Cauliflower (Brassica oleracea) belongs to the family Cruciferae. It is among attractive vegetables due to its nutritional importance and is extensively grown in Peshawar region. But there are certain limiting factors for its quantitative and qualitative production. Among these insect pests are great one and sometimes cause complete failure of the crop. Some of such insects are enlisted as aphids (Brevicoryne brassicae), cabbage semilooper (Plusia aurichalcea), Diamond back moth (Plutella xylostella), cabbage butterfly (Pieris brassicae), Grass hoppers and Field cricked.
Of these insects the Cabbage butterfly (P. brassicae) has been considered the most destructive pest. This pest is distributed world wide and is found wherever cruciferous vegetables are grown. It was recorded as serious pest of cabbage, cauliflower, kohlrabi, broccoli, brussels and sprouts in cauliflower growing areas of the world. It also attacks turnip, radish, sarsoon and toria etc. Similar to other countries the Cabbage butterfly has also been reported as serious pest of cruciferous plants in Pakistan.
The larvae of the pest are sparsely covered with hairs. During its development a single larva consume 74-80 sq. cm leaf area. Leaves, branches, pods and the seeds of cabbage and cauliflower are eaten by the larvae[3,4].
Cabbage aphid (Brevicoryne brassicae) is another common pest of rape/mustard. This insect is the most abundant from Nov./Dec. to March/April when it infests various cruciferous oil seed crops and vegetables. The aphids suck the sap from the leaves throughout the season and when large colonies develop, the leaves become bleached and distorted and the plants are unable to develop a marketable head. Aphids play a prominent role in reducing the yield ranging from 50-80%.
Determination of population dynamics is prerequisite for the implementations
of control strategy against certain insect. A lot of work has been done in this
direction in the past[2,5,8-10]. The present study is the determination
of Cabbage butterfly and Cabbage aphids population on five cauliflower Cultivars
in Peshawar region.
MATERIALS AND METHODS
The studies on population dynamics of Cabbage butterfly and Cabbage aphids on different cultivars of cauliflower were carried out at the Research Farm of Entomology Section, Agricultural Research Institute, Tarnab, Peshawar. The technical and laboratory facilities were provided by the Entomology Section while the test cultivars were obtained from the Vegetable Section of the Institute.
Five cultivars of cauliflower namely Snowball, Snowdrift, Tropical, Pioneer and Meigettsal were sown in the field in Randomized Complete Block Design. Each cultivar was replicated three times in a subplot size of 3x2 m. Row to row distance was kept 75 cm, while plant to plant distance was 45 cm. There were 4 rows in each plot and each row had 10 plants. There was a total of 40 plants in each plot.
Seeds of the selected cultivars were sown in the month of September and were transplanted in October. Fertilizer, irrigation and all other agronomic practices were carried out in the experimental field as and when needed. All inputs for example fertilizer application, irrigation, hoeing and other agronomic practices remained same for all cultivars. Observation on population dynamics of insect pests started as soon as their infestation were noticed. Population density was determined on randomly selected plants at weekly interval.
Cabbage butterfly (Pieris brassicae): The population density of Cabbage butterfly was recorded on the basis of number of larvae per plant. All the open leaves and heads of the selected plants were observed thoroughly and the number of larvae found were recorded.
Cabbage aphids (Brevicoryne brassicae): Aphids were found feeding on the self sap from the leaves of the plants. Actual number of adult aphids was counted on both sides of the leaves examined at one square centimeter leaf area.
RESULTS AND DISCUSSION
Population dynamics of the Cabbage butterfly and Cabbage aphids on five cauliflower cultivars namely Snowball, Snowdrift, Tropical, Pioneer and Meigettsal were recorded at weekly interval throughout the season is presented in Table 1 and 2.
Cabbage butterfly (Pieris brassicae) no. of larvae per plant: The population density of Cabbage butterfly (Pieris brassicae) recorded on the basis of number of larvae/plant on randomly selected plants throughout the season is presented in (Table 1). The table shows that the Cabbage butterfly infestation started at the last week of October with an average population density of (50.00, 23.33, 73.33, 47.67, 0.00) on cultivars Snowball, Snowdrift, Tropical, Pioneer and Meigettsal, respectively and increases gradually. It remain at the peak during first week of November with an average population density of (52.33, 28.33, 86.67, 51.67, 0.00) on Cultivars Snowball, Snowdrift, Tropical, Pioneer and Meigettsal, respectively. Population density of the pest declined gradually till the end of December and reaches to an average population density of (5.67, 0.00, 0.00, 0.00 and 0.00) larvae/plant. The result of pest incidence is some what similar to that of Qureshi and Atwal who reported that Pieris brassicae was observed on cauliflower crop from the month of October and from May to September.
Cultivar Meigettsal showed best performance against Cabbage butterfly by attracting the least population. Cultivar snowdrift and pioneer were next in performance against Cabbage butterfly. While Cultivars snowball and tropical developed the highest population. These observations are in agreement with that of Matin et al. They reported that leaf damage by pieris brassicae in varieties snowball and snowdrift was highly significant.
Cabbage aphids (Brevicoryne brassicae) no. of aphids per centimeter sq. leaf area: The population density of Cabbage aphids (brevicoryne brassicae) recorded on the basis of number of adult aphids per cm2 leaf area on randomly selected plants throughout the season in presented in (Table 2).
The table shows that the aphids infestation started at the last week of October with an average population density of (11.33, 0.00, 0.00, 0.00 and 0.00) on Cultivars Snowball, Snowdrift, Tropical, Pioneer and Meigettsal, respectively and increases gradually. It remains at the peak from Ist week of November to mid of November with an average population density of (26.67, 0.00, 0.00, 0.00 and 31.76) and (0.00, 0.00, 0.00, 23.67 and 26.67) on Cultivars Snowball, Snowdrift, Tropical, Pioneer and Meigettsal, respectively.
The population declines on the onset of cold weather and the crop progress
towards maturity at the end of December and reaches to an average population
density of (0.00, 0.00, 0.00, 5.00, 7.66) aphids/1 cm-2 leaf area.
|| Population density of cabbage butterfly (Pieris brassicae)
larvae on 5 cauliflower cultivars/varieties
|| Population density of Cabbage aphids (Brevicoryne brassicae)
on 5 cauliflower cultivars/varieties
|Means within a column followed by different letters are significantly
different from each other at 5% level of probability.
Anova followed by LSD test.
These results are in conformity Atwal who reported that the
aphids remain most abundant during November December in Autumn season and cloudy
and cold weather is very much favorable. These slight differences might be due
to climatic conditions of the concerned regions or due to the presence of natural
enemies in the field.
As reported by Hagen and Bosch who observed that lady birdbeetle and green lacewings feed on aphids as larvae and adult. Similarly, it also tally with the finding of Weber et al. who reported that the abundant aphids species in autumn near harvest is Brevicoryn brassicae.Results showed that Cultivar snowdrift performed the best against aphids as no aphid was observed on this Cultivar throughout the season. Cultivar tropical and snowball were next in performance against aphids, while Cultivars Meigettsal and pioneer developed the highest pest population.