Abstract
While the effect of several factors such as predator and prey size, morphology and developmental stage on intraguild predation (IGP) is widely investigated, little is known about the influence of diet on the occurrence and outcome of IGP. In the present study, the effect of the diet experienced during larval development on IGP between the ladybird Harmonia axyridis and the syrphid Episyrphus balteatus is investigated. Four diets were tested for H. axyridis: eggs of the Mediterranean flour moth Ephestia kuehniella, pea aphids, Acyrthosiphon pisum, in an ad libitum amount, pea aphids in a limited amount, and honey bee pollen. For E. balteatus only the two aphid diets were tested. First, experiments were performed to determine the quality of the various diets for development of both predators. Second, IGP experiments between H. axyridis and E. balteatus were performed both in Petri dishes and on potted pepper plants. The diet of both species influenced the incidence of IGP between H. axyridis and E. balteatus both in Petri dishes and on potted plants. In general, smaller larvae of H. axyridis (those fed on poor or restricted diet) fed more on hoverflies than large (well-nourished) ladybird larvae. Further, poorly nourished (smaller) larvae of E. balteatus were more susceptible to predation than well-fed (larger) hoverfly larvae. The observed effects were not only due to the lower fitness of larvae of both predators reared on an inferior quality diet but also to changes in predator behaviour. The results from this study show that IGP interactions are influenced by a multitude of factors, including feeding history of the organisms involved, and emphasize the importance of taking these factors into account in order to fully understand the ecological relevance of IGP.
Highlights
Intraguild predation (IGP) is an interspecies interaction that has been widely investigated since the publication of Polis et al [1]
The longer development for H. axyridis larvae fed with pollen was caused by a slower development of all instars compared to larvae fed with a diet of E. kuehniella eggs or an ad libitum number of aphids
Food ration and quality substantially affected the fitness of larvae of both H. axyridis and E. balteatus
Summary
Intraguild predation (IGP) is an interspecies interaction that has been widely investigated since the publication of Polis et al [1]. Polis et al [1] and Denno & Fagan [8] suggested that intraguild predators that were primarily feeding on nutrient-deficient food could compensate for the limitation of specific nutrients such as nitrogen through IGP This hypothesis was not supported by the study of Kagata & Katyama [9], who investigated nitrogen content and nitrogen-use efficiency of the harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), in intraguild interactions with the seven-spot ladybird, Coccinella septempuncata L. Several combinations were tested between larvae of both predators reared on the different diets to investigate how their feeding history affects IGP incidence Experiments were done both in Petri dishes and on potted pepper plants, in order to assess the influence of spatial complexity on intraguild interactions
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