Predicting bee community responses to land-use changes: Effects of geographic and taxonomic biases.

Land-use change and intensification threaten bee populations worldwide, imperilling pollination services. Global models are needed to better characterise, project, and mitigate bees' responses to these human impacts. The available data are, however, geographically and taxonomically unrepresentative; most data are from North America and Western Europe, overrepresenting bumblebees and raising concerns that model results may not be generalizable to other regions and taxa. To assess whether the geographic and taxonomic biases of data could undermine effectiveness of models for conservation policy, we have collated from the published literature a global dataset of bee diversity at sites facing land-use change and intensification, and assess whether bee responses to these pressures vary across 11 regions (Western, Northern, Eastern and Southern Europe; North, Central and South America; Australia and New Zealand; South East Asia; Middle and Southern Africa) and between bumblebees and other bees. Our analyses highlight strong regionally-based responses of total abundance, species richness and Simpson's diversity to land use, caused by variation in the sensitivity of species and potentially in the nature of threats. These results suggest that global extrapolation of models based on geographically and taxonomically restricted data may underestimate the true uncertainty, increasing the risk of ecological surprises.

Indirect interaction between a fungal plant pathogen and a herbivorous beetle of the weed Cirsium arvense.

Interactions between plants and their natural enemies are well studied, but investigations on the indirect interactions between plant enemies that simultaneously exploit a host plant are rare. Yet these plant-mediated interactions are important because they may affect not only the impact of plant antagonists on plant survival but may also influence the performance of the other plant exploiters. This study focused on the indirect effects of a systemic infection of creeping thistle, [irsium arvense (L.) Scop., with the necrotrophic fungus Phoma destructiva (Plowr.) on the phytophagous leaf beetle Cassida rubiginosa Müller, by examining egg deposition, food plant choice, and larval and pupal performance of the beetle. Thus, the results give a broader view than most other studies of plant-mediated effects of a pathogen on a phytophagous insect. Since both the beetle and the fungus are considered as agents for the biological control of C. arvense, the results are also of interest for applied ecology. Potted plants of C. arvense were inoculated with a conidiospore suspension of P. destructiva to cause a systemic infection of the plants. In a cage experiment, ovipositing females of C. rubiginosa showed a significant preference for healthy thistles. In dual-choice tests, adults of C. rubiginosa preferred leaf discs from healthy thistles over those from Phoma-infected thistles. The beetles also consumed significantly more leaf tissue from healthy than from infected plants. Development time from freshly hatched larvae until pupation was significantly longer for larvae fed on infected leaves. The weight of last-instar larvae and pupae was lower, and larval and pupal mortality was higher when larvae had been fed with infected compared to healthy leaves. Thus, the combined use of both potential biological control agents may be of lowered efficiency because (1) C. rubiginosa avoided infected thistles for both egg deposition and adult feeding and (2) Phoma infection negatively affected larval development and increased larval and pupal mortality of the beetle.

Insects as vectors of plant pathogens: mutualistic and antagonistic interactions.

Interactions between plants and their herbivores and pathogens are mostly analysed separately, thereby neglecting mutualistic or antagonistic interactions between these antagonists and possible joint effects on the host. We studied interactions between the weed Cirsium arvense, the rust fungus Puccinia punctiformis and three herbivorous insects, the aphids Aphis fabae ssp. cirsiiacanthoidis and Uroleucon cirsii, and the beetle Cassida rubiginosa. All three insect species mechanically transported spore material and significantly increased rates of P. punctiformis infection in healthy thistles. The interaction between C. rubiginosa and the fungus was antagonistic. Although C. rubiginosa transferred spores, biomass of adults was significantly reduced, development of adults tended to be prolonged and mortality increased when feeding on plants infected with P. punctiformis. In contrast, the relationship between the aphid U. cirsii and P. punctiformis was mutualistic: U. cirsii profited by fungal infection and formed significantly larger colonies on fungus-infected plants. Although the differences in insect performance suggest that aphids may be better vectors than the beetle, infection rates were similar. This is the first study to demonstrate that the relationship between herbivores, which increase the dispersal of a pathogen, and the pathogen itself can be mutualistic or antagonistic, depending on the species.