Population dynamics, Brevicoryne brassicae, cabbage, chinese cabbage, cauliflower, broccoli, radish.

Brassicaceae are considered as "cool season" vegetables because they can withstand light freezing temperatures. Most cole crops thrive best at temperatures between 60 and 65 F. The species and genus from wild species prevalent in the Mediterranean region, Brassica oleracea was developed throughout western and central Europe. Although they are similar, they are not the same. Each group has had many variations created, varying in terms of insect susceptibility, temperature tolerance, form, colour, and growing season (Maynard and Hochmuth 1997). The most frequent pests among the many insect species that attack cruciferous vegetables are aphids. Although it originated in Europe (Sharma et al., 2022), the cabbage aphid, B. brassicae is now widespread across the temperate and warm temperate zones of the world (Blackman and Eastop 2000). This aphid is a severe pest of cabbage and a specialist of plants in the Brassicaceae family (Gabrys et al., 1997). B. brassicae reduces cabbage output from 70% to 80% when there is a strong infestation (Khattak et al., 2002; Rustamani et al., 1988). The infected plants grow slowly, losing 9-77% of their seed production and 11% of their seed oil content (Kelm and Gadomski 1995). Numerous studies on various aphid species have been conducted in the past across the nation, but the information on the relationship between the five brassicae crops (cabbage, chinese cabbage, broccoli, cauliflower, and radish) and the weather in the area has been relatively scarce. Therefore, the present experiment was conducted to study the population dynamics of cabbage aphid on brassicae crops.

A. Location of the experiment

The experiment was conducted at the experimental farm as well as in the Department laboratory, SASRD, NU, Medziphema Campus, under Chumukedima district, Nagaland during 2021-2022 crop seasons which lies at 21° 45′43″ North latitude and 93°C 52′04″ East longitudes at an elevation of 310 meters above sea level (MSL). The climate of this region was sub-humid with an average annual rainfall ranges from 2000-3000 mm. The moderate mean temperature ranges from 21 to 32°C during summer and winter from 10-15°C that rarely goes below 8°C with a relative humidity of 70 to 80%. The soil was sandy loam, acidic in nature with a pH ranging from 4.5-6.5.

B. Experimental details

Cabbage (Fire Ball), Cauliflower (Candid Charm), Broccoli (Green Magic), and Chinese cabbage (Melody) were sown in nursery on 15th November, 2021 and one month old seedlings were transplanted at a spacing of 45cm × 60cm and Radish (Japani White) radish were planted at 30cm × 10cm. Field experiment was carried out in Randomized Block Design (RBD) having four replication on each crop with five treatment. Aphids were counted from five randomly selected and tagged plant from each replication of all crops. Observation of the cabbage aphid population began two weeks after transplanting and was conducted by counting the population from one square inch of leaf area from two leaves per plant (top and bottom leave), by examining on both sides of the leaf at five randomly selected plants in each plot of five brassiace crops, and both nymph and adult were taken into consideration at weekly intervals until the crops were matured. Meteorological parameters viz., temperature, relative humidity and rainfall were collected and correlated with aphid population.

Population dynamics of cabbage aphid (Brevicoryne brassicae L.) on different brassicae crops is presented in Fig. 1 and Table 1.

As evidence from Table 1 and Fig. 1 the population of cabbage aphid, B. brassicae on cabbage was observed throughout the cropping period. The weekly observation on cabbage aphid population showed that first appearance of cabbage aphid population was started from 3rd week of January, 2022 with a mean population of 0.63 aphids per plant. It was low at the beginning but gradually started to increase and reached its highest peak in the second week of March with a mean population of 3.80 aphids/plant. The second highest population was observed in the following week with a mean population of 3.53 aphids/plant (Table 1). 

Present findings are similar with Aslam et al. (2007) who reported that the population of B. brassicae was highest during early to mid-March. However, Bhavani and Punnaiah (2006) reported that the highest population of cabbage aphid was observed during the second week of February while the minimum population was observed during last week of March which is contradictory with the present findings. The differences may be due to the variation in environmental conditions.

