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J. Crop Sci. Biotech. 2010 (September) 13 (3) : 195 ~ 202 DOI No. 10.1007/s12892-010-0025-2 RESEARCH ARTICLE

Effect of Different Cole Crops on the Biological Parameters of Pieris brassicae (L.) (Lepidoptera: Pieridae) under Laboratory Conditions Fazil Hasan1*, M. Shafiq Ansari 1

Department of Plant Protection, Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh 202002, India

Received: January 29, 2010 / Revised: May 30, 2010 / Accepted: September 20, 2010 Ⓒ Korean Society of Crop Science and Springer 2010

Abstract The effect of different cole crops was studied on biological parameters of Pieris brassicae (L.) in the laboratory at 28 ˚C, 65% RH, and 12L:12D photoperiod. The results indicated that host plants significantly affected the life history , i.e. survival of developmental stages, oviposition period, and sex ratio of P. brassicae. Comparative study on different host plant revealed that P. brassicae required a maximum of 40 days to complete generation on cabbage, cauliflower, and broccoli. The survivorship and expectation of life declined gradually with the advancement of age; the life expectancy of newly deposited eggs was 23.96 days while it was 8.12 days at the time of adult emergence on cabbage. However, the fluctuations of mortality parameter were seen on all the cole crops. On cabbage, 100% hatching of eggs with low larval mortality were noticed. The highest net reproductive rate (R0) occurred on cauliflower, i.e. 27.1 followed by cabbage 24.89, females per female per generation. Intrinsic rate of increase (rm), was found to be highest (0.09558954) on cauliflower followed by broccoli and cabbage, 0.078886 and 0.077551 females per female per day, respectively. The smallest rm (0.059469 females per female per day) occurred on radish which shows that P. brassicae did not perform well on radish. In addition, P. brassicae may double in 7.2 days on cauliflower, 8.7 days on broccoli, and 8.9 days on cabbage. The sex ratio was computed as 1.5:1, female:male, respectively on cabbage. Key words: fertility life table parameters, host plants, mortality, Pieris brassicae, sex ratio

Introduction The term 'cole crops' refers to plants in the crucifer family within the genus Brassica (more specifically, varieties of the species Brassica oleracea) that have similar pest complexes. These crops include some of the most popular internationally grown vegetables such as cabbage (Brassica oleracea var. capitata), cauliflower (B. oleracea var. botrytis), Chinese cabbage (B. chinensis), broccoli (B. oleracea var. italica), brussel sprouts (B. oleracea var. gemmifera), etc. (Published report by Riley and Sparks). These originated in the Mediterranean era and were introduced into India during the Mughal period (Das 1992; Sood 2007; Hasan 2008). These crops are rich in minerals like iron, magnesium, phosphorous, etc. Besides these crops, rapeseed

Fazil Hasan ( ) Email: [email protected] Fax: +91- 9259167918

The Korean Society of Crop Science

mustard is also an important oilseed crop next to groundnut in India. All these crops are cultivated in the winter season and prefers 60 - 70 ˚F for their optimal growth and can withstand light frost without injury (Iowa State University, Extension 1896). Late varieties will continue to grow at fall temperatures as low as 41 ˚F, but few varieties make much growth above 78 ˚F (Hodges and Neild 1992). The cole crops are extensively grown in tropical and subtropical regions of the world (Das 1992). India is world's largest producer of vegetables ahead of China (Shanmungaveu 1989; Weinberger and Srinivasan 2009), but the per capita consumption is quiet lower (Dhandapani et al. 2003). It has been estimated that damage from insect pests alone causes more than 40% of yield loss on vegetable crops annually. Pajmon (1999) listed 38 insect pests on the cole crops, among these cabbage butterfly, Pieris brassicae, is one of the most destructive (Bhalla and Pawar 1977), causing damage at all the

