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The soft scale Toumeyella martinezae infests the arborescent cactus Myrtillocactus geometrizans. This scale is, in turn, parasitized by the wasp Mexidalgus toumeyellus and forms a mutualistic relationship with the ant Liometopum apiculatum. This study assessed how ant and/or parasitoid presence influenced parasitism rates and the population growth of the scale insect. Experimental treatments included scale populations with ant access (control) or ant exclusion, and parasitoid exclusion with ant access. Scale population growth rates were estimated using Lefkovitch projection matrices, built based on the individual monitoring of approximately 5400 scales. The average parasitism rate was higher in the “with ants” treatment (18.66%) than under ant exclusion (5.42%). In the absence of parasitoids, the scale population growth rate (λ = 1.532) was 8% higher than in the control treatment (λ = 1.423). Population growth was negative (λ = 0.636) when ants were excluded. These results indicate that interaction with the mutualistic ant is the primary factor sustaining a positive scale population growth. In contrast, the impact of the parasitoid alone is insufficient for effectively controlling the soft scale pest.

Plants respond to herbivory in diverse, complex ways, ranging from avoidance or tolerance to indirect defense mechanisms such as attracting natural enemies of herbivores, i.e., parasitoids or predators, to strengthen their defense. Defense provided by parasitoids to cultivated plants is well documented and is used in biological control programs. However, its effectiveness on wild plants under natural conditions has been little studied. Such is the case of the cactus Myrtilllocactus geometrizans (known in Mexico as garambullo), which is consumed by the soft-scale insect Toumeyella martinezae (herbivore) which, in turn, is host to the parasitoid wasp Mexidalgus toumeyellus, and mutualist with the ant Liometopum apiculatum, that tenders and protects it. This study explores the role of the parasitoid as an indirect defense, by examining its effect on both the herbivore and the plant, and how this interaction is affected by the presence of the mutualistic ant. We found that scales adversely affect the cactus’ growth, flower, and fruit production, as well as its progeny’s performance, as seedlings from scale-infested garambullo plants were shorter, and it also favors the presence of fungus (sooty mold). The parasitoid responded positively to herbivore abundance, but the presence of ants reduced the intensity of parasitism. Our results show that parasitoids can function as an indirect defense, but their effectiveness is reduced by the presence of the herbivore’s mutualistic ant.

Domestication promotes divergence between wild and cultivated plants. The “plant domestication-reduced defense” hypothesis proposes that cultivated plants have lower chemical defenses and resistance against herbivores than their wild counterparts. Yet, the effects of domestication on the interactions between perennial crops and insect herbivores have not been well-documented. In this study, we hypothesized that domesticated avocado ( Persea americana ) has lowered resistance against insect herbivores. To test this hypothesis, we measured variation in plant traits (fruit and seed size, seed germination, and plant growth), chemical defenses (total phenolics), and resistance against two leaf-chewing insect herbivores—a specialist ( Copaxa multifenestrata ) and a generalist ( Spodoptera frugiperda )—among seven avocado genotypes across a domestication gradient: wild (ancestral) genotypes, five (intermediate) landraces (“Blanco,” “Lonjas,” “Vargas,” “Zarcoli,” and “Rodolfo”), and the cultivated (modern) “Hass.” Our results showed that seeds from “Hass” have a lower germination rate and slower growth and have shorter fruits and seeds than the landraces and wild genotypes. “Hass” leaves also had lower amounts of total phenolics than the landraces; however, no differences were found between “Hass” and the wild genotypes. There was no effect of genotype on larval mass gained for both herbivores. However, C. multifenestrata had longer larval longevity on “Hass” and the wild genotypes, whereas S. frugiperda larval longevity showed no differences among genotypes. Moreover, C. multifenestrata inflicted more damage on “Hass,” whereas S. frugiperda inflicted more damage on “Lonjas” than on the other genotypes. In general, bigger fruit and seeds were positively correlated with plant size and phenolic content, and total phenolics were positively correlated with S. frugiperda and negatively correlated with C. multifenestrata larval performance. However, despite the genotypic variation in plant traits, phenolic content, and resistance against two herbivores with different levels of specialization, there was no clear support for the “plant domestication-reduced defense” hypothesis in avocado.

