RESUMO
Vertical stratification is known in diverse arthropod communities in forests, but little is known about nesting ecology of trap-nesting bees and wasps in Neotropical forests. We studied the vertical colonization of trap-nests by solitary bees and wasps in two forests in Argentina. We obtained 204 nests of seven bee and six wasp species, with 1040 brood cells from which 660 hosts and 32 parasites (21 parasitoid and 11 kleptoparasite) adults emerged from four groups (five species of wasps [Chrysididae, Eulophidae, and Ichneumonidae], four flies [Bombyliidae and Sarcophagidae], three bees [Apidae and Megachilidae], and one species of beetle [Meloidae]). The number of nests, reproductive success, parasitism rate, and mortality did not differ between canopy and understory, nor did the number of brood cells, emerged adults per trap-nest, and total abundance per transect. We found similar assemblages of trap-nesting bees and wasps in both forests, but contrary to our expectations, we did not find any significant difference in the analyzed variables. Our results suggest that access to resources used by trap-nesting bee and wasp females was at least similar, and/or that the microclimatic conditions were homogeneous in canopy and understory. Moreover, our results agree with those reported by some researchers but contrast with others, demonstrating the great variation in the response of bees and wasps nesting in preexisting cavities to vertical stratification in forests and the need for more studies about this topic.
Assuntos
Abelhas/fisiologia , Florestas , Comportamento de Nidação , Vespas/fisiologia , Animais , ArgentinaRESUMO
Plants interact with a myriad of microorganisms that modulate their interactions within the community. A well-described example is the symbiosis between grasses and Epichloë fungal endophytes that protects host plants from herbivores. It is suggested that these symbionts could play a protective role for plants against pathogens through the regulation of their growth and development and/or the induction of host defences. However, other endophyte-mediated ecological mechanisms involved in disease avoidance have been scarcely explored. Here we studied the endophyte impact on plant disease caused by the biotrophic fungus, Claviceps purpurea, under field conditions through (1) changes in the survival of the pathogen´s resistance structure (sclerotia) during overwintering on the soil surface, and (2) effects on insects responsible for the transportation of pathogen spores. This latter mechanism is tested through a visitor exclusion treatment and the measurement of plant volatile cues. We found no significant effects of the endophyte on the survival of sclerotia and thus on disease inocula. However, both pathogen incidence and severity were twofold lower in endophyte-symbiotic plants than in non-symbiotic ones, though when insect visits were prevented this difference disappeared. Endophyte-symbiotic and non-symbiotic plots presented different emission patterns of volatiles suggesting that they can play a role in this protection. We show a novel indirect ecological mechanism by which endophytes can defend host grasses against diseases through negatively interacting with intermediary vectors of the epidemic process.