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Biological Parameters of Pieris brassicae on various cole crops

growing stages (seedling, vegetative, and flowering) (Gangwar 1980; Siraj 1999; Lal and Ram 2004; Sachan and Younas et al. 2004; Hasan 2008; Bhandari 2009). Females lay batches of eggs on their host plant in the spring. Caterpillars emerge and feed on the host plant as a group until the late fourth or early fifth instar when they disperse over the plant (Blatt et al. 2008). At the end of the fifth instar, they begin wandering off the plant in search of a pupation site. The number of eggs per batch can vary from seven to 105 (Kristensen 1994; Blatt et al. 2008), but on average there are between 30 and 50 eggs per batch (Feltwell 1982). It is an oligophagous pest with a wide host range and is known to infest 83 species of food plants belonging to Cruciferae. It has a Palearctic distribution from North Africa across Europe and Asia to the Himalayan Mountains (Jainulabdeen and Prasad 2004; Raqib 2004). In India, it passes winter in the plains and migrates to hilly regions during summer (Gupta 1984). It breeds on rapeseed-mustard in the month of September and remains active until April. The young caterpillars feed gregariously on leaves, resulting in defoliation of the plants (Jainulabdeen and Prasad 2004; Younas et al. 2004; Hasan 2008). Larvae eat not only the leaves but also branches, pods, and the seeds of cabbage and cauliflower (Siraj 1999) and cause serious damage economically. On cabbage and cauliflower, the caterpillars sometime bore into the heads and becomes very destructive (Hasan 2008; Sharma and Gupta 2009). During development, one single larva of P. brassicae consumes 74 - 80 cm2 leaf area (Younas et al. 2004). Moreover, this pest has developed resistance against some insecticides (Sharma and Gupta 2009). The strategies for controlling this insect pest on vegetable crops in general need a detailed study. Life tables are powerful tools for analyzing and understanding the impact that an external factor has upon the growth, survival, reproduction, and rate of increase of an insect population (Bellows et al. 1992). In addition, the classical life table is used primarily to understand the age dynamics of adult population studies under controlled laboratory conditions. The objective of this study was to determine effects of different cole crops on age-specific life table, female fertility table, and on the number of both sexes emerging of P. brassicae under controlled environmental conditions.

Materials and Methods Insect rearing and experimental conditions Different cole crops viz., cabbage, cauliflower, mustard, broccoli, and radish were raised in the winter season of 2007 - 2008 at the experimental field of the Department of Plant Protection, Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh, India. The seedlings of all crops were sown in pots 3 x 3 m. All crops were monitored regularly so as to assess the attack of the cabbage butterfly, P. brassicae. The egg laying commenced on cabbage, cauliflower, and broccoli in the months of November and December, and on mustard and radish in the months of December and January. Eggs were found in clusters on the lower and upper sides of

the leaves of the plants. They were collected from respective crops, brought into the laboratory, and placed in a BOD incubator calibrated at 28 ˚C coupled with 65% relative humidity. After calculating the percent hatching from eggs, 100 newly hatched, healthy larvae were selected and reared in plastic vials (10 x 12 cm) along with respective food in the form of fresh leaves. Progeny of laboratory reared P. brassicae was used in the experiments. Fresh food from respective cole crops in the form of leaves were supplied to the larvae and filter paper was changed daily to maintain hygienic conditions.

Effect of different cole crops on age-specific life table Freshly emerged adults males and females were sorted out from stock culture and kept in jars (25 x 15 cm) provided with sugar solution as a food for adults and fresh leaves of respective cole crops for oviposition by females. The eggs laid by females were counted and kept in batches of 10 and replicated 10 times for construction of the life table (100 cohort). The number of alive and dead, out of 100 larvae was recorded daily every 24 h on all respective cole crops and removed from experimental jars. After a series of molts, the larvae pupated, the deformed pupae were counted, and then discarded.

Effect of different cole crops on female fertility table One female and two males, all newly emerged, of P. brassicae were transferred on the respective food plants into jars (25 x 15 cm). A new male was added whenever another male died. Thus, female have alternative males for mating during lifetime. Female fecundity, pre-oviposition, oviposition, and post-oviposition periods were also calculated. Life tables were constructed based on Birch (1948) and Southwood (1978). For adults, the survival rate from birth to age x (Ix), fecundity (Mx, total number of offspring produced at age x), and mx (female offspring produced at age x) were calculated according to Birch (1948). From these data, the intrinsic rate of increase (rm, females per female per day), the net reproductive rate (R0, females per female per generation), finite rate of increase (λ, individuals per females per day), the mean generation time (T, In (R0)/rm), and the doubling time (DT, day) were estimated using dedicated software.

Effect of different cole crops on the number of both sexes emerging To determine the effect of different cole crops on the sex ratio, the eggs were allowed to develop to adulthood on all the respective host plants and incubated at 28˚C temperature coupled with 65% relative humidity and photoperiod (L: D) of 12 : 12 were maintained through adult development and then the sex was determined.

