Daily Feeding Habits of an Aphid Parasitoid: Influence of the Distance between Host and Food
Résumé
In ecosystems, deciding to search for food or for hosts compels parasitoids to a major trade-off in their decision-making between their future and immediate reproductions. If they forage for food, especially carbohydrates sources, parasitoids increase their lifespan, acquire energy to disperse and to search for hosts later on, and uptake nutrients invested in egg maturation. Foraging for hosts will allow the females to lay eggs and therefore increase their reproductive success, but it will deplete their reserves. The choice they make relies on factors among which their nutritional state and environmental factors such as the distance between the hosts and the food sources. This distance is determinant in the need for parasitoids to cover the energetic costs when commuting, meaning when they search alternatively for food and for hosts. This distance might therefore help to predict how often parasitoids need to feed. Providing parasitoids with food sources in the field through floral strips or intercropping could reduce the distance between their trophic resources, increase their food uptake and result in a higher biological control of pests. The frequency at which parasitoids females need to feed in order to optimize their time between ovipositing or re-strengthening through food uptake is unknown. Some studies have attempted to know more on their daily feeding habits, but no direct observation has been made so far. In this study, we used a camera connected to a movement detection software in order to estimate the extrafloral nectar (EFN) uptake frequency and the uptake duration by Aphidius ervi Haliday [Hymenoptera; Braconidae] females, either in the absence of its aphid host or in its presence, at two distances from the EFN providing plant, under controlled conditions. A segmentation and clustering method identified a daily temporal structure of feeding events. In the absence of hosts, parasitoid females fed twice a day, in the morning and in the evening, never in the dark phase. Interestingly, in the presence of Sitobion avenae Fabricius [Hemiptera: Aphididae] aphids (either right next to the EFN providing plant or 80cm away), females tended to feed only once a day, in the morning. The distance range used in the study, representing the spatial detachment between intercrops commonly used, did not show any influence of the distance on the feeding patterns of the parasitoids.
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