On Chinese cabbage the population started appearing from the end of January onwards. There was a marginal increase in aphid population and reached its highest population on chinese cabbage in the second week (0.93 aphids/plant) followed by third week on the month of March (0.83 aphids/plant) when the maximum and minimum temperature (°C), relative humidity (%) and rainfall (mm) were 33.50°C, 12.20°C, 92%, 37% and no rainfall respectively. The population was found till the harvesting of the crop. The result are in accordance with Indira et al. (2001) who found that B. brassicae had its peak population in the second week of March.   

Table 1: Population dynamics of cabbage aphid (Brevicoryne brassicae L.) on different brassicae crops.

In contrast to the present study, Raj and Sharma (1991) observed the maximum population of aphid during the first week of April. The variation could be due to prevailing climatic conditions.

There was no population of B. brassicae on cauliflower in the mid of January. The population started appearing on cauliflower on the last week of January and a significant increase was observed in the last part of February and reached its maximum population in the first week of March with a mean population of 2.58 aphids/plant. During this period the maximum and minimum temperature (°C), relative humidity (%) and rainfall (mm) were 31.00°C, 12.40°C, 94%, 37% and no rainfall respectively. The population was found till harvesting of the crop. Younas et al. (2004) observed that the aphid infestation was started at the last week of October with an average population density ranging from 0-11.33 aphids/cm2 on five cauliflower cultivars and increased gradually and remained at the peak from 1st week of November to mid of November with an average population density of 0.00-31.76 aphids/cm2 and 0.00-26.67/cm2 on five cultivar which is at variation to the present study as the incidence of aphid in Nagaland appear slightly late. Bhat et al. (2012) reported two peak population of the aphid during October and June which is in contradictory with the present findings. The variation could be due to prevailing climatic conditions. However, Dogra et al. (2001) recorded the peak population of B. brassicae during the second week of March which corroborate with the present study.

The population of B. brassicae in broccoli revealed that its infestation initiated in the third week of January (0.55 aphids/plant). The population was low in the beginning but increased considerably by the last of February with a mean population of 2.18 aphids/plant. It reached its highest peak during the first week of March with a mean population of 2.78 aphids/plant. The population was high till the harvesting of the crop. During this period the maximum and minimum temperature (°C), relative humidity (%) and rainfall (mm) were 31.00°C, 12.4°C, 94%, 37% and no rainfall respectively. In contrast to the present study Bhevani and Punnaiah (2006) reported that the highest aphid population was observed on second week of February while the lowest was on the last week of March. Jahan et al. (2013) also found that the aphid population reached its peak infestation during the first half of November and later reduced from the second half of November. The variations could be due to different climate conditions.

No population was found at the beginning of growing period of radish. The population started to appear from 4th week of January, 2022 with a mean population of 0.13 aphids/plant which gradually increased and reached its highest population with 0.93 aphids/plant in the 2nd week of March, 2022. Lowest population was found on radish as compared to other crops. Indira et al. (2001) found that the peak population of B. brassicae during second week of March. However, Jahan et al. (2013) studied on the population density of B. brassicae and found that aphid population reached peak infestation during the first half of November which are in contradictory with the present study. During the study period presented on Table 3, the correlation data between B. brassicae population and weather parameters on cabbage revealed that the aphid population was significant and positively correlated with the maximum and minimum temperature and negatively significant with the maximum and minimum relative humidity and non-significant with rainfall.

Table 2:  Meteorological observations during the period of study (January 2022 to March 2022).

Table 3: Correlation coefficient (r) of cabbage aphid, B. brassicae with weather parameters recorded during January 2022 to March 2022.

