Leandro Sousa-Souto

Fluctuating asymmetry of and herbivory on Poincianella pyramidalis (Tul.) L.P. Queiroz (Fabaceae) in pasture and secondary tropical dry forest

Plants subjected to stressful environments tend to be more asymmetric with reduced defenses and are therefore more vulnerable to herbivory. This study investigates the relationship between herbivory and fluctuating asymmetry (FA) in Poincianella pyramidalis in two contrasting habitat types in the Brazilian caatinga (shrublands). We tested the following hypotheses: that FA occurs in P. pyramidalis; that FA of P. pyramidalis leaves is greater in individuals located in pasture than in those located in secondary tropical dry forest; that herbivory by insects (leaf chewers and leaf miners) increases in parallel with increases in the level of FA; and that herbivory is more common in pasture than in secondary tropical dry forest. In each of the two environments, we sampled 20 plants and evaluated 400 leaflets. We submitted FA data to the Shapiro-Wilk test of normality, and we investigated the other variables using generalized linear models. We found that FA was present in all P. pyramidalis individuals evaluated but was greater in those located in the more degraded habitat (pasture). In addition, although herbivory was similar between the two habitats, there was positive relationship between FA and herbivory. This indicates that herbivores select plants that are more asymmetric, regardless of the type of habitat involved, which might be attributable to the mechanisms posited in the plant stress hypothesis.

Vegetation structure determines insect herbivore diversity in seasonally dry tropical forests

Vegetation structure can often determine insect herbivore fauna in forests, but this mechanism has been demonstrated in seasonally dry tropical forests (SDTFs) only at small spatial scales. In this study we evaluated the effects of the geographical location of SDTFs and vegetation structure on insect herbivore communities (leaf-chewing and sap-sucking guilds) in three Brazilian ecoregions (Cerrado, Cerrado/Caatinga transition, and Caatinga). We tested the following predictions: (1) insect herbivore species composition, richness, abundance and beta diversity differ among forests in different ecoregions; (2) insect richness, abundance and beta diversity are positively related to tree richness and density; (3) spatial turnover of species is the primary mechanism that generates herbivorous insect β-diversity in different ecoregions, and is positively influenced by tree richness. The composition, richness, and abundance of herbivorous insects differed over SDFs along the gradient of Cerrado and Caatinga. Both herbivore guilds responded positively to tree richness. Tree density only determined the richness and abundance of sap-sucking herbivores. Insect β-diversity was similar among Cerrado and transition areas, but lower in Caatinga itself; β-diversity was also positively affected by tree richness. Species turnover, as opposed to nestedness, was the main mechanism generating β-diversity, but itself was not related to tree richness. We demonstrate in this study the importance of landscape diversity and availability of local resources for herbivorous insect communities, and we emphasize the importance of SDTF conservation in different ecoregions as a result of species turnover.

Is there a bottom-up cascade on the assemblages of trees, arboreal insects and spiders in a semiarid Caatinga?

Predator–prey dynamics regulate the community structure of arthropods and may be affected by changes in their habitat. Bottom-up effects influence the distribution of arboreal insects changing, in turn, the availability of resources and shelter for the spider assemblage. This study examines the effect of habitat structure (tree richness and density) on the assemblages of herbivorous insects and spiders along a gradient of secondary forest succession in a semiarid Caatinga in northeastern Brazil. Insect and spiders were collected by beating the foliage during dry and wet seasons in 2010 and 2011. Plant richness and density varied significantly among stages of succession. In total, 2,590 arboreal insects were collected, corresponding to 14 orders and 151 morphospecies. In addition, we sampled 896 canopy spiders, encompassing 14 families and 53 morphospecies. Insect richness and abundance were negatively related with habitat structure, while spider richness increases with tree richness. We did not find any relationship among insects and spiders but there were differences in species composition of insects among all successional stages, determined by changes in vegetation structure. However, this effect does not extend to the species composition of spiders that remain similar in the different stages of secondary succession. We conclude that habitat structure had a partial bottom-up effect on arboreal insects and spider assemblages, indicating that this factor regulates the richness, abundance and species composition of arboreal insets and species richness of spiders. Thus, habitat structure promotes the maintenance of insects and spider diversity in fragments of Caatinga.

Changes in leaf chlorophyll content associated with flowering and its role in the diversity of phytophagous insects in a tree species from a semiarid Caatinga

Phytophagous insects choose their feeding resources according to their own requirements, but their feeding preferences in the semiarid Caatinga have rarely been studied. Flowering trees leads to a greater diversity of flower visitors and their predators in the host plant, but little is known about why the diversity of phytophagous insects not associated with flowers is also increased. The purpose of this study was to evaluate the diversity of sap-sucking, wood-boring and leaf-chewing insects associated with leaf chlorophyll content in flowering and non-flowering plants of Poincianella pyramidalis, an endemic tree of Caatinga. We used a leaf chlorophyll index (LCI) as a surrogate for resource quality, and an entomological umbrella to collect phytophagous insects. We show that trees which bloomed demonstrated higher chlorophyll content, greater abundance and a significant difference in the composition of phytophagous insect species when compared to non-flowering trees (p < 0.05). The results suggest that not only the presence of flowers themselves, but also the higher nutritional quality of leaf tissue, can explain the differences in species diversity and abundance of phytophagous insects. Exceptional flowering trees in the Caatinga area studied may thus act as spots of high quality resources, favouring changes in the diversity of insects in this environment.

Trail‐following behaviour and biological aspects of the gregarious caterpillar Brassolis sophorae (Lepidoptera: Nymphalidae)

Brassolis sophorae (Linnaeus), the coconut palm caterpillar, is a pest in the Northeast region of Brazil. Despite its great importance, information about the biology and behaviour of this insect is scarce. B. sophorae caterpillars are gregarious, and they remain in a nest during the daytime and only come out at dusk to feed. When caterpillars leave the nest to forage, they lay down a trail of silk that leads the group to the feeding site. In spite of this, there is no scientific evidence showing whether trail‐following behaviour in B. sophorae caterpillars is mediated by silk‐associated chemical cues. This gregarious behaviour has probably hampered biological studies of this species. We determined biological parameters (number of instars and development time of each instar) of the larvae and conducted behavioural assays to assess whether trail‐following behaviour of B. sophorae is mediated by chemical (silk extract) or physical (solvent‐washed silk) cues, or a combination of both. Measurements of the head capsule width showed that B. sophorae larvae pass through six instars in an average period of 12 days per instar. Dual‐choice tests in a Y‐shaped arena showed that the larvae significantly preferred to walk on a silk‐covered surface over a clean one and on a silk extract over hexane alone. When caterpillars were given the choice of walking on silk or on solvent‐washed silk, they did not show a preference for either treatment. These results demonstrate the presence of pheromonal compounds in the silk of B. sophorae although the communication between caterpillars of B. sophorae is also mediated by physical cues. The results of this study broaden knowledge on the trail‐following behaviour of immature larvae as well as the biology, morphology and behaviour of this insect.

First record of Bledius caribbeanus Blackwelder, 1943 (Coleoptera: Staphylinidae: Oxytelinae) from Brazil and distributional extension of B. hermani Caron and Ribeiro- Costa, 2007

Two species of Bledius Leach, 1819 (Coleoptera, Staphylinidae, Oxytelinae) are recorded for northeastern Brazilian coast. The occurrence of B. caribbeanus Blackwelder, 1943 is reported for the first time in Brazil and the geographical distribution of B. hermani Caron and Ribeiro-Costa, 2007 is extended.