The importance of adverse weather conditions for behaviour and population ecology of an aphid parasitoid

1. Weather conditions are known to influence insect behaviour and population dynamics. We investigated how wind and rain affect reproductive success and parasitization patterns of the aphid parasitoid Aphidius rosae in rose bushes. 2. A model was developed to simulate the life history of females foraging in the field under different environmental conditions. The model was parameterized using field and laboratory data on foraging behaviour of A. rosae. Field data on the daily occurrence of wind and rain were used for the simulation of different weather conditions. 3. When 1 day in the life of a female was modelled, both wind and rain reduced the number of aphid colonies and rose bushes visited. During rain the parasitoid ceased all foraging activities, resulting in a negative correlation between the number of eggs being laid in visited aphid colonies, and the duration of rain during a day. During wind, the parasitoid continued to forage at a reduced rate, which led to increasing rates of parasitism in encountered aphid colonies during long wind intervals. 4. In a field study, we linked patterns of parasitism in aphid colonies to the weather conditions at the time when the eggs were laid by the parasitoids. The results confirmed the predictions of the model and showed that wind and rain change the distribution of parasitism among host colonies. 5. When the lifetime reproductive success of foraging females was simulated, both wind and rain affected parasitoid reproductive success. Even if weather conditions were benign, the reproductive success of females was greatly reduced compared to the maximum achievable oviposition numbers in the absence of any bad weather periods. Weather conditions had a less pronounced effect on parasitoid life history if travel mortalities between patches were taken into consideration. 6. Both bad weather conditions and travel mortality led to a strong skew in the Frequency distribution of female reproductive success. A small proportion of females was able to realize oviposition numbers close to the maximum lifetime fecundity, as measured in the laboratory.