EFFECTS OF PARASITISM BY LYSIPHLEBUS TESTACEIPES (HYMENOPTERA, APHIDIIDAE) ON TRANSMISSION OF BEET YELLOWS CLOSTEROVIRUS BY BEAN APHID (HOMOPTERA, APHIDIDAE)

The effect of parasitism by Lysiphlebus testaceipes (Cresson) on the p otential of the bean aphid, Aphis fabae Scopoli, to vector beet yellow s closterovirus to sugar beet was examined under laboratory and field conditions. In laboratory experiments, we found no significant differe nces in virus transmission between parasitized and nonparasitized aphi ds at 2, 3, 4, and 5 d following parasitism. In cage experiments, para sitized and nonparasitized aphids were placed onto source plants for v irus in the middle of separate flats of sugar beet plants, The inciden ce of beet yellows closterovirus was greater within the parasitized tr eatments than within the nonparasitized treatments. This result indica ted that parasitized aphids were more mobile than nonparasitized aphid s. In field studies, sugar beet plants were infested with parasitized and nonparasitized viruliferous aphids at 3 and 5 wk following sugar b eet emergence. In both trials, virus incidence in plants right next to the virus source was greater in the parasitized treatments than in th e nonparasitized treatments. At 3 wk after sugar beet emergence, paras itized aphids transmitted beet yellows closterovirus to a mean (+/-SEM ) of 14.3% (5.84) of the remaining plants in the plots; however; nonpa rasitized aphids did not transmit virus to any remaining plants. At 5 wk following sugar beet emergence, nonparasitized aphids spread virus to a mean (+/-SEM) of 16.2% (5.29) of the plants remaining in the plot s, whereas parasitized aphids spread virus to a mean (+/-SEM) of 13.5% (3.50) plants. The age of the sugar beet plant had no significant eff ect on virus transmission because percent transmission was similar in both trials.