Data analysis The following assumptions were used in the documenta-

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tion of age specific life-table. 1. x = age of the insect in days 2. lx = number of individuals that survived at the beginning of each age interval x 3. dx = number of individuals that died during the age interval x 4. 100qx = per cent mortality, computed through the following equation: (1) 100qx = [dx/ lx] x 100 5. ex = expectation of life or mean life remaining for individuals of age x Life expectation was calculated by using the equation: (2) ex = Tx / lx To obtain ex, two other parameters Lx and Tx were also computed as below 6. Lx = the number of individuals alive between age x and x+1 and calculated by the equation: Lx = lx+1 (x+1)/2 (3) 7. Tx = the total number of individuals of x age units beyond the age x and obtained by the equation: Tx = lx + (lx + 1) + (lx + 2)………………..+lw (4) Where, lw = the last age interval The following parameters were also computed for female fertility table: 1. Net reproductive or replacement rate (R0): referred to as the "carrying capacity" of the average insect under defined environmental conditions. The information on the multiplication rate of a population in one generation is obtained from the following equation: (5) R0 = Ix mx 2. Mean length of generation (T): denoted as the mean period between the birth of the parent and the birth of their offspring. This period is a weighed approximate value since the progeny is produced over a period of time and not at a definite time. The calculation followed the method suggested by Dubin and Lotka (1925). T = ∑ [Ix. mx. X] / ∑ [Ix. mx] (6) 3. Intrinsic rate of increase (r): defined as the instantaneous rate of increase of a population in a unit time under a set of ecological condition (Birch 1948). A rough and accurate estimate of the intrinsic rate of increase (r) can be calculated by using the following equation: (I) r = [Loge R0] / T (for rough estimation) (II) e-rx. Ix mx = 1 (for accurate estimation) (7) where 'R0' represents net reproductive rate and 'T' represents mean length of generation. 4. Finite rate of increase (λ): provides the information about the frequency of the population multiplication in a unit of time (Birch 1948). λ= er (8) Taking loge on both sides we get loge λ= loge er, where, λ= Antiloge er 5. Potential fecundity (Pf): expresses the total number of eggs laid by an average female in her life span. It is obtained or calculated by adding up the age-specific fecundity column. Pf = ∑ mx (9)

6. Doubling Time (DT): defined as the time required for the population to double and is calculated as follows: DT = Loge 2/r (10) 7. Annual Rate of Increase (ARI): This can be calculated from the intrinsic rate of increase (r), finite rate of increase (λ), doubling time (DT), or the net reproductive rate (R0) assuming that the rate of increase was constant throughout the year. ARI = 365 = e365r = 2365/DT = R0365/T (11) Jackknife pseudo-values were calculated with a computer program (La Rossa and Kahn 2003). The data collected from the variation in number of both sexes emerging on different cole crops were subjected to analysis of variance (ANOVA) by using the language program "R 2.11.1" unless stated otherwise. If significant differences were detected, the mean values were compared using Duncan's multiple range test (DMRT).

Results Effect of cole crops on age-specific life table of P. brassicae

Fig 1. Survivorship (lx) and life expectancy (ex) of P. brassicae on different cole crops, cabbage (A), cauliflower (B), mustard (C), radish (D), and broccoli (E). (E= incubation period; I-V L= first - fifth larval period; PP = prepupal period; P = pupal period; A = adult period)

Comparative study on age-specific life table of cabbage butterfly on different host plants revealed that it required s maximum of 40 days to complete s generation on cabbage, cauliflower, and broccoli, 38 days on radish, and 39 days on

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of newly deposited eggs was 23.96 days while it was 8.12 days at the time of adult emergence on cabbage (Fig. 1A).