The effect of vegetal cover on growth and leaves production of Pittocaulon praecox in two contrasting sites, close and open, in a xerophytic shrub was evaluated. In each site length, number of leaves, total growth, soil temperature, humidity, CO₂ concentration and litter production were recorded. Data were analyzed by Repeated Measures Analysis of Variance and a t test. The low temperature (20.79 ± 2.8 °C), higher CO₂ concentration (169.10 ± 12.19) and humidity (40.13 ± 8.26) were recorded in the close site were shrubs are taller (t118 = 3.83, P = 0.0002) and produce more leaves (86.21 ± 43.31 gr). The vegetal cover has an important effect on growth and leaves production of Pittocaulon praecox in the studied area. Se evaluó el efecto de la cobertura vegetal en la producción y crecimiento de hojas de Pittocaulon praecox en dos sitios contrastantes, cerrado y abierto, en un matorral xerófilo. En cada sitio se registró longi­tud, número de hojas y crecimiento total, temperatura, humedad, concentración de CO₂, y cantidad de hojarasca producida. Se hizo un análisis de varianza de medidas repetidas y una prueba de t. La menor temperatura (20,79 ± 2,8 °C), mayor concentración de CO₂ (169,10 ± 12,19) y humedad (40,13 ± 8,26) se registraron en el sitio cerrado, donde los arbustos crecen más (t118 = 3,83, P = 0,0002), producen más hojas (86,21 ± 43,31 gr) y alcanzaron mayor tamaño. Se concluye que la cobertura vegetal influye en el crecimiento y producción de hojas de Pittocaulon praecox.

Pests in agroecosystems reduce crop productivity. Parasitoid wasps are effective biological control agents for agricultural pests; however, their role in natural ecosystems remains uncertain. In the arid regions of central Mexico, the soft scale insect Toumeyella martinezae infests the cactus Myrtillocactus geometrizans , the fruits of which are highly valued locally. This scale insect maintains a mutualistic relationship with ants and is targeted by a parasitoid wasp. We evaluated the effect of the ant presence on the parasitoid’s effectiveness in controlling the scale insect. Using exclusion experiments, we measured parasitism rates and scale population growth under varying combinations of ant and parasitoid presence. Parasitoids reduced scale population growth, but not sufficiently for effective pest control. Ant presence was more important in sustaining scale populations with positive growth rates. Effective management of this pest should therefore focus on reducing the ants’ protective role, with parasitoids used as a complementary strategy.

Plants respond to herbivory in diverse, complex ways, ranging from avoidance or tolerance to indirect defense mechanisms such as attracting natural enemies of herbivores, i.e., parasitoids or predators, to strengthen their defense. Defense provided by parasitoids to cultivated plants is well documented and is used in biological control programs. However, its effectiveness on wild plants under natural conditions has been little studied. Such is the case of the cactus Myrtilllocactus geometrizans (known in Mexico as garambullo), which is consumed by the soft-scale insect Toumeyella martinezae (herbivore) which, in turn, is host to the parasitoid wasp Mexidalgus toumeyellus, and mutualist with the ant Liometopum apiculatum, that tenders and protects it. This study explores the role of the parasitoid as an indirect defense, by examining its effect on both the herbivore and the plant, and how this interaction is affected by the presence of the mutualistic ant. We found that scales adversely affect the cactus’ growth, flower, and fruit production, as well as its progeny’s performance, as seedlings from scale-infested garambullo plants were shorter, and it also favors the presence of fungus (sooty mold). The parasitoid responded positively to herbivore abundance, but the presence of ants reduced the intensity of parasitism. Our results show that parasitoids can function as an indirect defense, but their effectiveness is reduced by the presence of the herbivore’s mutualistic ant.

Soil contamination by hydrocarbons and its effects on population health and welfare is a growing concern, especially in urban environments with industrial activity. Indicator species complement the information obtained from the measurement of environment quality by using physicochemical variables. The objective of this study was to evaluate the response of a springtail species that could be potentially used as a bioindicator of hydrocarbon contaminated sites. We studied the effects of seven diesel concentrations on survival and other population parameters of Orthonychiurus folsomi under laboratory conditions; we evaluated the springtails response on survival, fecundity, population size, hatching and development time. Survival and fertility were analyzed by using generalized linear models (GLM). An ANOVA test was used to analyze the final population size and a Kruskal–Wallis test for oviposition, hatching, and development times. Results showed that diesel has negative effects on some population parameters. The most evident effects were recorded above 500 mg/kg concentrations. A significant decrease in survival, fertility, and population size was recorded in function of diesel concentration increase. The estimated LC50 for survival was 955 mg/kg. Oviposition and hatching time increased significantly when diesel concentrations were above 500 mg/kg, while development time increased slightly at low diesel concentrations but decreased at concentrations above 500 mg/kg. Population final size decreased as soil diesel concentrations increased. Due to the sensitive and rapid response of O. folsomi , it could be useful to detect diesel-contaminated soil, mainly in urban areas.

