Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al.

Temperature thresholds and thermal requirements for the development of the rice leaf folder, Cnaphalocrocis medinalis

Chintalapati Padmavathi1a, Gururaj Katti1, V. Sailaja1, A.P. Padmakumari1, V. Jhansilakshmi1, M. Prabhakar2, Y.G. Prasad2

1Directorate of Rice Research, Rajendranagar, Hyderabad, 500 030, India 2Central Research Institute for Dryland Agriculture, Santoshnagar, Hyderabad, 500 059, India Downloaded from Abstract The rice leaf folder, Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) is a predominant

foliage feeder in all the rice ecosystems. The objective of this study was to examine the http://jinsectscience.oxfordjournals.org/ development of leaf folder at 7 constant temperatures (18, 20, 25, 30, 32, 34, 35° C) and to estimate temperature thresholds and thermal constants for the forecasting models based on heat accumulation units, which could be developed for use in forecasting. The developmental periods of different stages of rice leaf folder were reduced with increases in temperature from 18 to 34° C. The lower threshold temperatures of 11.0, 10.4, 12.8, and 11.1° C, and thermal constants of 69, 270, 106, and 455 degree days, were estimated by linear regression analysis for egg, larva,

pupa, and total development, respectively. Based on the thermodynamic non-linear optimSSI by guest on December 1, 2014 model, intrinsic optimum temperatures for the development of egg, larva, and pupa were estimated at 28.9, 25.1 and 23.7° C, respectively. The upper and lower threshold temperatures were estimated as 36.4° C and 11.2° C for total development, indicating that the enzyme was half active and half inactive at these temperatures. These estimated thermal thresholds and degree days could be used to predict the leaf folder activity in the field for their effective management.

Keywords: biology, developmental thresholds, degree days, life table, pest forecast models Abbreviations: SSI, Sharpe-Schoolfield-Ikemoto; TN, Taichung Native Correspondence: a [email protected] Received: 16 February 2012 Accepted: 10 October 2012 Published 30 September 2013 Copyright: This is an open access paper. We use the Creative Commons Attribution 3.0 license that permits unrestricted use, provided that the paper is properly attributed. ISSN: 1536-2442 | Vol. 13, Number 96

Cite this paper as: Padmavathi C, Katti G, Sailaja V, Padmakumari AP, Jhansilakshmi V, Prabhakar M, Prasad YG. 2013. Temperature thresholds and thermal requirements for the development of the rice leaf folder, Cnaphalocrocis medinalis. Journal of Insect Science 13:96. Available online: http://www.insectscience.org/13.96

