Energy budget of Pieris brassicae L. larvae (Lepidoptera: Pieridae) fed on four host plant species

Agriculture Ecosystems and Environment, 10 (1983) 385--398 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

385

ENERGY BUDGET OF PIERIS B R A S S I C A E L. LARVAE (LEPIDOPTERA: PIERIDAE) FED ON FOUR HOST PLANT SPECIES B.R. KAUSHAL Department o f Zoology, Kumaun University, Nainital 263002 (India) L.K. VATS Department o f Zoology, Kurukshetra University, Kurukshetra 132119 (India) (Accepted 7 September 1983)

ABSTRACT

Kaushal, B.R. and Vats, L.K., 1983. Energy budget of Pieris brassicae L. larvae (Lepidoptera: Pieridae) fed on four host plant species. Agric. Ecosystems Environ., 10: 385-398. Energy budgets were evaluated for the larval development of Pieris brauicae fed on leaves of Brassica oleracea vat. capitata, B. oleracea var. botrytis, B. oleracea vat. sarson and Nasturtium montanum. F o o d consumption, assimilation and tissue growth values were maximum for the larvae fed on B. oleracea vat. capitata and minimum for the larvae fed on N. montanum. Mean values of approximate digestibility (AD), efficiency of conversion of digested food into body tissue (ECD) and efficiency of conversion of ingested food into b o d y t i ~ u e (ECI) fall within the values reported for other leaf-eating lepidopterans. An equivalent weight of the following materials had calorific values in the order given: faeces < food plant < larval stages < pupal stage.

INTRODUCTION

A number of workers have carried out a considerable a m o u n t of work on the energy flow through the larval stages of lepidopterans (Hiratsuka, 1920; Evans, 1939a,b; Waldbauer, 1964, 1968; Schroeder, 1971, 1972, 1973, 1976; Axellson et al., 1975; Migula, 1975; Barley and Singh, 1977; Vats et al., 1977; Mackey, 1978; Vats and Kaushal, 1980). Pieris brassicae larvae are a serious pest of cruciferous and non-cruciferous plants. However, no information is available on the exploitation of food materials by the larval stages of this pest. The main objective of the present study was to provide an approximation of energy flow through P. brassicae larvae fed on four plant species: Brassica oleracea var. capitata (cabbage), Brassica oleracea var. b o t r y t i s (cauliflower), Brassica oleracea var. sarson (sarson) and N a s t u r t i u m m o n t a n u m (garden nasturtium).

0167-8809/83/$03.00

© 1983 Elsevier Science Publishers B.V.

386 MATERIALS AND METHODS Cabbage leaves bearing the eggs of P. brassicae were gathered, and kept in glass cages, dimensions 65 × 30 × 30 cm, covered with a wire gauze to maintain a stock culture in the laboratory. Each female laid an average of 50 eggs. Eggs were kept at a room temperature of 20--25°C and a relative humidity of 50--65%. On emergence, the larvae were transferred to four food plants and kept separately in glass cages. The larvae were deprived of food for a b o u t 30 min before and after the feeding experiment. Preparatory experiments have shown that active egestion in larvae selected for feeding experiments almost ceases within 30 min of the withdrawal of food. Before the start of the experiment, each larva was weighed and kept in a 1 5 ~ m diameter petri dish covered with a plastic sieve. After 24 h of feeding, the larvae, the unconsumed leaves, and the egesta were collected from each petri dish. The larvae were weighed. The unconsumed leaves and the egesta were oven-dried at 80 ° C for 48 h till a constant weight was reached. The larvae of the first instar, being small, were kept in groups of 20 each and an average value for each replicate was calculated. The larvae which died during the course of the experiment were replaced by larvae of approximately the same age from the stock culture maintained for each host plant. Five replicates were taken for each of the four food plants. The calorific values of the host plants, the larvae and the faecal matter were determined by adiabatic b o m b calorimetry. F o o d consumption was calculated as the difference between the initial weight o f the leaves provided and the weight of unconsumed plant material at the end of the experiment, after correcting for weight loss in the food material due to respiration and transpiration within this period. Dry weight equivalents o f the food consumed were estimated from the percentage of dry matter in all the four plant species separately. Percentage dry matter was obtained by oven
Assimilation Consumption Tissue growth

