Effects of Rainfall, Number of Male Inflorescences and Spikelets on the Population Abundance of Elaeidobius kamerunicus (Coleoptera: Curculionidae)

Abstract

Elaeidobius kamerunicus was first introduced to Malaysia from Cameroon as an oil palm pollinator in 1981. Since then, oil palm pollination has improved and the need for assisted pollination has reduced. Fruit set development and fruit production also saw significant improvements, until a reported decline that began in the late 1980s. Several factors may have contributed to such decline, but most researchers believe it is due to the low E. kamerunicus population. Therefore, a study was conducted to determine whether the amount of rainfall and the number of male inflorescences and spikelets influenced the population abundance of E. kamerunicus in Ladang Lekir, Perak, Malaysia. Sampling was performed each month in oil palm subplots, three for each age of palm age, from October 2015 to September 2016. A total of nine spikelets (three from the top, middle and base of a male inflorescence) were randomly selected from each male inflorescence on each chosen palm. They were cut early in the morning to avoid the weevil's most active time, thus making collection easier. The number of weevils congregating on each spikelet was then counted. The average number of E. kamerunicus per hectare (ha) living on oil palms aged four and six were 21,086 and 25,712, respectively. The amount of rainfall and the number of male inflorescences and spikelets were found to positively correlate with the E. kamerunicus population. The number of male inflorescences showed strong correlation with the E. kamerunicus population. However, in-depth study is needed to determine the relationship between E. kamerunicus and fruit set.

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

“…One study has shown that the population of E. kamerunicus increases as the oil palm ages, which is related to the number of spikelets in the oil palm inflorescences. The older the oil palm, the higher the spikelets, and thus the higher the E. kamerunicus population [ 57 ]. The compactness of the flower, represented by the number and length of the spikelets, affects the population abundance per bunch of E. kamerunicus [ 57 ].…”

“…The older the oil palm, the higher the spikelets, and thus the higher the E. kamerunicus population [ 57 ]. The compactness of the flower, represented by the number and length of the spikelets, affects the population abundance per bunch of E. kamerunicus [ 57 ]. The length of the anthesising spikelets is positively correlated with the number of E. kamerunicus on the male inflorescences [ 32 ].…”

“…However, data on the optimum number of available spikelets required to maintain the abundance of the E. kamerunicus population is still lacking. The optimum number of E. kamerunicus per spikelet is reported to be between 15 and 30 for good pollination, although varying reports exist [ 52 , 57 ]. These varying reports could be due to the genetic material of the oil palms, as well as soil types and palm age [ 57 ].…”

“…The optimum number of E. kamerunicus per spikelet is reported to be between 15 and 30 for good pollination, although varying reports exist [ 52 , 57 ]. These varying reports could be due to the genetic material of the oil palms, as well as soil types and palm age [ 57 ]. To ensure sufficient pollen supply, it is recommended to have at least two male palms per hectare in plantations with a high sex ratio, and assisted pollination can be used in plantations with insufficient male inflorescences [ 45 , 102 ].…”

“…Heavy rains can decrease pollination efficiency because they reduce inflorescence visits. While there may be a low rate of pollen transfer, pollen can accidentally be removed from the weevils’ bodies [ 27 , 57 , 76 , 116 ]. A reduction in pollen densities carried on the weevil’s body would mean an inadequate pollen supply, resulting in a low oil palm fruit set [ 57 , 76 , 117 ].…”