J. Sci. Dev. 2009, 7 (Eng.Iss. 2): 159 - 164 HA NOI UNIVERSITY OF AGRICULTURE THE STUDY ON BIOLOGICAL CHARACTERISTICS OF Brontispa longissima (GESTRO) (COLEOPTERA: CHRYSOMELIDAE) Nghiên cứu đặc điểm sinh học của Bọ dừa Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae) Ho Thi Thu Giang1, Satoshi Nakamura2 1Ha Noi University of Agriculture 2Japan International Research Center for Agricultural Sciences, Tsukuba 305-8686, Japan Corresponding author email: [email protected] TÓM TẮT Đặc điểm sinh học của bọ dừa Brontispa longissima (Gestro), loài sâu hại nguy hiểm đối với cây dừa đã được nghiên cứu trong phòng thí nghiệm ở nhiệt độ 25oC, ẩm độ từ 60 - 70%. Lá cây Typha angustifolia được sử dụng làm thức ăn cho bọ dừa. Thời gian giao phối kéo dài trung bình là 9,0 ± 1,3 phút. Thời gian trước trưởng thành kéo dài 22,5 ± 1,4 ngày. Trưởng thành cái sống trên 2 tháng và trung bình số trứng đẻ trong một đời của một con cái là 24,5 ± 4,4 trứng. Trưởng thành tập trung đẻ trứng vào ban đêm. Thời gian phát dục của trứng ngắn hơn khi nhiệt độ tăng, ẩm độ trên 95% tỷ lệ nở của trứng cao. Sâu non có 4 tuổi. Từ khóa: Brontispa longissima, sinh học, tập tính giáo phối, thời gian phát dục. SUMMARY The adult biology and developmental time of egg coconut hispine beetle, Brontispa longissima (Gestro), the most serious pest of coconut palms were studied in the laboratory at 25oC, 60-70% RH and 12L: 12D photoperiod. Leaves of Typha angustifolia Lesser were recommended to use as food for mass rearing. The duration of mating of B. longissima averaged 9.0 ± 1.3 min. The pre-oviposition of adult was 22.5 ± 1.4 days. Female laid on average 24.5 ± 4.4 eggs, adult longevity was over 2 months. Egg deposition of B. longissima is higher during the night time compared to the day time. Larvae in general have 4 instars. Temperature had a significant effect on developmental time of larvae, the higher temperature, the shorter duration of development. High humidity (>95%) is suitable for survival rate and development of B. longissima eggs. Key words: Biology, Brontispa longissima, development time, mating behaviour. 1. INTRODUCTION macroeconomic and environmental impacts. This species has spread to new areas at a rapid pace in The Coconut plant plays a major role in the the region. B. longissima attacked coconut palm economy of many countries in the Asia and the (Cocos nuciferae), oil palm (Elaeis guineensis), Pacific region by providing food and income from sago palm (Metroxylon sagu), beetle palm (Areca coconut products. This important crop contributes catechu) and ornamental palm. to the economy and livelihood of small holders. Fu The scientific information on this pest has had Yuenguan et al., 2004 showed that these economies few reports. In order to better understand this are threatened due to a serious outbreak of the species, the following researches were carried out Coconut hispine beetle Brontispa longissima to investigate the biology and life history of B. (Gestro) that is one of the potentially most serious longisima such as developmental time, oviposition, pests of coconut palms. The beetle can cause mating duration and adult longevity. Understanding significant production losses, and high infestation basic information on the beetle may play an levels may result in tree death (Voegele, 1989). important role for developing biological control Thus, lost coconut palms may have serious methods against the beetle. 159 The study on biological characteristics of Brontispa longissima (GESTRO)... 2. MATERIALS AND METHODS leaves on which they were oviposited and put in petri dishes with a piece of filter paper, moistened 2.1. Host rearing by cotton tissue. The humidity inside of the Adults of B. longissima were collected in petridish was measured using data logger. Thailand in 2007. They were kept at 25 ± 1°C Moistened set up 60% and 95%. They were kept at temperature, 60 ± 10% Humidity and L12:D12 25°C, L12:D12 photoperiod. photoperiod in the Japan International Research 2.6. Effect temperature on survival and Centre for Agricultural Sciences (JIRCAS), developmental time of eggs Tsukuba, Japan. The adults were fed on leaf material of Typha angustifolia Lesser Bulrush, Eggs of B. longissima were put in Petri dishes which was replaced every two days. (diameter: 3.5 cm) with a piece of moistened cotton and placed in incubator set at 20, 25 and 30°C. 2.2. Mating behaviour Every day it was checked twice for recording One pair of B. longissima newly emerged was whether the larvae had hatched to determine egg kept in vials with typha leaf. Mating time and survival and development time of the eggs. mating duration were recorded from observations 2.7. Larval instar distinguishing which took place every 2 hours from 8:00 am. to 8:00 pm.and every 5 min. Measurement of the lengths of Mandible and Cercus of larval instars everyday under 2.3. Time egg deposition stereoscopic microscope. Recorded number of eggs laid and observations in 12 days subsequently. This was checked twice a 3. RESULTS AND DISCUSSION day (8:00 am. and 20:00). Light set at 12L: 12 D (Light turn on at 8:00 am. and turn off at 20:00). 