× 100 X i00

Assimilation Tissue growth Ecological growth efficiency (ECI) = X I00 Consumption

387 OBSERVATIONS AND DISCUSSION Females lay eggs on the undersurface of the leaves of cruciferous plants (mainly cabbages and cauliflowers) which are yellowish in colour, turning orange after some time and ultimately black at the time of emergence. There are five larval instars of which the last on each food plant is of the longest duration. Soon after emergence, larvae start feeding on their egg shell, later moving on to the leaves of the host plants.

CALORIFIC VALUES The calorific values of different biological materials are given in Table I. Larvae had higher calorific values compared to food plants and faecal matter due to accumulation of fats, as reported by Schroeder (1972, 1973), Axellson et al. (1974), Migula (1974), Bailey and Singh (1977), Mackey (1978) and Vats and Kaushal (1980). Other workers have also reported higher values for lepidopteran larvae. Schroeder (1972) reported a calorific value of 5.3 cal mg-1 for the larval stages of Platysomia cecropia against 5.1 cal mg-' for the food plant and 5.05 cal mg-1 for the faecal matter. Similarly, Mackey (1978) observed that the calorific value of Cyclophragma leucosticta larvae (5.68 cal mg -~) was higher than that of the food plant (4.8 cal mg-~) and egesta (4.47 cal rag-:). Vats and Kaushal (1980) reported calorific values of 5.2, 4.78, 5.6 cal mg-~ dry weight for the larvae of Belenois mesentina, Capparis decidua leaves and the faecal matter, respectively. Further, pupae had the maximum calorific value as stored energy in them is utilized during metamorphosis. Schroeder (1972, 1973), Axellson et al. (1975), Migula (1975), Bailey and Singh (1977), Vats et al. (1977) and Mackey (1978) also reported m a x i m u m calorific values for the pupae.

TABLE I Calorific content (cal rng-I dry wt. of different biological materials (mean ± 1 SD) (All values based on dry wt.) H o s t plant fed

Larvae (all i n ~ a r s )

Pupae

Host plant

Egesta (all instars)

B r a u i c a oleracea vat. capita Brassica oleracea vat. botrytis Brassica c o m p e s t r i s var. sarson Nasturtium montanum

4.943 ± 0.86

5.238 ± 0.27

4.168 ± 0.34

3.224 ± 0.41

4.836 ± 0.64

5 . 0 1 2 ± 0.3

3.948 ± 0.13

3.038 ± 0.38

4.625 ± 0.78 4.134 ± 0.61

4.841 ± 0.25 4.476 ± 0.16

3.864 ± 0.42 3.543 ± 0.46

2.835 ± 0.27 2.892 ± 0.34

388 ENERGY BUDGET

The data on duration of instars, initial biomass of the larvae, consumption, egesta, assimilation and tissue growth are presented in Table II. Initial biomass of larvae fed on cabbage increased from 0.107 to 36.296 cal per insect. For cauliflower, the equivalent values were 0.101 to 32.235 cal per insect; for sarson they were 0.101 to 28.815 cal per insect, and for nasturtium 0.095 to 23.99 cal per insect. Maximum values of initial biomass were obtained for the larvae fed cabbage leaves and minimum values for larvae fed on nasturtium leaves. The last two instars contributed more than A