Effect of different cole crops on the female fertility table

Fig. 2. Mortality (dx) of developmental stages of P. brassicae on different cole crops, cabbage (A), cauliflower (B), mustard (C), radish (D), and broccoli (E). (EM=egg mortality; I-V LM= first °© fifth instar mortality; PPM = pre-pupal mortality; PM = pupal mortality; AM = adult mortality)

mustard (Figs. 1 and 2). The survivorship and expectation of life declined gradually with advancement of age (Figs. 1 and 2). However, the fluctuations of mortality parameter were seen on all the cole crops (Fig. 2). The highest percent (25) of unhatched eggs were found on mustard followed by 18% on cauliflower, 12% on radish on the last day (5th) of the incubation period (Figs. 2C, 2B, and 2D, respectively). While on cabbage and broccoli, 100% hatching of eggs was recorded (Figs. 2A and 2E). It was demarcated in Fig. 1 that the early instars stages are more susceptible than late instar stages. Hence, the highest mortality of early instar stages was found on all the host plants. The highest mortality of the first instars (seven individuals) were found on mustard at the 6th day followed by six individuals on cauliflower on the 8th day, and five individuals on radish at the 9th day of the developmental period but on radish the late instars stages, even the pupal stage, were also found susceptible and the highest mortality occurred. The continuous fluctuation in the mortality parameters were seen in Fig. 1d. On radish eight and five pupa were found to have died during the middle and at the end of the pupal period, respectively. The mortality at the adult stage was recorded after three days of emergence from pupa on cabbage, cauliflower, and mustard, and after four days on broccoli, whereas on radish the mortality of adults began the next day of emergence from pupa and continued until the death of the remaining individual adults (Fig. 2D). The life expectancy declined with advancing of age. The highest life expectancy was found on cabbage in comparison to other cole crops (Fig. 1). For example, the life expectancy

Total fecundity of P. brassicae was significantly influenced by different host plants (f = 0.89, df = 14, p = 0.758) and was higher on cabbage than other cole crops (Table 1). The lowest mean fecundity (m x ), 99 eggs per female, occurred on broccoli. Daily reproduction was also affected by different host plants in the following order: cabbage < cauliflower < mustard < radish < broccoli (Table 1). It was apparent that female oviposited the eggs during a definite period of pivotal age. The female starts to lay eggs after 2 days of the pre-oviposition period in cabbage, mustard, radish, and broccoli, and 3 days after in cauliflower. The longest duration of natality of 6 days was encountered on cabbage and cauliflower while the shortest was on radish (4 days). There was a significant difference in the net reproductive rate (R0) of P. brassicae on all the cole crops (Table 2). The highest net reproductive rate (R0) occurred on cauliflower, (27.1), followed by cabbage (24.89), and broccoli (14.96 females/female/generation). However, the smallest net reproductive rate (R0), 7.76 females per female per generation, was recorded on radish. The fractional difference between capacity of increase (r c), and intrinsic rate of increase (rm) was found to be highest (0.09558954) on cauliflower, followed by broccoli, and cabbage, 0.078886 and 0.077551 females/female/day, respectively. The smallest rm (0.059469 females per female per day) occurred on radish which showed that P. brassicae did not perform well on radish. Infinite rate of increase (λ) is always greater than the intrinsic rate of increase. In the present study, the infinite rate of increase (λ) was similar on cabbage and broccoli and was computed as 1.08 individuals per females per day. However, the highest infinite rate of increase 1.10 individuals per females per day was recorded on cauliflower. There was an insignificant difference on mean generation time (Tc) on different host plants and 34.60 days found on cabbage. It was calculated that mean and corrected generation time are almost same with an insignificant difference. In addition, P. brassicae may become double in 7.2 days on cauliflower followed by 8.7 and 8.9 days on broccoli and cabbage, respectively (Table 2).

Effect of different cole crops on the number of both sex emerging Sex ratio is also influenced by the host plants and the results obtained in this study showed that the host plant had a considerable effect on the number of each sex of P. brassicae. It was apparent that the population of female and male was recorded significantly greater on cabbage (f = 0.51, df = 14, p = 0.619, and f = 0.48, df =14, p = 0.592, respectively) compared to other cole crops (Fig. 3). However, it was also inferred from the pooled observations that the popu-

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Table 1. Age-specific female fecundity of P. brassicae on different cole crops Pivotal age (Day) x

Age-specific female survivorship lx

0.5-30.0 31.5-32.5 33.5 34.5 35.5 36.5 37.5 38.5 39.5 40.5

Value of e-rmxIx.mx

Fecundity

mx

lx.mx

% constitution of each group towards 'r'

lxmx.x Cabbage rm = 0.0775

Immature stages Pre-oviposition period 0.20 48.00 9.60 0.19 41.50 7.89 0.15 27.00 4.05 0.15 15.00 2.25 0.13 7.50 0.98 0.09 1.50 0.14 0.05 0.00 0.00 0.04 0.00 0.00 Total 140.5 24.89

