Host Search behaviour by Rhagoletis pomonella files: inter‐tree movement patterns in response to wind‐borne fruit volatiles under filed conditions

Responses of Rhagoletis pomonella (Wash) (Diptera: Tephritidae) to synthetic host fruit violates were studied in the field. Individually marked females were released in the centre of a 25 m 2 patch containing twenty‐five host trees ( Crataegus mollis var, toba ) and followed as they moved within and between trees. Fly response to three experimental conditions was studied: (1) ‘clean’ air; (2) synthetic host fruit violates (apple) permeating the patch; and (3) a single point source of odour placed c 1m away from the edge of the patch. Files in a patch permeated with host odour moved faster, exhibited more straightened‐out moves, and reached the edges of the patch more quickly than those exposed to clean air. Flies exposed to a point source of odour exhibited clear orientation responses, arriving consistently at the tree harbouring the source of odour. Odour exposure was intermittent and usually brief ( c . 20s ‐1 exposure) with intervals between exposure periods averaging 103s. Wind speed and direction were highly variable. Flies moved during wind ranging in speed form 0.5 to 4.4 m s ‐1 , with their activity being greatest at winds below 2m s ‐1 . Strong winds (>3.5 ms ‐1 ) either arrested movement or enhanced downwind displacement. Our observations tend to support the ‘series‐of‐steps’ hypothesis reviewed by Gibson & Brandy (1985) as a mechanism of close‐range host location (1‐5m from odour source). Our findings are discussed with respect to theoretical and practical implications of insect orientation mechanisms to odours, dispersal, and control strategies.