	Twoleaf nightshade	3	3.0	7.0	10.1
Asteraceae	Verbesina fastigiata B. L. Rob. & Greenm.	Tacote	1	4.0	5.5	10.0

Of the 79 trees found at the UIEG campus, 32 belong to the species Clethra oleoides L. O. Williams, 17 to Quercus candicans Née, and 13 to Q. scytophylla Liebm. The rest of the taxa had fewer than 10 individuals each (Table 2). One hundred seventy-five parasitic plant individuals were recorded, Struthanthus interruptus (Kunth) G. Don being the most abundant, with 79 individuals (Table 3).

Table 3. Number of individuals per species and average height above ground (AHAG) of parasitic plants recorded on the UIEG campus.

Family	Species	Common name	*AHAG*	Number of individuals
Family	Species	Common name	*AHAG*	Small	Medium	Large	Total
Loranthaceae	Struthanthus interruptus (Kunth) G. Don	True mistletoe	6.11	21	30	28	79
Bromeliaceae	Tillandsia usneoides (L.) L.	Spanish moss	5.98	6	12	34	52
Santalaceae	Phoradendron velutinum (DC.) Nutt.	Graft	11.4	5	8	15	28
Loranthaceae	Psittacanthus schiedeanus (Cham. & Schltdl.) G. Don	Cloud forest mistletoe	8.2	3	3	9	15
Convolvulaceae	Cuscuta sp.	Dodder	4.5	-	-	1	1

The normal diameter of the parasitized individuals ranged from 4.9 to 79.3 cm and an average of 26.89±17.88 cm. The taxon with the highest average Nd was Quercus martinezii C. H. Mull., with 47 cm, followed by Q. candicans, with 37.8 cm, and Hesperocyparis benthamii (Endl.) Bartel with 35.8 cm. The other taxa had diameters of less than 30 cm.

For the height (Th) of the parasitized individuals, there was a range of 4.3 m to 22.5 m, with an average of 11.4±4.6 m. Cypress or white cedar (Hesperocyparis benthamii) had the highest average height (14.8 m), followed by oak (Quercus candicans), with 14.1 m; white oak (Q. martinezii), with 13.5 m, and alder (Alnus acuminata Kunth) at 13.1 m. The other species recorded average heights of less than 13.0 m.

Five species belonging to five genera and four families were identified among the parasitic plants; Loranthaceae was the best represented, with two species; for Bromeliaceae, Santalaceae, and Convolvulaceae, only one taxon was identified.

The average height above ground level (AHAG) at which the parasitic plants were located was 6.85±4.20 m. Phoradendron velutinum was found at an average height of 11.4 m of its host, followed by Psittacanthus schiedeanus at 8.2 m, and Struthantus interruptus, at 6.11 m. In addition, 49.7 % of the parasitic plants were large, 30.3 % were medium-sized, and 20.0 % were small (Table 3).

The Shannon-Wiener (H’) value for the diversity of parasitic species on the UIEG campus was 1.2, the dominance (λ) was 0.32, with a richness of five species (⁰D), three abundant (¹D), and three very abundant (²D). Alnus acuminata and Clethra oleoides showed greater diversity of parasitic species (Table 4).

Table 4. Number of species (NS) and individuals of parasitic plants (NIPP) per host recorded at the UIEG campus.

Hosts	Parasitical plants
Hosts	CSP	PS	PC	SI	TU	NE	NIPP
Alnus acuminata Kunth	-	ü	ü	-	ü	3	18
Clethra oleoides L. O. Williams	-	ü	-	ü	ü	3	68
Hesperocyparis benthamii (Endl.) Bartel	-	-	-	-	ü	1	15
Quercus candicans Née	-	-	ü	ü	ü	3	32
Quercus martinezii C. H. Mull.	-	-	-	-	ü	1	21
Quercus scytophylla Liebm.	-	-	ü	ü	-	2	17
Solanum diphyllum L.	ü	-	-	ü	-	2	3
Verbesina fastigiata B. L. Rob. & Greenm.	-	-	-	ü	-	1	1
Total	1	1	3	5	5	5	175

CSP = Cuscuta sp.; PS = Psittacanthus schiedeanus (Cham. & Schltdl.) G. Don; PC = Psittacanthus calyculatus G. Don; SI = Struthanthus interruptus (Kunth) G. Don; TU = Tillandsia usneoides (L.) L.

The Coefficient of correlation between normal diameter, height, and crown diameter and the abundance of parasitic plants considering all the evaluated trees was significant for Nd, with r=0.30 (p<0.01), followed by Cd, with r=0.29 (p<0.05). At the species level, Alnus acuminata exhibited an r=0.76 (p<0.05) in relation to Th, and Quercus sp. had an r=0.36 with a Cd (p<0.05); the rest of the variables showed no correlation (p>0.05), with values of r=0.3, r=0.2, and r=0.19, respectively. This indicates that an increase in the normal diameter, crown, or height of the host does not translate into an increase in the abundance of parasitic plants.

In the correlation, the mensuration variables of the most abundant hosts, such as Clethra oleoides, and the number of individuals were not significant (Nd=0.32, Th=0.19, Cd=0.25); likewise, no significant relationships were observed for the species Quercus candicans and Q. scytophylla.

The families and species recorded in this work have been documented by other authors like Galván-González et al. (2022). Regarding species diversity, the recorded diversity is relatively low (H'=1.25, S=5), given that 40 species from different families (Balanophoraceae, Cytinaceae, Krameriaceae, Lennoaceae, and Olacaceae) are cited for the state of Guerrero(Galván-González et al., 2022), and the species examined herein represent only 12.5 % of the wealth of this group in the state. Struthanthus interruptus, the most abundant pest plant in the campus trees, is considered a generalist species, as it attacks timber, fruit, and ornamental trees, and even other mistletoes; it is also widely distributed in Mexico in general and in the state of Guerrero in particular (Conafor, 2021).

The mensuration variables of the trees (height, crown diameter, and normal diameter) do not show a significant relationship with the abundance of parasitic species, which suggests that these variables do not affect their presence. However, Arriola-Padilla et al. (2013) point out that mensuration variables can hurt parasitic species; when the host's branches are thin, these plants do not have time to complete their biological cycle and die, whereby the number of their individuals is reduced. In addition, they also tend to compete for nutrients from the host. Likewise, García-Cuevas et al. (2020) mention that parasitic plants cause minimal damage when hosts are abundant, as these species tend to persist for longer periods.

The authors thank the social service students for their support in the sampling.

Marisa Silva Aparicio: design, organization, data analysis and drafting of the manuscript; Jolissa Rosas Altamirano: design, organization, information analysis and drafting of the manuscript; Bernardo López López: data analysis and revision of the manuscript.

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