Distribution and transmission of endosymbiotic microorganisms in the oocytes of the pig louse, Haematopinus suis (L.) (Insecta : Phthiraptera)

All anoplurans live symbiotically with prokaryotic microorganisms hosted in specialized cells. termed mycetocytes. In nymphs and males mycetocytes are distributed between midgut epithelial cells. In females, besides the midgu t, mycetocytes are found in the reproductive organs where they are located at the base of ovarioles in contact with lateral oviducts. The mycetocyte-a ssociated symbionts are transmitted from one generation to the next transov arially. Here, the results of histological and ultrastructural studies on t he distribution and transmission of symbiotic microorganisms within the ova ries of the anopluran Haematopinus suis are presented. Interestingly, durin g advanced oogenesis (i.e., choriogenesis) of this species all symbionts ar e localized extracellularly and form a tight mass located at the posterior pole of the oocyte just below the hydropyle. In insects studied so far, suc h localization of transovarially transmitted microorganisms has been report ed only in the closely related species Haematopinus eurysternus.