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Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al. Introduction would be useful in developing models for pre- dicting its distribution and abundance. The rice leaf folder, Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae), is the most Materials and Methods widely distributed and commonly found foli- age feeder in all the rice growing tracts of Study site Southeast Asia. An increase in C. medinalis The study was conducted at the Directorate of population could be attributed to the large Rice Research, Hyderabad, India. The climate scale cultivation of high yielding varieties, ap- in this region is predominantly semi-arid, with plication of fertilizers, and continuous use of mean temperatures in the range of 22–42° C, insecticides leading to outbreak of this pest in and an average annual rainfall of 896 mm. La- several countries, including India (Khan et al. boratory experiments were conducted using 1988; Shanmugam et al. 2006; Kaushik 2010). environmental chambers (MLR 350H, C. medinalis damages the rice plant through- SANYO Electric Company, Downloaded from out the crop growth period. The larvae fold the http://panasonic.net/sanyo/) set at constant rel- leaves longitudinally by stitching the leaf mar- ative humidity (60 ± 5%) and photoperiod gins and feed by scraping the green mesophyll (14:10 L:D). tissue from within the folded leaves. This http://jinsectscience.oxfordjournals.org/ feeding causes linear, pale white stripes that Stock culture of test insect result in membranous patches (Fraenkel et al. A stock culture of C. medinalis was main- 1981). Among the climatic factors, tempera- tained in the glasshouse at the Directorate of ture is the most important, as it has profound Rice Research on rice cultivar Taichung Na- influence on the development and survival of tive 1 (TN 1). Adults (10 to 15 pairs) collected insects. The rate of insect development is af- from the field were kept for oviposition on 25- fected by the temperature to which insects are to 30-day-old TN 1 plants covered with a cy- exposed (Campbell et al. 1974). Insects re- lindrical mylar cage (45 cm height, 14 cm by guest on December 1, 2014 quire a certain amount of heat units (degree diameter) and were provided with honey (20% days) to develop from one life stage to the solution) as food. Every alternate day, pots other (Gordan 1999). Quantification of the re- were changed and the plants with eggs were lationship between insect development and shifted to wooden cages for hatching and fur- temperature is useful to predict the seasonal ther development. Larvae were shifted to fresh occurrence and population dynamics of the TN 1 plants when the green leaves got ex- insects. The ability of an insect to develop at hausted due to the folding and feeding. After different temperatures is an important adapta- completion of larval development, the pupae tion to survive under various climatic were transferred to a separate cage for adult conditions (tropical, subtropical, and temper- emergence. Freshly emerged adults were col- ate). So far, there is no published report from lected daily, paired, and kept for oviposition. India on the effect of constant temperatures on Egg laying was observed after 3 days of pre- C. medinalis. Hence, in the present study, de- oviposition period. These eggs were used in velopmental periods of different stages of C. the experiments. medinalis were examined at 7 constant tem- peratures to estimate the temperature thresholds and thermal requirements, which

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Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al. Development and survival at different con- 35° C, eggs were kept at ambient temperature stant temperatures (25 ± 5° C), and neonate larvae were shifted to Response to temperature was assessed by ex- the environmental chamber for further devel- posing C. medinalis eggs to 7 constant opment after hatching. temperatures (18, 20, 25, 30, 32, 34, and 35° C) in separate experiments, 1 temperature at a Temperature thresholds and thermal re- time, and allowing the eggs to develop into quirements adults. C. medinalis eggs (0–24 hr old) taken The degree day model (thermal summation from the stock culture were placed in Petri model) was used to estimate the linear rela- dishes (9 cm diameter) at the rate of 10 per tionship between temperature and the rate of Petri dish in order to determine the develop- development of C. medinalis (Campbell et al. ment time. Fifty eggs at a time from the same 1974). The reciprocal of developmental period cohort were kept on filter paper moistened to for each stage was calculated to obtain the rate saturation with distilled water and sealed with of development (1/day) at each temperature. Downloaded from Parafilm. The experiment was repeated thrice, Linear regressions were used to determine the each time with eggs from different cohorts. relationship between developmental rate and Thus, a total of 150 eggs were observed at temperature and to estimate intercept (a) and

each temperature. The Petri dishes with eggs slope (b). These linear regression lines were http://jinsectscience.oxfordjournals.org/ were placed in environmental chambers main- extended to obtain the lower threshold for de- tained at different constant temperatures. The velopment (T0), which corresponds to the eggs were observed daily in order to determine intersection with the abscissa (Davidson 1944; the hatching rates and development time at Wigglesworth 1972). After determining the each constant temperature. After hatching, lower temperature threshold for each stage, the each first instar larva was shifted to a separate thermal constant (the number of degree days Petri dish with 4 tender leaves of TN 1. Fresh required for complete development) was esti- leaves from 25- to 30-day-old TN 1 plants mated from the reciprocals of the fitted by guest on December 1, 2014 were provided as food daily until pupation. regression line (b-1). Thus, the degree days re- Petri dishes were checked every day until the quired for the development of each life stage larvae pupated. Moulting periods and dead starting from egg to adult were estimated. larvae were recorded daily in order to deter- mine the developmental periods and survival Sharpe-Schoolfield-Ikemoto (SSI) model, a rates at each stage. Survival rates were calcu- non-linear thermodynamic model improved by lated based on the number at the beginning Ikemoto (2005, 2008) and Shi et al. (2011) on and end of each stage. After pupation, pupae the basis of the SS model developed by Sharpe were transferred to individual glass tubes to and DeMichele (1977) and Schoolfield et al. observe adult emergence. The number of (1981), was used. The SSI model expression is males and females emerged was counted to as follows: know the sex ratio. The emerged moths at each constant temperature were paired and re- leased for oviposition on 25- to 30-day-old TN 1 plants covered with cylindrical mylar cage. The number of F1 eggs laid by each female was recorded to know the average fecundity. Since the hatching percentage was very low at Where,

