Heteroptera: Reduviidae), a Predator of Spodoptera Litura (Fabricius) (Lepidoptera: Noctuidae)
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1. BIOI. Control, 12 (2): 107-111, 1998 Life ta hie and intrinsic rate of increase of Sycanus collaris Fa bricius (Heteroptera: Reduviidae), a predator of Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) P. J. EDWARD GEORGE*, R. SEENIVASAGAN and G. KARUPPASAMY Entomology Research Institute Loyola College, Chennai 600 034, Tamil Nadu, India ABSTRACT: The life table studies on Sycancus collaris Fabricius (Heteroptera: Reduviidae) under laboratory conditions revealed that the net reproductive rate (RJ of the species was 30.46 female eggs / female. The true intrinsic rate of natural increase (rm) was 0.066. The population multiplied 1.59 times every week and the time taken for the doubling of predator was 10.56 days. The total nymphal duration was 49.3 ± 1.95 days. The life span of females was more (45.17 ± 1.83 days) than males (31.83 ± 2.48 days). KEY WORDS: Development, intrinsic rate of increase, life table, net reproductive rate, Spodoptera litura, Sycanus collaris Sycanlls collaris Fabricius (Hetero 1976) enabling determination of age ptera: Reduviidae) is an important reduviid distribution and mortality rate in natural reported to feed upon many lepidopteran populations. Life tables also provide a insect pests (Ambrose and Paniadima, valuable picture on the fecundity and 1988). Spodoptera litura (Fabricius) is a growth potential of the predator under major lepidopteran insect pest on many . prevailing environmental conditions. crop plants. A perusal ofliterature reveals Hence, the present study airns at generating paucity of information on life table of useful information in biology and also in predatory bugs on lepidopteran pests. Life constructing the population model of table is the most useful numerical aid in S. collaris on S. litura. studying population biology (Southwood, * Present address: Entomology Research Unit, St.Xavier's College, Palayankottai 627 002,Tamil Nadu EDWARD GEORGE et al. MATERIALS AND METHODS female offsprings produced per female in the age interval 'x'. The sum of the products Adults and nymphs of S. collaris were 'lxmx' is the net reproductive rate (R). The collected from the foot hills ofKodaikanal rate of multiplication ofpopulation for each (l0.0° N, 78.0° E), Madurai District of generation was measured in terms of Tamil Nadu, India and maintained in the females produced per generation. The laboratory at Entomology Research precise value of cohort generation was Institute, Loyola College, Chennai from calculated as follows: January to December, 1997 at temperature 30 ± 2° C; relative humidity 75-80 per cent; photoperiod 11- 13 h on the larvae of S. litura collected from cotton fields at Theni (9° 59' N, 77° 25' E), Madurai District of Tamil Nadu. Following mating, eggs were collected with the help ofa camel The arbitrary value of innate capacity brush and allowed hatching in small plastic for increase 'r'c was calculated from the containers (4cm diam; 4cm ht) with equation: moistened cotton swabs for maintaining optimum humidity. The cotton swabs were log R e 0 changed periodically to prevent fungal r =--- attack. After hatching all the nymphs were c reared individually in the same size plastic T c containers on 4 days old S. ldura as the prey. Advanced larval stages were provided This is an appropriate 'rm' value. The for the progressed nymphal instars. values of the negative exponent of e-mx Observations were made on hatching, ascertained from this experiment often lay nymphal development, adult emergence, outside the range. Forthis reason both sides and age specific mortality in respective of the equation were multiplied by a factor stage. After the emergence of adult, life of L£ 7-P~ sl x ~ S = 1096.6 (Birch, 1948). table was constructed using Birch (1948) formula as elaborated by Howe (1953) and The two values of .L. £. 7 -p f...l ~ I ,J.t ~ were then Watson (1964). plotted on the horizontal axis against their respective arbitrary 'fm' on the vertical axis. In life table statistics, the intrinsic rate Two points were then joined to give a line of increase was determined by using the that was intersected by a vertica11ine drawn 7 r equation L.l' e-'mXl m = 1 , where 'e' is the from the desired value of e - m" I m " x x x :x base ofthe natural logarithms, 'x' is the age (1096.6). of the individuals in days, \' is the number of individuals alive at age 'x' as the The precise generation time (T) was proportion of 1, and 1m I is the number of x then calculated from the equation: 108 Lifo table ofS. collaris log R e 0 10.1 7±1. 