Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2016
Publication Date: 6/1/2017
Citation: Mattison, E.D., Center, T.D., Grodowitz, M.J., Tipping, P.W. 2017. Morphology of the female reproductive system and physiological age-grading of Megamelus scutellaris (Hemiptera: Delphacidae), a biological control agent of water hyacinth. Florida Entomologist. 100(2):303-309.
Interpretive Summary: Water hyacinth is an economically important invasive plant impacting water bodies throughout the warm temperate regions of the U.S. While chemical applications have been shown to be a viable control strategy more long-term and sustaining management options are needed. Toward this goal, several host-specific insect agents from South America (i.e., the country of origin)have been released for the management of water hyacinth; the most recent agent released is the water hyacinth planthopper. Little is known about the reproductive biology of the water hyacinth planthopper so experiments were initiated to describe the female reproductive system and determine the relationship between changes in the morphology of the reproductive system to number of eggs laid. The female reproductive system is similar to many other insects being composed of two ovaries each containing a number of tubular structures (i.e., ovarioles) where the immature eggs develop. The only exception was the identification of a collar-like structure surrounding the base of the ovaries. Distinct changes in the female reproductive system were noted as higher number of eggs were laid and was closely related to collar length; and presence and appearance of cell material that accumulated in the base of the ovarioles (i.e., follicular relics). Taken together these characteristics can be used to estimate reproductive condition and number of ovulations in mass-rearing and field populations.
Technical Abstract: The morphology of the female reproductive system in Megamelus scutellaris Berg (Hemiptera:Delphacidae), a biocontrol agent of Eichhornia crassipes (Mart.) Solms, was examined using standard light microscopy techniques. Ovaries extracted from individuals dissected in phosphate buffered saline were examined using both stereo and compound microscopy. These were typical of other Delphacid planthoppers in that the reproductive system was composed of two ovaries with each consisting of 11 to 13 tubular ovarioles. The ovarioles within each ovary connected via a lateral oviduct and ultimately to the other ovary via a common oviduct. Ovaries were of the telotrophic meroistic type wherein nurse cells contained within the distal germarium did not descend individually with each maturing follicle. An enlarged sac-like bursa copulatrix opened into the common oviduct just posterior to the spermatheca. The bursa copulatrix contained globular structures which we interpreted to be spermatophores. Individual follicles consisted of an inner yolk-filled oocyte (in more mature follicles) with a distinct germinal vesicle or enlarged nucleus present in the proximal region of the follicle. Each oocyte was surrounded by a single layer of cells, termed the follicular epithelium, and the entire ovariole was surrounded by a thin membranous layer, the ovariole sheath. A unique structure surrounding the most distal portion of the lateral oviduct and appearing as a loose grouping of cells which opened proximally was visible at the base of each ovariole in reproductive females. This structure, which we termed the collar, did not appear to be attached to the ovarioles or the lateral oviduct tissues and has not previously been reported in other planthopper or insect species. The continuum of ovarian development was divided into three nulliparous and three parous stages based on ovariole differentiation, presence and appearance of follicular relics, and collar length, which increased linearly with increasing numbers of ovulations. Taken together these characteristics can be used to estimate reproductive condition and number of ovulations.