Rhagoletis pomonella (Diptera: Tephritidae) flies were exposed for 3 days in laboratory cages to yellowish, green or white surrogate leaves with or without food (sucrose) on the leaf surface. When tested in an arena minutes after fly removal from an exposure cage, yellowish surrogate leaves were more attractive to tested flies than green surrogate leaves irrespective of the nature of surrogate leaves to which flies had been exposed. However, flies exposed to green surrogate leaves having food exhibited greater propensity to alight on green surrogate leaves than flies exposed to yellowish or white surrogate leaves having food. This propensity disappeared when flies were tested 24 h after termination of exposure to green surrogate leaves having food. There was no evidence of enhanced propensity of flies exposed to yellowish surrogate leaves having food to alight on yellowish surrogate leaves when tested minutes after removal from an exposure cage. We discuss the potential ecological significance of the evidence presented here that R. pomonella flies are capable of learning to associate the presence of food with green color of leaf surface on which food could be found.
A nonpigmenting strain of Serratia marcescens Bizio isolated from dead and apparently diseased wild apple maggot flies, Rhagoletis pomonella (Walsh), was shown to be pathogenic to healthy apple maggot flies upon ingestion. The microorganism was detected in live adult alimentary canal organs four days post ingestion but produced death in some flies within 24 h when flies fed on a cell concentration of 4.7 × 104 cfu/ml and within 8 h when flies fed on filter-sterilized culture medium that previously contained a 21 h culture of S. marcescens. Increasing the cell concentration 10,000 fold did not lead to an increased rate of kill. Young flies (7-10 days old) were more susceptible to infection leading to death than were older flies (21-28 days old). The potential use of S. marcescens cells as control agents against apple maggot flies is negated by their pathogenicity to vertebrates; however, the potential use of toxic compounds produced by this strain of S. marcescens is discussed.