Olenecamptus Bilobus (Fabricius) (Coleoptera: Cerambycidae)
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Proc. Indian Acad. Sci. (Anim. ScL), Vol. 91, Number 3, May 1982, pp. 249-257. © Printed in India. Life and fecundity tables for the longicorn beetle borer, Olenecamptus bilobus (Fabricius) (Coleoptera: Cerambycidae) TN KHAN and P K MAITI Zoological Survey of India, 34, Chittaranjan Avenue, Calcutta 700 012, India MS received 18 July 1981 ; revised 30 December 1981 Abstract. The present paper deals with the life and fecundity tables for the cerarnbycid borer, Olenecamptus bilobus (Fabricius). Under a given set of condi tions and food supply, the population of this species increased with an infinitesimal and a finite rate. The population increased by 20 '41 times between two successive generations and 86·42 days were taken to complete one generation. The adults constituted only 1·29% to the population of the stable age, while eggs, larvae, pupae and dormant adults contributed to the extent of 24,95,68'22,4'38 and 1'16% respectively. Keywords. Life and fecundity tables; Olenecamptus bilobus (Fabricius); Artocarpus chaplasha Roxb.; stable age-distribution. 1. Introduction The longicorn beetle borer, Olenecamptus bilobus (Fabricius), is found predomi nantly in the Oriental region with an extended distribution up to the Papuan and Malagasy subregions. The species is one of the most common sap-wood borers of a number of dead or dying timber yielding plants. The bionomics and life history of this species have been dealt with by Khan and Maiti (1980). The observations reported here, are concerned with the life and fecundity tables, including the stable age-distribution of the species. The infinitesimal (r.) and finite (A.) rates of increase, net reproductive rate (R.) and the mean generation time were the basic parameters used in the present communication to assess the popu lation growth in the laboratory. 2. Material and methods The present study was based on the material collected during the period of 1978-80 under a research project on the" Ecological interaction and economic status ofthe xylophagous insects ofthe Islands of Andaman and Nicobar ", under the guidance of'one of us (P K Maiti). During the course of the study, a number of logs of Artocarpus chaplasha Roxb., infested with the immature stages of O. bilobus, 249 P .(8)--4 250 T N Khmt and P K MaW was collected from several field sites of South Andaman and held in galvanized iron cages (70 cm x 37ern x 37 cm) for the emergence of the adult beetles in the laboratory. The newly emerged beetles were sexed and 50 pairs of males and females were each separately kept ill glass breeding-cages (36cm x22cm x 22cm), containing a layer of moist sandy soil at the bottom. Moist sandy soil was however, kept to minimise the loss of moisture from the breeding-cages. The beetles were provided with fresh green leaves and twigs of Ficus religiosa L. for food and freshly cut billets, measuring 25.... 30 em in length and 8..., 12 em in dia meter, of Artocarpus chaplasha Roxb. for oviposition, both ofwhich were renewed everyday between 900 and 1000 hr 1ST. The number of oviposition slits on the billets was counted and the total number of eggs laid thereon was recorded. Each day, the infested billets from the breeding-cages were assigned a batch.. number and placed in a galvanized iron cage (similar to those used for rearing the immature stages collected from the field sites), containing a layer of moistsandy soil at the bottom. In this case, however, the moist sandy soil was used to pre vent over desiccation from the infested billets, so that they could retain the mois ture content for a longer period for proper development of the progeny. Beginning from the third day following oviposition up to the completion of development of the progeny, three sample billets were taken out and dissected every alternate day between 1200 and 1400 hr 1ST, to study the development of egg, larva and pupa and other relevant phenomena. The adults, which emerged on a particular day, were transferred to separate cages for oviposition to determine the age-specific fecundity. The average fecundity of the females on subsequent days was recorded until all the females died, Since, the sex-ratio was 2~ : 10- (based on 1600 adults), the number of eggslaid per female was multiplied by 2/3 to get the number of female births (mz). Life and fecundity tables were constructed according to Birch (1948), elaborated by Howe (l953), Laughlin (1965) and Atwal and Bains (1974). The innate capacity of increase (r",) and finite rate (A.) were calculated. The values of x (pivotal age in days), lz (survival of females at different age inter vals), and m, (number of female progeny per female) were worked out. Observa tions were also made on the stable age-distribution (per cent distribution) of various age groups by calculating the birth-rate and death-rate when reared in a limited space. During the course of these studies in the laboratory, the maximum and minimum temperatures recorded were 29.7° C and 26· 5° C respectively, while the relative humidity prevailed between 67' 5% and 93 '0%. 