International Journal of Advanced Science and Research International Journal of Advanced Science and Research ISSN: 2455-4227 Impact Factor: RJIF 5.12 www.allsciencejournal.com Volume 3; Issue 2; March 2018; Page No. 120-127 Population dynamics and host preference of a major pest, Scirpophaga incertulas Walker (Pyralidae: Lepidoptera) Souren Dutta1, Nayan Roy2* 1 Department of Zoology, Rabindra Mahavidyalaya, Champadanga, Hooghly, Burdwan, West Bengal, India 2 Department of Zoology, MUC Women’s College, Burdwan, West Bengal, India Abstract In this modern era with increasing human population there is a need to increase rice production per unit of land through sustainable management strategies. The stage-specifc life table study of this notorious rice pest, Scirpophaga incertulas, also known as yellow stem borer (YSB), will be useful for their sustainable ecological management in the field. It helps to understand their population dynamics for safer and ecofriendly management of the pest. The life table study of S. incertulas on rice (Oryza sativa [R]) and non rice [NR] weed (Echinochloa colona) showed four distinct stages with five larval instars and represent similar pattern of development with significant variations (P< 0.001). The gross reproductive rate (GRR) and net reproductive rate (R0) on R was significantly higher than NR weed which ultimately influence the fecundity. The rm, λ, Tc and DT of S. incertulas on R plant was significantly higher than NR weed. These differences in the demographic parameters are due to the variation in their nutritional quality of respective kind of host plants. So, for first step management of the notorious insect pest, S. incertulas, is very essential to weed the NR areas which ultimately would reduce the population size of the pest in the field condition. Their further management strategies may include different ecofriendly control measures guided by their population parameters. At this point population dynamics based ecofriendly approaches would obviously help in the conservation of natural enemies which would bring down the pest load below economic threshold (ET) and eventually lower broad spectrum pesticides use which generally brings pest resurgence and pest resistant problems. There may be few limitations in the methodical scientific study but this particular population dynamics based study somehow has triple- E (Environmental, Ecological and Economical) sustainability for any kind of pest management in near future. Keywords: Scirpophaga incertulas walker, YSB, Oryza sativa, Echinochloa colona, nutritional quality, life table, population dynamics, ecological management. 1. Introduction this pest attack by larval feeding and subsequent inter-nodal Rice, Oryza sativa L. (Family: Poaceae) is the most important penetration during vegetative and reproductive stage and food crop for more than two thirds of the population of India finally results in the characteristic symptom of dead heart and more than fifty percent of the world population [1-3]. India (DH) and whitehead (WH) at vegetative and reproductive is the second largest producer of rice in the world. Rice growth stage of rice plant respectively [18, 33]. Control consumes almost 50 per cent of irrigation water and the water strategies in current use against the pest are largely based on crisis is the greater threat to rice cultivation in India [4]. chemical insecticides but intensive use creates an ecological Another threat is the various types of insect pests those ravage imbalance through destruction of non-target beneficial insects, the rice fields throughout the world including tropical and and accumulation of toxic residues in the environment [34-40]. subtropical Asia [5-10]. They are the most important biological Also the resistant rice varieties and the use of pheromones as constraints limiting rice yield potential and reflect large scale well as natural enemies like predators and parasites in the reduction both in quality and quantity [5, 11]. The rice crops of management of YSB population have not been promising [17, Asia are dominated by the rice bugs belong to the genus 19, 25, 26, 30, 31, 41]. Leptocorisa [5, 10-13] and yellow stem borer (YSB) or paddy In this modern era with increasing human population there is a stem borer (PSB) belong to the genus Scirpophaga [6, 7, 14-20]. need to increase rice production per unit of land through They also aggregate on non rice (NR) weeds (Echinochloa economically and environmentally sustainable strategies. spp. Paniculum spp. Cyperus spp. etc.) grown in and around Today, the population dynamics based ecological pest paddy fields [21]. As rice is the staple food of most Asians, management (EPM) are very essential for timely adoption of there is a need to control or manage populations of those different IPM strategies. Life table study is a central theme in pests. The YSB, Scirpophaga incertulas Walker (Pyralidae: ecological research to