|Johnson, A - CLEMSON UNIVERSITY|
|Stephenson, M - UNIVERSITY OF GEORGIA|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 25, 2002
Publication Date: December 1, 2002
Citation: Jackson, D.M., A. W. Johnson, and M. G. Stephenson. 2002. Survival and development of Heliothis virescens (Lepidoptera: Noctuidae) larvae on isogenic tobacco lines with different levels of alkaloids. J. Econ. Entomol. 95:1294-1302. Interpretive Summary: Pyridine alkaloids, including nicotine, are important natural compounds with insecticidal properties that are found in tobacco. In 1990 and 1991, eighteen tobacco lines that varied in levels of alkaloids were grown in at Tifton, GA, Oxford, NC, and Florence, SC. There was a significant negative correlation between alkaloid levels and natural infestations of tobacco budworm larvae, an important pest of tobacco. There was a negative relationship between levels of alkaloids and survival and development of budworm larvae caged onto individual tobacco leaves. Larvae survived and developed best on the bud leaves where alkaloid levels were low, and survival was poorer on the lower leaves where alkaloids were higher. Budworm larvae appear to avoid the detrimental effects of nicotine by feeding primarily on the bud leaves with the lowest levels of these alkaloids. Hatching larvae that move to lower leaf positions have little chance of survival.
Technical Abstract: Pyridine alkaloids were measured in 18 isogenic tobacco lines, Nicotiana tabacum L., from 3 parental sources ('NC 95', 'SC 58', and 'Coker 139'). At Florence, SC and Tifton, GA, there were significant correlations between alkaloid levels in bud leaves (leaves just below the apical meristem) and natural infestation ratings of tobacco budworm larvae, Heliothis virescens (F.). At Oxford, NC, bud leaves were artificially infested with budworm larvae, and after 6 wk there was a significant correlation between alkloid levels and larval weights. During the 2nd yr of this study, 4 entries from the NC 95 isoline were grown at Oxford. Samples were taken every 2 wk from leaf positions 1 (bud leaves), 5-6, 9-10, 13-14, and 17-18 below the top of the plant. When plants were small (wk 4), there were few differences in alkaloid levels between bud leaves and leaves lower on the plant. However, by wk 8 alkaloid levels were much higher in the lower leaves. Later in the season there were only slight differences in the alkaloid levels between the top leaves and lower leaf positions. Second instar tobacco budworms were placed on individual, intact leaves, and larval survival and weight gain were evaluated after 1 wk in the field. The survival and development of tobacco budworm larvae were negatively correlated with levels of alkaloids and leaf positions. Larvae survived and developed at the highest rates on the bud leaves of each entry where alkaloid levels were low, and in general, survival was poorer on the lower leaves where alkaloids were higher. Tobacco budworm larvae appear to avoid most of the detrimental effects of tobacco alkaloids by feeding primarily on the bud leaves with the lowest alkaloid levels. Hatching larvae that move to lower leaf positions have little chance of survival.