Allelochemics ingestion

Illius, A. W. and Jessop, N. S. (1995). Modeling metabolic costs of allelochemical ingestion by foraging hethivotes.JournalofChemicalEcologyZl, 693-719. 

Barbehenn R (2001) Roles of peritrophic membranes in protecting herbivorous insects from ingested plant allelochemicals. Arch Insect Biochem Physiol 47 86-99 Barbehenn RV, Martin MM (1998) Formation of insoluble and colloidally dispersed tannic acid complexes in the midgut fluid ofManduca sexta (Lepidoptera Sphingidae) an explanation for the failure of tannic acid to cross the peritrophic envelopes of lepidopteran larvae. Arch Insect Biochem Physiol 39 109-117... 

Bolser RC, Hay ME (1996) Are tropical plants better defended Palatability and defenses of temperate vs tropical seaweeds. Ecology 77 2269-2286 Boyle RR, McClean S (2004) Constraint of feeding by chronic ingestion of 1,8-cinole in the brushtail possum (Trichosurus vulpecula). J Chem Ecol 30 757-775 Brattsten LB (1992) Metabolic defenses against plant allelochemicals. In Rosenthal GA, Berenbaum MR (eds) Herbivores their interactions with secondary plant metabolites. Academic, New York, pp 175-242... 

The demonstration that eclectic mechanisms have been evolved by insects for coping with the potentially toxic concomitants of their ingested nutrients necessitates careful analyses of the processing of each of these compounds by each adapted herbivore. Furthermore, it is important to realize that in Itself, sequestration is nothing more than an end product of a series of reactions that may reflect selective absorption, metabolism of specific compounds, and excretion of selected allelochemics ). In the present review, these diverse processing strategies will be explored in order to illustrate the various ways in which a multitude of herbivores accommodate potential plant toxins. IVo lepidopterous species will be used as models which, hopefully, will emphasize both the elegance and complexity identified with insects as processors of plant-derived compounds. 

Metabolism. Plant allelochemlcs Ingested by herbivores may be metabolically altered in the digestive tract or after absorption across the gut into the hemolymph. In some cases metabolism of these compounds results in compounds known to be considerably less toxic than the original natural products and thus constitutes true detoxication. On the other hand, the toxicological significance of many of these metabolites is unknown for either their producers or for potential predators. While these allelochemical derivatives may be much more amenable to sequestration than their parent compounds, it will not prove surprising if they are sometimes true detoxication products. 

Selective Sequestration. Sequestration of plant natural products is an idiosyncratic phenomenon, and there is little indication that the profiles of insect-stored allelochemics in any way mirror those of their plant food sources. In general, each insect species treats Ingested plant allelochemics distinctively, so that a compound excreted in toto by one species may constitute the main sequestration product of another. Unfortunately, while these sequestrative idiosyncrasies are quite evident, their significance is not. 

Ingested alkaloids can also be utilized for defense even if these compounds are still present in the intestine. For example, grasshoppers and the larvae of many species of butterflies and moths regurgitate when tactually disturbed. The enteric fluid, fortified with alkaloids such as PAs, can function as a highly effective topical deterrent against small invertebrate predators.33 Thus the plant has adapted its host plant s allelochemicals to function as a secretion that can be accurately applied in aggressive confrontations. 

Inhibition of digestive processes. Food uptake can be reduced by a pungent or bitter taste in the first instance, as mentioned eariier. The next step may be the induction of vomiting, diarrhea, or the opposite, constipation, which negatively influences digestion in animals. The ingestion of a number of allelochemicals such as emetine, lobeline, morphine, and many other alkaloids causes these symptoms (312). 

Some animals, such as monkeys, parrots, or geese, ingest soil. For geese (185) it was shown that the ingested soil binds dietary allelochemicals, especially alkaloids (185). This procedure would reduce the allelo-chemical content available for resorption. 

BARBEHENN, R.V., Roles of peritrophic membranes in protecting herbivorous insects from ingested plant allelochemicals. Arch Insect Biochem Physiol, 2001, 47, 86-99. 

Brattsen, L. B., Fate of ingested plant allelochemicals in herbivorous insects, in Molecular Aspects of Insect-Plant Associations (L. B. Brattsen and S. Ahmad, eds.), 211-255, Plenum Press, New York, 1986. 

Although a considerable body of information on insect responses to plant N-fertilization has accumulated since 1930 (at least 200 studies), the results are generally not comparable because of variable experimental conditions (e.g. different plant cultivars, soils, insects, temperature). Furthermore, effects of seasonal variation in quantity and quality of plant N content and biochemically associated allelochemics upon post-ingestive growth performance indices of insects were generally unknown at that time, as were the effects upon herbivores of fertilizer-induced variation in plant chemistry (Jones, 1976 Scriber, 1984). 

Catalpol (18) isolated from Buddleja cordobensis showed a series of allelochemical effects related to DNA synthesis in the insect Tribolium castaneum by inhibition of tag DNA polymerase activity with an IC50 value of 47.8 pM. Thus, it exhibited post-ingestive toxic effects showing a reduction in the efficiency of conversion of injected food [177]. 

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