Insect pest damage increases faba bean (Vicia faba) yield components but only in the absence of insect pollination.

Identifying and quantifying crop stressors interactions in agroecosystems is necessary to guide sustainable crop management strategies. Over the last 50 years, faba bean cropping area has been declining, partly due to yield instabilities associated with uneven insect pollination and herbivory. Yet, the effect of interactions between pollinators and a key pest, the broad bean beetle Bruchus rufimanus (florivorous and seed predating herbivore) on faba bean yield has not been investigated. Using a factorial cage experiment in the field, we investigated how interactions between two hypothesized stressors, lack of insect pollination by bumblebees and herbivory by the broad bean beetle, affect faba bean yield. Lack of bumblebee pollination reduced bean weight per plant by 15%. Effects of the broad bean beetle differed between the individual plant and the plant-stand level (i.e., when averaging individual plant level responses at the cage level), likely due to high variation in the level of herbivory among individual plants. At the individual plant level, herbivory increased several yield components but only in the absence of pollinators, possibly due to plant overcompensation and/or pollination by the broad bean beetle. At the plant-stand level, we found no effect of the broad bean beetle on yield. However, there was a tendency for heavier individual bean weight with bumblebee pollination, but only in the absence of broad bean beetle herbivory, possibly due to a negative effect of the broad bean beetle on the proportion of legitimate flower visits by bumblebees. This is the first experimental evidence of interactive effects between bumblebees and the broad bean beetle on faba bean yield. Our preliminary findings of negative and indirect associations between the broad bean beetle and individual bean weight call for a better acknowledgment of these interactions in the field in order to understand drivers of crop yield variability in faba bean.

Type of organic fertilizer rather than organic amendment per se increases abundance of soil biota.

Addition of organic amendments is a commonly used practice to offset potential loss of soil organic matter from agricultural soils. The aim of the present study was to examine how long-term addition of organic matter affects the abundance of different soil biota across trophic levels and the role that the quality of the organic amendments plays. Here we used a 17-year-old fertilization experiment to investigate soil biota responses to four different organic fertilizers, compared with two mineral nitrogen fertilizers and no fertilization, where the organic fertilizers had similar carbon content but varied in their carbon to nitrogen ratios. We collected soil samples and measured a wide range of organisms belonging to different functional groups and trophic levels of the soil food web. Long-term addition of organic and mineral fertilizers had beneficial effects on the abundances of most soil organisms compared with unfertilized soil, but the responses differed between soil biota. The organic fertilizers generally enhanced bacteria and earthworms. Fungi and nematodes responded positively to certain mineral and organic fertilizers, indicating that multiple factors influenced by the fertilization may affect these heterogeneous groups. Springtails and mites were less affected by fertilization than the other groups, as they were present at relatively high abundances even in the unfertilized treatment. However, soil pH had a great influence on springtail abundance. In summary, the specific fertilizer was more important in determining the numerical and compositional responses of soil biota than whether it was mineral or organic. Overall, biennial organic amendments emerge as insufficient, by themselves, to promote soil organisms in the long run, and would need to be added annually or combined with other practices affecting soil quality, such as no or reduced tillage and other crop rotations, to have a beneficial effect.

Insecticide resistance in pollen beetles over 7 years - a landscape approach.

BACKGROUND: In spite of considerable interest in the impact of pesticides on pest populations, few attempts have been made to link resistance patterns of insect pests to land-use features across spatial and temporal scales. We hypothesise that pollen beetle pesticide resistance increases in areas with a high proportion of oilseed rape and with an even mixture of winter and spring oilseed rape owing to high pesticide selection pressure in such areas. RESULTS: Here, we investigated 7 years of lambda-cyhalothrin (Karate(®) ) resistance in field-collected pollen beetle adults from a total of 180 sampling points across ten regions in Sweden. We found a positive effect on pollen beetle pesticide resistance of proportion of oilseed rape and even spring-winter oilseed rape mixture. However, this was true only for the regional spatial scale. Significant land-use effects in the long-term models, with oilseed rape data averaged over a longer (4 years) period of time, suggested an effect of regional landscape history on current pest resistance. CONCLUSION: For successful control of pollen beetle pesticide resistance, we suggest a long-term regional strategy for oilseed rape management. This land-use approach provides a framework for further investigations that integrate resistance management into landscape research.