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Fig. 1. Relationship between food c o n s u m e d and initial dry weight in different larval instars. (A) Brassica oleracea var. capitata: Y =--0.097 + 0.925 X (r = 0.999, P < 0 . 0 0 1 ) ; (B) B. oleracea var. botrytis: Y = --0.096 + 0.101 X (r = 0.998, P < 0.001); (C) B. oleracea vat. sarson: Y = - - 0 . 2 4 9 + 0.111 X (r = 0.998, P
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390 95% o f t h e t o t a l initial biomass as has also been r e p o r t e d b y Axellson et al. ( 1 9 7 5 ) , Vats et al. {1977) a n d Vats and Kaushal {1980). T h e caterpillars c o n s u m e d a total o f 5 1 4 . 5 8 cal, 4 2 0 . 6 1 2 cal, 3 4 7 . 0 8 3 cal a n d 2 9 0 . 8 1 cal o f c a b b a g e , cauliflower, sarson a n d n a s t u r t i u m leaves, respectively. A significant positive linear relationship was observed for all t h e f o o d plants w h e n initial b i o m a s s was p l o t t e d against the f o o d c o n s u m p t i o n {Fig. l ( a - d ) ) . C o n s u m p t i o n increased with t h e increase o f biomass. T h e p e r c e n t age r e q u i r e m e n t s o f f o o d for the c o n s e c u t i v e stages c a l c u l a t e d f r o m t o t a l c o n s u m p t i o n f o r t h e w h o l e d e v e l o p m e n t p e r i o d are: 0.33, 1.64, 2.75, 1 8 . 5 9 and 7 6 . 6 9 % o n c a b b a g e ; 0.37, 1.66, 3.11, 1 8 . 6 2 and 7 6 . 2 4 % o n c a u l i f l o w e r ; 0 . 4 3 , 1 . 6 3 , 3.66, 19.51 a n d 74.77% o n sarson; and 0.45, 1.64, 3.84, 1 9 . 8 9 a n d 7 4 . 1 8 % o n n a s t u r t i u m leaves.

TABLE III Weight-specific parameters for food intake, assimilation and tissue growth (cal cal-~ day-~) in Pieris brassicae larvae fed on four host plant species (mean ± 1 SD) Stage

C o n s u m p t i o n (C) (cal cal-I day -I)

Egesta (E) (cal cal-~ day -~)

Assimilation (A) (cal cal-~ day -~)

Tissue growth (cal cal-~ day -~)

13.08 9.77 8.42 6.79 5.53

~ 0.24 ± 0.73 ± 1.65 ± 0.71 ± 1.40

4.62 3.55 3.35 2.89 1.83

± 0.10 ± 0.30 ± 0.32 ± 0.65 + 0.26

Brassica oleracea var. capitata (cabbage)

1st instar 2nd instar 3rd instar 4th instar 5th instar

16.10 13.39 12.72 11.20 10.87

± 0.54 ± 0.84 ± 1.41 + 0.81 ± 0.94

3.02 3.61 4.3 4.41 5.34

± 0.72 ± 1.03 ± 1.22 ± 1.39 ± 1.68

Brassica oleracea var. botrytis (cauliflower) 1st instar 2 n d instar 3rd instar 4th instar 5th instar

15.38 11.13 10.96 10.41 9.95

± ± ± + ±

0.42 0.56 1.43 0.78 0.87

3.01 3.04 4.28 4.94 5.04

± ± ± ± ±

0.62 0.98 0.98 0.83 1.03

12.37 8.09 6.68 6.47 4.91

-* 0.34 ± 0.79 ± 1.15 ± 1.09 ± 1.16

4.42 2.90 2.50 2.17 1.62

± ± ± ± ±

0.19 0.23 0.20 0.24 0.13

Brassica oleracea var. sarson (sarson) 18t instar 2 n d instar 3rd instar 4th irtstar 5th instar

