A physiological age-grading system for Neochetina eichhorniae (Warner) (Coleoptera: Curculionidae), a biological control agent of water hyacinth, Eichhornia crassipes (Mart.) Solms

Neochetina eichhorniae has a meroistic reproductive system composed of a pair of ovaries each subdivided into two tube-like ovarioles. The ovarioles consist of two main regions, the distal germarium and the proximal vitellarium. The vitellarium houses the developing follicles, which mature sequentially. The two ovarioles in each pair connect proximally via the lateral oviducts. The paired ovaries join one another via the common oviduct. Ovarian development involves two distinct phases: a nulliparous (meaning "no eggs") phase and a parous (meaning "with eggs") phase. Each phase undergoes three sequential stages, named N1, N2, and N3 and P1, P2, and P3 for the nulliparous and parous categories, respectively. The degree of maturity of the proximate follicles and the extent of follicular differentiation distinguish the nulliparous stages. The quantity and quality of follicular relics (and, by association, the number of egg ovulations) distinguishes the parous phases. The overall condition of the ovaries can be characterized from the number of developing follicles in the ovarioles as well as the integrity of the follicular cellular material. Samples from field populations in Texas revealed distinct seasonal changes in physiological age structure and condition of the reproductive system. This physiological age-grading system can be an important tool for assessing age structure and relative reproductive health of N. eichhorniae populations or other weed biological control agents with similar reproductive systems