Olfactory learning and memory in the disease vector mosquito,Aedes aegypti

Abstract

Olfactory learning in blood-feeding insects, such as mosquitoes, could play an important role in host preference and disease transmission. However, standardised protocols allowing testing of their learning abilities are currently lacking, and how different olfactory stimuli are learned by these insects remains unknown. Using a Pavlovian conditioning paradigm, we trained individuals and groups of Aedes aegypti mosquitoes to associate an odorant conditioned stimulus (CS) with a blood-reinforced thermal stimulus (unconditioned stimulus; US). Results showed, first, that mosquitoes could learn the association between L-lactic acid and the US, and retained the association for at least 24 h. Second, the success of olfactory conditioning was dependent upon the CS -some odorants that elicited indifferent responses in naïve mosquitoes, such as L-lactic acid and 1-octen-3-ol, were readily learned, whereas others went from aversive to attractive after training (Z-3-hexen-1-ol) or were untrainable (β-myrcene and benzyl alcohol). Third, we examined whether mosquitoes' ability to learn could interfere with the action of the insect repellent DEET. Results demonstrated that pre-exposure and the presence of DEET in the CS reduced the aversive effects of DEET. Last, the nature of the formed memories was explored. Experiments using cold-shock treatments within the first 6 h posttraining (for testing anaesthesia-resistant memory) and a protein synthesis inhibitor (cycloheximide; to disrupt the formation of longterm memory) both affected mosquitoes' performances. Together, these results show that learning is a crucial component in odour responses in A. aegypti, and provide the first evidence for the functional role of different memory traces in these responses.

Learning and Memory in Disease Vector Insects

“…Since Charlwood et al 's study in Papua New Guinea [6] - possibly the first study to explicitly investigate memory in a vector - more recent studies have assessed the abilities of mosquitoes to perform associative learning (see Box 1) to visual and olfactory stimuli [13, 15-18], including some studies that failed to demonstrate learning [19]. In an example demonstrating aspects of associative learning in Cx.…”

“…Employing a training procedure that provided a high degree of temporal and quantitative control of the CS and US delivery, Vinauger et al [18] showed that Ae. aegypti mosquitoes can associate L-lactic acid, a host emitted volatile compound, with a blood-reward.…”

‘We like it wet’: a comparison between dissection techniques for the assessment of parity inAnopheles arabiensisand determination of sac stage in mosquitoes alive or dead on collection

“…They also imply that a potential control technique aimed specifically at young insects should work preferentially outdoors. Young, naïve mosquitoes may be attracted to a wider range of potential hosts than older insects, which may return to feed on hosts that they have fed on previously (Vantaux et al, 2014; Vinauger, Lutz & Riffell, 2014). Odour baited traps that target such young insects may be one possible approach.…”

Sperm chemotaxis promotes individual fertilization success in sea urchins

“…To compare paired male performance within the same trial, relative orientation was calculated as θ a,male1 −θ a,male2 . We also computed a preference index (PI) for each male, in which PI=[number of sperm oriented towards the attractant (θ a <90 deg) −number of sperm oriented away from the attractant (θ a >90 deg)]/ (total number of sperm) (Vinauger et al, 2014). The index takes a value of PI=1 when all sperm are oriented towards the attractant and PI=−1 when all sperm are oriented away from the attractant.…”