<div>Background: Cassia angustifolia Vahl, senna, known for medicinal properties belongs to family fabacea is a hardy plant, suitable for saline and rainfed conditions serving as a host for caterpillars of Catopsilia pyranthe L. butterflies suffering up to 90 per cent defoliation. An attempt was made to record butterfly migrations due to an outbreak of the lepidopteron pest on senna which is the first report on butterfly migration in western arid region. 
 
Methods: Surveys made in different districts for accurate quantification of butterflies passing within 5 minute through a 10 meter wide strip. For diurnal pattern, observations were taken on hourly basis. Correlation of butterfly density with weather parameters was worked out. 
 
Result: Migration was mainly in South West direction in a steady line connecting Jaisalmer, Jodhpur, Pali, Sirohi and Ajmer. The highest density (1360 butterflies/10m/5 minute) accounting for 16,320.0 butterflies/10m/hour and 97,920.0 butterflies/10m/day recorded in Keru (Jodhpur) representing bell shape curve of diurnal movement with a maximum activity between &nbsp;12.00 noon and 1.00 PM.</div>

<div style="text-align:justify">Outbreak of Catopsilia pyranthe L. on Senna (Cassia angustifolia Vahl) and Migration in Western Arid Region of India</div>