The main influences on the specificity of hoverfly larvae (Diptera: Syrphidae) to particular aphids are outlined. There are four main ones: aphid species, host plant, parasitoid impact and the presence of ants. Studies in the literature are used to illustrate the effect of these factors on larval performance. The use of single components of fitness as measures of performance can be misleading: only "individual fitness" includes all the appropriate components of survival, development time and reproduction. Even generalists appear to choose among aphids on the basis of expected fitness. A new level of complexity is therefore required in studies of food specificity in predatory syrphids.
The taxonomy of European Eristalinus syrphid flies is reviewed. New data on their life histories, biological notes and a key to species using pupal characters are provided. The larvae and puparia of Eristalinus taeniops (Wiedemann, 1818) and Eristalinus megacephalus (Rossi, 1794) are described for the first time, including new morphological characters of the thoracic respiratory process of all species. The morphology of the male genitalia of E. megacephalus is described and compared with that of E. taeniops.
The results of our morphological studies of the male genitalia and molecular data (mitochondrial COI and nuclear 28S rDNA) do not support the traditional adult classification based on the patterning on the eyes (fasciate vs punctate). We present a phylogeny of the species based on molecular data. The molecular and morphological data indicate that the relationship between some species with punctate eyes and those with fasciate eyes may be closer than with other species with punctate eyes. Moreover the results of the molecular studies support two clades, which does not accord with the traditional arrangement of this group of Syrphidae.
Accordingly we propose that the characters of male genitalia stated by Kanervo in 1938 (but subsequently largely ignored) for arranging the European species of the Eristalinus-Eristalodes-Lathyrophthalmus complex, are suitable for classifying these species.
A review of all known descriptions of immature stages of the species of the genera Scaeva Fabricius, 1805, Ischiodon Sack, 1913 and Simosyrphus Bigot, 1882 is presented using SEM illustrations. The third instar larval and/or pupal morphology of Scaeva dignota (Rondani, 1857), Scaeva mecogramma (Bigot, 1860) and Simosyrphus grandicornis (Macquart, 1842) are newly described. All species of the genera studied in this paper are very similar for all the studied characters of their immature stages, including the chaetotaxy. Molecular characters of the mitochondrial cox1 gene (1128bp) were used for inferring relationships of the studied taxa. The nuclear internal transcribed spacer 2 (ITS2) was additionally applied for species delimitation of the closely related species Scaeva selenitica and S. dignota. The Palaearctic Scaeva species could be split into two groups based on the analysis of morphology of posterior respiratory process. These groups were previously diagnosed as S. selenitica-group [i.e., S. selenitica (Meigen, 1822), S. dignota (Rondani, 1857), S. mecogramma (Bigot, 1860)] and S. pyrastri-group [i.e., S. pyrastri (Linnaeus, 1758), S. albomaculata (Macquart, 1842), S. latimaculata (Brunetti, 1923)]. Semiscaeva Kuznetzov, 1985 and Scaeva Fabricius, 1805 are the available names for these two natural groups that should be classified as subgenera; the former name is proposed for S. selenitica-group and the latter for S. pyrastri-group. Mecoscaeva Kuznetzov, 1985 syn. n. is transferred as a junior synonym of the subgenus Semiscaeva Kuznetzov, 1985 according to the principle of the first reviser. Based on the analysis of immature stages, the generic name Ischiodon Sack, 1913 syn. n. is proposed as a junior synonym of the genus Simosyrphus Bigot, 1882. The similarity of immature stages between Scaeva s. str. and Simosyrphus grandicornis Macquart, 1842, Simosyrphus aegyptius (Wiedemann, 1830) comb. n. and Simosyrphus scutellaris (Fabricius, 1805) comb. n. is discussed. All the proposed subgeneric and generic taxa based on morphological studies received high support employing molecular characters.
The intra- and interspecific variability in the West Palaearctic tibialis-group species of the subgenus Pandasyopthalmus (Diptera: Syrphidae: Paragus) was analysed. Novel immature and molecular characters were studied and the traditionally used adult characters reviewed with the aim of establishing the status of the most widespread taxa of the tibialis-group in the Palaearctic region. Moreover, a review of the morphology of the larvae of the subgenus Pandasyopthalmus is also presented and includes the first description of the chaetotaxy of the larval head of Syrphidae. The larval morphology showed a continuum between two extremes. There is intraspecific variability in the male genitalia characters typically used for diagnostic species identification in this group. Molecular characters of the mitochondrial cytochrome c-oxidase subunit I (COI) was invariant for the West Palaearctic Pandasyopthalmus taxa analysed. Despite the fact that no great differences were found when compared with Afrotropical tibialis-group individuals (uncorrected pairwise divergence 0.17-0.35%), the divergences of the West Palaearctic vs. Nearctic and Austral-Oriental tibialis-group taxa varied between 1.15-2.75% (uncorrected pairwise divergence). Molecular characters of the nuclear ribosomal internal transcribed spacer region (ITS2) revealed several molecular haplotypes of a dinucleotide repeat that was not constrained to morphospecies or to populations of the same geographic origin. The closely related and morphologically similar species of the tibialis-group known from the West Palaearctic region are separable in most cases only by the shape and size of male postgonites. The results of this study support the presence of a single polymorphic taxon in the West Palaearctic region (or a very recent origin of the taxa studied). Moreover larval morphology and the lack of a clear relation between ITS2 haplotypes and the geographic distribution or adult morphology, support the taxonomic implications of barcode taxonomy based on mitochondrial DNA for this species-group of Syrphidae.
The duration of the increase, peak and decline in abundance of the immature stages of sycamore and cereal aphids each year is ephemeral. These temporary resources are exploited by a sequence of aphidophagous insect predators. The temporal sequence in the appearance of the immature stages of coccinellids and syrphids in the sycamore and cereal aphid systems is defined. In spring in the sycamore aphid system and early summer in the cereal aphid system the immature stages of syrphids consistently appeared before those of coccinellids. In the case of the sycamore aphid the autumnal peak in abundance was on average larger than the spring peak, and although attacked by more syrphids, it was not exploited by coccinellids. These temporal patterns in the attack sequence are associated with a difference in the lower developmental thresholds (LDT) of these two groups of predators. The LDT of syrphids (4°C) enables them to be active at lower temperatures and to develop faster between 10° and 27°C than coccinellids, whose LDT is 10°C. As a consequence, early in the year, when temperatures are low but increasing, syrphids appear before and complete their development more quickly than coccinellids, and in the latter half of the year, when temperatures are generally lower and decreasing, only syrphids are likely to be able to complete their development before the aphids disappear. Thus, the niche shift between syrphids and coccinellids is possibly more a consequence of a phylogenetic constraint than a response to competition and or intraguild predation. The relevance of these findings for the ecology of intraguild predation is discussed.