Evaluation of cultural control and resistance‐breeding strategies for suppression of whitefly infestation of cassava at the landscape scale: a simulation modeling approach

Background: The whitefly Bemisia tabaci is an important vector of virus diseases, impacting cassava production in East Africa. To date, breeding efforts in this region have focused on disease resistance. Here we use a spatially‐explicit simulation model to explore how breeding strategies for whitefly resistance will influence the population dynamics of whitefly in the context of regional variation in cassava crop management practices. Results: Simulations indicated that regions with a short cropping cycle and two cropping seasons per year were associated with high whitefly abundance. Nymph mortality and antixenosis resistance mechanisms were more effective than mechanisms that lead to longer whitefly development times. When spatial variation was introduced in heterogeneous landscapes, however, negative consequences of the antixenosis effect were observed in fields containing whitefly susceptible varieties, unless the proportion of whitefly resistant variety in the landscape was low (~10%) or the amount of matrix in the landscape was high (~75%). Conclusion: We show the importance of considering cropping regime and landscape management context when developing and deploying whitefly‐resistant cassava varieties. Recommendations differ significantly between regions. There may also be unintended negative consequences of higher whitefly densities for whitefly susceptible varieties if uptake of the new variety in a landscape is high, depending on the mechanism of resistance and the landscape context. Furthermore, we show that in some cases, such as where there is substantial fallow combined with a short single‐season crop, the management characteristics of the existing cropping regime alone may be effective at controlling whitefly populations

Trait-Based Response of Deadwood and Tree-Related Microhabitats to Decline in Temperate Lowland and Montane Forests

Forest decline caused by climate change has been a growing challenge for European foresters for decades. The accumulation of tree-related microhabitats (TreMs) and deadwood during decline can enhance stand structural heterogeneity and provide crucial habitat features for many forest ecological guilds. We analysed changes in deadwood and TreM assemblages using a trait-based approach in three case studies: drought-induced decline in highland Pyrenean fir and lowland oak forests, and windstorm/pest-induced dieback in highland Bavarian spruce forests. Decline caused significant changes in deadwood and TreM characteristics and composition in three forest contexts. However, tree density with cavities, exudates, or crown deadwood was not linked to decline intensity. Declining conifer forests had more large deadwood and downed woody debris, and their TreM assemblages were more saproxylic, less epixylic, and included more cracks and exposed sapwood. TreM assemblages in drought-declining forests had higher diversity, functional richness, and more dead tops than healthy stands. In Bavarian spruce forests, there was more decayed downed deadwood, and the TreM assemblages were more associated with the base of the tree, snags, and logs. Overall, forest decline significantly boosts ecological niche resources, typically scarce in managed forests, which could benefit many forest biodiversity groups. Though post-disturbance management should respect tree species-dependent economic balance and avoid phytosanitary risks, it should also consider the ecological benefits of decline-induced heterogeneity.peerReviewe

Review of the APS SR RF systems.

The Advanced Photon Source (APS) is a 7-GeV full energy storage ring (SR) for generating synchrotron radiation with an injector. The storage ring cavities consist of four groups of four single cells powered by up to four 1-MW klystrons for up to 300-mA operation. A review of the operation of the rf system as well as rf-related beam dynamics is presented. This review includes rf power distribution, low-level feedback, control law, beam loading, beam instabilities, higher-order modes, and beam-induced multipactoring