Differential stylet penetration behaviors of two Aphis gossypii biotypes in relation to host or vector infection with citrus tristeza virus

Citrus tristeza virus (CTV) is one of the most important citrus disease agents worldwide. The impact of CTV on American agriculture has been significant, affecting 50 million trees with economic losses of several hundred million dollars. In California this virus is predominantly transmitted by two distinct Aphis gossypii biotypes, the cotton and melon aphids. Stylet penetration behaviors performed by cotton and melon aphids were recorded on ‘Mexican lime’ and ‘Madame Vinous’ citrus plants using the Giga8 DC Electrical Penetration Graph (EPG) monitor. Five 2-way factorial tests were performed to compare feeding activities of each biotype on CTV-infected vs. non-infected citrus plants. Different tests compared inoculative vs. non-inoculative aphids, to determine whether the presence of the virus in either the plant or insect had an affect on aphid feeding activity. Each aphid was recorded for 12 hours on specified host plants. All DC EPG waveforms were measured and statistically analyzed for duration and frequency. Non-inoculative cotton aphids displayed the phloem salivation waveform (E1) more frequently than did melon aphids, however melon aphid displayed the phloem ingestion waveform (E2) more frequently. Although some studies do not discriminate between the two biotypes, this study suggests that the melon aphid is better at acquiring CTV whereas the cotton aphid is better at inoculating CTV.