Are parenchymal cells a source of supplemental diet for aphids?

Prior to feeding on phloem, aphids perform a preamble of brief intracellular punctures of the cortical parenchyma, ingesting a small amount of cytoplasm from each cell. Given the length of time aphids spend puncturing parenchyma cells before and after phloem feeding, we propose that they are not just testing for potential hosts or mobilizing phloem nutrients, but are actively engaged in 'cytoplasmic feeding'. We combine the electrical penetration graph (EPG) technique to monitor feeding behavior of Myzus persicae (Sulzer) (Hemiptera: Aphididae) with confocal fluorescence microscopy to determine the uptake of parenchyma cytoplasm in the model plant Arabidopsis thaliana (L.) Heynh. (Brassicaceae). Aphids repetitively punctured parenchyma cells throughout the monitoring period, both before and after phloem feeding. As aphids puncture parenchyma cells of A. thaliana expressing cytoplasmic yellow fluorescent protein, the protein is ingested, increasing the intensity in the aphid stylet. The extended time of high-frequency punctures of parenchyma cells prior to phloem sap ingestion avoids the dilution of the intestinal content resulting from immediate phloem feeding. The enriched nutrient content of parenchyma cytoplasm has time to be absorbed by the intestine into the hemocoel without dilution and excretion in the honeydew.

Automated summary

Before feeding on phloem, aphids puncture cortical parenchyma cells and ingest cytoplasm as a form of "cytoplasmic feeding". Using a combination of EPG and confocal fluorescence microscopy, it is observed that aphids repeatedly puncture parenchyma cells and ingest cytoplasm from Arabidopsis thaliana. This extended period of puncturing prior to phloem feeding allows the aphids to absorb and utilize the enriched nutrient content of parenchyma cytoplasm without dilution and excretion.