|Tumlinson Iii, James|
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2000
Publication Date: 7/1/2001
Interpretive Summary: Caterpillars cause plants to release chemicals, called elicitors, that attract predators of the caterpillars. However, different species caterpillars cause plants to release chemicals that are attractive to predators of that caterpillar species. Studies conducted at the Center for Medical, Agricultural and Veterinary Entomology, USDA-ARS, Gainesville Florida have been studying the mechanisms responsible for production of these insect produced plant elicitors. They have discovered that larvae of two very important pests, the Cotton bollworm and the Tobacco budworm, degrade these plant elicitors in the gut at different rates. Thus, the elicitors produced by the Tobacco budworm are degraded much more rapidly than by the Cotton bollworm. This may explain why different amounts of elicitors are found in oral secretions of different caterpillar species and could help explain why plants respond differently to feeding damage by different species of caterpillars.
Technical Abstract: Feeding by larvae of Heliothis virescens and Helicoverpa zea induced cotton, corn and tobacco plants to release different proportions of volatiles attractive to natural enemies of the lepidopterous larvae. Volicitin, and some of the analogous compounds, originally identified in the oral secretions of Spodoptera exigua, and which act as elicitors of plant biosynthesis and release of volatiles, were also found in oral secretions of TBW and CEW. However, the amounts of these compounds, particularly N-(17-hydroxy-linolenoyl)-L-glutamine (volicitin), 17- hydroxylinolenic acid, and N-linolenoyl-L-glutamine, varied among batches of oral secretions and more so in TBW than in CEW. This variation was due to cleavage of the amide bond of the fatty acid- amino acid conjugates by an enzyme, or enzymes, originating from the midgut. The enzymatic activity in midguts and hindguts of TBW was significantly greater rthan that found in the guts of CEW. Furthermore, HPLC analyses showed tha CEW frass contained N-linolenoyl-L-glutamine in more than 0.1% wet weight, while this conjugate was only 0.003% wet weight in TBW frass. These results indicated that physiological difference between these two species affect the proportions of volicitin and its analogs in the caterpillars. Whether this causes the different volatile profiles released by plants damaged by each caterpillar species was not determined. Although immediate deactivation of degradative enzymes allowed more accurate determination of quantities of the elicitors in regurgitant from each species, the amounts in the oral secretions that contact the damaged leaf tissues when the caterpillars are chewing will be difficult to determine.