3. Results and discussion The maximum duration of incubation, development of larva, pupa and dormant adult has been observed to be 5, 50, 15 and 7 days respectively. Present observa tions on the duration of different developmental stages correspond strikingly with those observed by Khan and Maiti (1980). The number of individualS survived between different developmental stages is presented in table 1. From the data presented in the table the developmental survival rate has been estimated at 0·441. The figures of the mature females emerged from the immature stages have been pooled and a grouping of a day interval of age is employed. The results are Life and fecundity tables for Olenecamptus bilobus (Fabr.) 251 Table J. Survival of different developmental stages of Olenecamptus bilobus (Fabr.) on Artoceupus chap/asha Roxb. Number survived Batch No. No. of eggs Egg period Larva 1 period Pupal period Dormant (0-5 days) (6-55 days] (56-70 days) adult period (71-77 days) 1 379 334 235 197 173 2 456 390 274 230 205 3 503 434 303 263 233 4 412 348 244 201 175 5 517 429 29::1 247 204 6 450 396 280 233 206 7 391 341 241 200 178 8 342 286 203 169 149 9 401 341 238 199 l'i6 10 279 237 171 143 131 Total 4148 3536 2479 2077 1830 Table 2. Observed,as wen as, smoothed distribution of mortality amor.g the mature females of Olenecamptus bilobus (Fabr.). Age of the mature females Observed Smoothed Observed Smoothed in days I. I. d. d. x 1 854 854'00 24 45'68 '} 830 808'32 60 70'63 3 770 737'69 100 88'70 4 670 648'99 95 98'55 5 575 550'44 94 100-44 6 481 450'00 101 95'21 7 380 354'79 89 85'17 s 291 269-62 78 72'05 9 213 197' 57 60 58'25 10 153 139' 32 50 44'32 11 103 95-00 36 32'63 12 67 62'37 20 22-90 13 47 39-47 17 15'39 14 30 24'(8 16 9'92 15 14 1~-'46 14 14' 46 85·~ 854-00 -- ---=------ <O·20~. I 869'77e-o.018300U' X';= 1$-86; n = 12; P = 0'10; l = ' , 252 T NKltan and P K Maiti presented in table 2, where the customary symbols have been used, i.e., I. being the number of individuals which survive to the age x and d.th:enumber dying between the ages x and x + 1, so that in the present table, d, = I; - I.+!. The raw data have then been smoothed. For smoothening of the raw data, there are many a satisfactory method of which the following one seems to be most convenient: Defining /.l. as the force of mortality at the age x ; 1 d/~ - I dX = fl.· Now, if the force of mortality is assumed to be directly proportional to the age and u, = 2h2 M, where 2h2 is a constant, then by integration we get (1) Putting 1./10 = p., and Q. = 1 - p., " h. Q. = 1 - e- z', and, by differentiation we have, 2 dQ. = 21z Xe- h'" dX ; the probability of dying between the ages» and X + dlf being given by the right-hand member of the last equation. Then if M be the mean age at death, from which, by integration we get, M = JTc. 21z The observed and the smoothed values of I. have been presented in table 2, and in testing the agreement between the smoothed and observed I., Chi-Square .test is employed. It has been observed that )(2 = 15·86 and for n = 12, P = (0'20), 0,10, which shows that the fit is satisfactory. As a matter of interest, it might be worth mentioning that the same type of equation has been found to give an excellent fit in the case of 524 female vestigial Drosophila (data from Pearl and Parker 1924)and in case of 119 voles (Microtus agrestis) (Leslie and Ranson 1940). The life and fecundity tables for O. bilobus on Artocarpus chaplasha Roxb. based on the smoothed 1:. values, is given in table 3, which has been calculated from tl e following equation; (2) considering the 83rd, 84th; 85th, ..., 98th day of the pivotal age as the Oth, lst, 2nd, "', 15th day of the age of mature females (Vide table 2). In the present table, the I. column presents theadult survival rate only, while m; givesthenumber Life and fecundity tables for Olenecamptus bilobus (Fabr.) 253 Table 3.