321.60 272.03 143.78 82.13 36.56 5.20 0.00 0.00 861.29

0.714 0.160 0.073 0.036 0.014 0.002 0.000 0.000 1.00

0.5-30.0 Immature stages 31.5-32.5 Pre-oviposition period 33.5 0.25 45.00 11.25 34.5 0.20 40.00 8.00 35.5 0.18 25.00 4.50 36.5 0.18 12.50 2.25 37.5 0.17 5.00 0.85 38.5 0.10 2.50 0.25 39.5 0.07 0.00 0.00 40.5 0.03 0.00 0.00 Total 130 27.10

376.88 276.00 159.75 82.13 31.88 9.63 0.00 0.00 936.25

0.458 0.296 0.151 0.069 0.024 0.006 0.000 0.000 1.00

0.5-30.0 Immature stages 31.5-32.5 Pre-oviposition period 41.50 4.56 33.5 0.11 31.00 3.41 34.5 0.11 25.00 1.75 35.5 0.07 6.50 0.32 36.5 0.05 2.00 0.10 37.5 0.05 0.00 0.00 38.5 0.04 0.00 0.00 39.5 0.04 Total 106 10.15

152.92 117.64 62.12 11.86 3.75 0.00 0.00 348.31

0.475 0.331 0.159 0.028 0.008 0.000 0.000 1.00

0.5-30.0 Immature stages 31.5-32.5 Pre-oviposition period 33.5 0.08 42.50 34.5 0.08 37.00 35.5 0.08 12.50 36.5 0.05 8.00 37.5 0.04 0.00 38.5 0.04 0.00 Total 100

3.40 2.96 1.00 0.40 0.00 0.00 7.76

115.26 102.12 35.50 14.60 0.00 0.00 267.48

0.453 0.380 0.121 0.045 0.000 0.000 1.00

0.5-30.0 Immature stages 31.5-32.5 Pre-oviposition period 33.5 0.16 41.50 6.64 34.5 0.15 36.00 5.40 35.5 0.15 12.50 1.87 36.5 0.12 7.50 0.90 37.5 0.10 1.50 0.15 38.5 0.08 0.00 0.00 39.5 0.03 0.00 0.00 40.5 0.02 0.00 0.00 Total 99 14.96

222.44 186.30 66.56 32.85 5.62 0.00 0.00 0.00 513.77

0.473 0.355 0.114 0.051 0.008 0.000 0.000 0.000 1.00

Table 2. Effect of different cole crops on the life indices of P. brassicae Parameters

Cabbage 24.89 Net reproductive rate (R0) Intrinsic rate of increase (rm) 0.0775 Finite rate of increase (λ) 1.08 Mean length of generation (Tc) 34.60 Correct generation time (τ) 34.53 Doubling time (DT) 8.93

Different cole crops Cauliflower Mustard Radish Broccoli 27.10 10.15 7.76 14.96 0.0956 0.0676 0.0594 0.0789 1.10 1.07 1.06 1.08 34.54 34.31 34.46 34.33 34.41 34.30 34.45 34.29 7.25 10.25 11.65 8.78

71.400 16.000 7.300 3.600 1.400 0.200 0.000 0.000 100.00 Cauliflower rm = 0.0956 45.754 29.570 15.117 6.869 2.359 0.630 0.000 0.000 100.00 Mustard rm = 0.0676 47.500 33.100 15.900 2.800 0.800 0.000 0.000 100.00 Radish rm = 0.0594

Fig. 3. Effect of different cole crops on the number of female (A) and male (B) emergence of P. brassicae. Means followed by same letters are not significantly different by DMRT.

Discussion Genetic diversity of maize genotypes

45.300 38.041 12.109 4.564 0.000 0.000 100.00 Broccoli rm = 0.0789 47.300 35.500 11.400 5.100 0.800 0.000 0.000 0.000 100.00

lations of females were highest on all cole crops compared to male populations. The highest number of females (18 individuals) was recorded on cabbage from the 30 individual adults and the sex ratio (female:male) was computed as 1.5:1, respectively.

