Decrease of memory retention in a parasitic wasp: an effect of host manipulation by Wolbachia?

Abstract

Several factors, such as cold exposure, aging, the number of experiences and viral infection, have been shown to affect learning ability in different organisms. Wolbachia has been found worldwide as an arthropod parasite/mutualist symbiont in a wide range of species, including insects. Differing effects have been identified on physiology and behavior by Wolbachia. However, the effect of Wolbachia infection on the learning ability of their host had never previously been studied. The current study carried out to compare learning ability and memory duration in 2 strains of the parasitoid Trichogramma brassicae: 1 uninfected and 1 infected by Wolbachia. Both strains were able to associate the novel odors with the reward of an oviposition into a host egg. However, the percentage of females that responded to the experimental design and displayed an ability to learn in these conditions was higher in the uninfected strain. Memory duration was longer in uninfected wasps (23.8 and 21.4 h after conditioning with peppermint and lemon, respectively) than in infected wasps (18.9 and 16.2 h after conditioning with peppermint and lemon, respectively). Memory retention increased in response to the number of conditioning sessions in both strains, but memory retention was always shorter in the infected wasps than in the uninfected ones. Wolbachia infection may select for reduced memory retention because shorter memory induces infected wasps to disperse in new environments and avoid competition with uninfected wasps by forgetting cues related to previously visited environments, thus increasing transmission of Wolbachia in new environments.

Effects of temperature and superparasitism on quality and characteristics of thelytokous Wolbachia-infected Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) during mass rearing

“…To avoid superparasitism, females can detect and discriminate host quality before depositing eggs and can label the host with host marking pheromone (HMP) after oviposition 21,36 . However, infected females show a lower host discrimination ability 11,23,37 . Because they may be unable to recognise host eggs parasitised by other wasps, they are more likely to lay their own egg clutches, resulting in superparasitism.…”

“…We also found that females showed a lower rate of superparasitism with lower Wolbachia titres induced at high temperature, possibly due to Wolbachia inducing memory loss in infected females. Infected wasps often show reduced memory duration, and may “forget” information on host quality or previously parasitised eggs 37 . This hypothesis is supported by studies showing that Wolbachia can invade the brain and replicate rapidly in the central nervous system of its host 38,39 .…”

Wolbachia infection may improve learning and memory capacity of Drosophila by altering host gene expression through microRNA

“…Our previous study reveal Wolbachia mediates the expression of dopamine related genes, and decreases the sleep quality of their insect hosts (Bi et al, 2018). Kishani Farahani et al revealed that Wolbachia-infected wasps display shorter memory retention in new environments compared with uninfected wasps; in this way, they can increase the broadcast of Wolbachia by forgetting the trace connected with previous environments (Kishani Farahani et al, 2017) It was reported that wVulC Wolbachia-infected Armadillidium vulgare, a terrestrial isopod, had worse ability to learn and memorize the correct direction after training compared to a Wolbachia-free group. Wolbachia infection in A.…”

Co-occurrence of thelytokous and bisexual Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) in a natural population

“…Phylogenetic analysis based on ITS-2 gene apparently supported that our two strains are part of the highly homogeneous T. dendrolimi genetic pool and can be assumed to have similar genetic backgrounds, as suggested by Kishani et al . 44,70 . Such relationship was further substantiated by similar COI-based reconstruction and by undifferentiated COI and Cytb sequences between two strains.…”