IMPACT OF Elaeidobius kamerunicus (Faust) INTRODUCTION ON OIL PALM FRUIT FORMATION IN MALAYSIA AND FACTORS AFFECTING ITS POLLINATION EFFICIENCY: A REVIEW

Abstract

The oil palm pollinating weevil, Elaeidobius kamerunicus, has become the single most important insect pollinator of the commodity crop in Malaysia and Indonesia, 40 years after its introduction. However, in 2020, the average national oil extraction rate (OER) has decreased from 20.21% to 19.92%. The decline was attributed to the lower oil palm fruit bunch quality. This has raised concerns on the pollination efficiency of the pollinator. As such, the factors affecting the pollination efficiency of E. kamerunicus were thoroughly discussed in this review. Eight factors, which were categorised into intrinsic and extrinsic factors, were discussed in detail. Intrinsic factors discussed are the genetic make-up of E. kamerunicus and its population level. Meanwhile, factors such as planting materials, soil types, plant physiological condition, volatiles emission, diseases/predators threatening E. kamerunicus and climatic factors were discussed in the extrinsic factors. Methods for maintaining a healthy pollinator population were suggested, as well as an emphasis on future studies based on the shortlisted factors.

Factors Affecting Pollination and Pollinators in Oil Palm Plantations: A Review with an Emphasis on the Elaeidobius kamerunicus Weevil (Coleoptera: Curculionidae)

“…In Malaysia, Thrips hawaiiensis (Thysanoptera) and Pyroderces (Lepidoptera) are regarded as native oil palm pollinators [ 27 ]. However, according to reports by Lepesme and Syed as cited in [ 28 ], Pyroderces spp. has a strong preference for female inflorescences and is active for only two to three hours post-sunset [ 29 ], leading to the belief that these insects do not contribute to pollination services in oil palm.…”

“…Following its arrival in Malaysia between July and December 1980, E. kamerunicus was present in virtually all oil palm estates in Malaysia by April 1982 [ 58 ]. As there have been no further introductions since then, it is assumed that these pollinating weevils may have a limited genetic basis, leading to inbreeding depression and negatively influencing their pollinating efficiency [ 28 ].…”

“…The loss of progeny fitness is a major impact of inbreeding depression [ 59 , 61 , 62 ]. In a study of leaf beetles [ 61 ], inbreeding depression caused a decrease in larval and adult survival, a decline in reproductive output, and prolonged larval development, while other observations reviewed by [ 28 ] included a compromised immune system ( Formica exsecta ) and an impacted sex ratio ( Uscana semifumipennis ).…”

“…Meanwhile, ref. [ 65 ] suggested that the E. kamerunicus population introduced to Asia and South America may have experienced a genetic bottleneck, which is supported by [ 28 ] as the introduced weevils are originally from Western and Central Africa, and the introductions were made from a small number of weevils, resulting in a limited genetic base among these populations. This is congruent with the low haplotype number across all Asian weevil populations reported by [ 65 ].…”

“…Most populations in Indonesia were found not to result from inbreeding, suggesting that the introduced weevils have maintained a healthy genetic diversity. This phenomenon may be attributed to the “purging” of deleterious recessive alleles that are responsible for inbreeding depression, which can occur even in natural conditions [ 28 , 60 ]. This could explain the lack of inbreeding observed in the introduced E. kamerunicus populations in Southeast Asia [ 68 ].…”