Gloria Rosell

Characterization of an Antennal Carboxylesterase from the Pest Moth Spodoptera littoralis Degrading a Host Plant Odorant

Background Carboxyl/cholinesterases (CCEs) are highly diversified in insects. These enzymes have a broad range of proposed functions, in neuro/developmental processes, dietary detoxification, insecticide resistance or hormone/pheromone degradation. As few functional data are available on purified or recombinant CCEs, the physiological role of most of these enzymes is unknown. Concerning their role in olfaction, only two CCEs able to metabolize sex pheromones have been functionally characterized in insects. These enzymes are only expressed in the male antennae, and secreted into the lumen of the pheromone-sensitive sensilla. CCEs able to hydrolyze other odorants than sex pheromones, such as plant volatiles, have not been identified. Methodology In Spodoptera littoralis, a major crop pest, a diversity of antennal CCEs has been previously identified. We have employed here a combination of molecular biology, biochemistry and electrophysiology approaches to functionally characterize an intracellular CCE, SlCXE10, whose predominant expression in the olfactory sensilla suggested a role in olfaction. A recombinant protein was produced using the baculovirus system and we tested its catabolic properties towards a plant volatile and the sex pheromone components. Conclusion We showed that SlCXE10 could efficiently hydrolyze a green leaf volatile and to a lesser extent the sex pheromone components. The transcript level in male antennae was also strongly induced by exposure to this plant odorant. In antennae, SlCXE10 expression was associated with sensilla responding to the sex pheromones and to plant odours. These results suggest that a CCE-based intracellular metabolism of odorants could occur in insect antennae, in addition to the extracellular metabolism occurring within the sensillar lumen. This is the first functional characterization of an Odorant-Degrading Enzyme active towards a host plant volatile.

Biorational Approaches for Insect Control by Enzymatic Inhibition

Conventional insecticides are highly toxic to many living organisms as well as to the environment; consequently, new biorational and more specific approaches to pest control have been developed. In this paper, we present an update of those approaches resulting from studies on inhibition of enzymes involved in key processes of insects life, particularly growth, molting and development of larvae and intraspecific communication of adults. The enzymes covered include pheromone degrading enzymes, pheromone biosynthetic enzymes, oxidoreductases, juvenile hormones, juvenile hormone epoxide hydrolases, proteases, molting hormones and phenoloxidases. Although these approaches refer to control of insect pests, many of them can be in principle also considered suitable for medicinal chemistry studies, since the mechanism of action of these inhibitors on related enzymes is quite similar, if not equal, in both fields.

Degradation of pheromone and plant volatile components by a same odorant-degrading enzyme in the cotton leafworm, Spodoptera littoralis.

Background Odorant-Degrading Enzymes (ODEs) are supposed to be involved in the signal inactivation step within the olfactory sensilla of insects by quickly removing odorant molecules from the vicinity of the olfactory receptors. Only three ODEs have been both identified at the molecular level and functionally characterized: two were specialized in the degradation of pheromone compounds and the last one was shown to degrade a plant odorant. Methodology Previous work has shown that the antennae of the cotton leafworm Spodoptera littoralis, a worldwide pest of agricultural crops, express numerous candidate ODEs. We focused on an esterase overexpressed in males antennae, namely SlCXE7. We studied its expression patterns and tested its catalytic properties towards three odorants, i.e. the two female sex pheromone components and a green leaf volatile emitted by host plants. Conclusion SlCXE7 expression was concomitant during development with male responsiveness to odorants and during adult scotophase with the period of male most active sexual behaviour. Furthermore, SlCXE7 transcription could be induced by male exposure to the main pheromone component, suggesting a role of Pheromone-Degrading Enzyme. Interestingly, recombinant SlCXE7 was able to efficiently hydrolyze the pheromone compounds but also the plant volatile, with a higher affinity for the pheromone than for the plant compound. In male antennae, SlCXE7 expression was associated with both long and short sensilla, tuned to sex pheromones or plant odours, respectively. Our results thus suggested that a same ODE could have a dual function depending of it sensillar localisation. Within the pheromone-sensitive sensilla, SlCXE7 may play a role in pheromone signal termination and in reduction of odorant background noise, whereas it could be involved in plant odorant inactivation within the short sensilla.

Moths behaving like butterflies. Evolutionary loss of long range attractant pheromones in castniid moths: a Paysandisia archon model.

Background In the course of evolution butterflies and moths developed two different reproductive behaviors. Whereas butterflies rely on visual stimuli for mate location, moths use the ‘female calling plus male seduction’ system, in which females release long-range sex pheromones to attract conspecific males. There are few exceptions from this pattern but in all cases known female moths possess sex pheromone glands which apparently have been lost in female butterflies. In the day-flying moth family Castniidae (“butterfly-moths”), which includes some important crop pests, no pheromones have been found so far. Methodology/Principal Findings Using a multidisciplinary approach we described the steps involved in the courtship of P. archon, showing that visual cues are the only ones used for mate location; showed that the morphology and fine structure of the antennae of this moth are strikingly similar to those of butterflies, with male sensilla apparently not suited to detect female-released long range pheromones; showed that its females lack pheromone-producing glands, and identified three compounds as putative male sex pheromone (MSP) components of P. archon, released from the proximal halves of male forewings and hindwings. Conclusions/Significance This study provides evidence for the first time in Lepidoptera that females of a moth do not produce any pheromone to attract males, and that mate location is achieved only visually by patrolling males, which may release a pheromone at short distance, putatively a mixture of Z,E-farnesal, E,E-farnesal, and (E,Z)-2,13-octadecadienol. The outlined behavior, long thought to be unique to butterflies, is likely to be widespread in Castniidae implying a novel, unparalleled butterfly-like reproductive behavior in moths. This will also have practical implications in applied entomology since it signifies that the monitoring/control of castniid pests should not be based on the use of female-produced pheromones, as it is usually done in many moths.

