Plant resistance to aphids might be present in different plant tissues, such as the epidermis, mesophyll and phloem, but not all of them play a key role in determining the feeding preference of aphids. In this study, electrically recorded feeding behaviors of cabbage aphids were combined with choice tests and microscopic observations to understand the feeding preference of cabbage aphids on oilseed rape cultivars. The choice tests showed that more cabbage aphids survived on ‘Qianyou18’, and less on ‘Zhongshuang11’, compared with the other cultivars. The results of the choice tests were paradoxical with the results analyzed from the general and mesophyll-associated variables. The thick upper epidermis with bushy long trichomes on the leaves of ‘Zhongshuang11’ delayed the first probe of the cabbage aphids. The duration of phloem-feeding was similar among the four cultivars although there were differences in the hindrance of the mesophyll. However, salivation was increased when the aphids fed on ‘Zhongshuang11’, further indicating that the leaf’s physical properties could be important for aphid feeding preference on the four cultivars.

Transferrins (Trfs) are multifunctional proteins with key functions in iron transport. In the present study, a Trf (PxTrf) from Plutella xylostella was identified and characterized. The PxTrf consisted of a 2046-bp open reading frame, which encoded a 681 amino acid protein with a molecular weight of 73.43 kDa and had an isoelectric point of 7.18. Only a single iron domain was predicted in the N-lobe of PxTrf. Although PxTrf was expressed ubiquitously, the highest levels of expression were observed in the fourth instar larvae. PxTrf transcript level was highest in fat bodies among various tissues. The PxTrf transcript levels increased significantly after the stimulation of pathogens. A decrease in PxTrf expression via RNA interference enhanced the susceptibility of P. xylostella to the Isaria cicadae fungus and inhibited hemocyte nodulation in response to the fungal challenge. In addition, a considerable increase in the pupation rate was observed in larvae treated with double-stranded PxTrf (dsPxTrf). Overall, according to the results, PxTrf may participate in P. xylostella immunity against fungal infection and insect development.

Electropenetrography (EPG) was used to study the feeding preference of Brevicoryne brassicae Linnaeus (Hemiptera: Aphididae) on Brassica napus L. We assessed the probing behaviors of B. brassicae on three B. napus cultivars (Qinyou10, Zhongheza88, and Qinyou79) at three developmental stages (two leaf, four leaf, and six leaf stages). The four leaf treatment had a shorter duration of pathway phase and a longer time to first intracellular stylet punctures on Qinyou10 compared to other cultivars, and the longest total ingestion duration on Qinyou10 and the shortest on Qinyou79, indicating a preference for Qinyou10 over Qinyou79. This cultivar preference is also reflected in the field with higher aphid densities on Qinyou10 in the previous investigation. In the two leaf treatment, we found a longer total probing duration and a shorter non-probing duration on Zhongheza488 compared to Qinyou10. In the six leaf treatment, we found a longer duration in time to the first probe, more probes, and longer d...