Abstract

Field experiments were carried out for four years (2012-13 to 2015-16) to study the seasonal dynamics of tobacco caterpillar, Spodoptera litura in castor and its relationship with different weather parameters during kharif season in Telangana State. Moth catches of S. litura were observed throughout the crop season, wherein maximum catches (44.8 to 124 moths/trap/week) were observed during mid- August to late-October [33rd to 43rd Standard Meteorological Week (SMW)]. Peak oviposition (2.0 to 14.8egg-masses/5 plants) and larval incidence (14.4 to 48 larvae/5 plants) of S. liturawas recorded during mid-August to mid-November (33rd to 46th SMW) coinciding with the vegetative to primary spike development stage of the crop. The correlation analysis indicated that the moth catches and larval population of S. litura showed significant positive correlation with weather parameters viz., maximum temperature, minimum temperature, rainfall and rainy days, while egg-masses of S. litura showed significant negative correlation with morning relative humidity and minimum temperature.The stepwise regression analysis revealed that minimum temperature, rainy days, wind speed and evening relative humidity could explain 64 per cent variation in S. litura moth catches. Among all the variables morning relative humidity was found to contribute significantly and showed 59 per cent effect on the population fluctuation of eggmasses, while rainy days and maximum temperature could explain 51 per cent variation in larval population of S. litura in castor.The models were validated with independent data 2015-16. The overall results suggested that the models can be used for predicting the population of S. litura in castor for optimizing management strategies.

Highlights

  • Castor (Ricinus communis L.) is an industrially important non-edible oilseed crop in India.Its seed oil has vast and varied industrial applications such as lubricants, paints, cosmetics, medicines, plasticizers etc

  • Observations on the moth emergence, egg and larval population of S. litura on castor were recorded starting from germination to harvest of the crop (23 July to 4 February i.e. 30th to 5thstandard meteorological week).The sex pheromone traps were used to record the seasonal dynamics of S. litura moths

  • The results revealed that moth catches and larval population of S. litura had significant positive correlation with maximum temperature (r=0.461 and 0.523, respectively), minimum temperature (r=0.613 and 0.422, respectively), rainfall (r=0.711 and 0.444, respectively) and rainy days (r=0.703 and 0.406, respectively).The egg-masses of S. litura showed significant negative correlation with morning relative humidity (r = -0.768) and minimum temperature (r= -0.624)

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Summary

Introduction

Castor (Ricinus communis L.) is an industrially important non-edible oilseed crop in India.Its seed oil has vast and varied industrial applications such as lubricants, paints, cosmetics, medicines, plasticizers etc. One of the major constraints that limit castor productivity is the excessive damage caused by lepidopteran pests and the magnitude of the problem is quite high in Southern India resulting in lower seed yields. S. litura is polyphagous in habit, feeds on variety of host plants and survives throughout the year in a given agro-ecosystem (Gedia et al, 2009). Though castor is the most preferred host of S. litura, the pest status does not remain static on castor and largely influenced byweather parameters. Since the information available on this aspect on castor is meager, the present study was undertaken for four consecutive years (2012-16) with the primary objective of determining the seasonal dynamics of male moth catches, egg-masses and larval population of S. litura in castor. The secondaryobjective was to understand the role and reliability of weather parameters for predicting the population of S. litura in castor

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