14.34 11.78 11.03 9.95 9.01

± + ± ± ±

1.12 1.80 0.76 1.04 1.91

2.72 3.29 3.52 4.90 4.99

± ± ± ± ±

0.84 0.86 1.03 1.21 0.90

11.62 8.49 7.51 5.05 4.02

± ± ± + ±

0.18 1.06 0.67 1.03 0.89

3.29 2.55 2.14 1.86 1.41

± + ± ± ±

0.13 0.17 0.16 0.21 0.18

1.74 1.53 1.35 1.96

2.97 3.38 4.26 4.44

~ ± ± ±

0.56 0.72 0.90 1.30

10.96 8.73 6.23 5.45

± ± ± ±

0.25 0.98 1.05 0.93

3.01 2.58 1.94 1.82

± ± ± ±

0.47 0.13 0.15 0.24

Nasturtium m o n t a n u m Ist instar 2 n d instar 3rd instar 4th instar

5th instar

13.93 12.11 10.49 9.89

± + ± ±

8.99 ± 1.70

4.65 ± 1.80

3.34 ± 1.34

1.36 ± 0.08

391

Thus, more than 90% of the total food is consumed by the last two instars because of their maximum weight; this is the case for all the food plants. Schroeder (1972, 1973), Axellson et al. (1975), Migula (1975), Bailey and Singh (1977), Mackey (1978), Vats et al. (1977) and Vats and Kaushal (1980} also observed a maximum consumption in the last two instars of lepidopteran larvae. Bailey and Singh (1977) reported that sixth instar larvae of Mamestra configurata alone consumed 80.1% of the total ingestion. However, when weight-specific consumption (calories of food per calorie of insect biomass per day) was considered, values decreased from first to last instar (Table III). Maximum weight-specific consumption was obtained for the first instar and minimum for the final instar. Vats et al. (1977) also reported similar findings but there was no regular pattern in the larvae of Belenois mesentina (Vats and Kaushal, 1980). The steep increase in the amount of food consumed during fourth and fifth instars is due to the change in the way the caterpillars feed and the duration of these instars. The caterpillars of the first and second instars feed on the bottom of the leaves, eating chiefly the palisade tissue and epidermis. In the later instars, they disperse and feed upon small veins containing more cellulose, which is poorly digested (Strawinski, 1929). The food of caterpillars in the later stages contains less palisade tissue, which according to Rybicki (1954) is a factor deciding the amount of plant mass consumed. Similar observations have been made by Chlodny (1967), Schroeder (1972, 1973), Axellson et al. (1975), Migula (1975), Bailey and Singh (1977), Mackey (1978), and Vats and Kaushal (1980). EGESTA

Higher consumption in the fourth and fifth instars resulted in higher production of egesta by the larvae. These two instars on the food plants accounted for more than 95% of the total egestion. Weight-specific egestion showed a gradual increase from first instar to the last instar (Table III). A slightly curvilinear relationship was observed for cabbage and positive linear relationship was obtained on the remaining food plants when egestion was plotted against food consumption [Fig. 2(a--d)]. The curvilinear relationship obtained for cabbage leaves corresponds to higher rates of consumption and egestion. Kasting and McGinnis (1962), Waldbauer (1964, 1968), Mukerji and G u p p y (1973), Mathavan and Pandian (1974) and Vats and Kaushal (1980) have also reported that there is a high correlation between the amount of food eaten and the amount defaecated. The quantity of egesta produced on plants fed in the present study is comparable to Waldbauer's (1964) observation on Protoparce sexta which also produces different amounts of egesta when fed on different food plants. This is explained by differences in the digestibility.

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Fig. 2. Relationship between consumption and egesta. (A) B rassica oleracea vat. capitata: Y ffi 7.093 + 0.201 X (r = 0.998, P<0.001); (B) B. oleracea var. b o t r y t i s : Y ffi 3.824 + 0.194 X (r ffi 0.999,P<0.001); (C)B. oleraceavar, sarson: Y ffi 3.306 + 0.186 X (r = 0.998, P<0.001);(D) N a s t u r t i u m m o n t a n u m : Y = 3.26 + 0.189 X (r = 0.998, P<0.001). T h e e g e s t i o n / c o n s u m p t i o n ratio is 46.4% f o r cabbage, 49.3% for caulif l o w e r , 52.8% for sarson, and 49.4% for n a s t u r t i u m leaves w h i c h falls w i t h i n t h e 3 3 . 9 - - 5 5 . 8 % range f o u n d in t h e literature ( C h l o d n y , 1 9 6 7 ; A x e l l s o n et al., 1 9 7 5 ) . T h u s t h e e s t i m a t e d values o f c o n s u m p t i o n a n d e g e s t i o n in t h e p r e s e n t s t u d y s e e m t o be r e a s o n a b l e . ASSIMILATION A t o t a l o f 2 7 5 . 7 6 cal, 2 1 3 . 5 cal, 1 8 3 . 0 5 cal and 1 4 7 . 1 8 cal energy w a s assimilated by t h e larvae f e e d i n g o n cabbage, c a u l i f l o w e r , sarson and nasturt i u m leaves, respectively. T h e last t w o instars larvae assimilated 93.85% o f

