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Spring oilseed rape is severely affected by early season herbivory of various flea beetle species. Flea beetle pest management strategies with less reliance on conventional chemical insecticides are direly needed. However, the current knowledge of flea beetle ecologies and life cycles is insufficient to design and inform such strategies effectively. Using a combination of pitfall and emergence traps, we followed the life cycles of flea beetles in 13 spring oilseed rape fields in south central Sweden, measuring densities in three sampling seasons: spring activity at crop seedling stage, summer emergence of the new generation, and emergence of overwintered adults in the following spring in the adjacent grassy field margins. We found a strong positive relationship between densities of emerging Phyllotreta atra, P. striolata and P. undulata in summer and their densities earlier in spring. Flea beetle assemblage composition differed across the seasons, driven by changes in the relative abundances of different species. While assemblages emerging in summer were filtered for species reproducing in spring oilseed rape, assemblages emerging from the grassy field margins in the following spring were again more heterogeneous. Spring activity peaks and summer emergence peaks differed among species, with P. vittula having an earlier activity peak and emerging earlier than most other species. This knowledge of spatiotemporal habitat use can contribute to a more effective flea beetle management in spring oilseed rape. Especially summer emergence in the fields became apparent as a so far unexplored point in time to control flea beetle pests. [ABSTRACT FROM AUTHOR]

Reliably predicting pest damage would allow farmers to reduce insecticide use without incurring economic losses and thus contribute to agricultural sustainability. However, means to predict pest severity are lacking.We assessed whether crop feeding injury caused by flea beetles in spring oilseed rape can be predicted from flea beetle pest densities in the previous season using 22 years of suction trap catches of flea beetles in combination with crop feeding injury data from 293 fields.We found a strong positive relationship between the densities of flea beetles of the genus Phyllotreta in the summer and autumn activity period of the previous year and crop feeding injury caused by flea beetles in spring oilseed rape the following year. Autumn weather or the total cover of spring oilseed rape in the study region did not improve the prediction further.Pest monitoring using suction traps is thus a promising tool to predict crop feeding injury and can reduce insecticide use in years with low pest pressures. [ABSTRACT FROM AUTHOR]

Loss in seed yield and therefore decrease in plant fitness due to simultaneous attacks by multiple herbivores is not necessarily additive, as demonstrated in evolutionary studies on wild plants. However, it is not clear how this transfers to crop plants that grow in very different conditions compared to wild plants. Nevertheless, loss in crop seed yield caused by any single pest is most often studied in isolation although crop plants are attacked by many pests that can cause substantial yield losses. This is especially important for crops able to compensate and even overcompensate for the damage. We investigated the interactive impacts on crop yield of four insect pests attacking different plant parts at different times during the cropping season. In 15 oilseed rape fields in Sweden, we estimated the damage caused by seed and stem weevils, pollen beetles, and pod midges. Pest pressure varied drastically among fields with very low correlation among pests, allowing us to explore interactive impacts on yield from attacks by multiple species. The plant damage caused by each pest species individually had, as expected, either no, or a negative impact on seed yield and the strongest negative effect was caused by pollen beetles. However, seed yield increased when plant damage caused by both seed and stem weevils was high, presumably due to the joint plant compensatory reaction to insect attack leading to overcompensation. Hence, attacks by several pests can change the impact on yield of individual pest species. Economic thresholds based on single species, on which pest management decisions currently rely, may therefore result in economically suboptimal choices being made and unnecessary excessive use of insecticides.