Involvement of Follicular Patency in the Ovarian Developmental Block in Virus-infected, MdSGHV, House Flies, Musca domestica (Diptera: Muscidae).

The Musca domestica salivary gland hypertrophy virus (MdSGHV) is known to have marked effects on the female Musca domestica L. (or common house fly) reproductive system, particularly regarding the size and functionality of the ovaries. Examination of the terminal ovarian follicles can help determine if and how MdSGHV mechanistically causes the block in ovarian development. In this study, terminal ovarian follicle lengths were measured and monitored for patency using Trypan blue dye staining. We examined the effect of MdSGHV infection on female house fly ovarian follicles and attempted to rescue the diminished ovarian follicles in MdSGHV-infected house flies through the application of a hormonal treatment (i.e., methoprene). Comparison of patency in control saline-injected females, virus-injected females with no methoprene application, and virus-injected females with topical methoprene application revealed that none of the virus-infected flies showed an increase in terminal follicular length beyond stage 3 follicles (staging according to Adams 1974). Additionally, none showed evidence of patency. In control, saline-injected females, we found the threshold length of the terminal follicles for the onset of patency to be 600 µm. When examined at 48, 72, and 96 h post-eclosion, average follicle length for infected females seldom reached 250 µm and they also failed to display patency. Thus, the virus is somehow involved in shutting down the mechanism involved in follicular patency. The lack of patency in infected follicles may also be one of the determining factors preventing vertical transmission of the pathogen.