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Background: The breeding system of Mammillaria magnimamma was initially described as hermaphroditic. However, some individuals in a natural population at Valle del Mezquital exhibited a seemingly non-functional androecium. Objectives: To determine the breeding system of M. magnimamma through morphological characterization of floral types. Study site and years: The study was conducted at Valle del Mezquital, Mexico, during the 2019 reproductive season. Methods: We characterized floral polymorphism by means of scanning electron microscopy and morphometric analysis of 18 floral traits. Pollinator frequency, size and number of seeds, and germination rate were compared between flower types. Results: 87.85 % of the plants were hermaphrodites, and 12.15 % were females with non-functional androecium, with significantly smaller stamens, indehiscent anthers, and malformed pollen. Female flowers were shorter (14.007 ± 0.742 mm) and had smaller (1.856 ± 0.151 mm) nectar chambers than hermaphroditic flowers (15.821 ± 0.450 and 2.194 ± 0.090 mm, respectively). Although pollinators visited hermaphrodites (124 visits) about twice as often as pistillate flowers (60 visits), the latter produced more numerous (F1,26 = 8.320, P = 0.003) and larger  (Hc = 4.637, P = 0.031) seeds that also germinated faster (Hc = 70.59, P < 0.0001). Conclusions: This M. magnimamma population exhibits a gynodioecious breeding system with both hermaphroditic and male sterile female plants. Females produce more, higher quality seeds, which favour their maintenance in the population.

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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 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.

Antecedentes: Las flores son elementos reproductivos costosos que presentan balances costo/beneficio en sus estructuras. La diversidad de éstas se ha atribuido a factores bióticos como las interacciones con sus visitadores florales y abióticos como las características del ambiente. Preguntas: ¿La morfología floral de M. geometrizans está relacionada con los tipos de vegetación? ¿La comunidad de artrópodos visitadores florales se relaciona con la morfología floral y/o el tipo de vegetación? ¿La morfología floral y la comunidad de artrópodos tendrán relación con la perturbación del ambiente? Especie de estudio: Myrtillocactus geometrizans (Mart. ex Pfeiff.) Console Sitio de estudio y fecha: Selva Baja Caducifolia y Matorral Xerófilo en las Reservas de la Biosfera Tehuacán-Cuicatlán, Puebla Barranca de Metztitlán, Hidalgo. México. Marzo 2017. Métodos: En los cuatro sitios (dos días por sitio), durante el pico de floración de M. geometrizans, se calculó el índice de disturbio, se recolectaron 30 flores (N = 120) y los artrópodos visitadores florales. Se determinaron la morfología floral y los artrópodos. Resultados: Los sitios de la Barranca de Metztitlán presentaron el mayor índice de disturbio, las flores más chicas y mayor número de estructuras florales. Los visitadores florales fueron más abundantes en los matorrales xerófilos, particularmente en el sitio más perturbado donde el grupo funcional más relevante fue el de los polinizadores. Conclusiones: Se encontraron diferencias significativas en la morfología floral de M. geometrizans relacionadas a los tipos de vegetación y ubicación geográfica. Se reportó una compensación entre tamaño y producción de estructuras florales.

Diversity and trophic structure of grain insect communities were examined in Olotillo, Nal‐Tel and Comiteco maize landraces cultivated within a milpa agroecosystem by Zapotec ethnic groups in Mexico. Higher insect diversity was expected in Olotillo, whose cultivation comprises a wide variety of agroecosystems, and low insect abundance in Nal‐Tel with small grains and thick testa. Forty Olotillo cobs were collected at low, medium and high elevations, and 40 each of Nal‐Tel at low elevation and Comiteco at high elevation. Cobs were monitored for 30 days under controlled laboratory conditions until all insects emerged. Thickness of testa of 400 grains from each landrace was measured. Community composition and trophic structure were described and standard diversity indices were estimated. A total of 9,708 insects, corresponding to five orders, 24 families and 36 species, were recorded, with six species not previously reported in this region. Insect guilds were composed of 70% phytophages, 22% parasitoids and 8% predators. Species richness was S = 27, 16 and 8 in Olotillo, Comiteco and Nal‐Tel, respectively. Nal‐Tel and Olotillo had the highest diversity index values (H′ = 1.32 and 1.2, respectively) and no significant differences; Comiteco had the lowest value (H′ = 0.65) and differed significantly from the other landraces. Comiteco and Olotillo, which have large grains and thin testa, showed higher insect abundance than Nal‐Tel, which has small grains and thick testa and showed lower abundance. Results support our hypotheses and highlight the role of traditional crop management in insect agrobiodiversity maintenance and conservation.

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.