Effects of pH on feeding responses in the apple maggot fly, Rhagoletis pomonella (Diptera : Tephritidae)

Phagostimulatory effects of pH values of sucrose on Rhagoletis pomonella ad ults were studied in the laboratory. Flies were standardized for age, diet and food deprivation. Two presentation schemes were employed. The first var ied pH value (3.0-10.0) with sucrose concentration kept constant at 40%. Th e second varied both sucrose concentration (8%, 24% and 40%) and pH value ( 5.0-8.0). Fly feeding propensity was evaluated by observation of fly accept ance or rejection of sucrose and duration of feeding. When tested on red wo oden spheres treated with 40% sucrose, fly feeding acceptance was significa ntly greater when pH ranged from 5.0 to 8.0, and duration of feeding was si gnificantly longer at pH 6.0-7.0. At pH less than or equal to 4.0 or pH gre ater than or equal to 8.0, feeding propensity was significantly reduced. De crease in sucrose concentration significantly increased fly sensitivity to pH. Males were more responsive to varying pH than females. The sucrose pH s hown to stimulate maximal feeding response was 6.4. Such information is rel evant to formulation improvement of a coating mixture of sucrose and insect icide applied to red spheres as part of apple maggot fly control programs. (C) 1999 Elsevier Science Ltd. All rights reserved.