The roles of nicotine and natural enemies in determining larval feeding site distributions of Manduca sexta L. and Manduca quinquemaculata (Haworth) on tobacco

Abstract

Field observations indicated that hornworms select feeding sites non-randomly on tobacco. We tested the hypotheses that differences in feeding site locations of larvae of Manduca sexta L. and Manduca quinquemaculata (Haworth) (Lepidoptera: Sphingidae) on tobacco could be explained by differential nicotine concentrations within plants and leaves, species-specific responses to nicotine, or pressure exerted by natural enemies. Results showed that third-instar larvae of M. sexta fed more proximally and centrally on the leaf, whereas M. quinquemaculata fed more distally. Withinplant selection of leaves did not differ; both species selected leaves in the middle region of the plant. Nicotine concentrations in a high nicotine genotype, NC95, varied within each leaf, increasing 2 -3 fold from the basal to apical portion of the leaf, and within each plant, increasing 7 -10 fold from the first fully expanded leaf to the twelfth (lowest) leaf. In laboratory bioassays, both Manduca species responded to nicotine as a feeding deterrent. Electrophysiological studies demonstrated that gustatory organs of both species responded to nicotine at concentrations found in tobacco leaves and that M. quinquemaculata generally showed a less vigorous response to nicotine than M. sexta. Field mortality of M. sexta due to parasitism by Cotesia congregata (Say) and to parasitism and predation combined differed among feeding sites; predation alone did not. Results suggest that although nicotine concentration and species specific responses to nicotine play a role in determining feeding site locations, pressure exerted by natural enemies, especially parasitism by C. congregata, is more important.

Nicotine's Defensive Function in Nature

“…Such behavior suggests that nicotine plays an important role in determining feeding sites of M. sexta larvae , as has been suggested in a study with cultivated tobacco (Kester et al 2002). While the relative toxic effects of anatabine and nicotine remain unstudied, these results are likely to underestimate the influence of nicotine on M.…”

The Effect of Larval Diet and Sex on Nectar Nicotine Feeding Preferences in Manduca Sexta (Lepidoptera: Sphingidae)

“…Nicotine increased larval mortality and time to pupation and reduced pupal weight (data not shown); negative effects of nicotine on larval performance are consistent with previous studies (Bentz & Barbosa 1990;Appel & Martin 1992;Glendinning 2002;Kester et al 2002).…”

ArabidopsisBasic Helix-Loop-Helix Transcription Factors MYC2, MYC3, and MYC4 Regulate Glucosinolate Biosynthesis, Insect Performance, and Feeding Behavior

“…Shroff et al (2008) observed that larvae of the generalist Helicoverpa armigera avoided leaf margins and veins of A. thaliana rosette leaves. Herbivorous insects often consume specific parts of their host and have evolved recognition cues to avoid poisoncontaining areas and structural defenses or to select nutritious tissues (Kester et al, 2002;Schoonhoven et al, 2005). The nonuniform GS distribution could thus explain the feeding behavior of S. littoralis larvae, which avoided tissues with high GS contents, and that of P. brassicae larvae, which were attracted by GS-containing tissues.…”