Ultrastructural changes in the midgut epithelium of unfed lone star ticks with increasing age

The gross morphology of the gut epithelium of adult lone star ticks (Amblyomma americanum ) (L.) reared in the field was examined at 2-month intervals as ticks increased in age for 1 year. Additional ticks 28 months of age were also examined. Morphological changes observed with the light microscope were priamrily associated with the color and distention of the gut caeca and changes in the tissue staining affinities for Mallory's trichrome and Prussian Blue stains. Ultrastructurally, changes from newly molted to 8-month-old lone star ticks were observed in the amounts of lipid, siderosomes, and myelinosiderosomes in cells of the epithelium. Examination of 28-month-old ticks revealed little intracellular lipid but an apparent increase in lysosomal activity. Basal infoldings of the plasma membrane and basal lamina (par of the basement membrane) were common in 10-, 12-, and 28-month-old ticks. The data suggest that some undetermined proportion of the blood meal is converted to lipid, which may be later metabolized for energy.