Distribution and metabolism of exogenous ecdysteroids in the egyptian cotton leafwormSpodoptera littoralis (lepidoptera: noctuidae)

Abstract

After ingestion of various amounts of either [3H]ecdysone or [3H]20‐hydroxyecdysone (0.8 ng to 10 μg) by sixth instar larvae of the Egyptian cotton leafworm Spodoptera littoralis, apolar metabolites are rapidly detected in the gut and frass. Hydrolysis of the apolar products with Helix hydrolases releases solely [3H]ecdysone or [3H]20‐hydroxyecdysone, respectively. This, coupled with the formation of chemical derivatives (acetonide and acetate) which cochromatograph with authentic reference compounds on hptlc and hplc demonstrates that these apolar metabolites consist of ecdysone or 20‐hydroxyecdysone esterified at C‐22 with common long‐chain fatty acids. The major fatty acids have been identified by RP‐hplc and their contribution to the mixture determined. In contrast, [3H]ecdysone injected into the haemolymph of S. littoralis is metabolized to yield 20‐hydroxyecdysone, ecdysonoic acid, and 20‐hydroxyecdysonoic acid. Thus, two different pathways exist for the metabolism of ecdysteroids in this species. In addition to an essentially polar pathway operating on injected and endogenous ecdysteroids, exogenous ecdysteroids entering the gut of S. littoralis are detoxified, yielding apolar ecdysteroid 22‐fatty acyl esters which are rapidly excreted. The significance of these results in relation to the effects of ingested ecdysteroids on S. littoralis is discussed. Arch. Insect Biochem. Physiol. 34:329–346, 1997. © 1997 Wiley‐Liss, Inc.

The effects of ingested ecdysteroid agonists (20‐hydroxyecdysone, RH5849 and RH5992) and an ecdysteroid antagonist (cucurbitacin B) on larval development of two polyphagous lepidopterans (Acherontia atropos and Lacanobia oleracea)

“…In the haemolymph (Figure 8c) and carcass (Figure 8d), in addition to material co-chromatographing with 20E, two peaks were observed. Comparing these results to those obtained previously after injection of [ 3 H]20E into the haemolymphs of Spodoptera littoralis and Lacanobia oleracea (Blackford & Dinan, 1997a; Blackford et al, 1997), the peak eluting in fractions 3-4 is likely to represent 20-hydroxyecdysonoic acid and the peak eluting in fractions 13-14 is probably 20,26-dihydroxyecdysone. Similar peaks are observed in the gut contents ( Figure 8e) and frass ( Figure 8f) after injection, although the broad nature of the 20E peak suggests that this material may represent more than one compound.…”

“…This led to the suggestion that, where they occur in plants, they contribute to the deterrence of invertebrate predation (Galbraith & Horn, 1969). However, only a few insect species have been tested for their susceptiblity to ingested ecdysteroids and, of these, some are susceptible (Kubo et al, 1983;Arnault & Sláma, 1986;Tanaka & Takeda, 1993;Tanaka & Naya, 1995;Blackford & Dinan, 1997b) while others are unaffected even by very high concentrations (Robbins et al, 1968;Kubo et al, 1987;Robinson et al, 1987;Tanaka & Naya, 1995;Blackford et al, 1997). Thus, the developmental importance of ecdysteroids to insect development and their structural differences to vertebrate steroid hormones encourage the search for compounds which interfere with this hormonal system.…”

“…Consequently, it is not surprising that A. atropos is tolerant to high concentrations of dietary 20E. However, unlike other tolerant lepidopterans (Heliothis spp., Spodoptera littoralis and L. oleracea: Kubo et al, 1987;Robinson et al, 1987;Blackford et al, 1997;Blackford & Dinan, 1997a), ingested 20E is not esterified with long-chain fatty acids at C-22; rather it is excreted unmetabolised. Injected [ 3 H]20E, on the other hand, is extensively metabolised to polar metabolites.…”

Diversity of detoxification pathways of ingested ecdysteroids among phytophagous insects

“…In the case of P. interpunctella, the detoxification mechanisms are more complex, as they involve both a dehydrogenase/epimerase reaction and 22acylation. The situation is similar in S. littoralis (Webb et al, 1995(Webb et al, , 1996Blackford et al, 1997). The lack of 3-epimerization in O. nubilalis was an unexpected finding, as such a reaction is widespread in lepidopteran larvae (Weirich and Bell, 1997;Lafont et al, 2005).…”

Identification and Characterization of Genes Involved in Ecdysteroid Esterification Pathway Contributing to the High 20-Hydroxyecdysone Resistance of Helicoverpa armigera

“…Some Helicoverpa species (Helicoverpa virescens and Helicoverpa zea) can tolerate high concentrations of 20E in their diet without any detrimental effects (Kubo et al, 1981). Blackford et al (1996Blackford et al ( , 1997 also found that exogenous application of 20E could not affect the normal growth and development of Spodoptera littoralis and Lacanobia oleracea (Blackford et al, 1996;Blackford and Dinan, 1997b). Furthermore, in those noctuid insects, the high resistance is mainly due to the effective conversion of the ingested ecdysteroids into 22-long-chain-fatty-acyl esters in the gut (Kubo et al, 1987;Robinson et al, 1987;Zhang and Kubo, 1993;Blackford et al, 1997).…”