Ohio

Determining which Aphid Species Act as Vectors of Mosaic Viruses on Pumpkin

Principal investigator:

 Celeste Welty, Extension Entomologist, Dept. of Entomology, Columbus

Abstract:

 Watermelon mosaic virus (WMV) has become common in Ohio pumpkin fields in recent years and is of great concern to commercial growers. Pumpkins are grown on over 3,300 acres in Ohio as a high-value crop for which yield and quality of fruit produced are important. Viruses can reduce yield but more commonly affect quality by causing lumpy fruit with uneven color. We know that WMV is vectored by aphids, but we have not known which of >48 species of aphids trapped in pumpkin fields are the vectors. The objective of this project was to determine which common species of aphids are capable of transmitting WMV to pumpkin plants, and whether certain species are more efficient vectors than others. We will be better able to evaluate aphid monitoring methods and host reservoirs once we know which aphid species can act as vectors.

Aphids of 5 species were tested: Rhopalosiphum maidis (corn leaf aphid), Capitophorus elaeagni (artichoke aphid), Aphis gossypii (melon aphid; species confirmation pending), Macrosiphum euphorbiae (potato aphid), and Myzus persicae (green peach aphid). A winged aphid of each species was caught in the field then reared on appropriate host plants in a greenhouse until a large colony developed. Wingless adult female aphids from the colony were starved for 2 or 6 hours, exposed to a WMV-infected pumpkin leaf for one minute, then placed on clean individually-caged pumpkin plants for 24 hours to allow virus transmission. Plants were held for 3 weeks after exposure to aphids, then leaves were removed and frozen for testing by ELISA to verify presence of virus. We used one aphid per plant, ten plants per replicate and five replicates per species. As of early December, the transmission tests are completed for four species and nearly completed for one species. ELISA testing is underway and has shown that 21% of plants exposed to melon aphid developed WMV. Based on visual symptoms, we expect that WMV also was transmitted by green peach aphid but not by corn leaf aphid, artichoke aphid, or potato aphid. Results should be complete by late December 1997.

Extension Program Implementation:

An interim report was given at a pumpkin twilight meeting on 30 September in southern Ohio and at a vegetable school in northern Ohio on 19 November. Full results will be presented at our annual growers' congress in February 1998 as well as at regional schools and in newsletters.

For further information contact Celeste Welty , Assistant Professor, Dept. of Entomology, The Ohio State University or the Ohio IPM Office.

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