Ubiquitous Water-Soluble Molecules in Aquatic Plant Exudates Determine Specific Insect Attraction

Abstract

Plants produce semio-chemicals that directly influence insect attraction and/or repulsion. Generally, this attraction is closely associated with herbivory and has been studied mainly under atmospheric conditions. On the other hand, the relationship between aquatic plants and insects has been little studied. To determine whether the roots of aquatic macrophytes release attractive chemical mixtures into the water, we studied the behaviour of mosquito larvae using olfactory experiments with root exudates. After testing the attraction on Culex and Aedes mosquito larvae, we chose to work with Coquillettidia species, which have a complex behaviour in nature and need to be attached to plant roots in order to obtain oxygen. This relationship is non-destructive and can be described as commensal behaviour. Commonly found compounds seemed to be involved in insect attraction since root exudates from different plants were all attractive. Moreover, chemical analysis allowed us to identify a certain number of commonly found, highly water-soluble, low-molecular-weight compounds, several of which (glycerol, uracil, thymine, uridine, thymidine) were able to induce attraction when tested individually but at concentrations substantially higher than those found in nature. However, our principal findings demonstrated that these compounds appeared to act synergistically, since a mixture of these five compounds attracted larvae at natural concentrations (0.7 nM glycerol, <0.5 nM uracil, 0.6 nM thymine, 2.8 nM uridine, 86 nM thymidine), much lower than those found for each compound tested individually. These results provide strong evidence that a mixture of polyols (glycerol), pyrimidines (uracil, thymine), and nucleosides (uridine, thymidine) functions as an efficient attractive signal in nature for Coquillettidia larvae. We therefore show for the first time, that such commonly found compounds may play an important role in plant-insect relationships in aquatic eco-systems.

Bacterial Communities Associated with Culex Mosquito Larvae and Two Emergent Aquatic Plants of Bioremediation Importance

“…The submerged plant leaves were dominantly colonized by Alphaproteobacteria , Betaproteobacteria , Gammaproteobacteria , Cyanobacteria and Sphingobacteria also typically found on plant leaves [24,52]. Similar to our findings, Tanaka and coworkers also found the family Comamonadaceae ( Betaproteobacteria ) to be the most abundant family predominating in pond water [52].…”

“…Some macrophytes release secondary plant compounds, such as phenols and alkaloids, which affect bacterial communities [15,20,21,22,23,24]. These properties are likely to influence the pollutant removal efficiency of treatment wetlands and, more importantly, the growth of mosquitoes and beneficial invertebrates.…”

The characteristics of the most troublesome mosquito species (Diptera: Culicidae) in Poland

“…Also certain number of commonly found, highly water-soluble, low-molecularweight compounds, several of which (glycerol, uracil, thymine, uridine, thymidine) induce attraction for larvae. These compounds appear to act synergistically, since a mixture of these five compounds attract larvae at natural concentrations much stronger than those found for each compound tested individually (Serandour et al 2008).…”

Environmental drivers for Coquillettidia mosquito habitat selection: a method to highlight key field factors

“…The powder obtained after lyophilization was resuspended in 50 ll acetonitrile and 100 ll BSTFA-TCMS (99:1) reagent (Supelco). The derivatization (silylation) reaction was carried out as described previously (Sérandour et al, 2008).…”

“…adult numbers (average/year) were measured in 24 h trapping periods (ClaeysMekdade & Sérandour, 2009) undetectable from the water surface (Brothers, 2005;LaPointe, 2007). The larval and pupae stages are localized at the bottom of densely overgrown aquatic habitats where they remain attached to root macrophytes in deep nutrient-rich and hypoxic sediments (Sérandour et al, 2006(Sérandour et al, , 2008. This insect-plant interaction appears to be regulated by the need of the continuously submerged larvae to find oxygen in the aerenchymal channels of roots (Laurence, 1960).…”