17 days (Table 1) and the total T=----- number of eggs in the lifetime was r m 10S.67±S.69. The finite rate of increase (A) was The population growth statistics of S. r calculated as e m' The weekly multiplication collaris revealed that the net reproductive of predator population was calculated as rate (30.46) was lesser than the gross r 7. e m The doubling time was calculated as reproductive rate (48.5 ) due to a sharp log 21 log A. decline in the survivorship value of the parent females (Table 2). Mean length of RESULTS AND DISCUSSION generation (T) was 41.01 days that approximated the true generation time (T) The incubation period ofS. collaris was of 51.82 days duration which the species 7.17 ± OA1 days and the durations of I, II, multiplied 30.46 times. The innate capacity III, IV and V nymphal instars were of natural increase (rc )wasO.031 whilethe 6.6±0.51, 6.3± 0.48, 6.9±0.S7, 13.1± 0.99 true intrinsic rate of increase (rm ) was and 16.4± 1.26 days, respectively. The total 0.043. With a finite rate of increase of1.07, nymphal period was 49.3±1.95 days. the population was able to multiply 1.59 Females lived longer (4S.17±1.83 days) days times every week on S. litura. The than males (31.83± 2.48 days). The pre population of the predator doubled in 1 0.56 oviposition period of female was days. Table 1. Biological data of S. collaris on S. Jilura Parameter Mean ± SD (days) Incubation period 7.17±0.41 Nymphal duration I Instar 6.60 ± 0.51 II Instar 6.30 ± 0.48 III Instar 6.90 ± 0.57 IV Instar 13.10 ± 0.99 V Instar 16.40 ± 1.26 Total nymphal duration 49.30 ± 1.95 Longevity Male 31.83 ± 2.48 Female 45.17 ± 1.83 Pre-oviposition period IO.17± 1.17 [09 EDWARD GEORGE et al. Table 2. Population growth statistics of S. collaris reared on S. litura Growth reproductive rate (GRR) 48.50 Net reproductive rate (R) 30.46 Mean length of generation (T) 41.01 Innate capacity for increase in numbers (r) 0.031 Corrected rro 0.043 Corrected generation time (T) 51.82 Finite rate of increase in numbers (1) 1.07 Weekly multiplication 1.59 Doubling time (days) 10.56 The population growth statistics for institutional facilities and suggestions. indicated the capability of rapid increase in Thanks are also due to the Ministry of population size with a strong possibility of Environmental and Forests, New Delhi for bringing about an effective check of financial support. S. fitl/ra population. Venkatesan et al. (1997) reported that the reduviid REFERENCES (Cydnocoris gilvus Burm.) bug with efficient oviposition and voracious feeding, Ambrose, D. P. and Paniadima, A. 1998. was effective in suppressing the population Biology and behaviour of a harpactorine of S. litura. Similar results were reported assassin bug Sycanus pyrrhomelas by Claver (1998) with the reduviid, Walker (Hemiptera: Reduviidae) from Rhynocoris kumarii Ambrose and South India. Journal ofSoil Biology and Livingstone. The studies carried out to Ecology, 8 (1): 37-58. evaluate the reproductive potential of S. col/aris on S. litura were restricted to Birch, L. C. 1948. The intrinsic rate of the laboratory. Though the results obtained natural increase in an insect population. so far were promising, the actual potential Journal of Animal Ecology, 17: ofthis predator could be assessed only after 502-510. conducting large scale release and subsequent evaluation studies. Claver, M. A. 1998. BiocontroI potential ACKNOWLEDGMENTS evaluation of a reduviid predator, Rhynocoris kumarii Ambrose and The authors express their thanks to Livingstone (Insecta: Hemiptera: Prof TN. Ananthakrishnan, Chairman and Reduviidae) against three chosen cotton Principal investigator, Entomology insect pests. Ph. D. thesis, M. S. Research Institute, Loyola college, Chennai University, Tirunelveli. IlO Li(e table ofS. collans Howe, R. W. 1953. The rapid prey species on feeding response, determination of intrinsic rate of development and reproduction of the increase of an insect population. Annals reduviid, Cydnocoris gilvus Burm. C?i Applied Bi%gy, 40: 134 - 151. (Heteroptera: Reduviidae). Entomon. 22 (1): 21-27. Southwood, T. R. E. 1976. Ecological Methods with particular reference to the study of insect populations. Chapman Watson, T. F. 1964. Influence of host plant and Hall, London, 524 pp. condition on population increase of Tetranychus telarius (L) (Acarina: Venkatesan, S., Seenivasagan, R. and Tetranychidae). Hilgardia, 35: 273 - Karuppasamy, G. 1997. Influence of 332. ill .