Published online by Cambridge University Press: 21 August 2009
INTRODUCTION
The developmental hormone systems of insects and crustaceans are probably best understood of all the arthropods (for reviews, see Gilbert, Iatrou & Gill, 2004; Wainwright & Rees, 2001). In other arthropod classes, information concerning the identification and functional significance of hormones is fragmentary or non-existent. The endocrine regulation of development and reproduction in ticks (acarines) has been reviewed (Oliver & Dotson, 1993; Lomas & Rees, 1998; Chang & Kaufman, 2004; Rees, 2004) and the reader is referred to these for further detail. However, there is a relative lack of new work in this field.
Blood meals are critical in ticks for triggering various events, including the endocrine system (see Chapter 8). In adult female ixodid ticks, the transition between the slow feeding phase and the rapid engorgement phase (that has been defined as the critical weight: Harris & Kaufman, 1984; Lindsay & Kaufman, 1988; Weiss & Kaufman, 2001) seems to be a critical control point for regulation of many endocrine events, including salivary gland degeneration, vitellogenesis and egg production (see Chapters 3 and 8). Thus, females prematurely removed from the host below the critical weight retain a host-seeking strategy and can reattach to a host if given the opportunity, do not undergo salivary gland degeneration and will not lay eggs. However, females prematurely removed above the critical weight are unable to reattach to a host, undergo salivary gland degeneration and will lay as many eggs as the acquired blood meal will support.
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