Trans-generational effects on diapause and life-history-traits of an aphid parasitoid

Abstract

Transgenerational effects act on a wide range of insects' life-history traits and can be involved in the control of developmental plasticity, such as diapause expression. Decrease in or total loss of winter diapause expression recently observed in some species could arise from inhibiting maternal effects. In this study, we explored transgenerational effects on diapause expression and traits in one industrial and one wild strain of the aphid parasitoid Aphidius ervi. These strains were reared under short photoperiod (8:16 h LD) and low temperature (14 °C) conditions over two generations. Diapause levels, developmental times, physiological and morphological traits were measured. Diapause levels increased after one generation in the wild but not in the industrial strain. For both strains, the second generation took longer to develop than the first one. Tibia length and wing surface decreased over generations while fat content increased. A crossed-generations experiment focusing on the industrial parasitoid strain showed that offspring from mothers reared at 14 °C took longer to develop, were heavier, taller with wider wings and with more fat reserves than those from mothers reared at 20 °C (8:16 h LD). No effect of the mother rearing conditions was shown on diapause expression. Additionally to direct plasticity of the offspring, results suggest transgenerational plasticity effects on diapause expression, development time, and on the values of life-history traits. We demonstrated that populations showing low diapause levels may recover higher levels through transgenerational plasticity in response to diapause-induction cues, provided that environmental conditions are reaching the induction-thresholds specific to each population. Transgenerational plasticity is thus important to consider when evaluating how insects adapt to changing environments. 2000; Tougeron et al., 2017a). Recent studies indicated a decrease in diapause expression in someAphidius populations, in both natural and laboratory conditions (Tougeron et al., 2017b). We questioned whether a low proportion of diapausing individuals in some Aphidius populations could be due to a genetic loss of diapause or to the inhibition of plastic diapause expression due to the maternal environment. The first aim of this study was to measure the consequences of maternal effects on diapause incidence, developmental time and life-history traits, as parasitoid mothers could induce or inhibit diapause in their offspring and affect their traits depending on the environmental signals they perceive. The second aim was to investigate the propensity of parasitoids to increase diapause levels and modify trait value over several generations exposed to diapause-inductive conditions.To achieve these goals, we chose two contrasted strains of the parasitic wasp Aphidius ervi Haliday (Hymenoptera: Braconidae) regarding diapause induction. The first one has been reared for mass rearing production by a biological control company under non-diapausing conditions for decades. It expresses b...