Factors Affecting Transmission of Tristeza Virus by Melon Aphids13

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Abstract
A study of the transmission of tristeza virus by the melon aphid, Aphis gossypii Glover, revealed very small differences in transmission rate when infected source plants (orange seedlings) and Key lime indicator plants, Citrus aurantifolia (Christm.) Swingle, were held in an air-conditioned greenhouse or in an insectary, but the development of symptoms in the indicator plants was accentuated and speeded up in the insectary where temperatures ranged up to 15°C higher in the summer and 10°C lower in the winter than temperatures in the greenhouse. Young 2 to 6-inch Key lime plants were as good virus indicators as older 8 to 12-inch plants. The efficiency of the melon aphid as a vector of tristeza varied from 1 population to another. Numbers of transmissions were higher with 200 aphids per plant than with 10 to 50 aphids per plant, but the rate of transmission was not proportional to the number of aphids per plant. Mixed populations of nymphs and adult aphids transmitted tristeza virus as well as populations of adult aphids. Starvation of aphids for 2 and 4 hours before feeding did not increase the transmission of tristeza virus. Transmission of the virus to indicator plants by aphids feeding on thorns and on mature or immature leaves of infected plants was not significantly different, and transmission of the virus by aphids reared on cotton, Gossypium hirsutum L., was not significantly different from transmission by aphids reared on kenaf, Hibiscus cannabinus L.