Bet-Hedging Diapause Strategies in Stochastic Environments

In many insect species, adult emergence spreads over several years because of the existence of prolonged diapause in certain individuals. From stochastic models, we show that diversified bet-hedging strategies (mixed strategies with emergence after 1 or 2 yr) are more fit than simple diapause strategy (emergence after 1 yr) or fixed prolonged diapause strategy (emergence after 2 yr) in isolated chestnut weevil populations. This conclusion applies to a large range of survival rates in prolonged diapause and is insensitive to initial conditions, magnitude of temporal autocorrelation, distribution of demographic parameters, and quoted values of population size limitation. However, the shape of the fitness distribution as a function of prolonged diapause frequency changes greatly in the absence of population size limitation. Whatever the survival rate during prolonged diapause, we find that there is no genotypic advantage to extending diapause for all chestnut weevil larvae to more than 1 yr. Our models predict selection of bet-hedging strategies over a large range of prolonged diapause frequencies. This result is consistent with the existence of several mixed strategies in a population. Emergences after 3 yr are not crucial for selection or for the dynamics of mixed strategies in the chestnut weevil.