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ARS Home » Southeast Area » Fort Lauderdale, Florida » Invasive Plant Research Laboratory » Research » Publications at this Location » Publication #75237

Title: A PHYSIOLOGICAL AGE-GRADING SYSTEM FOR NEOCHETINA EICHHORNIAE WARNER (COLEOPTERA: CURCULIONIDAE), A BIOLOGICAL CONTROL AGENT OF WATERHYACINTH EICHHORNIA CRASSIPES (MART.) SOLMS.

Author
item GRODOWITZ, MICHAEL - US ARMY ENGINEERS
item Center, Ted
item FREEDMAN, JAN - US ARMY ENGINEERS

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: How many insects does it take to kill a waterhyacinth? This question is commonly voiced by the general public when biological control is discussed. The naivete of this question lies in the fact that it belies the belief that all individuals within the population are the same and have identical effects at all locations all during the year. Obviously, this is not true. A population comprised solely of males, for example, would have less impact that a population that included reproducing females. Likewise, not all females are the same. Some are old and past the age of reproduction, some are young and pre- reproductive, some are mature and fertile. In addition, nutrients available in the plant impact the vigor of the population by affecting reproduction. In order to assess the effectiveness of a biological control program, it is important to know whether the structure of the bioagent population varies in this manner. It is also important to be able to define this structure for a particular location and to know how this varies over time. For example, a reservoir manager might expect biological control agent to eliminate a weed at a time when the population of the agent is in a non-reproductive state. That manager might then incorrectly conclude that the agent is ineffective. This paper describes a system for defining the reproductive status of a weevil that is one of the key biological control agents of waterhyacinth in the U. S.

Technical Abstract: Neochetina eichhorniae, the mottled waterhyacinth weevil, 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 extent of follicular differentiation distinguishes the nulliparous stages. The quantity and quality of follicular relics(and, by association, the number of egg ovulations) distinguishes the parous phases. In addition, 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. In the process of testing this system on field populations in Texas, we observed 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 and may be useful for other weed biological control agents with similar reproductive systems.