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Fig. 3. R e l a t i o n s h i p b e t w e e n assimilation and c o n s u m p t i o n . ( A ) B r a s s i c a o l e r a c e a var. Y - - - 6 . 1 5 7 + 0 . 5 7 7 X (r = 0 . 9 9 8 , P < 0 . 0 0 1 ) ; ( B ) B . o l e r a c e a var. b o t r y t i s : Y = - - 3 . 5 9 8 + 0 . 4 4 9 X (r = 0 . 9 9 9 , / ) < 0 . 0 0 1 ) ; (C) B. o l e r a c e a vat. s a r s o n : Y ffi - - 3 . 4 2 7 + 0 . 6 5 1 X (r = 0 . 9 9 8 , P < 0 . 0 0 1 ) ; ( D ) N a s t u r t i u m m o n t a n u m : Y ffi - - 2 . 6 3 9 + 0 . 5 2 6 X (r ffi 0 . 9 9 9 , P< 0.001). capitata:

cabbage, 93.3% of cauliflower, 92.93% of sarson and 92.16% of nasturtium leaves. Assimilation increased from first instar to last instar on all the food plants (Table II). Total assimilation was higher by 1.87 times for the larvae feeding on cabbage leaves (maximum assimilation) than the larvae feeding on nasturtium leaves (minimum assimilation). Weight-specific assimilation followed a pattern similar to that of consumption (Table III). A positive linear relationship existed between food assimilation and consumption [ Fig. 3(a--d) ]. Chlodny (1967), Axellson et al. (1975), Bailey and Singh (1977), Vats et al. (1977), Mackey (1978) and Vats and Kaushal (1980) also reported an increase in the amount o f food assimilated with increased food consumption. TISSUE G R O W T H

The distribution o f tissue growth in the fourth and fifth instars is: 93.4% of total tissue growth on cabbage, 92.9% on cauliflower, 92.97% on sarson

394

and 92.7% on nasturtium. Schroeder (1973) and Bailey and Singh (1977) reported that 90 and 95.44% of the total tissue growth occurred in the last two instars of Platysomia cecropia and M. configurata, respectively. Mackey (1978) observed only 50% of the total production in the last two instars of Cyclophragma leucosticta. Total tissue growth of the larvae fed on cabbage leaves was 2.13 times higher than that of larvae fed on nasturtium leaves (Table II). A

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Fig. 4. Relationship between tissue growth and consumption. (A) Brassica oleracea var. capitata: Y = -2.716 + 0.127 X (r = 0.99, kO.001); (B) B. oleracea var. botrytis: Y = -2.155 + 0.164 X (r = 0.996, P
395

