Figure 1. Nicotine oxidation does not benefit M. sexta larvae.

Larval (a) mass [(mean± SE) F_{4, 172} = 45.2, P≤0.05, n = 36, 34, 37, 33 and 37 for water, nicotine, NNO, cotinine and CNO, respectively] and (b) mortality (%) after 10 d of feeding on artificial diet containing water (control) or 0.1% (fresh mass) nicotine, NNO, cotinine or CNO (n = 30). (c) Waldbauer assay-based quantification of excreted (%) metabolites by fourth-instar larvae fed artificial diet containing 0.1% (fresh mass) metabolite [(mean± SE) F_{3, 25} = 4.3, P≤0.05, n = 6 for nicotine, NNO and cotinine and 8 for CNO]; (n. a.≡ not applicable). (d) Nicotine, NNO, cotinine or CNO are not degraded in frass over the 24 h period of the Waldbauer assays. Fresh frass was spiked with each metabolite to attain the final concentration of 0.5%; the spiked frass was extracted and analyzed after zero and 24 h of incubation to quantify the recovered metabolite. Every bar represents data from 3 replicates (n = 3). (e) Melanization of cotinine-fed (right) larva. (f) Discharge kinetics of hemolymph-injected (70±2.5 µg≡ 0.001% of larval fresh mass) nicotine, NNO, cotinine or CNO (n = 5). Lower-case letters and asterisks in (a), (c) and (e) indicate significant differences (P≤0.05) by one-way ANOVA; in (b), asterisk indicates significant differences (P≤0.05) in frequencies (and displayed percentages) by Fisher's exact test.