Antennal esterase cDNAs from two pest moths, Spodoptera littoralis and Sesamia nonagrioides, potentially involved in odourant degradation

Rapid degradation of odours after interaction with olfactory receptors is a critical step of the signal reception process. However, the implied mechanisms are still largely unknown in vertebrates as well as in insects. Involvement of odourant‐degrading enzymes in odourant degradation within the antennae has been shown in some insect species and, in particular, esterases could play a key role in degradation of sex pheromones from Lepidoptera. Using a PCR‐based strategy, we isolated cDNAs encoding two new esterases from two moths which used acetates as pheromone compounds: the Egyptian armyworm Spodoptera littoralis and the Mediterranean corn borer Sesamia nonagrioides. In antennae, both transcripts were clearly restricted to olfactory sensilla, suggesting their involvement in the degradation of odourant acetate components.

Biosynthetic pathways of the pheromone of the Egyptian armyworm Spodoptera littoralis

Abstract Most insect pheromones comprise multicomponent blends of geometric or optical isomers, and one major question is how insects produce species‐specific ratios of components for successful reproductive isolation. Key enzymes suggested to be involved in pheromone biosynthesis are acetyl‐coenzyme A carboxylase and fatty acyl synthetase, chain‐shortening enzymes, desaturases, elongases, reductases, oxidases, and alcohol acetyl transferases. The female pheromone composition of the Egyptian armyworm Spodoptera littoralis (Boisd.) is highly dependent on the origin of the strain. In this review, we present a summary of the different reported pheromone compositions of the moth, including from our recent studies on this subject, as well as the biosynthetic routes to the different components and the molecular approaches involved. In addition, the key role played in the proposed biosynthetic pathways by a number of important biosynthetic enzymes, such as chain shortening enzymes, desaturases and alcohol acetyl transferases, is outlined, as well as the latest developments on the inhibition of these enzymes.

New fluorinated derivatives as esterase inhibitors. Synthesis, hydration and crossed specificity studies

A variety of new fluorinated chemicals have been prepared for the first time and tested as inhibitors of esterases, one of the main enzymes involved in pheromone catabolism, in two economically important pests, the Egyptian armyworm Spodoptera littoralis (SL) and the Mediterranean corn borer Sesamia nonagrioides (SN). Using the respective major component of the pheromone as substrate, the K(m) and V(max) of the antennal esterase of both insects resulted to be 5.66 x 10(-4) M and 8.47 x 10(-6) Mmin(-1) for SL and 1.61 x 10(-7) M and 1.25 x 10(-7) Mmin(-1) for SN, pointing out that SN esterase has a higher affinity for its corresponding substrate than SL. In general, the trifluoromethyl ketones (TFMKs) exhibited higher inhibitory potency than the corresponding difluoromethyl ketones (DFMKs) or difluoroaldehydes (DFAs). The compounds appeared to hydrate differently in aqueous solution, the extent of hydration following the order: alpha,alpha-DFMKs<alpha,alpha-difluoro-beta-thioalkylmethyl ketones<TFMKs<beta-thiotrifluoromethyl ketones<alpha,alpha-DFAs. No clear correlation has been found between the K(hyd) and the inhibitory potency and no specificity has been found when the chemicals were assayed on extracts of both insects.

Synthesis and anti-inflammatory activity of rac-2-(2,3-dihydro-1,4-benzodioxin)propionic acid and its R and S enantiomers

Summary Racemic (R,S)-2-(2,3-dihydro-1,4-benzodioxin-6-yl)propionic acid (3) has been prepared from 2,3-dihydro-1,4-benzodioxin. R-(−)-Pantolactone has been used as auxiliary for the synthesis of R-3 and S-3. The anti-inflammatory properties of the new carboxylic acids are described and compared with other anti-inflammatory agents. The highest activity is exhibited by compound biS-3.

Novel tricyclic spiropiperidines. Synthesis and adrenergic activity of spiro[1,3-benzodioxolopiperidines] and spiro[1,3-benzodioxanepiperidines]

Summary The synthesis of new series of spiropiperidines is reported. Some of these compounds showed interesting adrenergic activity. The biological activities of the new compounds were evaluated on-guinea pig atria (β1), guinea-pig trachea (β2) and rat vas deferens (α). Compounds 6a, 6c and 6f showed activity comparable to propranolol, in spite of being tertiary amines.

Electrophysiological and Behavioral Responses of the Black-Banded Oak Borer, Coroebus florentinus, to Conspecific and Host-Plant Volatiles

Aspects of the chemical ecology of the black-banded oak borer, (BBOB) Coroebus florentinus (Coleoptera: Buprestidae), were studied. Odors produced by males and females were similar, both qualitatively and quantitatively. Nonanal, decanal, and geranylacetone, identified in the headspace of both sexes, elicited strong electroantennographic responses from male antennae, but not from female antennae. In dual-choice olfactometer experiments, a blend of these three compounds was attractive to both sexes; males responded to decanal alone, while females responded to geranylacetone alone, suggesting that these compounds are responsible for activity of the blend to the respective sexes. Antennae of both sexes responded electroantennographically to the green leaf volatiles (E)-2-hexenal, (E)-2-hexenol, 1-hexanol, (Z)-3-hexenyl acetate, and n-hexyl acetate, all identified from the host plant Quercus suber. In behavioral experiments, only females were attracted to host-plant odors, and in tests with synthetic compounds, females were attracted to (E)-2-hexenol, 1-hexanol, and (Z)-3-hexenyl acetate. It is likely that these compounds play a role in foraging and/or oviposition behavior of BBOB females.