The effect analysis of the diapause duration on the hatching parameters of the artificial semi-annual population of Lymantria dispar caterpillars

The paper investigates the existence of a relationship between the diapause duration and the temperature threshold of hatching, the variances in temperature and hatching time of the artificial six-month population of Lymantria dispar caterpillars. A half-year population gives two generations a year under artificial conditions. A comparative analysis of these parameters with similar parameters of the hybrid population of L. dispar, as well as studies by other authors, has been carried out. The Eigen quasispecies model was used for the mathematical formalization of the evolution process. The results of this work can be used to study the evolution of L. dispar.

Prolonged diapause has sex-specific fertility and fitness costs

Diapause in seasonal environments allows insects to survive adverse seasons. However, individuals can sometimes enter a prolonged diapause for more than a year, and also skip favourable seasons, which can bring additional costs through e.g. loss of metabolic resources. At the same time, prolonged diapause can be beneficial if it allows individuals to have a risk-spreading strategy to skip potentially suboptimal breeding seasons. We studied if prolonged diapause (2-year diapause) negatively affects the fertility and fitness of female and male Colorado potato beetles (Leptinotarsa decemlineata) compared to control (1-year diapause) beetles. We also tested the parental effects on the subsequent chemical stress tolerance of their offspring. We found that prolonged diapause carried fertility costs only for females who were less fertile than the control females. However, no differences in fertility were observed in males. Furthermore, prolonged diapause in females resulted in offspring with lower larvae-to-adult survival even though these offspring had accelerated development times. In contrast, paternal diapause duration had no effects on their offspring larvae-to adult survival, but prolonged diapause males sired offspring with slower development times than control males. Perhaps to compensate the costs related to prolonged diapause both older parents produced or sired offspring with higher body mass than control parents. Despite the differences in emergence mass, parental diapause duration did not affect offspring insecticide stress tolerance. The difference between females and males most likely results from the observed differences in prolonged diapause females’ capacity to fight against cellular oxidative damage which was poorer compared to the control females. Even though prolonged diapause allows individuals to have a risk-spreading strategy it carries sex-specific fertility and fitness costs indicating that selection could favour this in males but not in females.

Diapause incidence and duration in the pest mango blossom gall midge, Procontarinia mangiferae (Felt), on Reunion Island

The mango blossom gall midge, Procontarinia mangiferae, is a multivoltine species that induces galls in inflorescences and leaves of the mango tree, Mangifera indica. In subtropical Reunion Island, populations of P. mangiferae are observed all-year round, but the pattern and the role of dormancy in their life cycle have never been documented. We performed field and laboratory experiments using more than 15,000 larvae. We demonstrated that a larval diapause may affect a part of the midge population, regardless of the season. The total duration of the diapause varied from 6 weeks to more than 1 year. One year of field monitoring showed that the highest incidence of diapause was observed in larvae collected during the summer from mango leaves, where it affected approximately one-third of the individuals. This facultative diapause allows the permanent presence of P. mangiferae in the orchards. By recording diapause duration during 22 weeks under controlled conditions, we showed that high temperatures (26 °C) increased diapause duration and extended the range of the dates of diapause emergence, whereas cool temperatures (20 °C) shortened diapause duration and shortened the range of the dates of emergence from diapause. A temperature decrease from 26 to 20 °C triggered the emergence of diapausing individuals. These mechanisms ensure the synchronization of the emergence of diapausing individuals with the appearance of mango inflorescences, which is also induced by cool winter temperatures.