Costs and benefits of larval jumping behaviour of Bathyplectes anurus.

Bathyplectes anurus, a parasitoid of the alfalfa weevils, forms a cocoon in the late larval stage and exhibits jumping behaviour. Adaptive significance and costs of the cocoon jumping have not been thoroughly studied. We hypothesised that jumping has the fitness benefits of enabling habitat selection by avoiding unfavourable environments. We conducted laboratory experiments, which demonstrated that jumping frequencies increased in the presence of light, with greater magnitudes of temperature increase and at lower relative humidity. In addition, when B. anurus individuals were allowed to freely jump in an arena with a light gradient, more cocoons were found in the shady area, suggesting microhabitat selection. In a field experiment, mortality of cocoons placed in the sun was significantly higher than for cocoons placed in the shade. B. anurus cocoons respond to environmental stress by jumping, resulting in habitat selection. In the presence of potential predators (ants), jumping frequencies were higher than in the control (no ant) arenas, though jumping frequencies decreased after direct contact with the predators. Body mass of B. anurus cocoons induced to jump significantly decreased over time than cocoons that did not jump, suggesting a cost to jumping. We discuss the benefits and costs of jumping behaviour and potential evolutionary advantages of this peculiar trait, which is present in a limited number of species.

The social environment affects mate guarding behavior in Japanese beetles, Popillia japonica.

The effect of the social environment on post-copulatory mate guarding duration in Japanese beetles, (Popillia japonica Newman), was examined in a laboratory experiment. The mate guarding durations of beetles in different sex ratios and densities were observed for 10 hours. Guarding duration was longer when females were larger, suggesting the presence of 'cryptic' male mate choice. Densities, but not sex ratio, affected the duration of guarding bouts, with males guarding for longer at higher densities. This result implies that males increase their guarding duration under conditions in which their female may be likely to be encountered by other males. The lack of a sex ratio effect on the duration of guarding bouts is consistent with other studies on this species that indicate males have difficulty distinguishing females from males. Consequently, because the sex ratio on food plants is typically male-biased, a paired male may react just to density, treating surrounding individuals as if they were mostly males. The total amount of time males spent guarding was lower at lower densities and at male-biased sex ratios; this suggests that after ceasing to guard one female, males were less able to find a subsequent mate under these conditions.