Seasonal Incidence and Infestation Pattern of Sunflower Head Borer (Helicoverpa armigera) and Leaf Eating Caterpillar (Spodoptera litura) under the Influence of Climatic Factors

Abstract

Field experiments were conducted at Regional Research and Technology Transfer Station (RRTTS), Ranital, Bhadrak, OUAT during the summer seasons of 2019-20 and 2020-21 to study the seasonal incidence of sunflower head borer and leaf-eating caterpillar in sunflower in relation to the abiotic factor. The seasonal incidence of the target insects, Spodoptera litura and Helicoverpa armigera, was investigated using pheromone traps installed in the unprotected sunflower plots (10 m x 5 m) at the research block. The trap catches of male adults were expressed as a number of males trapped per trap per week. In the observation plots, the sunflower hybrid Aruna was cultivated with the approved agronomic package of techniques without any plant protection measures. Weekwise larval populations of Spodoptera litura and Helicoverpa armigera were counted from 10 randomly selected tagged plants starting from the initiation of damage and expressed as larval intensity i.e. average larval population per plant. Besides, weekwise incidence of the pest (leaf damage by tobacco caterpillar and head damage by head borer) were also recorded. The findings of the investigation indicated that tobacco caterpillars' adult activity commenced from the 5th to 6th standard weeks (1st and 2nd week of February) and peak activity in the 11th standard week (3rd week of March). Similarly, the larval population began to appear in the 6th to 7th standard weeks in 2020 and 2021, respectively with a peak population build-up stage during the 12th standard week and their activity steadily decreased as the cropping season progressed. The peak infestation stage coincided with the period of maximum larval activity and the pest caused sizable damage from the early vegetative stage to the peak flowering stage of the crop. The sunflower head borer (Helicoverpa armigera) infested sunflower crops throughout the reproductive stage of the plant with adult activity beginning in the 9th to 10th standard weeks (last week of February-first week of March) and attaining the peak in the 12th to 13th standard weeks (3rd-4th week of March). Similarly, the larval population began to appear in the 10th to 11th standard week and reached the peak in the 13th to 14th standard week (last week of March to first week of April). Various environmental parameters viz. temperature, relative humidity and rainfall were collected from the automated weather station of Gramin Krishi Mausam Sewa (GKMS) located at RRTTS, Ranital., These abiotic factors were correlated with trap catch, larval intensity, leaf damage head damage to study the influence of ecological parameters on pest incidence and infestation. The findings of the investigation indicated that among the abiotic factors temperature had a positive influence and relative humidity exhibited a negative effect on the population and damage of Spodoptera litura. All the temperature variables and bright sunshine hour (BSH) exhibited a significant positive correlation and relative humidity (afternoon) had a significant negative correlation with the head damage Helicoverpa armigera.