Thus from the data on consumption and tissue growth, it is seen that cabbage was the most suitable f o o d plant and nasturtium the least suitable. Cabbage leaves produced the highest weight larvae and nasturtium leaves the lowest weight larvae. Probably quality of f o o d was responsible for the maxim u m tissue growth on cabbage and minimum on nasturtium leaves. Gordon (1959), Burlacu (1967), Morowitz (1968), Waldbauer (1968), Feeny (1970) and Whittaker and Feeny (1971) argue that food quality is often a major factor limiting herbivore growth. Maximum weight-specific tissue growth was obtained in the first instar larvae on all the four f o o d plants and minimum in the last instar larvae. Our results agree with that o f Vats et al. (1977) and Vats and Kaushal (1980). Figure 4 (a--d) represents the relationship between tissue growth and consumption. A slightly non-linear curve is found for all the food plants. The regression line intersects the ordinate at a point below zero, showing that tissue growth occurred only on taking food. This is in contrast to the results of Vats et al. (1977) where some tissue growth occurred before consumption of the food, probably due to ingestion of egg-shells. EFFICIENCIES OF FOOD UTILIZATION Percentage values of approximate digestbility and the efficiencies of conversion of ingested and digested food into b o d y tissue are summarised in Table IV. Maximum values of approximate digestibility (AD) were obtained for the first instar larvae and minimum for the last instar larvae on all the food plants. Schroeder {1972), Bailey and Singh (1977) and Mackey (1978) also recorded similar results for the larvae o f P. cecropia, M. configurata and C. lecosticta, respectively. Approximate digestibility (AD) declined with age in B o m b y x mori, while in Agrotis larvae it remained more or less constant in the last three instars (Waldbauer, 1968). Vats et al. (1977) reported that AD n o t only declined with age, b u t also within t w o stages of the last instar larvae. Larvae of Belenois mesentina also showed a gradual decline in AD (Vats and Kaushal, 1980). Mean AD on cabbage leaves was 67.3%, 63.9% on cauliflower, 63.9% on sarson and 62.7% on nasturtium. Maximum values of AD {81.25%) was obtained for cabbage-fed larvae. Evans (1939b) reported 92% AD on the first day for a group o f Smenthurus populi larvae fed on Sal/x leaves. The mean value of AD was 42.0% for Bornbyx rnori fed on Morus alba leaves (Hiratsuka, 1920), 41.3% for Pachysphinx modesta fed on Populus leaves (Schroeder, 1973) and 49.6% for C. leucosticta fed on K. alba leaves (Mackey, 1978). Vats and Kaushal (1980) reported 75.5% AD for Belenois mesentina larvae fed on Capparis decidua leaves. The differences in the rates of digestibility and quality o f f o o d resulted in varied values o f AD in the lepidopteran larvae. Tissue growth efficiency or the efficiency of conversion of assimilated

396 TABLE IV E f f i c i e n c i e s o f f o o d u t i l i z a t i o n in t h e larvae o f P. brassicae fed o n f o u r h o s t p l a n t s ( m e a n ± 1SD)

Stage

Approximate digestibility ( A D ) (%)

Tissue g r o w t h efficiency ( E C D ) (%)

Ecological g r o w t h efficiency (ECI) (%)

35.29 36.34 39.73 42.53 33.06

28.67 26.53 26.30 25.79 16.82

Brassica oleracea vat. capitata 1st i n s t a r 2nd instar 3rd i n s t a r 4th instar 5th instar

81.25 77.73 66.21 60.63 50.89

Mean

67.34

± ± ± ± ±

2.62 1.74 4.49 3.36 4.50

± ± ± ± ±

1.22 1.28 2.56 4.34 2.87

37.39

± ± ± ± ±

1.82 1.94 2.68 3.20 1.94

± ± ± ± ±

1.42 1.71 2.34 1.80 1.51

± ± ± ± ±

1.25 1.40 1.95 2.25 1.98

± ± ± ± ±

1.03 1.54 1,27 1.74 1.95

24.82

Brassica oleracea var. botrytis 1st i n s t a r 2nd instar 3rd instar 4th instar 5 t h iv.star

80.42 72.65 60.98 56.31 49.30

Mean

63.93

± ± ± ± ±

2.39 7.73 2.76 4.82 3.90

35.71 35.88 37.36 39.80 33.05

± ± ± ± ±

0.90 1.64 2.18 2.32 1.98

36.36

28.72 26.06 22.78 20.88 16.29 22.95

Brassica compestris var. sarson 1st i n s t a r 2nd instar 3rd instar 4th instar 5th instar

