Regional tritrophic relationship patterns of five aphid parasitoid species (Hymenoptera: Braconidae: Aphidiinae) in agroecosystem-dominated landscapes of southeastern Europe.

A regional survey of the complex tritrophic associations (parasitoid-aphid-plant) of aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae) was carried out to determine and explore the patterns of those associations in various types of environments. Here, we present trophic relationship patterns of the five aphid parasitoid species in crop and noncrop habitats in southeastern Europe, and we contrast them in a regional (Mediterranean [MED] versus continental [CNT]) context. In total, 79 aphid host taxa were identified in this survey. Forty-two of these were recorded from noncrop plants only, 21 from crop plants only, and 18 were present on both types of plants. This means that approximately 74% of all the parasitoid-aphid trophic interactions that support the persistence of the five selected parasitoids are entirely (54%) or partially (20%) associated with noncrop plants. The correspondence of parasitoid-aphid combinations among habitat/region combinations is very high and specific. Our results suggest that Mediterranean and continental regions are clearly distinguished by a contrasting pattern of trophic interactions in crop habitats, whereas the noncrop habitats contribute in lesser degree to these differences. For the crop/noncrop breakdown, the number of nonspecific interactions was larger than expected in crop habitats, whereas in noncrop habitats the abundance of partially specific and specific interactions was larger. The analysis of variance for the regional and habitat distribution of mean aphid host number per parasitoid was highly significant. When both regions were analyzed separately, the parasitoid/crop design showed significant parasitoid effects as well as interactions, whereas the habitat effect was not significant for the Mediterranean region and highly so for the continental region. This highly complex pattern suggests that the mean number of parasitized aphid species is not distributed among parasitoids, regions, and habitats in a similar manner. Even with these complexities taken into account, the overall trend is that noncrop habitats support more parasitoid-aphid combinations and more so in the continental than in Mediterranean regions, although not always statistically significant. As mentioned, large number of noncrop aphid hosts, especially for Lysiphlebus fabarum (Marshall), Praon volucre (Haliday) and Aphidius colemani Viereck, can significantly enhance the population buildup for these important parasitoids around agroecosystems. These facts can be important in biological aphid pest control in the region. Although not easily quantified, the overall positive effects of larger parasitoid diversity in noncrop habitats are undoubtedly related to the distribution and structure of noncrop habitat patches in agroecosystems at a landscape scale.