Analysis of EPG Recorded Probing by Cabbage Aphid on Host Plant Parts with Different Glucosinolate Contents

Probing behavior of adult apterous Brevicoryne brassicae (L.) was monitored with the electical penetration graph (EPG) technique on Sinapis alba L. Old, young, and mature leaves, as well as the generally preferred stems were compared with respect to probing activity and glucosinolate content. Compared to leaves, EPGs on stems showed much prolonged initial probes, which more often led to phloem-phase waveforms and successively to sustained phloem ingestion. However, reaching the first phloem phase within a probe was delayed on stems so that the time to the first phloem phase within the experiment was rather similar on the different plant parts. This suggests that superficial (epidermal and mesophyll) factors are more favorable in stems than in leaves but for deeper tissues, i.e., mesophyll and vascular bundle cells, the situation seems reversed, except for the phloem sieve elements, which seemed more or at least equally suitable. 3-Butenyl, p-hydroxybenzyl, and benzyl glucosinolates were found in all parts. It is concluded that further research on distribution and compartmentation of glucosinolates within plant tissues is needed for a better understanding of the correlations found with some B. brassicae probing parameters.