To understand the factors governing the diversity, abundance and host associations of parasitoids attacking frugivorous drosophilid flies on Iriomote-jima, a subtropical island of Japan, we monitored parasitism on several occasions over the period 2003–2009. Fifteen drosophilid and 12 parasitoid species were recorded. Three species of Drosophila, D. bipectinata, D. albomicans and D. takahashii, bred abundantly in banana baits, though their abundance varied between years and seasons. Frequent parasitoid species were Asobara japonica, A. pleuralis (Braconidae), Leptopilina ryukyuensis and L. pacifica (Figitidae). L. victoriae was recorded only in December 2003. In addition, host acceptance and host suitability of the four most frequently recorded parasitoid species were studied in the laboratory. Most parasitoid and drosophilid species showed species-specific associations with more than one antagonist species, suggesting that they have been subjected to complex coevolutionary interactions. In addition, host range of most of the parasitoid species included one of the three major Drosophila species, suggesting that the abundance of potential hosts is one of the factors determining the evolution of parasitoid host use., Biljan Novkovic ... [et al.]., and Obsahuje seznam literatury
The abundance and microhabitat use of rodents were investigated in four different habitats: two rain-fed crop fields with differing stone bund density, an irrigated field and bushland. A total of 444 individual small mammals belonging to six rodent and one shrew species were recorded in trapping grids and line transects. Of these, 230 individuals (52%) belonged to three pest rodent species of crop fields in northern Ethiopia: Stenocephalemys albipes (65%), Mastomys awashensis (25%) and Arvicanthis niloticus (10%). Population abundance of the three species was higher in the early dry season compared to the rainy season. While the bushland was significantly (p < 0.05) favoured by S. albipes and M. awashensis in both seasons, the irrigated field was preferred by Arvicanthis niloticus in the early dry season. In the early dry season, the microhabitat use of A. niloticus was strongly associated with the type of ground cover (herb) (R2adj = 0.152, P < 0.01). While M. awashensis was associated with vegetation density (R2adj = 0.13, P < 0.01), S. albipes was associated with vegetation cover (R2adj = 0.102, P < 0.001). The findings indicate that co-occurring pest rodent species prefer different microhabitats. Understanding their co-occurrence particularly in crop fields is vital for crop protection as they are known serious agricultural pests in northern Ethiopia.
Semi-natural habitats are key components of rural landscapes because they shelter a significant number of overwintering arthropods that are beneficial to agriculture. However, woodlots are semi-natural habitats with high patch-level heterogeneity and this aspect has been poorly studied. The purpose of this study was to determine the influence of woodlot heterogeneity on overwintering ground beetles. Woodlot heterogeneity was characterized in terms of distance from the woodlot boundary and date of the most recent logging operation. We used emergence traps to quantify the population density of ground beetles that overwintered in the different parts of the woodlot. In woodlot edges the densities and species richness of ground beetles were significantly higher than in the rest of the woodlot. Ground beetles that are active in crop fields overwintered in the edges but not in the inner zone of the woodlot. Species assemblages of ground beetles overwintering in the edges were highly diverse. The date of the most recent logging operation did not explain the distribution of ground beetles that overwintered in the woodlot. Our results show that woodlots, and in particular their edges, are used as a winter shelter by ground beetles that spend part of their life in crops, which potentially favours biological control in adjacent crop fields. and Anthony Roume, Annie Ouin, Laurent Raison, Marc Deconchat.
The abundance of Coleoptera, Diptera and Collembola on different species of fungi was investigated in relation to the size and abundance of fungal resources at different spatial scales; i.e., the size of the fungal fruiting body, the quality of resource in terms of number of conspecific sporophores growing within a radius of 50 cm, crowding of the clumps of fruiting bodies, and the quality of resource within a plot (20 m × 30 m). Multiple linear regression analyses showed that the influential spatial scale varied among the arthropod orders. The amount of resource at the scale of a clump made a significant contribution to the abundance of Coleoptera, and the fruiting body size significantly affected the abundance of Diptera on each fungal species. Collembolan abundance was significantly affected by the crowding of the clumps of fruiting bodies and the number of fruiting bodies per plot. These results suggest that the spatial distribution of fungal fruiting bodies may determine whether they are selected by arthropods visited.
The impact of transgenic Bt-maize, expressing the Cry1Ab protein, on aphids, leafhoppers, cutworms and wireworms was evaluated at the farm scale by comparing their abundance on Bt-plots and those sown with the isogenic variety over three consecutive growing seasons. The impact of Bt-maize was different on each of the three-herbivore groups. There were significantly more aphids on the Bt-maize but in terms of aphid species, the difference was only statistically significant for Sitobion avenae and not for the other three most abundant species (Metopolophium dirhodum, Rhopalosiphum padi and Macrosiphum euphorbiae). The analysis of aphid age structure showed consistently more individuals on Bt-plots; differences were significant for alates, apterous adults and young nymphs of R. padi, apterous adults and apterous fourth instar nymphs of S. avenae, alates, apterous adults and apterous fourth instar nymphs of M. dirhodum. Leafhoppers (Zyginidia scutellaris), particularly mature nymphs, were also more abundant on the Bt-maize. In spite of this there was no difference in leafhopper damage to Bt and non Bt-maize. The reasons for this are unclear but may be due to changes in Bt-maize that favoured aphids and leafhoppers. Differences in aphid and leafhopper densities were not high enough to affect yield. However, they may have affected the availability of prey for polyphagous predators such as Orius sp. The Bt-maize did not affect the incidence of cutworms (Agrotis segetum) or wireworms (Agriotes lineatus). These results indicate that Bt-maize does not have a negative impact on the non-target maize biocenosis at the farm scale.