MATERIALS AND METHODS

Different cole crops viz., cabbage (Brassica oleracea var. capitata), cauliflower (Brassica oleracea var. botrytis), gobhi sarson (Brassica napus) and yellow sarson (Brassica rapa var. yellow sarson) were raised in the winter season of year 2005-2006 at experimental field of the Department of Plant Protection, Faculty of Agriculture Sciences, Aligarh Muslim University, Aligarh, India. These all crops were sown in plot size 3x4 m during the last week of October and each replicated thrice in Randomized Block Design (RBD). All these crops were monitored regularly so as to assess the attack of cabbage butterfly, Pieris brassicae. The egg laying commenced on cabbage and cauliflower in the first week of November, while on rapeseed-mustard (gobhi sarson and yellow sarson) in the last week of November. Eggs were found in clusters on the lower sides of the leaves of few plants. They were collected from respective crop fields and brought them in laboratory and placed in BOD incubator calibrated at 25±1°C coupled with 65±5% relative humidity and the photoperiod of 12 h L:12 h D. After calculating percent of hatching from eggs, one hundred newly hatched larvae were collected and reared in plastic vials (10x12 cm) along with selective food in the form of leaves. This procedure was followed for rearing P. brassicae on respective food. When the caterpillars reached in to third larval instar, were reared individually till the formation of adult in plastic vials sized 6x10 cm and their subsequent death was also noticed till the culmination of generation. Whereas, in field condition, the eggs were found on lower leaf of the plants and they were wrapped randomly through the nylon mesh on the leaf of respective host plant. After hatching, larvae were fed on desired host plants inside nylon mesh. On adult emergence, to obtain the potential fecundity of female, the males and females were collected and caged in different sized nylon mesh cage on respective host plants. The cage was specially designed with respect to crop height, for cabbage and cauliflower the cage height was 2 feet, for yellow sarson, it was 3 feet and for gobhi sarson, the cage was 6 feet in height. The meteorological data also recorded for field study.

The data collected for the development of P. brassicae were subjected to analysis of variance (ANOVA) or the Critical Difference (CD) was calculated by using formula:

The mean values were compared using Duncan’s Multiple Range Test (DMRT).

The data on survival and mortality of P. brassicae were computed and dealt here under. The developmental stage is defined as the age of insect at which insect being survived and also denoted by x. Where, l_x represents the number of individuals surviving at the beginning of each age interval out of 100. The Apparent Mortality (100 q_x) gives the information on percentage of individuals entering to next stage and was calculated by using the formula:

k-value is the key factor, which is primarily responsible for increase or decrease in number of butterflies from one generation to another and was computed as the difference between the successive values for log l_x and the total generation mortality was calculated by adding the k-values of different development stages of the cabbage butterfly, which is designated/indicated as K (Varley and Gradwell, 1960; Southwood, 1978).

Where, k_o, k₁, k₂, .......k_n are the k-values at egg, first instar, second instar, third instar, fourth instar, fifth instar, pre-pupal and pupal stages.

RESULTS AND DISCUSSION

It was inferred from Table 1 that the overall development of P. brassicae was recorded significantly higher on yellow sarson (40.70±2.38 and 37.87±1.93 days) and lower on cabbage (34.15±1.80 and 33.12±1.95 days) under laboratory and field conditions, respectively (p≤0.05). Similarly, the total immature development was also tuned high value on yellow sarson (36.55±2.24 and 33.45±1.76 days) as compared to low on cabbage (29.05±1.66 and 27.5±1.78 days) in both situations, respectively. While, adult development was recorded maximum on cabbage (5.10±0.14 and 5.62±0.17 days) in contrast to minimum on yellow sarson (4.15±0.14 and 4.42±0.17 days) under laboratory and field conditions, respectively (Table 1). Similar study also made by Bhatia et al. (1995), Thakur et al. (1998) and Metspalu et al. (2003).

