Effects of hydrolyzable and condensed tannin on growth and development of two species of polyphagous lepidoptera: Spodoptera eridania and Callosamia promethea

Abstract

The effects of tannins on survival, growth, and digestion were compared in two polyphagous species of Lepidoptera (one, the southern armyworm, a forb-feeder; and the other, the promethea silkmoth, a tree-feeder). Two different types of tannins (hydrolyzable and condensed) were incorporated into artificial basal diets in order to determine whether or not differential survival and growth would result between the forb feeder, which normally does not encounter tannins in its natural diet, and the tree-feeder, whose host species include many tanniniferous plants from several different families.Neonate larvae of the forb-feeding armyworms exhibited significantly suppressed 10-day growth rates at all tannin concentrations tested (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0% of wet weight) for both the hydrolyzable and the condensed tannin compared to the control diet, however no dose-effect was detectable. In contrast, there were no detectable differences in neonate survival or growth through the first 10 days for the tree-feeding promethea silkmoth larvae fed diets with either tannic acid or quebracho tree condensed tannin.In order to determine the physiological mechanisms of action of these tannins against armyworms, we conducted detailed physiological bioassays of biomass and nitrogen utilization by penultimate instar larvae. Standard gravimetric feeding studies with both tannic acid and the quebracho tree condensed tannin demonstrated that reduced relative growth rates (RGR's) of Spodoptera eridania Cram. were due to the suppressed relative consumption rates (RCR's) and decreased conversion efficiencies (ECD's) rather than due to digestibility-reduction (as reflected by approximate digestibility, AD). As with the neonate larval growth rate suppression, there were no detectable dose responses at the different concentrations of tannic acid (0.25, 0.50, 0.75, 1.00, 2.50, and 5.0 percent) and condensed tannins from quebracho (0.25, 0.50, 0.75, 1.0, and 2.5 percent) in our penultimate instar studies.

Failure of tannic acid to inhibit digestion or reduce digestibility of plant protein in gut fluids of insect herbivores

“…This study, in conjunction with other studies which have failed to produce any evidence that dietary tannins reduce digestive efficiency in any insect (Betnays et al, 1980;Klocke and Chan, 1982;Reese et al, 1982;Manuwoto et al, 1985;Manuwoto and Scriber, 1986), adds further support to our contention that tannins do not deserve the status they have been accorded as general, allpurpose, digestibility-reducing substances. It is now abundantly clear that the digestive systems of insects possess a number of attributes that effectively counter the potential protein-precipitating capacity of tannins.…”

“…In order to ensure that our position not be misinterpreted, we wish to emphasize that we are not proposing that tannins are innocuous chemicals that pose no problems to insect herbivores. There is no question that tannins can act as toxins (Berenbaum, 1984;Bernays et al, 1980;Manuwoto et al, 1985;Manuwoto and Scriber, 1986;Steinly and Berenbaum, 1986) and feeding deterrents (Bernays, 1981;Klocke and Chan, 1982;Reese et al, 1982;Manuwoto et al, 1985) to nonadapted insects. We are only arguing that there is no evidence that tannins reduce the nutritional value of an insect' s food by inhibiting digestive enzymes or by reducing the digestibility of ingested proteins, and further that the failure of tannins to interfere with digestion is readily explained on the basis of welldocumented characteristics of the digestive systems of herbivorous insects.…”

“…While there is evidence that tannins act as digestion-inhibiting substances in certain species of vertebrates, possibly by interfering with the growth and metabolism of rumen microorganisms (Waterman et al, , 1984, to date there has been no experimental demonstration that tannins ever act as digestibility-reducing or digestion-inhibiting substances in any herbivorous insect species (Bernays, 1981;Martin and Martin, 1984;Martin et al, 1985). The adverse effects that dietary tannins have on the growth and development of tannin-sensitive insects appear to be due instead to the properties of these polyphenols as feeding deterrents (Klocke and Chan, 1982;Reese et al, 1982;Manuwoto et al, 1985;Manuwoto and Scriber, 1986) and toxins (Berenbaum, 1984;Bernays et al, 1980;Manuwoto et al, 1985;Manuwoto and Scriber, 1986;Steinly and Berenbaum, 1986).…”

Effects of synthesized tannin on the growth and survival of a generalist herbivorous insect, the common cutworm, Spodoptera litura Fabricius (Lepidoptera: Noctuidae).

“…However, these predictions have not always held up to experimental study. Some studies have reported that tannin has no effect on certain herbivores Klocke and Chan, 1982;Manuwota and Scriber, 1986;Martin et al, 1987;Smith et al, 1992;McArthur and Sanson, 1993). One study has even suggested that tannin can be utilized by herbivores as a nutrient substrate (Bernays and Woodhead, 1982).…”

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“…However, some herbivores are well adapted to tannin-containing plants (Manuwoto and Scriber, 1986;Barbehenn and Martin, 1992). Despite numerous investigations, the precise mechanisms of tannin-herbivore interactions are still unknown.…”