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Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al. r = Mean development rate (1/day) my of Sciences) was used to estimate the T = Absolute temperature (K) (237.15° K = 0° thermo-dynamic model parameters. C) R = Gas constant (1.987 cal/deg/mol) Rate isomorphy ∆HA = Enthalpy of activation of the reaction Rate isomorphy implies that the proportions of that is catalyzed by the enzyme an organisms developmental stage durations (cal/mol) are unaffected by temperature (van Rijn et al. ∆HL = Change in enthalpy associated with 1995). Since the rate isomorphy is a conse- low-temperature inactivation of the quence of equality among the lower enzyme (cal/mol) developmental thresholds, statistical methods ∆HH = Change in enthalpy associated with (Jarosik et al. 2002, 2004; Honek et al. 2003; high-temperature inactivation of the Shi et al. 2010) were used for comparing the enzyme (cal/mol) lower development thresholds. In this method, Downloaded from TL = Temperature at which the enzyme is ½ ratios of time spent in each developmental active and ½ low-temperature inactive stage (proportion) at different constant tem- (K) peratures were calculated from the data on the TH = Temperature at which the enzyme is ½ duration of development in a particular stage

active and ½ high-temperature inac- divided by the total pre-imaginal development http://jinsectscience.oxfordjournals.org/ tive (K) (egg + larva + pupa). Analysis of covariance TΦ = Intrinsic optimum temperature at which (ANCOVA) was performed using the arcsin the probability of enzyme being in the square root of proportion as a response varia- active state is maximal (K) ble and temperature as a covariate. A ρΦ = Development rate at the intrinsic opti- significant (p < 0.05) increase or decrease in mum temperature TΦ (1/day) the proportion was considered as violation of assuming no enzyme inactivation the assumption of rate isomorphy (Kuang et al. (days -1) 2012). by guest on December 1, 2014

In this model, the intrinsic optimum tempera- Life table ture (TΦ) for development is the most A life table was constructed according to Ju et important thermal parameter. Ikemoto (2005) al. (2011) using Morris-Watt model (Moris devised a program for estimating the parame- 1963), which is explained in the following ters in the SSI model. Shi et al. (2011) equation: modified this program and developed SSI-P, which runs on R statistical software (www.r- I = G2/N0 project.org) for faster estimation of the param- eters. Ikemoto et al. (2012) further improved derived from survival rates SE, SL1, SL2, SL3, this program, creating OptimSSI-P by incorpo- SL4, SL5, SP, SA, FPF, P♀, where I is the popu- rating the optimization algorithm of Nelder lation trend index; N1 is the number in next and Mead (1965), wherein TΦ was estimated generation; N0 is the number in the current along with its confidence intervals. In this pa- generation; SE, SL1, SL2, SL3, SL4, SL5, and SP are per, OptimSSI program (version 2.7), which the survival rates of eggs, 1st instar, 2nd instar, runs on R statistical software, version 2.15.0 3rd instar, 4th instar, 5th instar, and pupae, re- (provided by Dr Peijian Shi, Chinese Acade- spectively; SA is the survival rate of adults; F is the number of initial eggs; PF is the number

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of average eggs laid by females; and P♀ is the female proportion of adults.

