Influence of tobacco leaf exudates on activities of two species of predacious bugs

The influence of tobacco leaf exudate levels on selected activities of the stilt bug (SB), Jalysus wickhami Van Duzee, and the big-eyed bug (BEB), Geocoris punctipes (Say), was evaluated in the laboratory and in the field. Tobacco entries utilized in these studies were GR 115, a burley breeding line with low exudate levels and non-sticky leaves; TN 86, a burley cultivar with moderate exudate levels and sticky leaves; and PDJA 309, a flue-cured breeding line with high exudate levels and very sticky leaves.

In both no-choice and free-choice laboratory tests, SB demonstrated ovipositional non-preference for low-exudate leaves; whereas, BEB exhibited ovipositional non-preference for high-exudate leaves. In other laboratory experiments, predation by BEB on tobacco aphids and tobacco budworm eggs was increased on low-exudate leaves. SB predation was not influenced by leaf exudate levels, with one exception, predation on tobacco budworm eggs was reduced on high exudate leaves of PDJA 309.

In the field, SB were most prevalent on tobacco with moderate or high exudate levels and high numbers of tobacco aphids and were not influenced by numbers of tobacco flea beetles. BEB were most prevalent on tobacco with low exudate levels and were not influenced by the number of tobacco aphids or tobacco flea beetles. On tobacco with moderate or high exudate levels, SB adults were concentrated in the middle third of the plant early in the growing season, and both adults and nymphs were concentrated in the top third of the plant late in the growing season. BEE adults were concentrated in the bottom third of the plant early in the growing season and in the middle and bottom thirds of the plant late in the growing season. On tobacco with low exudate levels, BEB adults were evenly distributed among the three plant regions during the entire growing season. Tobacco flea beetles were most abundant on low-exudate tobacco; however, relative densities among plant regions and tobacco entries were inconsistent from year to year, and no clear trends in their distribution were discerned. Tobacco aphids were most abundant on moderate or high-exudate tobacco and they were concentrated on younger leaves located at the top of the plant on both high-exudate and low-exudate tobacco.