-The objective of this work was to assess the effects of integrated crop-livestock systems, associated with two tillage and two fertilization regimes, on the abundance and diversity of the soil macrofauna. Four different management systems were studied: continuous pasture (mixed grass); continuous crop; two croplivestock rotations (crop/pasture and pasture/crop); and native Cerrado as a control. Macrofauna was sampled using a modified Tropical Soil Biology and Fertility method, and all individuals were counted and identified at the morphospecies level for each plot. A total of 194 morphospecies were found, distributed among 30 groups, and the most representative in decreasing order of density were: Isoptera, Coleoptera larvae, Formicidae, Oligochaeta, Coleoptera adult, Diplopoda, Hemiptera, Diptera larvae, Arachnida, Chilopoda, Lepidoptera, Gasteropoda, Blattodea and Orthoptera. Soil management systems and tillage regimes affected the structure of soil macrofauna, and integrated crop-livestock systems, associated with no-tillage, especially with grass/legume species associations, had more favorable conditions for the development of "soil engineers" compared with continuous pasture or arable crops. Soil macrofauna density and diversity, assessed at morphospecies level, are effective data to measure the impact of land use in Cerrado soils.

In the humid tropics, slash-and-burn cultivation causes changes in the composition of soil biota communities. We investigated the soil macro-invertebrates (body length ≥ 2 mm) in five sites, two at Maripasoula, an Aluku village along the Maroni river (French Guiana), with short fallow (≈ 8 years), and the other three at Elahe, a Wayana village along the same river, with long fallow (≈ 25 years). We report observed species richness, the corresponding estimates by bootstrap and its associated standard deviation. At both sites the cultivation led to impoverished communities. The overall observed species richness i.e. γ diversity was ca. twice as larger in Elahe than in Maripasoula. The landscape at Maripasoula was dominated by highly disturbed areas with the direct consequence that local species richness relied on

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The spatio-temporal distribution of Aphis gossypii (Glover) was studied for a 4-year period in a plot of Gossypium hirsutum located in Bangui, Central African Republic. A study of the temporal evolution of the number of aphids by means of non-linear regression indicated a rapid population increase during the first 8 weeks of cotton cultivation. The overdispersion of the aphids was found to be significant during most of the season. We tested three population dispersion models; Iwao's model and Taylor's power law describe the relationship between the mean m and variance r 2 for the number of aphids, and the Nachman's model describes the functional dependence between m and the proportion p of non-infested cotton plants. The results of these statistical tests indicate that only the Taylor's model was not rejected. The aphidsÕ aggregation increases with population density. The regression parameter confidence intervals for each of the 4 years of observation prove the stability of the Taylor's model. The model r 2 ¼ 45m 1.3 is recommended when the environmental and cultural conditions are similar to those of our study.

The combined effects of isolation within an unfavourable matrix and vegetation development were studied in patches of scrub vegetation on a tropical inselberg (Nouragues, French Guiana). Three thickets ~10 m 2 area were sampled, located at ~30 m distance from each other, in which the same vegetation types were present at less than 3 m distance: canopies of Clusia minor (Clusiaceae) and Myrcia saxatilis (Myrtaceae), two stages of thicket development, and zones of destruction by fire. The shallow organic soil was sampled over ~2 dm 2 and down to 10 cm. The matrix was comprised of granite without any soil development. Arthropods were classified into morphospecies and their food diets were characterized by optical methods. The effect of isolation (between-thicket variation) on morphospecies composition was negligible, while that of vegetation type and fire (within-thicket variation) was prominent, as ascertained by principal component analysis and tested by partial redundance analysis. The importance of keystone structures (stages of vegetation development) was stressed, and interpreted to the light of taxonomic and foodweb knowledge.