Abstrakt
Here we present our data collected in Greece during 2017-2018 on 50 aphid colonies per year, living on different plants, which were monitored every 3 days during the whole season (from aphid appearance to disappearance on each plant). In exactly the same way, we collected data for an additional 100 plants in the Czech Republic, which gave us 200 colonies altogether.
Data for each colony were fitted by an aphid model. For individual plants, outliers from the trend of this dependence gave us an indication of the presence of predators (mainly ladybirds) on a plant (and eating some aphids).
This, together with direct observations of predators, gave us information about the presence of predators in the colony. The results indicate that model successfully describes the dynamics of aphid populations in colonies, where no signs of predators (outliers or directly observed individuals) were observed during the whole existence of the colony.
Regarding predators, no larvae were present for long periods on individual herbaceous plants (because they moved between the plants, died, dropped off or disappeared for unknown reasons), whereas on trees (or large stands of plants of the same species, like, e.g., nettles) they were present. This means that the classical predator-prey models can describe the dynamics of ladybird-aphid systems only on individual trees.
However, for getting a good fit, equation has to be used instead of classical logistic growth of prey, and no predator reproduction can be considered, as during the colony existence, the ladybird larvae do not achieve reproductive age and even if they do, the new adults fly away. On herbaceous plants, the prey dynamics follows the model with certain random disturbances, caused by foraging predators arriving to the colony at random instants for only a short period of time.