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

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.

Agroecological practices in oil palm plantations: examples from the field

“…Can trapping actually help to control the pest in a satisfactory way alone or could it have a vicious counterproductive attraction? Allou et al (2008) demonstrated that synthetic pheromone and EFB as the co-attractant mimic Oryctes monoceros reproduction sites only, where males emit this specific aggregation pheromone. Immature females or those having just laid eggs need to feed on fresh palm tissue to initiate a new oogenesis process and are hence not attracted by the pheromone lure.…”

“…Immature females or those having just laid eggs need to feed on fresh palm tissue to initiate a new oogenesis process and are hence not attracted by the pheromone lure. Consequently, trapping can only have a partial effect in attracting insects and reducing their damage (Allou et al, 2008). Moreover, a trial was conducted in Indonesia, in order to investigate the spatial correlation between the resident population, pheromone traps and damages on palms .…”

Female mating failures in insects

“…The response of mated and virgin females varies as a function of the source of host volatiles (Knight, 2006; Landolt & Guédot, 2008). In rhinoceros beetles, nearly all females captured in traps baited with male‐produced sex pheromone are mated, compared with half of the females sampled at breeding sites where they oviposit (Allou et al., 2008). This contrasts with the Asian longhorn beetles where 100% of females captured in traps baited with male‐pheromone or host plant volatiles alone are mated, compared with 15% of mated females in traps with a combination of pheromone and host volatiles (Nehme et al., 2010).…”

Ovarian development of Agrilus planipennis: effects of age and mating status and influence on attraction to host volatiles

“…Female reproductive maturity (i.e., mating status and development of ovaries) has been shown to influence which host volatiles a female is attracted to; for example, reproductive maturity of female African rhinoceros beetles, Oryctes monoceros (Olivier), affects their orientation toward volatiles signaling feeding vs. oviposition sites (Allou et al, 2008). Grant et al (2010) suggested that because bark sesquiterpenes are released when hosts are stressed, they may act as an oviposition cue or attractant for females.…”