Asian J Agri Biol, 2013, 1(1):2-7. LIFE TABLE STUDIES OF TRILOCHA VIRESCENCE (BOMBYCIDAE: LEPIDOPTERA) ON FICUS NITIDA Muhammad Asif Aziz 1, Ayesha Iftkhar 1 and Muhammad Hanif 2 1Department of Entomology, PMAS-Arid Agriculture University Rawalpindi, Pakistan 2Department of Mathematics and Statistics, PMAS-Arid Agriculture University Rawalpindi, Pakistan ABSTRACT The life table of Trilocha virescence was constructed in the laboratory which is a serious Lepidopterous pest of Ficus nitida . The study declared different impact of larval and adult mortality on the population. Pre reproductive mortality was 30% and 70 percent of the individuals’ survived up to the maturity and took part in reproduction. Larval mortality was greater in 1 st instar than all other stages. No mortality was observed in 4 th and 5 th larval instar in subsequent stages. High mortality during 1 st instar may exert significant negative effect on the insect population and may be best used for applying control tactics. The net reproductive rate of the insect was 45.44 per individual per generation. Keywords: Trilocha virescence , stage specific, cohort, life table, life expectancy, mortality rate, survivorship INTRODUCTION revealing the maximal growth potential of a population (Gabre et al, 2004). Life tables used Computing life tables is a fairly current can make quantitatively and qualitatively approach used by entomologists to study the evaluation of various host plants insects’ population dynamics. With the recent (Ambegaonkar and Bilapate, 1981). emphasis on population dynamic studies of Two kinds of life tables have been developed: insects, the usefulness of life table in this area (1). ecological life tables for natural is becoming more recognized. A life table is a populations of animals; and, (2) life tables for tabular device which describes for every laboratory populations of animals. They may be particular age of interval. further categorized as horizontal or age-specific In ecological study, life table is an important life tables and vertical, or time-specific life analytical tool, which provides detailed tables. The horizontal life table usually is made information of population dynamics to generate from data obtained by studying all or a portion simple but more informative statistics. It also of a population belonging to a single gives a comprehensive description of the generation. Vertical life tables involve analysis survivorship, development and expectation of of the age structure of a population life (Ali and Rizvi, 2007; Yzdani and Samih (Southwood, 1966). Age specific life tables 2012; Gabre et al., 2004). Life tables may be provide a concise summary of mortality and used to study inherent differences in the reproductive schedules and can help explain survivorship and reproductive strategies of why certain species proliferate in particular populations under different ecological regimes environment (Afrane et al., 2007). Trilocha (Afrane et al., 2007). Life table, studies provide virescence is a member of family Bombicidae an opportunity to assess and evaluate the and important pest of Ficus nitida, which is an impact of specific mortality factors acting on ornamental shurb of medium size. T. viresence insect population (Harcourt, 1969; Bellows et can be considered as a voracies feeder of Ficus al ., 1992; Mohapatra, 2007). It can also give nitida leaves. Its larvae in 4 th and 5 th stages are information about the changes which occur capable of eating more than one leaf per day during the developmental stages and their and can cause severe defoliation of the plant in relationship with different environmental case of severe infestation. So the studies were factors (Atwal and Bain, 1974). Life tables conducted with the aim to find out constructed using laboratory data collected survivorship, mortality, life expectancy and under controlled conditions and are useful in reproductive rate of Trilocha virescence on Ficus nitida. *Corresponding author: e-mail: [email protected] 2 Asian J Agri Biol, 2013, 1(1):2-7. MATERIALS AND METHODS Survival Fraction of a particular stage = [l x of a particular stage] / [l x of subsequent stage] Trilocha virescence culture: For conducting life table of T. virescence under ambient Mortality Survival Ratio (MSR): MSR gives condition, its egg batches were collected from the information regarding increase in the Ficus nitida and reared in Biological Control population which can occur in a specific stage Laboratory, Department of Entomology, PMAS if the mortality had not occurred in that stage Arid Agriculture University, Rawalpindi. These and was calculated by the using the equation: eggs were kept in petri dishes provided with Mortality Survival Ratio of a particular stage = slightly moistened filter papers and allowed to [Mortality in a particular stage] / [l x of hatch. From these batches 100 newly