understand the temporal and spatial Lepidoptera) is one of the major pests in all rice producing patterns in population dynamics which can be used for modern areas particularly in south East Asia [7, 15, 19, 22-31]. Only YSB EPM [42-49]. Life tables are used to calculate the vital statistics shares about 89.50% of the total rice borer population in West on pest population dynamics and also give a comprehensive Bengal, India [14, 18, 32]. Recurrent rice grain yield loss due to description of the survivorship, development, fecundity, 120 International Journal of Advanced Science and Research mortality and life expectancy [43, 44, 46-50]. This can also stepwise examine the pest population data during Boro season describe duration and survival at each life stage which allow in 2016 and 2017. Primary culture was established by prediction of the population size and age structure of a pest collecting the pupae of S. incertulas from the same paddy field insect at any time [42, 45-49]. Life table is widely useful and was kept in a mating cage of 20×10×2 cm. After the technique in insect pest management, where developmental emergence, the male and female adults were allowed for stages are discrete and mortality rates may vary widely from mating and the mated females were released into the cage of one life stage to another [46-49, 51]. It is very helpful to determine size 90×210×150 cm containing selected R and NR weed the key mortality factors responsible in a particular stage separately. After oviposition, the R and NR weed leaves within which the maximum mortality of the pest is obtained containing the egg masses were clipped off and their bases [43, 44, 46-50]. Thus, by knowing such most vulnerable stages were wrapped in moist cotton to keep them fresh until from life table, one can make time based application of hatching. These were then placed on a moist filter paper in the different control measures for proper management of the pest Petri dishes of diameter 10.5 cm, and were exposed for population. Rizvi et al. [52] were conducted both, age-specific embryonic development in laboratory condition (27±1°C, (horizontal) and stage-specific (vertical) life-table of cabbage 65±5% RH and a photoperiodism of 12:12 [L:D]). The dates butterfly, Pieris brassicae on various cole crops. But, in my at which eggs hatched were recorded. On hatching, first instar current study, I have used only the stage-specifc life table larvae were detected from the egg mass with the help of hand approach as it is with lower biasness and more useful in the lens and collected with the help of camel hairbrush and the field condition [46-49]. There are several reports on the life table immature stages of the borer were reared on the selected host study of different pest species were conducted [50, 52] but few plants separately for the constraction of their respective life of them concerned with the influence of host phytochemicals table. Developmental time and survivability of S. incertulas in their life table parameters [46, 47, 49]. Only few studies have was determined on rice (R) and non-rice (NR) weed under the been made in the past to correlate the incidence of YSB with same laboratory condition as described by Dutta and Roy [5]. environmental factors as well as their population dynamics Duration and survival for each stage were recorded in the and ecofriendly management practises [7, 15, 16, 19, 22-31]. So, laboratory condition of three generations for construction of there is a need to develop a standard cohort life tables on both their stage-specific life table as described by Roy [46-49] as well R and NR weed to understand their population dynamics for as Dutta and Roy [5]. safer and ecologically sustainable management of the pest. 2.4 Life table parameters 2. Materials and Methods The construction of S. incertulas life table includes several 2.1 Host Plants parameters which were calculated with the formulae of Rice (R) [Oryza sativa L.; Family: Poaceae; cv. Shatabdi, IR- Southwood [42, 43], Ricklefs and Miller [53], Carey [44, 45], Krebs 36 (Boro season)] [1, 2] and Non-rice (NR) weed [Echinochloa [54], Price [55], and Schowalter [56]. These parameters include [21] colona, Family: Poaceae] were collected randomly from probability of survival from birth to age x (lx), proportion the pesticide free controlled agroecosystem during 2016 and dying each age (dx), mortality (qx), survival rate (sx) per day 2017 near Chinsurah Rice Research Center (22°53' N, 88°23' per age class from egg to adult stages. Using these parameters, E), Hooghly, West Bengal, India. the following statistics like, average population alive in each stage (Lx), life expectancy (ex), exponential mortality or 2.2 Phytochemical analysis killing power (kx), total generation mortality (K or GM), The freshly harvested rice (R) and non-rice (NR) weed were generation survival (GS), gross reproductive rate (GRR), net collected randomly from the same fields.