The computed results showed that the population of B. brassicae was substantially related with maximum and minimum temperature, maximum and minimum relative humidity, respectively. Similar finding was reported by Pal and Singh (2012) who found that the population build-up of B. brassicae was positively correlated to maximum temperature, minimum temperature and negatively correlated to relative humidity. In contrast, Kumar et al. (2009) observed that the aphid population exhibited non-significant negative correlation with maximum and minimum temperature, maximum and minimum relative humidity, rainfall and sunshine hours. Patra et al. (2012) also reported that correlation study between weather parameters and aphid population showed negative influence of temperature, relative humidity and rainfall on population growth of aphid.

On chinese cabbage the correlation showed that the aphid population had significant positive correlation with the maximum and minimum temperature but negatively with maximum and minimum relative humidity but non-significant with rainfall. Shalini and Kamal (2016) observed that the population of B. brassicae had significant positive influence of maximum and minimum temperature but there was no influence of rainfall in the population which corroborate the present findings. Bhavani and Punnaiah (2006) observed significant positive correlation between relative humidity and aphid population which is at variation to the present findings.

Correlation analysis on cauliflower showed that the aphid population was significantly and positively correlated with the maximum temperature and negatively significant with minimum relative humidity while non-significant with relative minimum temperature, maximum relative humidity and rainfall. Pal and Singh (2012) also recorded that the population build-up of B. brassicae was positively correlated to maximum temperature minimum temperature and negatively correlated to relative humidity and total rainfall. Patra et al. (2012) also reported that correlation study between weather parameters and aphid population showed negative influence of temperature, relative humidity and rainfall on population growth of aphid.

From correlation analysis of B. brassicae population on broccoli with weather parameters, there was significant positive correlation between aphid population and maximum temperature but negative with minimum relative humidity while non-significant with minimum temperature maximum relative humidity and rainfall. Similar finding was observed by Pal and Singh (2012) who reported that the population of B. brassicae was positively correlated to maximum temperature and negatively correlated with relative humidity and Shalini and Kamal (2016) who reported that the aphid population had significant positive influence of maximum temperature and negative influence of humidity. In contrast, Amini et al. (2012) observed that there was no significant relationship between weather values recorded and aphid population observed in the field. Patra et al. (2012) reported that aphid population showed negative influence of temperature, relative humidity and rainfall on population growth of aphid which is similar to the present findings.

Correlation analysis on radish indicated that the aphid population had significant positive correlation with the maximum temperature but found to have negative significant correlation with maximum and minimum relative humidity while non-significant with minimum temperature and rainfall. The result is supported by Shalini and Kamal (2016) who observed that the aphid population had significant positive correlation with maximum temperature and negative correlation with relative humidity and non-significant with rainfall. However, Raj and Sharma (1991) showed that temperature and relative humidity had no significant impact on the population build-up of B. brassicae and rainfall caused a reduction in the population which is at variation with the present findings.

Table 4: Extent of parasitization on B. brassicae in field condition on Cabbage, Chinese cabbage, Cauliflower, Broccoli and Radish during January, 2022 to March, 2022.

As depicted in Table 4, the first parasitized aphid in cabbage was recorded on 12 February, 2022 (7th SMW). The highest aphid parasitization (12.10%) was recorded on 12 March, 2022 (11th SMW), and the lowest (6.93%) was recorded on 12th February, 2022 (7th SMW). Dochovskiene et al. (2012) observed Diaretiella rapae reduced the population of cabbage aphid, B. brassicae by 15.5% in manure fertilized and 12.90% in synthetically fertilized plants which are more or less similar to the present findings. Sable et al. (2008) reported maximum parasitization of cabbage aphid by Aphidius spp. with 76.4 and 82.3% in 2002-03 and 2003-04 respectively. Shah et al. (2013) conducted studies on the seasonal dynamics of insect pest and their natural enemies in cabbage and cauliflower ecosystems and recorded high rate of parasitization of Myzus persicae by Aphididus colemani (90.2±5.6%) and Brevicoryne brassicae by Diaeretiella rapae (80.5±6.8%) by end of November. Chandra and Kushwaha (1987) reported that Aphidius spp. was a minor parasitoid which was effective from August to December, parasitizing upto 22.4% of aphids on mustard, cabbage and cauliflower which is at variation with the present findings. The differences may be attributed to differences in prevailing climatic conditions and cultivars.

