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Sterol inhibition in Chilo partellus

Published online by Cambridge University Press:  19 September 2011

H. C. Agarwal
Affiliation:
Department of Zoology, University of Delhi, Delhi-110007, India
Renu Gupta
Affiliation:
Department of Zoology, University of Delhi, Delhi-110007, India
Rita Rath
Affiliation:
Department of Zoology, University of Delhi, Delhi-110007, India
Versha Goel
Affiliation:
Department of Zoology, University of Delhi, Delhi-110007, India
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Abstract

Like most other insects, Chilo partellus requires sterols such as cholesterol in the diet. Freshly hatched larvae grown on a chemically defined diet take about 27 days to become adults. However, when an azasteroid, 25-azacholesterol is added to the diet in concentrations ranging from 0.5 ppm to 25 ppm, the time taken to become adults became 41 days at 5 ppm azasteroid. The maximum larval weight decreased to 76 mg from 140 mg as compared to the control insects. In larvae reared on a diet with 10 ppm azacholesterol, about 60% larvae died. The mortality was almost complete at a dose of 25 ppm. The larvae, pupae and adults reared on the chemically defined diet contained sitosterol, stigmasterol, cholesterol, compesterol and isofucosterol. No desmosterol was, however, detected in these insects. Inclusion of 25-azacholesterol in the diet led to the detection of desmosterol in these insects. It was observed that the cholesterol concentration decreased greatly, whereas sitosterol and stigmasterol concentration increased. This showed that the azacholesterol inhibited the dealkylation of C29 plant sterols to cholesterol, probably at the level of Δ-24-sterol reductase as evidenced by the accumulation of desmosterol. In some cases the adults were unable to separate themselves completely from the pupal cases. Some larval-pupal intermediates were also noted. It was further observed that the spermatogenesis was disturbed due to azacholesterol treatment. This may indicate that ecdysone biosynthesis is probably impaired. These results indicate that inhibition of steroid utilization may have the potential of being developed into a method for integrated pest management.

When 1, 2-dibenzoyl-1-tert-butylhydrazine was added to the diet at concentrations varying from 1 to 10 ppm, all the larvae died in all the concentrations tested, except 1 ppm. The larval weight was reduced to almost half due to the treatment and the larval duration increased as in case of 25-azacholesterol. However, the sterol composition of the insects did not change greatly.

Résumé

Comme la plupart d'autres insectes, le Chilo partellus a besoin des stérols tels que le cholestérol dans la nourriture. Les larves qui sortent de la coquille et grandissent sur une nourriture définie sur le plan chimique, deviennent adultes en 27 jours environ. Cependant, lorsqu'un azastéroide -25-azacholestérol est ajouté au régime dans des concentrations allant de 0,5 ppm á 25 ppm, le délai de devenir adulte passe á 41 jours à 5 ppm d'azastéroid. Le poids maximal de la larve a diminué de 140 mg à 76 mg par rapport aux insectes témoins. En cas de larves poussant sur une nourriture contenant 10 ppm d'azacholestérol, 60% environ de larves étaient mortes. Une mortalité quasiment complète était atteinte avec une dose de 25 ppm. Les pupes, les larves et les adultes qui ont grandi sur un régime défini chimiquement, contenaient du sitostérol, du stigmastérol, du cholestérol, du campestérol et de l'isofucostérol. Toutefois, aucun desmostérol n'a été détecté dans ces insectes. L'ajout du 25-azacholestérol dans le régime a conduit à la détection du desmostérol dans ces insectes. Il a été observé que la concentration de cholestérol a diminué sensiblement tandis que la concentration du sitostérol et du stigmastérol a augmenté. Ceci a démontré que l'azacholestérol a inhibé la déalkylation des stérols de plante C29 en cholestérol, probablement au niveau du réductase Δ -24 - stérol comme mis en évidence par une accumulation du desmostérol. Dans certains cas, les adultes étaient incapables de se séparer complètement des coquilles des pupes. Certains intermédiaires larvae-pupae ont également été notés. De plus, il a été observé que la spermatogénèse fut dérangée à cause du traitement d'azacholestérol. Cela indiquerait que probablement la biosynthèse d'ecdyson est perturbée. Ces résultats indiquent que l'inhibition de l'utilisation de stéroïde présenterait le potentiel d'être développée dans une méthode intégrée de lutte phyto-sanitaire.

Lorsaqu'on a ajouté 1, 2-dibenzoyl-1-tert-butylhydrazine à la nourriture aux concentrations allant de 1 ppm à 10 ppm, toutes les larves sont mortes dans toutes les concentrations soumises à l'essai, sauf 1 ppm. Le poids de la larve a diminué à environ la moitié à cause du traitement et la durée de larvae a augmenté comme dans le cas du 25-azacholestérol. Cependant, la composition en stérol des insectes n'a pas enregistré une modification sensible.

Type
Physiology, Behaviour and Biochemistry
Copyright
Copyright © ICIPE 1990

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