Ivone Rezende Diniz

Host specificity of Lepidoptera in tropical and temperate forests

For numerous taxa, species richness is much higher in tropical than in temperate zone habitats. A major challenge in community ecology and evolutionary biogeography is to reveal the mechanisms underlying these differences. For herbivorous insects, one such mechanism leading to an increased number of species in a given locale could be increased ecological specialization, resulting in a greater proportion of insect species occupying narrow niches within a community. We tested this hypothesis by comparing host specialization in larval Lepidoptera (moths and butterflies) at eight different New World forest sites ranging in latitude from 15° S to 55° N. Here we show that larval diets of tropical Lepidoptera are more specialized than those of their temperate forest counterparts: tropical species on average feed on fewer plant species, genera and families than do temperate caterpillars. This result holds true whether calculated per lepidopteran family or for a caterpillar assemblage as a whole. As a result, there is greater turnover in caterpillar species composition (greater β diversity) between tree species in tropical faunas than in temperate faunas. We suggest that greater specialization in tropical faunas is the result of differences in trophic interactions; for example, there are more distinct plant secondary chemical profiles from one tree species to the next in tropical forests than in temperate forests as well as more diverse and chronic pressures from natural enemy communities.

The global distribution of diet breadth in insect herbivores

Significance Dietary specialization determines an organism’s resource base as well as impacts on host or prey species. There are important basic and applied reasons to ask why some animals have narrow diets and others are more generalized, and if different regions of the Earth support more specialized interactions. We investigated site-specific host records for more than 7,500 species of insect herbivores. Although host specialists predominate, the proportion of specialists is affected by the diversity of hosts and shifts globally, supporting predictions of more exclusive tropical interactions. These results not only affect our understanding of the ecology of food webs, but also have implications for how they respond to environmental change, as well as for ecosystem management and restoration. Understanding variation in resource specialization is important for progress on issues that include coevolution, community assembly, ecosystem processes, and the latitudinal gradient of species richness. Herbivorous insects are useful models for studying resource specialization, and the interaction between plants and herbivorous insects is one of the most common and consequential ecological associations on the planet. However, uncertainty persists regarding fundamental features of herbivore diet breadth, including its relationship to latitude and plant species richness. Here, we use a global dataset to investigate host range for over 7,500 insect herbivore species covering a wide taxonomic breadth and interacting with more than 2,000 species of plants in 165 families. We ask whether relatively specialized and generalized herbivores represent a dichotomy rather than a continuum from few to many host families and species attacked and whether diet breadth changes with increasing plant species richness toward the tropics. Across geographic regions and taxonomic subsets of the data, we find that the distribution of diet breadth is fit well by a discrete, truncated Pareto power law characterized by the predominance of specialized herbivores and a long, thin tail of more generalized species. Both the taxonomic and phylogenetic distributions of diet breadth shift globally with latitude, consistent with a higher frequency of specialized insects in tropical regions. We also find that more diverse lineages of plants support assemblages of relatively more specialized herbivores and that the global distribution of plant diversity contributes to but does not fully explain the latitudinal gradient in insect herbivore specialization.

The Abundance of Insect Herbivore Species in the Tropics: The High Local Richness of Rare Species

Local sampling of larval lepidopterans on Erythroxylum host plant species in tropical savanna (cerrado) revealed a high species richness with low abundance per species. Cumulative numbers of morphospecies with increasing sampling effort yielded no asymptotic level of richness in sampling periods lasting 6 mo, 7 mo, and 23 mo. Peak richness was reached at 31 species in 1992 and 19 species in 1993, on the three Erythroxylum species sampled: E. deciduum, E. suberosum, and E. tortuosum. Less than one larva was found per plant during all sampling times, with a mean of 0.28 species per plant in 1992 and 0.12 in 1993. The number of specimens of all species combined discovered per plant was very low at 0.10 per plant. Many plants remained unattacked on any sampling date with 12 percent, 8 percent, and 16 percent of plants attacked in the species listed in order above. In general, there was an increase in species found during the late dry season when new leaves were produced, but plant phenology seemed to exert only a small influence. Comparisons with temperate samples of a similar kind, in savanna vegetation at the same altitude, indicate a very different assemblage. Comparison was based on four criteria: richness was from two to over three times higher in the tropics, even though sampling had not produced an asymptotic accumulation of species; the number of morphospecies per plant individual was similar at the sites, although total richness was lower in the temperate savanna; the number of total individuals per plant was 11-fold higher in the temperate samples; and the percent of plants with larvae present was over four times higher in the temperate zone (mean of 49%) than in the cerrado (12%). The high richness of relatively rare species in the cerrado site poses challenges in understanding the reasons for such rarity, the organization of such assemblages, the gradient of species richness from low to high latitudes, the estimation of biodiversity, and conservation management.

