The fleeting fragrance of time: Proof of time-based decision by a parasitoid
All animals need to adjust their foraging decisions with time when exploiting resources. The capacity of animals to perceive time and adjust their behaviors accordingly has been a topic of interest for some time but few evidences are currently available for insects. Bumble bees were shown to adjust their response by anticipating cues at fixed-interval, while negative results were obtained for honey bees. Time perception in parasitoid wasps has yet to be investigated, even if this group is one of the most studied in behavioural ecology. The objective of our study was to examine the ability of Microplitis croceipes (Hymenoptera: Braconidae) wasps to perceive time through learning by associating odours (strawberry or vanilla) to time intervals between hosts, larvae of Helicoverpa armigera (Lepidoptera : Noctuidae). An odour was associated to the duration of an interval between hosts, either short (five minutes) or long (thirty minutes), by using an oviposition reward. Females were then isolated, exposed to a last interval and released individually in a wind tunnel with the two odours sourced upwind. A secondary objective was to determine the importance of energy expenditure as a signal of time perception by restraining movement during the intervals.
When released in the wind tunnel, wasps flew significantly more toward the odour associated with the interval they had just experienced (Short interval test: 22 short odour choices vs. 5 long odour choices; Long interval test: 5 short odour choices vs. 23 long odour choices, P < 0.001). We also found that reducing the energy expenditure by preventing movement during the interval interfered with time perception (Free: 15 test odour choices vs. 3 alternative odour choices; Restrained: 7 test odour choices vs. 11 alternative odour choices, P < 0.05). These results provide the first experimental evidence of time perception in a parasitoid wasp. Most optimality models describing how female wasps exploit optimally resources used the fitness rate of gain, thus assuming some form of time perception. Our results also bring experimental support to this assumption. Energy expenditure seems to be involved in the capacity of parasitoid wasps to perceive time.