Seasonal incidence of major insect pests on different Brassica species

Introduction

Oilseed crops are considered as the backbone of agricultural economy since ancient times. The economically important mustard crop family Brassicaceae contains about 338 genera and 3702 species (Warwick et al, 2006) [15] . It has its origin in China and was first introduced in North East India (Shweta et al, 2017) [6] . The estimated area, production and yield of rapeseed-mustard worldwide is 36.68 mha, 72.42 mt and 1974 kg/ha, respectively (USDA, 2017-18) [14] . India is among the leading countries occupying third position in terms of rapeseed-mustard after China and Canada accounting for 19.8 and 9.8% of the total acreage and production worldwide (USDA, 2016-17) [13] . In India, Brassica juncea shares about 90% in area. Even after presence of good production technology, mustard crop fails to give potential yield in the country and suffers heavy yield losses due to various biotic and abiotic factors. Insect pests are the most important biotic factors responsible for reducing the crop yield. About 50 insect species have been found infesting rapeseed-mustard in India (Sharma and Singh, 2010) [8] . The insect pests found infesting rapeseed-mustard assumed to be of regional and sporadic significance include mustard aphid (Lipaphis erysimi), mustard saw fly (Athalia lugens), flea beetle (Phyllotreta cruciferae), painted bug (Bagrada hilaris), diamond back moth (Plutella xylostella), hairy caterpillar (Spilosoma obliqua), cabbage butterfly (Pieris brassicae) (Bakhetia et al., 2002) [2] . The hemipteran mustard aphid (Lipaphis erysimi) belong to Aphididae, is the most serious pest of mustard causing substantial yield losses ranging from 35.4 to 96%, 30% seed weight loss and oil loss 2.75%. The nymphs and adult of mustard aphid suck the sap from leaves, stem, inflorescences and pods result in plant stunting, flower withering and deformed pod formation (Atwal and Dhaliwal, 1997) [1] . Thus, it becomes necessary to monitor mustard aphid regularly during the peak breeding season and IPM module has been prepared in this direction to effectively control the pest population. The mustard saw fly (Athalia lugens) belongs to Tenthridinidae attacks 12 species of cruciferous and occasionally 7 species of non-cruciferous plants. It attacks at seedling stage of mustard crop in its grub stage. It was observed attacking at about 15 days after germination of the mustard crop and its population reaches at its peak in the month of December after which it declined (Tripathi, 1963) [12] . The painted bug (Bagrada hilaris) is capable of causing 66 to 99% yield losses in Brassica campestris and 27 to 68% in Brassica juncea. A reduction of 0.063 to 0.064 gm seed weight per plant and 0.036 to 0.039% reduction in oil content were reported at every increase in unit bug per plant (Verma and Pandey, 1981) [9] . A thorough knowledge of seasonal activity of insect pest helps in developing efficient pest management strategies in a particular set of agro climatic conditions. That's why studies were taken up to ascertain the agro-ecological study of insect pests in different oilseed Brassica species.

Materials and Methods

The experiment was conducted at Crop Research Centre in Govind Ballabh Pant Univerity of Agriculture and Technology, Pantnagar from seedling till pod filling stage of the mustard crop for the rabi season 2020-21. Six Brassica species (Brassica juncea, B. nigra, B. alba, B. napus, B. campestris, B. rapa) using eight varieties BSH-1, YST-151, Varuna, B. nigra, PM-31, GSC-6, B. alba and IJ-31.The experiment was laid down in RBD design having three replications and the varieties were sown in October last week (20 October, 2020).

Mustard aphid

The mustard aphid population was recorded from top 10 cm main shoot on five randomly selected tagged plants on weekly intervals from seedling till pod filling stage of the mustard crop.

Mustard saw fly, Painted bug and Flea beetle

Five places of one-meter square area in each plot were taken for the visual observation of larval population of mustard saw fly and adult population of painted bug and flea beetle. Population data of different insect pests was subjected to the analysis of variance (ANOVA) using simple RBD programme. The meteorological data at weekly intervals was obtained from the meteorological observatory at CRC in Pantnagar and were correlated with the population of insect pest complex. [9] also reported the first mustard aphid appearance in December third week. Aphid population in difference Brassica species were correlated with different weather parameters like maximum and minimum temperature, maximum and minimum relative humidity, rainfall, sunshine and wind velocity which showed non significant negative correlation with maximum temperature which is in close proximity with the findings by Malik and Sachan (2013) [4] ; positive non-significant correlation with minimum temperature except in B. nigra which showed non significant negative correlation and positive non significant correlation with maximum and minimum R.H. It showed non significant positive correlation with sunhine and wind velocity. Shah et al.

(2015) [10] also reported positive non significant correlation with sunshine and wind velocity. [3] also reported negative non significant correlation with mean R.H. Statistically, no significant difference was observed among the mean flea beetle adult and painted bug population in various species. It may be helpful in determining most susceptible crop stage to a particular pest species, peak period of pests thus, helpful in developing pest management story.

References

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