Patterns and correlates of interspecific variation in foliar insect herbivory and pathogen attack in Brazilian cerrado

Patterns of insect herbivore and leaf pathogen attack are described for 25 plant species (10 trees, 10 shrubs and five herbs) at a Brazilian savanna (cerrado) site. Plant and leaf traits were correlated with interspecific variation in attack by herbivores and pathogens in order to account for differences among plant species. Across all species, pathogen damage was 1.5 times higher than insect damage (17.3% vs. 6.8%, respectively). Most insect damage occurred to young leaves while they were expanding (end of the dry season). In contrast, pathogen attack was low on young expanding leaves at the end of the dry season, increased as those leaves matured in the wet season, but continued to increase through the next dry season. Protein-binding capacity was negatively associated with interspecific differences in insect damage to mature leaves. Protein availability and plant height were positive predictors of pathogen attack among plant species, while leaf expansion rate was a significant negative predictor. Interspecific differences in leaf phenology had little effect on the amount of damage caused by either insects or pathogens. However, new leaves produced during the wet season suffered less insect damage than leaves produced during the dry season, the time of greatest leaf production. Timing of young leaf production affected pathogen attack but the season of escape depended on plant species. In contrast, there was no evidence for escape in space as common species were less likely to suffer high pathogen attack than rare species. New and mature leaf toughness, and time for a leaf to reach full expansion all increased from herbs to shrub to trees, while mature leaf nitrogen decreased in that order.

Volatiles Mediating a Plant-Herbivore-Natural Enemy Interaction in Resistant and Susceptible Soybean Cultivars

Several studies have shown that herbivore-induced plant volatiles act directly on herbivores and indirectly on their natural enemies. However, little is known about the effect of herbivore damage on resistant and susceptible plant cultivars and its effect on their natural enemies. Thus, the aim of this study was to evaluate the attraction of the herbivorous pentatomid bug Euschistus heros and its egg parasitoid Telenomus podisi to two resistant and one susceptible soybean cultivars with different types of damage (herbivory, herbivory+oviposition, and oviposition). In a Y-tube olfactometer, the parasitoids were attracted to herbivory and herbivory+oviposition damaged soybean plants when compared to undamaged soybean plants for the resistant cultivars, but did not show preference for the susceptible cultivar Silvânia in any of the damage treatments. The plant volatiles emitted by oviposition-damaged plants in the three cultivars did not attract the egg parasitoid. In four-arm-olfactometer bioassays, E. heros females did not show preference for odors of damaged or undamaged soybean plants of the three cultivars studied. The Principal Response Curves (PRC) analysis showed consistent variability over time in the chemical profile of volatiles between treatments for the resistant cultivar Dowling. The compounds that most contributed to the divergence between damaged soybean plants compared to undamaged plants were (E,E)-α-farnesene, methyl salicylate, (Z)-3-hexenyl acetate, and (E)-2-octen-1-ol.

Lepidopteran caterpillar fauna of cerrado host plants

The cerrado biome is rich in caterpillar species although the general biology and ecology of most tropical species remains unknown. Three host plant genera (Byrsonima, Erythroxylum and Qualea) were examined for caterpillars in four cerrado sensu stricto areas near Brasi´lia (DF, Brazil), from 1991 to 1995. Altogether, more than 16000 host plants were sampled and less than 20% of them possessed caterpillars. All the caterpillars found were reared under laboratory conditions. We successfully reared 137 species of 24 lepidopteran families. The average number of caterpillar species per host species was 28.3. The faunal similarity among plant genera, as well as among study sites, was low, and not related to the distances between them. The low proportion of host plants with caterpillars and the high incidence of rare species appears to be a general pattern for the cerrado. A large proportion (74%) of the caterpillar species occurred on only one host plant family. The most frequent species were either specialists (restricted to one host plant genus) or generalists. We provide a brief outline of some taxonomic problems, some observations on general biology, and temporal and local patterns of some specific caterpillars species. The methodology used, which included weekly data collection, in restricted study areas of the same habitat, with the same sampling method for recording the caterpillar species on the same host plant species, can be used as a tool to explore biodiversity and to discuss some aspects of the conservation of cerrado insects.