Data analysis

The relationship between developmental peri- od (by stage and instar) and temperature was

analyzed following one-way ANOVA, and means were compared by Fisher’s least signif-

icant difference procedures using SAS, version 9.2 (SAS 2008). Linear regressions were per-

formed using SAS program.

Results Downloaded from

Development and survival Egg hatching varied from 16–82% in different Figure 1. Percent survival of different larval instars of Cnaphalocrocis medinalis at 7 constant temperatures. High quality constant temperatures, with minimum hatch- figures are available online. ing at 35° C and maximum at 25° C. Although http://jinsectscience.oxfordjournals.org/

there was egg development at 35° C, neonate larvae died during eclosion due to the expo-

sure to high temperature. The mean developmental time of eggs decreased from

9.51 days at 18° C to 3.10 days at 34° C, but increased to 3.58 days at 35° C, indicating a

non-linear response at extreme temperatures (Table 1). First, second, and third instars also by guest on December 1, 2014 showed similar trends of development with increases in temperature. C. medinalis com-

pleted development from egg to adult at all 5 temperatures ranging from 18–32°C. Beyond

34° C, development took place only up to fourth instar, and the larvae could not survive

thereafter. Survival of different larval instars of C. medinalis at 7 constant temperatures re-

vealed that the survival was highest at 25° C, Figure 2. Cumulative emergence of Cnaphalocrocis medinalis followed by 30° C (Figure 1). In the case of adults at each constant temperature . High quality figures are available online. first instar larvae, 68% survival was observed at 35° C because of non-exposure of neonate 64.10% in different temperatures. Cumulative

larvae to higher temperature, as these were adult emergence at these temperatures was shifted from ambient temperature to environ- best described by logarithmic curves with de-

mental chamber after hatching. Adult creasing increments over time. The continuous emergence occurred at temperatures from 18– lines in Figure 2 depict the curves best fitting

32° C (Figure 2). The proportion of females in the data. Emergence rates increased with in- the total adult population varied from 50– crease s in temperature, so that 100%

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Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al.

were 11.1° C and 455 degree days, respective- ly.

A thermodynamic non-linear model (Optim

SSI) was used to estimate the intrinsic opti- mum temperature (TΦ) for development.

Based on enzyme activity, other parameters were also estimated. In this program, the re-

sults of a linearized formula (Ikemoto and Takai 2000) based on the reduced major axis

method were also obtained. Lower develop- ment threshold values of 10.7, 10.9, 12.2, and

Figure 3. Linear and non-linear thermodynamic OptimSSI 11.2° C, with sum of effective temperatures of model fitted to the temperature dependent development of 71, 257, 116, and 445 degree days, were esti- Downloaded from Cnaphalocrocis medinalis. Circles indicate data points. Open cir- cles indicate data points outside the range of the linear model. mated for eggs, larvae, pupae, and total The curved line indicates the values of developmental rate pre- development, respectively (Table 3, Figure 3). dicted by the OptimSSI model, whereas the straight line denotes the values of linear fitting. The 3 open squares denote The intrinsic optimum temperature for the de- the predicted mean developmental rates at TL, TΦ, and TH. High velopment of eggs, larvae, pupae, and eggs to http://jinsectscience.oxfordjournals.org/ quality figures are available online. adult was estimated at 28.9, 25.1, 23.7, and emergence was attained earliest at 32° C (2 24.2° C, respectively. The lower and upper

days), followed by 30° C (3 days). More than confidence limits for each parameter and each 50% emergence was observed on the first day stage are presented in Table 4. Upper thresh-

at 32 and 30° C, and on the second and third old temperatures (TH) for eggs, larvae, pupae, days at 25 and 18° C, respectively. At 18° C, and total development were estimated at 35.7,

adult emergence was prolonged for about a 34.4, 37.5, and 36.4° C, respectively (Table 4). week. by guest on December 1, 2014 Rate isomorphy Temperature thresholds and thermal re- Estimates of parameters and standard errors

