Flea beetles in spring oilseed rape differ in phenology and habitat choices for reproduction and overwintering—Implications for pest management

Abstract

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.