81.02 72.03 60.19 53.24 50.29

Mean

63.35

± ± ± ± ±

2.01 2.90 3.64 4.67 4.84

28.31 30.08 32.19 36.70 29.95

± ± ± ± ±

1.24 1.71 2.19 3.70 2.27

31.45

22.93 21.67 19.37 18.65 15.66 19.66

Nasturtium montanum 1st i n s t a r 2nd instar 3rd i n s t a r 4th instar 5 t h irmtar

78.68 71.88 59.42 55.19 48.29

Mean

62.69

± + ± ± ±

2.27 2.47 3.54 2.92 3.45

27.47 29.64 31.09 32.45 30.55 30.24

± ± ± ± ±

1.79 1.85 2.28 3.10 2.65

21.62 21.31 18.48 18.38 14.75 18.91

food into body tissue (ECD) was lowest for the first instar larvae, increased up to fourth instar and declined in the last instar larvae on the plants fed. Barley and Singh (1977) observed that there was an increase in the ECD up to the fifth instar, but a decrease was seen in the last instar in Mamestra configurata. There was no set pattern in the larvae of CycIophragma leucostieta (Mackey, 1978). However, Vats et al. (1977) reported that ECD increased up

397

to the penultimate stage and declined afterwards. ECD did not follow a consistent pattern in the larvae of C. leucosticta (Mackey, 1978). Mean ECD values obtained for cabbage, cauliflower, sarson and nasturtium leaves are: 37.4, 36.4, 31.5 and 30.2%, respectively. Schroeder {1973, 1976) reported 57 and 44% ECD for the larvae ofPachysphinx modesta and Danaus plexippus, respectively; Bailey and Singh (1977) and Mackey (1978} als0 observed high ECD values (of 52.7 and 42.2%, respectively) for M.configurata and C. leucosticta. Vats and Kaushal (1980) reported 27.2% for the larvae of B. mesentina. B o m b y x mori were the most efficient larvae, converting 67% of the assimilated food into body tissue (Hiratsuka, 1920). Efficiency of conversion of ingested food into body tissue, or ecological efficiency (ECI) showed a gradual decline from first instar to the last instar. There was no set pattern for ECI in the larvae of M. configurata (Bailey and Singh, 1977) and C. leucosticta (Mackey, 1978}. Vats and Kaushal (1980) also reported a gradual decline of ECI in Belenois mesentina. Mean ECI in the present study was 24.8% for larvae fed on cabbage, 22.9% for those on cauliflower, 19.7 for those on sarson and 18.9% for those on nasturtium. ECI for the larvae of P. modesta and D. plexippus were 19 and 21%, respectively (Schroeder, 1973, 1976). Migula (1975) reported a 14.5% ECI for the larvae of Leucoma salicis. Waldhauer (1968) reported that in Agrotis orthogonia and Bornbyx mori, ECI declined from first to last instar larvae. Thus the values of AD, ECD and ECI show that cabbage was the best food for the larvae, followed by cauliflower, sarson and nasturtium. CONSUMPTION AT POPULATION LEVEL

The number of larvae surviving from a batch of 50 eggs on each food plant are given in Table V. On the basis of these observations, total consumption of each food plant by the surviving larvae can be calculated from Table II. The larvae developing from a batch of 50 eggs, from first to final instal would consume a total of 73.33, 40.74, 26.59 and 18.2 kcal of cabbage, cauliflower, sarson and nasturtium leaves, respectively. TABLE V Number of larvae surviving on each food plant (number observed on each food plant =

50) Food plant

1st instar* 2nd instar

3rd instar

4th iv.star

5th instar

B r a u i c a oleracea vat. capitata Brassica oleraeea vat. botrytis Brassica ¢ o m p e s t r i s vat. sarson Nasturtium montanum

45 (90.0)

42 (84.0)

39 (78.0)

35 (70.0)

32 (64.0)

41 (82,0) 39 (78.0) 35 (70.0)

36 (72.0) 35 (70.0) 31 (62.0)

31 (62.0) 30 (60.0) 26 (52.0)

29 (58.0) 26 (52.0) 24 (48.0)

25 (50.0) 24 (48.0) 20 (40.0)

*Figures in parentheses represent percentage of larvae surviving.

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