Table 1:	Developmental response of cabbage butterfly, Pieris brassicae on different host plants under laboratory and field condition
Same alphabets showed non-significance whereas the different alphabets denoted significance between the host plants, CD = Critical Difference

Fig. 1:	Development of cabbage butterfly, P. brassicae on different host plants under laboratory condition (L1 = First larval instar, L2 = Second larval instar, L3 = Third larval instar, L4 = Fourth larval instar, L5 = Fifth larval instar and PP = Prepupal stage)

Fig. 2:	Development of cabbage butterfly, P. brassicae on different host plants under field condition (L1 = First larval instar, L2 = Second larval instar, L3 = Third larval instar, L4 = Fourth larval instar, L5 = Fifth larval instar and PP = Prepupal stage)

They recorded shortest development of P. brassicae on cabbage than the other cole crops.

The Fig. 1 and 2 exhibited that the development of different stages of P. brassicae viz., egg, larval instars (1st to 5th), prepupal and pupal were registered their maximum period on yellow sarson followed by gobhi sarson, cauliflower and cabbage under both laboratory and natural condition. Nevertheless, the maximum period of adult (male and female) development was witnessed on cabbage as compared to other cole crops under both conditions (Fig. 1 and 2). These findings are in complete agreement with the findings of David and Gardiner (1962), Mitchell (1977), Chew (1980), Eltez (1999), Ramdhane and Ihsan (1999) and Gupta (2002). They calculated maximum egg hatching, minimum incubation period and shortest larval development of P. brassicae on cabbage as compare to other cole crops. However, Metspalu et al. (2003) opined that the gobhi sarson (Brassica napus) also preferred food of P. brassicae.

A remarkable difference was however recorded on mortality parameters of cabbage butterfly on different host plants under laboratory as well as field condition. Among developmental stages the highest percent mortality was recorded at pupal stages (14.89 and 21.74%) on yellow sarson and lowest at prepupal stage (3.39 and 3.51%) on cabbage under laboratory and field condition, respectively (Table 2 and 3). Likewise, the cabbage butterfly tuned their highest generation mortality on yellow sarson (0.3565 and 0.3645) in contrast to lowest on cabbage (0.2555 and 0.2486) in both situations, respectively. It was also inferred from Table 2 and 3 that the emerged adults were also recorded maximum on cabbage (52 and 48 individuals) followed by cauliflower (46 and 42 individuals), gobhi sarson (43 and 40 individuals) and yellow sarson (40 and 36 individuals) under laboratory and field conditions, respectively.

Table 2:	Survival, mortality and k-values of cabbage butterfly, P. brassicae on different host plants under laboratory condition
A = Cabbage, B = Cauliflower, C = Gobhi sarson and D = Yellow sarson, x = Developmental stages, lx = Individuals surviving at the beginning of each age interval, 100qx = Percent mortality, log lx = log value of surviving individuals, k = Factor responsible for increase or decrease in number from one generation to another and K = Total generation mortality

Table 3:	Survival, mortality and k-values of cabbage butterfly, P. brassicae on different host plants under natural condition
A = Cabbage, B = Cauliflower, C = Gobhi sarson and D = Yellow sarson, x = Developmental stages, lx = Individuals surviving at the beginning of each age interval, 100qx = Percent mortality, log lx = log value of surviving individuals, k = Factor responsible for increase or decrease in number from one generation to another and K = Total generation mortality

Similar observations also made by Hashmi et al. (1985), Rai et al. (1985) and Thakur and Deka (1997) on different cole crops in laboratory as well as field conditions. This study further strength by Sharma et al. (1999) they reported the number of emerged adults was highest in laboratory in comparison to field condition.

A comparative study revealed that P. brassicae took shorter period for their development in field condition as compared to laboratory with regard to all cole crops. Where, number of adults was recorded maximum in laboratory than the field condition on all cole crops. It is possible due to the presence of natural enemies (predators and parasitoids), abiotic factors (temperature, relative humidity and rainfall) and some unknown factors in the field condition. Therefore, it can be concluded from the present study that cabbage butterfly, Pieris brassicae exhibited their speedy development on cabbage with highest yield of adults in both laboratory and field conditions and the yellow sarson is the least preferred food.

ACKNOWLEDGMENT

The authors are grateful to authority of Department of Plant Protection, Faculty of Agricultural Sciences to support this research.