Biological Control of Water Hyacinth Under Conditions of Maintenance Management: Can Herbicides and Insects Be Integrated?

Abstract

/ We hypothesized that repeated herbicidal (maintenance) control of water hyacinth infestations in Florida suppressed biological control agent populations, especially the weevils Neochetina eichhorniae and N. bruchi. We therefore sampled water hyacinth and weevil populations at 54 sites distributed statewide. Half were under maintenance control, half were not treated with herbicides. General site conditions were assessed, demographic data were collected on weevil and plant populations, the reproductive condition of the weevils was determined, and plant nutrient and proximate composition of water hyacinth leaves were analyzed. Water hyacinth infestations under maintenance control were minimal when compared to unmanaged sites. Likewise, on a population basis, all weevil cohorts were much lower due to the paucity of plants. Plants at unmanaged sites, where weevil intensities were much higher, suffered high levels of stress and showed low growth potential. Lower percentages of the female weevils were reproductive at unmanaged sites when compared to managed sites, so densities of reproductives and immatures were similar at both site types. Reproductive status of the weevils improved with increased plant quality. Plant quality, in turn, declined as stresses arising from weevil feeding increased. Plant quality was positively correlated with plant growth potential and flower production. Thus, maintenance control improved plant nutritive quality thereby inducing reproductive vigor of the weevils, but ensuring plant regrowth and the need for future control. This suggests that biological and herbicidal controls should be integrated, using herbicides to maintain water hyacinth infestations below management thresholds but in a manner that conserves biological control agent populations. This approach would lead to improved plant nutritional quality that would, in turn, stimulate reproduction in biological control agent populations. KEY WORDS: Eichhornia crassipes; Neochetina eichhorniae; Neochetina bruchi; Phytophagy; Integrated control; Aquatic weeds

Impact of release of <i>Neochetina</i> spp. on growth and density of water hyacinth <i>Eichhornia crassipes</i>

“…By the result of this effect it drastically increases the water loss exposing the plant to pathogens finally reducing the plant growth (Julien, 2000). They are the most effective biological controller of water hyacinth when compared with other arthropods (Center et al, 1999b;Center and Van, 1989;DeLoach and Cordo, 1976). Among around 30 countries these weevils have been successfully utilized to control water hyacinth due to their host specific nature and effectiveness (Center et al, 2002;Firehun et al, 2015).…”

Current levels of suppression of waterhyacinth in Florida USA by classical biological control agents

“…Despite these facts, biological control is often ignored by some land managers as an asset for cutting costs, in part because of the difficulty or lack of information on integrating biological control into existing management programs. This is typified in Florida where, despite the widespread presence of damaging insect biological control agents on E. crassipes, there is no intentional integration with herbicides because many managers find it easier and simpler to follow routine and regular spray programs against aquatic weed populations (Center et al, 1999). Integrated control is technically feasible against E. crassipes as demonstrated by Haag et al (1988) and Haag and Habeck (1991) who designed and evaluated an integrated approach for E. crassipes using herbicides and biological control.…”

“…Samea multiplicalis (Guenée) (Lepidoptera: Crambidae) and Synclita obliteratis (Walker) (Lepidoptera: Crambidae) are two abundant generalist herbivores whose host range includes E. crassipes (Knopf and Habeck, 1976;Habeck et al, 1986). Evaluation studies have focused primarily on N. eichhorniae and N. bruchi using before and after release field studies with no-or non-persistent controls, or caged-tank studies with controls (Center and Durden, 1986;Center et al, 1999). It is difficult to maintain controls under field conditions because of agent dispersal and the presence of considerable biotic and abiotic environmental variation among sites.…”

A Review of the Invasive, Biological and Beneficial Characteristics of Aquatic Species Eichhornia Crassipes and Salvinia Molesta

“…Center et al (1999) showed that sustained herbivory of E. crassipes reduced proportionately biomass and floral structures. Normally E. crassipes will out-compete other floating aquatic plants; Center et al (2005) measured E. crassipes biomass production and compared to Pistia stratiotes and found that E. crassipes biomass yield was 41 times that of Pistia stratiotes.…”