Insects harbour a wild diversity of symbionts that can spread and persist within populations by providing benefits to their host. The pea aphid Acyrthosiphon pisum maintains a facultative symbiosis with the bacterium Hamiltonella defensa, which provides enhanced resistance against the aphid parasitoid Aphidius ervi. Although the mechanisms associated with this symbiotic-mediated protection have been investigated thoroughly, little is known about its evolutionary effects on parasitoid populations. We used an experimental evolution procedure in which parasitoids were exposed either to highly resistant aphids harbouring the symbiont or to low innate resistant hosts free of H. defensa. Parasitoids exposed to H. defensa gained virulence over time, reaching the same parasitism rate as those exposed to low aphid innate resistance only. A fitness reduction was associated with this adaptation as the size of parasitoids exposed to H. defensa decreased through generations. This study highlighted the considerable role of symbionts in host-parasite co-evolutionary dynamics

).Aphids harbour both an obligate bacterial symbiont, Buchnera aphidicola, and a wide range of facultative ones. Facultative symbionts can modify morphological, developmental and physiological host traits that favour their spread within aphid populations. We experimentally investigated the idea that symbionts may also modify aphid behavioural traits to enhance their transmission. Aphids exhibit many behavioural defences against enemies. Despite their benefits, these behaviours have some associated costs leading to reduction in aphid reproduction. Some aphid individuals harbour a facultative symbiont Hamiltonella defensa that provides protection against parasitoids. By analysing aphid behaviours in the presence of parasitoids, we showed that aphids infected with H. defensa exhibited reduced aggressiveness and escape reactions compared with uninfected aphids. The aphid and the symbiont have both benefited from these behavioural changes: both partners reduced the fitness decrements associated with the behavioural defences. Such symbiontinduced changes of behavioural defences may have consequences for coevolutionary processes between host organisms and their enemies.

Phenotypic plasticity refers to the environmental control of phenotypes. Cues experienced during development (developmental plasticity) or during adulthood (acclimatization) can both affect adult phenotypes. Phenotypic plasticity has been described in many traits but examples of developmental plasticity in physiological traits, in particular, remain scarce. We examined developmental plasticity and acclimatization in pheromone production in the butterfly Bicyclus anynana in response to rearing temperature. B. anynana lives in the African tropics where warm rearing temperatures of the wet season produce active males that court and females that choose, whereas cooler temperatures of the dry season lead to choosy less active males and courting females. We hypothesized that if male pheromone production is costly, it should be reduced in the dry season form. After describing the ultrastructure of pheromone producing cells, we showed that dry season males produced significantly less sex pheromones than wet season males, partly due to acclimatization and partly due to developmental plasticity. Variation in levels of one of the compounds is associated with differential regulation of a pheromone biosynthetic enzyme gene. This plasticity might be an adaptation to minimize pheromone production costs during the stressful dry season.

The Southeast Asian transboundary haze contains a mixture of gases and particles from forest fires and negatively impacts people’s health and local economies. However, the effect of the haze on organisms other than humans has not yet been sufficiently studied. Insects are important members of food webs and environmental disturbances that affect insects may impact whole ecosystems. Here we studied how haze directly and indirectly affects the survival, growth, and development of insects by rearing Bicyclus anynana butterflies under artificially generated smoke as well as reared in clean air but fed on plants previously exposed to smoke. Direct haze exposure significantly increased the mortality of caterpillars, increased larval development time, and decreased pupal weight, while indirect haze exposure, via ingestion of haze-exposed food plants, also affected development time and pupal weight. No smoke particles were found in the tracheae of subjects from the smoke treatment suggesting that the increase in development time and mortality of B. anynana under smoke conditions might be due to toxic smoke gases and toxic food, rather than particulate matter. These results document significant deleterious effect of haze smoke to the development, adult size, and survival of insects, key players in food-webs.

Many phytophagous insects have strong preferences for their host plants, which they recognize via odors, making it unclear how novel host preferences develop in the course of insect diversification. Insects may learn to prefer new host plants via exposure to their odors and pass this learned preference to their offspring. We tested this hypothesis by examining larval odor preferences before and after feeding them with leaves coated with control and novel odors and by examining odor preferences again in their offspring. Larvae of the parental generation developed a preference for two of these odors over their development. These odor preferences were also transmitted to the next generation. Offspring of butterflies fed on these new odors chose these odors more often than offspring of butterflies fed on control leaves. In addition, offspring of butterflies fed on banana odors had a significant naïve preference for the banana odors in contrast to the naïve preference for control leaves shown by individuals of the parental generation. Thus, butterflies can learn to prefer novel host plant odors via exposure to them during larval development and transmit these learned preferences to their offspring. This ability potentially facilitates shifts in host plant use over the course of insect diversification.

We review experimental and theoretical evidence that learning in insects and spiders affects the expression of mate preferences and of sexual signals, the evolution of both traits, and ultimately patterns of assortative mating, and speciation. Both males and females can modify their sexual preferences and signaling based on previous social interactions or the experience of visual, olfactory, gustatory, or auditory signals. Learning takes place during an early life exposure, previous personal sexual experiences or by observing the choices of others, and it can occur sometimes via very short (a few seconds) exposures to individuals or signals. We briefly review some of the molecular mechanisms that mediate learning in insects, as well as theoretical work that assesses how learning impacts the evolution of insect sexual traits and speciation. We suggest that future research should attempt to provide evidence of the adaptive nature of learning, which remains scarce in insects as well as in vertebrates, and explore further the mechanisms of learning in order to probe into their possible transgenerational inheritance. Future studies should also model how this process might further affect the evolution of sexual traits, and provide a unifying terminology for the underlying mechanisms of learning across diverse life-history contexts.

International audienceAs biological invasions, intentional introductions often result in a loss of genetic diversity in the new founder populations. In classical biological control programs, natural enemies introduced into novel environments are likely to suffer from population bottlenecks. Unlike invasive populations, individuals for biological control are typically kept in quarantine during several generations before being released in the field. This procedure reduces further the effective population size of the introduced populations, which thus increases the effects of inbreeding and genetic drift, resulting in a greater loss of genetic diversity. This study addresses the genetic consequences of the introduction of the parasitoid wasp Aphidius ervi, a successful biocontrol agent of important aphid target-pests in Chile. This was assessed by examining the genetic diversity and differentiation at nuclear and mitochondrial genetic markers in terms of (1) the magnitude of the genetic diversity loss after 38 years of the introduction of A. ervi, (2) the current level of genetic differentiation between Chilean introduced populations and putative native populations from France, and (3) the genetic relationships and magnitude of the genetic diversity loss between introduced populations of A. ervi in Chile compared to those introduced in North America. The results provide evidence that parasitoid populations suffered the effects of a moderate genetic bottleneck during the introduction, showing further a strong geographical genetic differentiation between populations in the natal and novel environments. In addition mtDNA sequences analysis showed evidence of a single main event of introduction in Chile, unlike the North American situation, where there is evidence for multiple introductions. The significance of the loss of genetic diversity during introductions related to the success of parasitoids as biocontrol agents in classical biological control programs is discussed

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