The galls induced by cynipids in host oaks have been proposed as biodiversity hotspots. They constitute support for the development of arthropod communities of great diversity and functional complexity that find in them nutrition and protection from external abiotic and biotic elements which change according to environmental gradients. We characterize the abundance, richness, and diversity of gall-inducing cynipids associated with the galls of the host oak Quercus rugosa, through an elevation gradient. This study was conducted on 140 oak trees belonging to seven populations (20/site) in central Mexico. We identified 39 gall-inducing cynipid species (Cinipini), three inquiline species of galls (Synergini), and seven parasitoids of gall-inducing cynipid (Chalcidoidea), and the secondary fauna was characterized by eleven arthropod orders. We detected a positive and significant effect exerted by the altitudinal gradient on abundance, species richness, and diversity of gall-inducing cynipids, parasitoids, inquilines, and secondary fauna (order richness level). We documented positive and significant relationships between the gall-inducing cynipids and their parasitoids, inquilines, and secondary fauna in terms of species richness, diversity, and abundance of individuals. Arthropod community composition associated with gall-inducing cynipids differed among localities. This study suggests that gall-inducing cynipids in Q. rugosa act as ecosystem engineers that modify the host plant to offer a new habitat to other arthropods. Also, our results supported that Cynipid gall acts to protect the galls-associated arthropod community from unfavorable abiotic conditions throughout the altitudinal gradient.

Soil fauna is essential for ecosystem dynamics as it is involved in biogeochemical processes, promotes nutrient availability, and affects the animal communities associated with plants. In this study, we examine the possible relationship between the soil microarthropod community on foliage production and quality of the shrub Pittocaulon praecox . We also examine the arthropods associated to its foliage, particularly the size of the main herbivores and of their natural enemies, at two sites with contrasting vegetation cover and productivity. The diversity of soil microarthropods was assessed from soil samples collected monthly under P. praecox individuals over 13 mo. Specimens collected were identified to species or morphospecies. Shrub foliage productivity was evaluated through the amount of litter produced. Resource quality was assessed by the mean content (percentage by weight) of N, C, S, and P of 30 leaves from each shrub. The mean size of herbivores and their natural enemies were determined by measuring 20 adult specimens of each of the most abundant species. We found a higher species richness of soil microarthropods and foliar arthropods in the open site, although the diversity of foliage arthropods was lower in the closed site. Shrubs growing in the closed site tend to produce more, larger, and nutritionally poorer (lower nitrogen content) leaves than open site. Herbivores and their natural enemies were also larger in the closed site. We found a significant positive relationship between the diversity and species richness of foliar arthropods and the nitrogen content of leaves. In general, species richness and diversity of both the foliar and soil fauna, as well as the size of organisms belonging to higher trophic levels, were affected by vegetation cover and primary productivity at each site. These findings highlight the need to simultaneously consider at least four trophic levels (soil organisms, plants, herbivores, and natural enemies) to better understand the functioning of these systems and their responses to environmental changes.

Se evaluó el efecto de la cobertura vegetal en la producción y crecimiento de hojas de Pittocaulon praecox en dos sitios contrastantes, cerrado y abierto, en un matorral xerófilo. En tres arbustos se registró longitud, número de hojas y crecimiento total, temperatura, humedad, C[O.sub.2] del suelo, y cantidad de hojarasca producida. Se hizo un análisis de varianza de medidas repetidas y una prueba de t. La menor temperatura (20,79 [+ ó -] 2,8 [grados]C), mayor concentración de C[O.sub.2] (169,10 [+ ó -] 12,19) y humedad (40,13 [+ ó -] 8,26) se registraron en el sitio cerrado, donde los arbustos crecen más (t118 = 3,83, P = 0,0002), producen más hojas (86,21 [+ ó -] 43,31 gr) y alcanzaron mayor tamaño. Se concluye que la cobertura vegetal influye en el crecimiento y producción de hojas de Pittocaulon praecox. Palabras clave. Biomasa, cobertura vegetal, factores abióticos, factores bióticos, fenología.