There was no parasitization on chinese cabbage in the month of January and February, 2022. Parasitized aphid was started to observed in the first week of March but there was significant increase in the following week reaching its maximum parasitization on 12th March with 11.60% and found till harvesting of the crop. Amini et al. (2012) found the parasitization rate of B. brassicae in flood irrigated fields ranged from 1% to 11.99% which coincides the present findings. However, Sharma et al. (2020) found that among the parasitoids, D. rapae parasitized 43.80 and 24.20 per cent on cabbage aphid, B. brassicae (L) during 2017 and 2018, respectively. Duchovskiene and Raudonis (2008) studied the rate of parasitism of B. brassicae by D. rapae and recorded that D. rapae reduced the population of B. brassicae by 23.9 to 26.2%. 

Bayhan et al. (2007) studied parasitization rate of D. rapae on B. brassicae on different brassicae cultivar and observed the highest parasitism of B. brassicae by D. rapae was found on cabbage (40.20%) and lowest on turnip (32.64%). The lower parasitization in the present study as compared to the above author may be due to differences in cultivar and weather parameters.

The first parasitized aphid in cauliflower was recorded in the mid of February (Table 4). The extent of parasitization ranged from 4.08% to 12.60%. The highest aphid parasitization was recorded on 12th March, 2022 (12.60%) and the lowest (4.08%) was recorded on 26th February, 2022. Similar findings was also reported by Duchovskiene et al. (2012) who observed that the D. rapae reduced the population of cabbage aphid, B. brassicae by 15.50% in manured fertilized and 12.90% in synthetically fertilized plants. The parasitization in the present study was found to be lower as compared to that reported by Chandra and Kushwaha (1987) who found that Aphidius spp. was a minor parasitoid which was effective from August to December, parasitizing upto 22.4% of aphids on mustard, cabbage and cauliflower.

The highest aphid parasitization (10.20%) on broccoli was recorded on 19th March 2022 (12th SMW), and the lowest (3.25%) was recorded on 19th February 2022 (8th SMW). Similar finding was reported by Amini et al. (2012) who recorded parasitism rate of B. brassicae ranged from 1.0 to 11.9% which is similar to the present findings. Sable et al. (2008) reported maximum parasitization of cabbage aphid by Aphidius spp. with 76.4 and 82.3% in 2002-03 and 2003-04 respectively. Chandra and Kushwaha (1987) reported that Aphidius spp. was a minor parasitoid which was effective from August to December, parasitizing upto 22.4% of aphids on mustard, cabbage and cauliflower which is at variation the present findings.

As shown in Table 4, no aphid parasitization was observed in the month of January and February, 2022. The parasitized population of aphid was started to appear in the first week of March and gradually increased and reached its maximum parasitization on radish on 12th March with 9.34%. The present findings is supported by Amini et al. (2012). Dochovskiene and Raudonis (2008) observed that D. rapae reduced the population of B. brassicae by 23.9-26.2% which is contradictory with the present study.

The weather has a significant impact on the pest's population dynamics. The study offers details on the timing of the initial infestation as well as the temperature-dependent peak activity of that specific insect. As a result, the population timing in this study is helpful for planning cabbage aphid management strategies during a critical infestation period.

Jesonkere Sutnga, H. Shila Devi, Imtinaro L., Damitre Lytan, Waluniba, Susanta Banik and Sabbithi Pavan (2024). Population Dynamics of Cabbage aphid, Brevicoryne brassicae L. on Five Brassicae species viz., Cabbage, Cauliflower, Broccoli, Chinese cabbage and Radish. Biological Forum – An International Journal, 16(1): 47-52.