Técnicas de coleta de besouros copronecrófagos no Cerrado

Passive collection methods, with the use of traps, have been used to collect beetles of the Scarabaeidae family. However, in the Cerrado (Brazilian savanna-like vegetation) there are few studies about these insects, despite its importance to the ecosystem and to the biological control of cattle pests. The aim of this work was to evaluate techniques of dung beetle (Coleoptera: Scarabaeidae sensu stricto) collections with the use of flight interception traps, pitfall traps baited with human faeces, and with carcass. The experiment was accomplished in three different phytophysiognomies (low tree and shrub savanna, semi-open scrub mixed with trees and gallery forests) of the Ecological Reserve of IBGE (Instituto Brasileiro de Geografia e Estatistica), 35 km away from Brasilia, DF, in the rainy season (October/1999 to January/2000) and in the dry season (May to August/2000). The pitfall trap baited with faeces and the low tree and shrub savanna presented the greatest richness and abundance of species. There was a positive association between rains and the temporal distribution of the beetles. The pitfall trap baited with human faeces is recommended to collect dung beetles.

A critical review on some closely related species of Tetranychus sensu stricto (Acari: Tetranychidae) in the public DNA sequences databases

Taxonomic misidentification of the specimens used to obtain DNA sequences is a growing problem reported for different groups of organisms, which threatens the utility of the deposited sequences in public DNA databases. This paper provides new evidence of misidentifications in molecular DNA public databases in phytophagous mites of the Tetranychidae family belonging to the group Tetranychus (Tetranychus). Several species in this group are of economic and quarantine importance in agriculture and among them Tetranychus urticae, a highly polyphagous mite causing outbreaks in many crops worldwide, is certainly the most studied. We analyzed and evaluated the identity of 105 GenBank accessions of ITS2 rDNA and 138 COI mtDNA sequences which were deposited as T. urticae and those of 14 other taxa morphologically closely related to Tetranychus sensu stricto. In addition, ITS2 and COI sequences of 18 T. urticae samples collected for this study and identified by morphological criteria, were generated and included in the analyzed dataset. Among the deposited sequences in the GenBank database, numerous cases of apparently mistaken identities were identified in the group Tetranychus s. str., especially between T. urticae, T. cinnabarinus, T. kanzawai and T. truncatus. Unreliable sequences (misidentified or dubious) were estimated at nearly 30%. In particular the analysis supports the invalidity of the controversial species status of T. cinnabarinus. More generally, it highlights the need of using combined morphological and molecular approaches to guarantee solid species diagnostics for reliable sequence accessions in public databases.

Alternative food sources and overwintering feeding behavior of the boll weevil, Anthonomus grandis boheman (coleoptera: curculionidae) underthe tropical conditions of central Brazil

The boll weevil causes serious damage to the cotton crop in South America. Several studies have been published on this pest, but its phenology and behavior under the tropical conditions prevailing in Brazil are not well-known. In this study the feeding behavior and main food sources of adult boll weevils throughout the year in Central Brazil was investigated. The digestive tract contents of insects captured in pheromone traps in two cotton fields and two areas of native vegetation (gallery forest and cerrado sensu stricto) were analyzed. The insect was captured all through the year only in the cerrado. It fed on pollen of 19 different plant families, on Pteridophyta and fungi spores and algae cysts. Simpson Index test showed that the cerrado provided greater diversity of pollen sources. In the beginning of the cotton cycle, the plant families used for pollen feeding were varied: in cotton area 1, the weevil fed on Poaceae(50%), Malvaceae and Smilacaceae (25% each); in cotton area 2 the pollen sources were Malvaceae (50%), Asteraceae (25%) and Fabaceae and Clusiaceae (25% each); in the cerrado they were Chenopodiaceae (67%) and Scheuchzeriaceae (33%). No weevils were collected in the gallery forest in this period. After cotton was harvested, the family Smilacaceae was predominant among the food plants exploited in all the study areas. These results help to explain the survivorship of adult boll weevil during cotton fallow season in Central Brazil and they are discussed in the context of behavioral adaptations to the prevailing tropical environmental conditions.

Composição de espécie de Arctiidae (Insecta, Lepidoptera) em áreas de Cerrado

The Cerrado biome covers 23% of the Brazilian territory and includes nearly one third of the estimated biota of the country. The aim of this article is to know the species composition of the nocturnal Arctiidae and describe the beta-diversity patterns among 14 Cerrado areas. We collected a total of 1,016 individuals, representing 197 morphospecies. Estimates of species richness using Jackknife 2 and Chao 2 indicated that the region should contain, respectively, 375.7 and 383.8 species. The regression between species richness and number of vegetation types in the sampled areas was not significant. The beta-diversity (Sorensen distance) among study sites was positively related to geographical distances. The multivariate analyses indicated that, except for Pedregulho, study areas in Sao Paulo State were distinct from those in Goias and Tocantins States. Pooling study sites within vegetation types revealed that fauna of gallery forests and “cerradoes” were similar and, together, were different from those collected in open vegetacional formations (“campo sujo” and “cerrado sensu stricto” ). We suggested that vegetation characteristics and geographical distance are important factors in the determination of Arctiidae assemblages in the Brazilian Cerrado.