quirements using the Ikemoto and Takai method (2000) to Extrapolation of linear regression lines of de- test the rate isomorphy of immature stages of

velopmental rate and temperature showed that C. medinalis are given in Table 2. ANCOVA the lower threshold temperatures (T0) for each results showed that the interaction was signifi-

life stage of C. medinalis were between 5.0 cant (p < 0.0001). Thus, the slopes of the and 13.0° C (Table 2). The T0 of 11.0° C, regression lines of 3 immature stages, i.e., egg,

10.4° C and 12.8° C were estimated for the larva, and pupa, were different, and hence rate development of eggs, larvae, and pupae, re- isomorphy was not evident.

spectively. The T0 varied between larval instars, having the lowest value (5.0° C) for 3rd Life table and population trend index th instar and the highest (13.0° C) for 4 instar Based on the survival rate, sex ratio, and fe- (Table 2). The estimated thermal constants (K) cundity, a life table was constructed for C.

for egg, larva and pupa were 69, 270, and 106 medinalis in order to know the potential of degree days, respectively. The T0 and thermal population growth (Table 5). In the table, the

constant for total develo pment (egg to adult) standard number of eggs was taken as the ini- tial count (150), and hatching rate of eggs

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Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al.

(Segg), survival rate of the five instars of larvae tellus, Scirpophaga incertulas, and S innotata (S1, S2, S3, S4, S5), and female proportion were (Rahman and Khalequzzaman 2004). In our based on the actual data from this study. Popu- study, the survival of C. medinalis larval in- lation trend index (I) was calculated for all the stars was highest at 25° C, followed by 30° C temperatures and was found to be highest at (Figure 1). Sato and Kishino (1978) also re- 30° C (14.46), followed by 25° C (12.16) and ported the highest survival of C. medinalis at 32° C (10.6), indicating that temperatures of 25° C and observed an increase in mortality 25–30°C were most favorable for C. medinalis with a decrease or increase in temperature, in- population growth. dicating a non-linear relationship. Cumulative emergence rates at constant temperatures re- Discussion vealed that 100% of adults emerged on day 1 at 32° C, while the emergence was prolonged Temperature is the most important and critical at 18° C, indicating faster development with abiotic factor exerting profound influence on increased temperature (Figure 2). Downloaded from the development of insects. The relationship between temperature and rate of development Estimation of lower threshold temperatures is crucial, as it influences insect biology, dis- and thermal constants for different stages of C.

tribution, and abundance (Braman et al. 1984; medinalis from linear regressions revealed http://jinsectscience.oxfordjournals.org/ Legg et al. 2000; Tobin et al. 2003). Devel- lower development threshold (T0) values at opment of C. medinalis at 7 constant 11.0, 10.4, and 12.8° C for eggs, larvae, and temperatures revealed decreases in develop- pupae, respectively (Table 2). Thermal con- mental time from egg to adult with increases stants of 69,270 and 106 degree days were in temperature (Table 1). At 32° C, total de- calculated for eggs, larvae, and pupae, respec- velopment was completed in 21.8 days, while tively. Intrinsic optimum temperature (TΦ) of it took 65.4 days at 18° C. A similar decreas- 24.2° C was obtained for the total develop- ing trend was observed in different stages ment from egg to adult, suggesting the by guest on December 1, 2014 from 18–34° C, but the duration increased at maximal active state enzymes involved in the 35° C. However, C. medinalis could not com- developmental process. The upper (TH) and plete its development at 34 and 35° C, as lower (TL) threshold temperatures were esti- larvae could not survive beyond 4th instar. Ear- mated at 36.4 and 11.2° C for total lier studies on C. medinalis from different development, suggesting that the hypothetical regions reported variations in the developmen- enzyme was half active and half inactive at tal periods of eggs, larvae, and pupae, and the these thresholds. This could be one of the rea- total developmental periods (egg to adult) sons for the incomplete development of the were in the range of 24–41 days (Lingappa larval stage at 34 and 35° C. The intrinsic op- 1972; Yadava et al. 1972; Velusamy and timum temperature along with its confidence Subramaniam 1974; Godase and Dumbre interval could be used as an indicator for the 1982; Padmavathi et al. 2006), but all these geographical distribution and place of origin results were based on experiments carried out of related species (Ikemoto 2003). This is also under ambient temperatures. A similar de- a potential tool for the construction of a phy- crease in the developmental period with an logenetic tree within a taxon (Ikemoto et al. increase in constant temperatures was reported 2012). in the case of other pyralid rice stem borers, e.g., Chilo suppressalis, C. polychrysa, C par-

