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Sex ratio and female sexual status of the coconut pest, Oryctes monoceros (Coleoptera: Dynastidae), differ in feeding galleries and pheromone-baited traps

Published online by Cambridge University Press:  29 July 2008

K. Allou ,
J.-P. Morin ,
P. Kouassi ,
F. Hala N'klo  and
D. Rochat
K. Allou
Affiliation:
CNRA, Station Cocotier Marc Delorme, Laboratoire de Défense des cultures, 07 BP 13 Abidjan 07, Ivory Coast
J.-P. Morin*
Affiliation:
CIRAD-CP, UR 31, TA 80/02 Avenue Agropolis, F-34398 Montpellier Cedex 5, France
P. Kouassi
Affiliation:
Université de Cocody – Laboratoire de Zoologie et de Biologie Animale de l'UFR Biosciences - 22 BP 582 Abidjan 22, Ivory Coast
F. Hala N'klo
Affiliation:
CNRA, Station Cocotier Marc Delorme, Laboratoire de Défense des cultures, 07 BP 13 Abidjan 07, Ivory Coast
D. Rochat
Affiliation:
UMR1272, Physiologie de l'Insecte, Signalisation et Communication, INRA, R.D. 10, F-78026 Versailles cedex, France
*
*Author for correspondence Fax: +33-1.30.83.31.19 Email: [email protected]
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Abstract

Oryctes monoceros is a serious coconut pest, causing up to 40% damage in tropical Africa. Synthetic aggregation pheromone, ethyl 4-methyloctanoate, has been used to lure adults to traps. Traps with pheromone plus decaying palm material captured a high proportion of males. This raises the question whether individuals, which damage palms are receptive to the pheromone. We studied the sex ratio of the insects feeding on coconuts and those attracted to pheromone traps. Sixty two percent of adults from feeding galleries on living coconut palms were females. Pheromone with rotting palm material lured 43% females. To investigate the reasons for this difference, we compared the reproductive system of females lured to the odour traps or feeding in coconut galleries, or present in old rotting stems. Ninety six percent of the females trapped by pheromone had mated, and were sexually mature. In the galleries on living palms, 46% of females were immature, and 24% had not mated. In old rotting stems where eggs are laid and larvae develop, a mixture of 52% mated and 48% virgin females was found. Therefore, the pheromone together with the odour of rotting coconut stems signals a reproduction site to beetles, particularly mature females. In practice, the pheromone-baited traps will help in reducing the dissemination of gravid females, but will not affect directly the numbers of immature ones attacking palms. Our results show that when using pheromones for monitoring or controlling insects, the physiological status of the insects may have unexpected effects on the outcome.

Keywords

Oryctes monoceroscoconutpheromone trappingfemale reproductive systemsex ratio
Type
Research Paper
Information
Bulletin of Entomological Research , Volume 98 , Issue 6 , December 2008 , pp. 581 - 586
Copyright
Copyright © 2008 Cambridge University Press

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