LOCALIZATION OF INSULIN-LIKE IMMUNOREACTIVITY IN THE SYNGANGLION OF NYMPHAL AND ADULT DERMACENTOR-VARIABILIS (ACARI, IXODIDAE)

Immunocytochemical staining based on a peroxidase-antiperoxidase metho d showed neurosecretory cells (NSC) reactive to bovine insulin in five of 18 paraldehyde fuchsin-positive neurosecretory regions (NSR) in th e synganglion of unfed adult Dermacentor variabilis. This is the first report of a neuropeptide in an ixodid tick. The insulin-specific immu noreactive cells included the posterior medial group of the protocereb ral center, posterior group of dorsal opisthosomal center, anterior la teral group of the dorso-lateral cheliceral center, dorsal group of th e frontal stomodeal center, and anterior group of the ventral palpal c enter. After feeding and mating, females no longer had immunoreactive cells in three of five NSR found in virgin, unfed females. However, tw o cells of the posterior group in dorsal opisthosomal center and anter ior lateral group of the dorso-lateral cheliceral center remained immu noreactive throughout feeding. Fed, mated males continued to display i mmunoreactive cells in four of five NSR found in the virgin, unfed mal es. All developmental stages of nymphs examined had insulin-specific i mmunoreactive cells in two of the five NSR found in unfed adults, incl uding two positively stained cells of the posterior group in dorsal op isthosomal center and anterior group of ventral palpal neurosecretory center.