Secondary plant substances, also called allelochemicals, play a major role in pest infestations. Glucosinolates (GLS) and their degradation products are powerful phagostimulants for herbivores feeding on Brassicaceae and deter the noncrucifer feeders but are tolerated by some generalist phytophagous insects such as the peach-potato aphid, Myzus persicae Sultzer. Do the allelochemical substances only effect the herbivores or do they also influence the predators of the pest? Broad bean, Vicia faba L. (GLS free), oilseed rape, Brassica napus L. (low GLS level), and white mustard, Sinapis alba L. (high GLS level), were used in this work as host plant for the prey. Although the two latter Brassicaceae species had positive effects on aphid reproductive rates, host plants displayed mixed influences on the performance of the predaceous twospotted lady beetle, Adalia bipunctata L. Both rape and mustard shortened development duration and increased adult weight of the twospotted lady beetle. No significant difference of lady beetle mortality was observed, depending on the prey host plant. Whereas, rape-fed M. persicae enhanced larger egg production and larvae emergence, mustard-fed M. persicae induced lower fecundity and egg viability of the beetles. Fitness of M. persicae on high GLS plant-fed A. bipunctata was lower than the other plants. Biological parameters of aphid predators are closely linked to chemical composition of Brassicaceae species. This work on allelochemical impact gave opportunities to better understand interactions of the plant-aphid-lady beetle tritrophic model and demonstrated that successful biological control of pests must integrate the environmental aspects of each trophic level.
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