Vertically transmitted endosymbionts persist for millions of years in invertebrates and play an important role in animal evolution. However, the functional basis underlying the maintenance of these long-term resident bacteria is unknown. We report that the weevil coleoptericin-A (ColA) antimicrobial peptide selectively targets endosymbionts within the bacteriocytes and regulates their growth through the inhibition of cell division. Silencing the colA gene with RNA interference resulted in a decrease in size of the giant filamentous endosymbionts, which escaped from the bacteriocytes and spread into insect tissues. Although this family of peptides is commonly linked with microbe clearance, this work shows that endosymbiosis benefits from ColA, suggesting that long-term host-symbiont coevolution might have shaped immune effectors for symbiont maintenance.

sex pheromones are released by adults of a species to elicit a sexual interaction with the other sex of the same species. Here we report an unexpected effect of a moth sex pheromone on the caterpillars of the same species. We demonstrate that larvae of the cotton leafworm Spodoptera littoralis are attracted by the moth sex pheromone and that this phenomenon is independent of sex determination. In addition, we show that the olfactory sensilla carried by the caterpillar antennae are sensitive to the pheromone and that the caterpillar sensilla express pheromone-binding proteins that are used by adult antennae to bind pheromone components. Finally, we demonstrate that the larvae are preferentially attracted to a food source when it contains the sex pheromone main component. A possible interpretation of these results is that the sex pheromone is used to promote food search in caterpillars, opening potential new routes for insect pest management.

In moths, the components of the female pheromone blend are detected in the male antennae by pheromone olfactory receptor neurons (Ph-ORNs) expressing narrowly tuned olfactory receptors. Responses to sex pheromones have generally been thought to be independent from the odorant background. However, interactions between pheromone components and plant volatiles have been reported at behavioral and detection levels. To document the mechanisms of such interactions, we analyzed Ph-ORN responses of Spodoptera littoralis to the main pheromone component, Z9E11-14:Ac, in the presence of 4 monoterpenes. To mimic natural contexts in which plant odors and pheromone emanate from different sources, the 2 stimuli were presented with different temporal patterns and from independent sources. Linalool reversibly reduced the firing response to Z9E11-14:Ac and produced an off effect. Geraniol and geranyl and linalyl acetates reduced the responses to Z9E11-14:Ac with a longer time course. Pulses of linalool over prolonged pheromone stimulation resulted in a discontinuous firing activity. Pulses of pheromone were better separated over a background of linalool, compared with odorless air. The data confirm that plant compounds may modulate the intensity and the temporal coding by Ph-ORNs of pheromone information. This modulation might positively affect mate location at high pheromone density especially nearby a pheromone source.

No abstract

Circadian rhythms are observed in mating behaviors in moths: females emit sex pheromones and males are attracted by these pheromones in rhythmic fashions. In the moth Spodoptera littoralis, we demonstrated the occurrence of a circadian oscillator in the antenna, the peripheral olfactory organ. We identified different clock genes, period (per), cryptochrome1 (cry1) and cryptochrome2 (cry2), in this organ. Using quantitative real-time PCR (qPCR), we found that their corresponding transcripts cycled circadianly in the antenna as well as in the brain. Electroantennogram (EAG) recordings over 24 h demonstrated for the first time a circadian rhythm in antennal responses of a moth to sex pheromone. qPCR showed that out of one pheromone-binding protein (PBP), one olfactory receptor (OR), and one odorant-degrading enzyme (ODE), all putatively involved in the pheromone reception, only the ODE transcript presented a circadian rhythm that may be related to rhythms in olfactory signal resolution. Peripheral or central circadian clock control of olfaction is then discussed in light of recent data.