| Biological characterization of pollinating weevil, Elaeidobius kamerunicus Faust was studied in the laboratory conditions and its pollination behavior was observed in the oil palm field in Hainan Province, P.R. China.(1) Visiting insects and main pollinators of oil palmOur results showed that E. kamerunicus was the most important insect pollinator of oil palm, Elaeis guineensis. Other insect species, such as Apis sp. and several insect species of Noctuidae, were preliminary identified as the pollinators. Atheta sp., Thrips hawaiiensis Morgan and several insect species of Nitidulidae were subservient to the flowers of oil palm.(2) Biological observation on E. kamerunicus in the laboratoryIt is clear that Elaeidobius kamerunicus is the most efficient insect pollinator of oil palm. Its biological and morphological characteristics in the laboratory were observed systematically. The insects were fed on the male inflorescences of oil palm under the laboratory conditions:24-28％, RH75%-95%, and photoperiod12L:12D, and then were recorded every4hours. The length, width and weight of insect body at different developmental stages were measured. The results showed the average periods of egg, the larval, the pre-pupal and pupal of E. kamerunicus were16.00±0.71h,2.63±0.05d,3.21±0.37d, and2.21±0.41d, respectively, and one generation period was13.67±0.75d. The body length and weight of the first instar larvae were1.70±0.08mm and0.0006±0.0001g, the third instar larvae were2.88±0.06mm and0.0021±0.0001g, and pupae were2.17-3.05mm and0.0015-0.0028g, respectively. The adults showed sexual dimorphism and the sex ratio (female to male) of the offsprings was1.65:1. All above data may provide a basic theoretical support for E. kamerunicus protection and utilization.(3) Behavior of E. kamerunicus after laboratory rearingThe mating and oviposition behavior of E. kamerunicus were observed in the laboratory. The results showed that a complete mating of E. kamerunicus involved three stages:before mating, during mating and after mating. There were many times for ejaculation in the whole mating process. To E. kamerunicus, the mean time for one copulation lasted437.33s; the time for pair-bonding before ejaculation was22.33s with each ejaculation of5.33s; and the time of post-copulatory guarding was85.67s. After the copulation, females bored a hole, and laid one egg each hole. (4) Pollination behavior of E. kamerunicus on oil palmIn this experiment, pollination activity of E. kamerunicus was observed in the oil palm field in Hainan, China. The number of weevils visiting the inflorescences were assessed by the use of sticky traps encircling the inflorescences, and by counting the weevils present on samples of spikelets. The anthesising male inflorescences were attractive to the weevils for six days, compared to that of female inflorescences for five days. The weevil population peaked on the third day of anthesis on male inflorescences, and on the second day of anthesis on female inflorescences. The activity of the weevils on the day with the highest population during anthesis, recorded an inactive period between7:00and8:00and consistent activity between11:00and12:00, and17:30and18:00. The number of female adult weevils was always greater than the male adults, irrespective of whether male or female inflorescences. To increase the population of E. kamerunicus in Hainan, some steps should be taken. These steps include release of adult weevils in oil palm plantations in Hainan, and control of the weevil’s pests and predators such as rats and harmful nematodes. |
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