1 Plant Health and Environmental Laboratory, Ministry for Primary Industries, Auckland, New Zealand.
2 Division of Chemical Ecology, Swedish University of Agricultural Sciences, Alnarp, Sweden
Gustatory receptors, housed in specialized gustatory sensillae, mediate an insect’s decision to accept or reject a host. The dynamics of receptor-ligand associations are largely unknown for gustatory receptors in pest insects. A class of these receptors, the sugar sensing receptors, were studied using the yellow fever mosquito, Aedes aegypti, as a model organism. In our two-choice feeding bioassays, 3-4 day old female mosquitoes preferred to feed on the sugar trehalose over water (at all tested concentrations) and trehalose plus an amino acid (at specific concentrations of amino acid – eg., leucine 0.001, 0.01 & 0.1mM) over trehalose alone (trehalose concentration kept constant- 10mM). Interestingly, the tested female mosquitoes didn’t show any preference between an amino acid alone (all tested amino acids) and water. Single-sensillum electrophysiological studies revealed that some labellar taste sensillae (eg., RD4) increase their neuronal firing rate on contact with a combined amino acid (e.g., leucine) sugar trehalose diet compared to sugar trehalose alone. Two gustatory receptors expressed in labellar tissues were identified as candidate sugar receptors potentially facilitating a synergistic electrophysiological and behavioural response on contact with sugar plus amino acid diets. These two receptors were initially tested for their sensitivity and specificity for binding to trehalose, through in vitro heterologous expression in Spodoptera frugiperda cells (Sf9 cells) and live cell calcium imaging. One of the two tested receptors showed a dose-dependent response to trehalose and further testing with this receptor revealed that it is more likely implicated in a synergistic response to leucine enriched trehalose diets.