The results indicated that host plants affected life history parameters of P. brassicae. Thus, survival of developmental stages, oviposition period, and sex ratio were significantly affected by different host plants. The survival of P. brassicae decreases continuously from day one until the end of generations on all host plants. Ahmad et al. (2007) found that the death rate of P. brassicae was superior during the initial days due to high mortality of early instars. However, the lowest mortality of early instar stages was found on cabbage than other cole crops. It may be due to the soft tissue texture (Gupta 2002), whereas, other cole crops like radish and mustard have hard tissue texture and spine like appendages (trichomes) on leaves resulting in high mortality at early instars (Ahmad et al. 2007). Furthermore, the production of chemicals, such as toxins and digestibility reducers, may interfere with the physiology of the herbivore and reduce growth and survival (Schoonhoven et al. 2005). During the late instar stages, the death rate decrease automatically on each host plant because the maxillae and mandibles of mouth parts get modified in these stages and larva can tend to eat plant leaves

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easily. A little mortality of larvae was also found at later stages of development, possibly due to the variation in nutritional value of host plants. Several studies supported the nutritional value of these crops (Font et al. 2005; Newkirk et al. 2007; Padilla et al. 2007; Scalzo et al. 2008). Among different host plants, another reason for low mortality on cabbage may be due to the choice of food. In contrast, the high mortality was recorded on radish followed by mustard. The maximum survival was recorded at a later stage of development on all the cole crops (Thapa 1987; Melspalu et al. 2003 ). In holometabolous herbivores (Lepidoptera, Coleoptera, Diptera, and Hymenoptera), the larval food is decided by the ovipositing female. Cabbage plants with a higher content of volatile allyl nitriles are more attractive for oviposition of P. brassicae than plants with lesser amounts of the volatiles because in the larvae of P. brassicae, allylglucosinolate (sinigrin) serves as an incitant and promotes biting activity (Mitchell 1977; Renwick 1983). P. brassicae are able to detect physiological differences among plants, sometimes 24 h after fertilization. Variables associated with a plant's physiological status are transpiration, water content of leaves, and nutrient concentrations. Wolfson (1980) makes a case for leaf-water content being an important indicator of the nutritional status of plants to ovipositing butterflies. Leaf-water content has been found to be associated with larval development in a number of studies (Soo Hoo and Fraenkel 1966; Reese 1977; Scriber 1977; Slansky and Feeny 1977; Rausher 1981) and with oviposition preferences in several other studies (Shorey 1964; Benepal and Hall 1967; Ives 1978). However, water content and nitrogen content are generally positively correlated (Mattson 1980) and both of these are related to transpiration rates. Consequently, oviposition is based on cues that correlate with the prospects of larval survival. The oviposition site is a critical factor for the young larvae seeking out hosts because the slow moving larvae find it difficult to reach the appropriate host plant. The neonate larvae usually suffer very high mortality if forced to leave their original host (Wittstock 2004). The intrinsic rate of natural increase (r m) is the most important parameters for describing the growth potential of a population under given climatic and food conditions because, rm reflects an overall effect on development, reproduction, and survival (Southwood and Handerson 2000; Kafil et al. 2007). Therefore, P. brassicae population that fed cabbage, cauliflower, and broccoli showed a higher intrinsic rate of increase resulting from faster development, higher survivorship, and oviposition rates. These three species are presumably more suitable hosts for this pest. Sood et al. (1994) studied the growth rate of P. brassicae by developing schedules on cabbage and cauliflower. He found that the multiplication rate was lower on cauliflower and higher on cabbage. Intrinsic rate of increase (r m) was comparatively higher in insects reared on cabbage than on cauliflower. However, in insects having a few and distinct generations per year, the innate capacity of natural increase (rc) is a valid approximation for rm (Laughlin 1965). The developmental period was faster on cabbage and cauliflower hence, the rm value was

higher on these crops than other cole crops. In addition, the finite rate of increase (λ) was comparatively higher on cabbage and cauliflower, and populations of P. brassica e double in the minimum duration on the same crops (Sood et al. 1994). Cole (1954) also reported a linear inverse relationship of rc to the generation time (T). Contrary to this, a shorter development time on cauliflower, radish, and mustard did not increase the value of rc which may be attributed to poor nutritional status and reduced survival of the cohort, resulting in low net reproductive rates. Host plant resistance decreased fecundity and becomes a cause of high mortality of the P. brassicae generally predicted by Painter (1951). Therefore, it can be concluded from the present study that P. brassicae prefers cabbage and cauliflower for speedy and healthy development with low larval mortality and highest number of adult yield than other cole crops.

Acknowledgments I am thankful to the University Grants Commission (UGC), New Delhi, India for providing a fellowship.

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