Characterization of the Probing and Feeding Behavior of Planococcus citri (Hemiptera: Pseudococcidae) on Grapevine

The citrus mealybug, Phnococcus citri (Risso) (Hemiptera: Pseudococcidae), is a vector of Grapevine leafroll-associated virus 3 (GLRaV-3), which causes severe damage to grapevines (Vitis spp.) worldwide. We studied the feeding behavior of P. citri on grapevine leaves and whole plants infected with GLRaV-3 and on artificial feeding membranes using DC-electrical penetration graphs (EPGs). P. citri ingested from phloem sieve elements, but it also spent long intervals in the xylem. Waveforms, not described before for mealybugs, were characterized, some of them resembling those of aphids: 1) one new pattern occurring within the phloem phase, named E23, correlated with honeydew excretion and positive ninhydrine reaction and therefore was associated with sap ingestion from the phloem sieve elements; and 2) an extracellular waveform, named G, also possibly associated with ingestion in artificial membranes, which probably represented xylem ingestion. The potential drops (pd) of P. citri showed two distinct phases (pd1 and pd2). The occurrence of pds was, on average, less frequent than in aphids (0.14/min), but they lasted much longer (32.5 s). The temporal analysis of 20 EPG recordings on detached leaves lasting 20 h showed great variability among individuals. Only 11/20 mealybugs reached the phloem phase, and ingestion from the phloem sieve elements (E23) was the predominant phloem-related activity. However, the G pattern was even more frequent, and most insects (16/20) showed xylem ingestion activities with an average duration of 8.7 h. This work represents the first step to identify specific stylet activities associated with the acquisition and inoculation of GLRaV-3 by P. citri.