Transgenerational phenotypic plasticity of diapause induction and related fitness cost in a commercial strain of the parasitoidAphidius erviHaliday

Diapause is an adaptation that insects have evolved to synchronize their life cycle with that of seasonal climatic changes and resources availability. However, cues for its induction are not always clear and, in some cases, a maternal effect may be involved. At the population level, just a part of the individuals may exhibit diapause with important consequences in terms of winter survival. Moreover, clear indicators of diapause state are difficult to identify. Diapause induction was thus investigated in the aphid parasitoid speciesAphidius erviHaliday (Hymenoptera: Braconidae) developing in the aphidSitobion avenae(Hemiptera: Aphididae) at four crossed photothermal regimes (16 degrees C and 8 degrees C, 16:8 h L:D and 8:16 h L:D), and during 2 successive generations. We analyzed the reliability of changes in mummy color to assess for the diapausing state compared to dissections, and we measured parasitoid morphological and physiological traits. We observed that the proportion of dark brown mummies increased after one generation under low photothermal regime compared to other regimes. No diapause was recorded at 16 degrees C, 16:8 h L:D, while we observed 16.2% and 67.5% diapause incidence at 8 degrees C, 8:16 h L:D, at 1st and 2nd generation, respectively. Diapause induction is thus increased by short day-length conditions and low temperatures as well as by maternal effects. All parasitoid life-history traits (weight, size, fat content, water content, egg-load, and longevity) were affected by the photothermal regime and/or the generation. These results raise new questions on the environmental thresholds needed to induce diapause and on survival and adaptation potential of commercially available parasitoid strains in different environments.

Automated summary

Diapause is an adaptation that insects use to synchronize their life cycles with seasonal changes in climate and resources. Short day-length conditions, low temperatures, and maternal effects have been found to increase diapause induction.