emerged subsequent stage] larvae were selected and shifted in petri dishes with the help of camel hair brush. Each petri Indispensable Mortality (IM): It indicates the dish was provided Ficus nitida tender leaves as that type of mortality which can be avoided if a larval food. All transferred larvae were the factors responsible for it are not permitted checked daily and their molting to the next to operate, whereas subsequent mortality stage or mortality were recorded carefully. factors are operating. Indispensable mortality Subsequent stages like pupa and adult were was calculated by the formula: also checked. After the emergence of adults, Indispensable Mortality = [No. of adults male and female were separated. Pairs were emerged] × [MSR of a particular stage] made, and each pair was placed in a separate petri dish. Adults were provided with special K-values: It is a mortality factor which has diet that includes water, methyl paraben, vital role in determining the increase or insect’s vitamin and sugar. Small pieces of decrease in number of individuals from one cotton soaked in the diet were placed in the generation to the next. The difference between petri dish until the adults completed their lives. ‘log l x’ of two successive insect stages reflects Dead males were replaced with the new ones. k-values, which can be used to obtain the total Fecundity and survival rate of each female generation mortality (K) as under: were recorded until their death. K = k L1 +k L2 +k L3 +k L4 +k L5 +k P Where, k L1 , k L2 . k L3, kL4 , k L5 and k P are the k- Life table Construction values at first instar, second instar, third instar, Stage Specific Life Table: For calculating this fourth instar, fifth instar and pupal stage of life table, stage specific data regarding Trilocha virescence. mortality and survival of different insect stages were taken from the age specific life table. Age Specific Life Table: The larvae were Following parameters were used to compute observed daily to determine the dead and alive stage specific life table. ones. Following parameter were used to x = Age of the insects in days construct the age specific life table Trilocha lx = Number surviving at the beginning of each virescence on Ficus nitida. interval, out of 100 x = Age of the insects in days dx = Number dying during the age interval, out lx = Number surviving at the beginning of each of 100 interval, out of 100 The information from above assumptions was dx = Number dying during the age interval, out used to compute different life table parameters of 100 as follows: 100q x = Mortality rate at the age interval x and Apparent Mortality (100q x): The information calculated by using formula regarding number of insects dying as a percent 100q x = [d x / l x] × 100 of number entering a particular stage can be To calculate e x, two other parameters like L x obtained from the apparent mortality, which and T x were also computed can be calculated as: Lx = Number of individuals alive between age Apparent Mortality = [d x / l x] × 100 Survival Fraction (Sx): The information x and x+1 obtained from the apparent mortality can be use Lx = l x+1 (x+1)/2 d to calculate survival fraction of each stage by Tx = The total number of individual of x age applying the formula: units beyond the age x 3 Asian J Agri Biol, 2013, 1(1):2-7. Tx = l x + (l x+1) + (l x+2)………..+ l w exhibited a slight increase in early days (up to rd Here, l w = Last age interval 3 day), after that it showed a steady declining ex = Expectation of life or mean life for trend (Fig. 1). individuals of age x, which was calculated by using following equation Stage specific life table of T. virescence ex = T x/l x Maximum apparent mortality was observed in first larval instar which declined slowly in later Cohort Life Table of Trilocha virescence : instars and reached to zero in 4 th instar to The larvae were observed daily to determine onward including pupal stage. The survival the dead and alive ones. Following parameter fraction was lower in earlier instars as were used to construct the life table of Trilocha compared to the later instars. Minimum virescence on Ficus nitida. survival fraction was observed in 1 st instar x = Age of the insects in days which started increasing from 2 nd instar and th lx = Number surviving at the beginning of each reached maximum at 4 instar. Mortality interval, out of 100 survival ratio, dispensable mortality and K- dx = Number dying during the age interval, out value showed the same trend as was seen in of 100 apparent mortality; their values were highest in st nd 100q x = Mortality rate at the age interval x and 1 larval instar, started decreasing from 2 calculated by using formula instar and reached to zero in the 4 th instar 100q x = [d x / l x] × 100 (Table 1). To calculate e x, two other parameters like L x and T x were also computed Cohort Life Table of T.