3.1. Frequency of mating duration 2.4. Oviposition Using a 5 min. interval classification 15 females Newly emerged males and females were kept of B. longissima observed copulation 45.16% of the together in glass vials (1.5 cm x 3.5 cm, diameter x females had a relatively mating duration 6-10 min height). They were provided with fresh typha and only 12.90% mating duration 11- 15min. The leaves T. angustifolia for feeding and oviposition, duration of mating average 9.0 ± 1.3 min (Fig. 1). which were replaced every 2 days. The numbers of Observations of 49 pairs of the mating behavior of eggs deposited on the leaf and on the walls of glass B. longissima in laboratory showed that the male and vials were counted every day. female could mate several times. There were a greater number of mating pairs in the afternoon 2.5. Effect of humidity on egg survival (14:00-18:00) than in the morning (8:00-12:00) Eggs of B. longissima were removed from typha (65.9 and 34.1%, respectively) (Fig 2.). 8 7 6 5 4 3 2 females of Number 1 0 0 - 5 6 -10 11-15 16 - 20 Mating duration (min.) Fig. 1. Distribution of B. longissima females according to mating duration and egg deposition 160 Ho Thi Thu Giang, Satoshi Nakamura 20 15 pair 10 5 of mating Number 0 8:00 10:00 12:00 14:00 16:00 18:00 Time in day Fig. 2. Diel periodicity of mating of Coconut beetle B. longissima 3.2. Oviposition Mean pre-oviposition was 22.5 ± 1.4 days The active oviposition B. longissima had also (mean ± SE). Number of eggs laid/female/day been studied and results are illustrated in Fig. 3. decline as females aged (Fig. 4). Eggs were laid The data show a total number of eggs were laid irregularly. The ovipositional peak occurred at 28 (179) and number of egg deposition was days after emergence. The mean total number of significantly higher during the night time (110) eggs laid by individual female was 24.5 ± 4.4. compared to the day time (69) (binomial test P = O’Connor (1940) reported that pre-oviposition is 74 0.003). days or one to two months (Waterhouse, 1987). The The result here may be indicated that the female of B. longissima lays an average of 5 - 100 active oviposition as well as active fly and attack eggs (O’Connor, 1940). coconut plants at night as reported by O’Connor, It is can be seen that there is difference in 1940. Also, according to Fenner (1984), the adults fecundity may be caused by factors that the effects are slow - moving and reluctant to fly during the of the different host plant are food for adult or day. effect of different temperatures, humidity. 120 100 80 60 40 9 20 Number of egg laid egg of Number 0 Night time Day time Fig. 3. Number of eggs deposition 161 The study on biological characteristics of Brontispa longissima (GESTRO)... 2 1.6 1.2 0.8 0.4 0 laid/day/female eggs of Number 1 16 20 24 28 32 36 40 44 48 52 56 60 65 69 Days after emergence Fig. 4. Mean daily oviposition of Coconut beetle B. longissima 3.3. Effect of humidity on egg survival survival of the eggs is much higher at the high humidity, it may aid rearing and maintaining the Voegele (1989) reported that natural egg beetle in the laboratory. hatchability is low as well. However, we consider The survival rate in the egg stage ranged that which factors are affected on egg hatchability. from 57.5 - 88% at 20 - 30ºC (Fig. 6) Percentage From this data humidity had a significant positive hatchability was highest at 20ºC. The mean effect on the survival rate of eggs (Fisher’s exact developmental period of egg decreased probability test, P<0.001). significantly as the temperature increased between The survival rate of eggs was 89.7% at 20 to 30ºC (F = 1508.55; df = 2; 219; P< 0.0001). humidity 95%, while it dropped to 3.1% at Developmental time was between 8.9 ± 0.06 days humidity 60% (Fig. 5). These results indicated that at 20ºC and 3.6 ± 0.061days at 30ºC (Fig.7).