Research Reports: Associations Between Waterhyacinth Weevils (Neochetina Eichhorniae and N. Bruchi) and Phenological Stages of Eichhornia Crassipes in Southern Florida

Abstract

We studied Neochetina eichhorniae and N. bruchi populations at 22 sites in southern Florida during mid-summer 1985. Species composition, reproductive females (as a percentage of total females), and flight muscle development of N. eichhorniae populations varied greatly among sites. N. bruchi populations were heterogeneous among sites for these parameters and for sex ratio. The prevalent waterhyacinth (Eichhornia crassipes) phenostage and degree of biocontrol stress accounted for much of this variation. A higher proportion (74%) of N. eichhorniae females contained functioning ovaries when collected from mature, healthy plants, as opposed to developing colonies (57%), or declining plant populations (34%). The proportion of N. bruchi females with functioning ovaries was similar on mature, healthy plants (61%) and developing colonies (54%), but less (24%) on declining plants. More females from stressed plant populations possessed fully-developed indirect flight muscles (N. eichhorniae 9%, N. bruchi 16%) than those collected from healthy plants (1% and 6% respectively). The proportion of the total weevil population (i.e. both species) composed of reproductively active females of either species was higher on mature, healthy plants than on declining plants, but N. eichhorniae populations consistently exceeded N. bruchi. Reproductive potential declined and vagility increased in both species on waterhyacinth suffering from weevil-induced stress. N. bruchi seemed more sensitive to plant quality than N. eichhorniae. Both species were ubiquitous, but N. eichhorniae was more abundant, comprising 70% of mid-summer weevil populations.