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Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al. The present results are in accordance with degree days were reported for the whole gen- Graf et al. (1992) who developed a simulation eration of green semi-looper, Naranga model by establishing a common developmen- aenescens, and no obvious differences were tal threshold of 12.4° C and thermal constants observed in their threshold temperatures and of 70, 280, 110, and 140 degree days for eggs, effective accumulated temperature between larvae, pupae, and adults of C. medinalis, re- constant temperature studies in the laboratory spectively. However, Wada (1979) reported and alternating temperature studies in paddy that the frequency of molting in the larval fields (Lu et al. 2002). The estimated tempera- stage of C. medinalis changes with the grow- ture thresholds and thermal constants are ing stage of the rice plant, and suggested that useful in the prediction of population peaks the thermal constant is influenced not only by (Taveras et al. 2004), to identify optimal time temperature, but also by the host plant. In an- of insecticide application (Tolley and Robin- other field study, Sato and Kishino (1978) son 1986), to estimate intrinsic rate of natural found that in the population of C. medinalis population increase (Kinjo and Arakaki 2002), Downloaded from from Sapporo, Japan, the thresholds of devel- to develop a forecasting system to monitor the opment for eggs, larvae, pupae, and total adult emergence and flight activity (Ahmad development, were 11.2, 11.9, 13.3, and 12.0° and Ali 1985), and to develop phenology

C, respectively. models (Jarosik et al. 2011). The threshold http://jinsectscience.oxfordjournals.org/ temperatures estimated, particularly TL and Analogous studies in another pyralid, Chilo TH, are also useful to study the impact of cli- partellus, revealed that it took 588.34 degree mate change on the distribution of a species days above 17.6° C for the completion of all (Kocmankova et al. 2010). developmental stages (Jalali and Singh 2001). Thermal constants of 705.56, 725.32, 703.30, Rate isomorphy testing by ANCOVA revealed 556.59, 655.34, and 837.95 degree days were a significant difference among the slopes of reported for C. polychrysa, C. suppressalis, C. linear regressions of different developmental by guest on December 1, 2014 partellus, Scirpophaga incertulas, S. innotata, stages of C. medinalis, indicating that the low- and Sesamia inferens, respectively, with the er development thresholds were different. mean developmental zero of 7.70–10.19° C in Possible reasons for the violation of the gen- different species (Rahman and Khalequz- eral rule of developmental isomorphy could be zaman 2004). Jarosik et al. (2011) reported the coarse estimates of development at high that closely related species shared similar temperatures or mortality at low temperatures thermal requirements because of common in- (Jarosik et al. 2002). trinsic optimum temperature and duration of development by comparing several phenology Life tables are powerful tools for understand- models. This intrinsic optimum temperature ing the changes in a population during could be used as an indicator for classifying different stages of growth, and are governed phylogenetic relatedness (Ikemoto 2005). In by a number of biotic and abiotic factors. The the natural fluctuating day and night environ- role of biotic factors in regulating the popula- ment, C. medinalis may be able to develop and tion of C. medinalis in the field was reported survive at higher temperatures than observed by Padmavathi et al. (2008) while constructing in the present constant temperature studies. and analyzing mortality and fertility life ta- Threshold temperature and effective accumu- bles. Data from our study indicated that lated temperatures of 10.07° C and 558.36 temperatures between 25 and 30° C were fa-

