Development of the Esophageal Bulb of the Apple Maggot, Rhagoletis pomonella (Diptera: Tephritidae): Morphological, Histological, and Histochemical Study1

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Abstract
The esophageal bulb (EB) of Rhagoletis pomonella Walsh was studied at several stages of development. Pupal development of the EB involves changes in the dimensions of epithelial cells and the formation of two types of muscles: permanent circular muscle surrounding the constricted stalk, and a previously undescribed muscle which originates on the ptilinum and inserts on the dorsum of the EB, and which degenerates soon after eclosion. The EB undergoes no significant alteration during adult life, and there is no evidence that it transports or stores nutrients, secretes enzymes, or sequesters wastes. Histochemical evidence suggests that fibrous material which begins to accumulate in the lumen of the EB during pupal development is derived from the cuticular intima. The material may restrict the escape of bacteria from the lumen. The EB may house a feeder culture of bacteria for slow release into the gut.