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Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al. vorable for the survival and multiplication of of Rice Research, and Dr. JS Prasad, Head, leaf folder populations. Entomology section, Directorate of Rice Re- search, for their encouragement and support A comparative analysis of the published data during the course of the study. We thank the sets indicated that the lower threshold value reviewers for useful suggestions that helped in obtained in this study (11.1) was similar to the improving the manuscript. report by Chang and Wu (1988). However, higher T0 values were reported from Japan and References the Northern part of China (Table 6). Thus, the variation in lower threshold and thermal con- Ahmad TR, Ali MA. 1985. Forecasting stant among leaf folder populations from emergence and flight of some Ephestia spp. different geographical areas could be attribut- (Lep., Pyralidae) based on pheromone ed to multiple factors, such as experimental trapping and degree-day accumulations. conditions, host-plant quality, thermal adapta- Journal of Applied Entomology 119: 611–614. Downloaded from tions to different geographical areas, and the method of estimation (Marchioro and Foerster Braman SK, Sloderbeck PE, Yeargan KV. 2011). 1984. Effects of temperature on the

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The authors are grateful to ICAR - National Cheng CH.1987. Investigation on bionomics Agricultural Innovative Project (NAIP C2046) of the rice leaffolder, Cnaphalocrocis for providing funds and facilities to carry out medinalis (Guenee) in the south of Taiwan. the work. We also thank Drs. TM Manjunath, Plant Protection Bulletin 29:135–146. S Lingappa, and NH Rao for their guidance and constructive suggestions. We are highly Davidson J. 1944. On the relationship between grateful to Dr Feng Ge and Dr Pei-jian Shi, temperature and rate of development of insects Chinese Academy of Sciences, Beijing, China, at constant temperatures. Journal of Animal for providing the OptimSSI program and guid- Ecology 13: 26–38. ing us in operating the program. We thank Dr. BC Viraktamath, Project Director, Directorate

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Table 1. Developmental time (days) of different stages of rice leaf folder, Cnaphalocrocis medinalis, at 7 constant temperatures.

All values are mean ± SE. ND = Not developed. Means followed by different letters in the rows are statistically different by LSD (p ≤ 0.05).

Table 2. Linear regression equations, lower developmental thresholds, and thermal constants of each developmental stage of Cnaphalocrocis medinalis.

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SE (Tmin) = 1.4 (Egg), 1.1 (Larva), 3.2 (Pupa). SE (K) = 0.7 (Egg), 4.5 (Larva), 7.1 (Pupa). *Parameters estimated by plotting developmental rates (y = 1/D, development duration in days) against temperatures (x).

T0 is the lower threshold for development that was calculated as x- intercept (-a/b) of the linear regression model. § = Thermal constant, calculated as 1/b of the regression model.

by guest on December 1, 2014

Table 3. Estimations of lower developmental thresholds and sum of effective temperatures by Ikemoto and Takai’s (2000) linear model.

LDT = Lower developmental threshold. SET = Sum of effective temperatures.

Table 4. Parameters of non- linear thermodynamic model (OptimSSI) for different stages of Cnaphalocrocis medinalis.

LCL = Lower confidence limit. UCL = Upper confidence limit.

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Journal of Insect Science: Vol. 13 | Article 96 Padmavathi et al.

Table 5. Life table of Cnaphalocrocis medinalis population at 7 constant temperatures.

ND = not developed.

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Table 6. Comparative thermal requirements for life stages of Cnaphalocrocis medinalis in Southeast Asia.

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by guest on December 1, 2014 T0 = Lower threshold temperature; K = Thermal constant (degree-days); - = not estimated; F = Female; M = Male.

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