Graham E Rotheray

Macroevolution of hoverflies (Diptera: Syrphidae): the effect of using higher-level taxa in studies of biodiversity, and correlates of species richness

We test a near‐complete genus level phylogeny of hoverflies (Diptera: Syrphidae) for consistency with a null model of clade growth having uniform probabilities of speciation and extinction among contemporaneous species. The phylogeny is too unbalanced for this null model. Importantly, the degree of imbalance in the phylogeny depends on whether the phylogeny is analysed at the genus level or species level, suggesting that genera ought not to be used uncritically as surrogates for species in large‐scale evolutionary analyses. Tests for a range of morphological, life‐history and ecological correlates of diversity give equivocal results, but suggest that high species‐richness may be associated with sexual selection and diet breadth. We find no correlation between species‐richness and either body size or reproductive rate.

The biodiversity and conservation of saproxylic Diptera in Scotland

Over a ten year period, 1988–1998, over 300 woodlands were visited throughout Scotland and 2061 records of saproxylic Diptera obtained. Of these 1574 were records of early stages; 258 species in 32 families were encountered; 206 species were reared of which 53 were red-listed, 9 were new to Britain and 10 were new to science. Most records came from native boreal trees such as Betula pubescens, Pinus sylvestris and Populus tremula. However, few saproxylic Diptera were specific to tree species, exceptions were 6 red-listed species associated with P. tremula and 5 red-listed species with P. sylvestris. In contrast, most saproxylic Diptera were specific to microhabitat or breeding site. The most important microhabitats were decaying sap under bark and decaying sapwood. Most red-listed species are restricted to Strathspey and north-east Scotland where relatively large stands of native boreal trees exist.

Pollen feeding larvae in the presumed predatory syrphine genus Toxomerus Macquart (Diptera, Syrphidae)

The morphology and biology of the larva of Toxomerus apegiensis (Harbach, 1974) are described from Suriname. This larva feeds on pollen of Olyra obliquifolia Steudel, a bambusoid grass (Poaceae) that grows in the understorey of tropical rainforests. The morphology of the larva of Toxomerus politus (Say, 1823), which feeds on pollen of corn, Zea mays, is redescribed. These species are the only known phytophages within the otherwise predatory genus Toxomerus. The cephalopharyngeal skeleton of T. apegiensis shows features that are hypothesized to be modifications towards pollen feeding. These features are absent in the larva of T. politus. Possible evolutionary scenarios of the development of phytophagy within Toxomerus are briefly discussed based on published information on phylogeny of the genus.

Larval stages of 17 rare and poorly known British hoverflies (Diptera: Syrphidae)

Third stage larvae of three species of phytophagous (Portevina maculata, Cheilosia albitarsis and C. antiqua), thirteen species of saprophagous (Callicera aurata, Brachyopa bicolor, B. insensilis, B. pilosa, Hammerschmidtia ferruginea, Myolepta potens, Brachypalpus laphriformis, Caliprobola speciosa, Criorhina berberina, C. floccosa, C. ranunculi, Pocota personata and Xylota tarda) and one possibly predatory species (Microdon devius) of Syrphidae are described. Most of the saprophagous species breed in dead wood and many are European rarities. Nine of the 17 species described are included in the British Red Data Books: 2. Insects (Shirt, 1987). For the larva of each species, recognition features and breeding sites are described.

Larval morphology and feeding patterns of four Cheilosia species (Diptera: Syrphidae) associated with Cirsium palustre L. Scopoli (Compositae) in Scotland

Four species of Cheilosia (Diptera: Syrphidae) were reared from Cirsium palustre in Scotland. The third-stage larva is similar in all four species but each can be recognized by the form of the posterior respiratory process. A modified prothorax and thickened bands of spicules on some of the segments may characterize the plant-boring type of Cheilosia larva. The univoltine Cheilosia grossa oviposits in batches on young stems. With three or more larvae per plant the tip of the stem is killed. The plant responds by producing a mass of basal stems in which larvae subsequently feed. Cheilosia fraterna and Cheilosia proxima do not oviposit in batches and are bivoltine. Cheilosia fraterna attacks mature stems and rosettes. Cheilosia proxima attacks only rosettes. Cheilosia albipila was reared only six times, from stems collected in July. Rates of parasitism were low and only two parasitoid species were recorded.

The early stages and breeding sites of four rare saproxylic hoverflies (Diptera: Syrphidae) from Spain

The puparial stage is described for each of four saproxylic hoverflies (Diptera, Syrphidae): Ferdinandea fumipennis Kassebeer, 1999, Mallota dusmeti Andréu, 1926, Myolepta difformis Strobl, 1909, and Myolepta obscura Becher, 1882. Early stages were collected at Cabañeros National Park in Ciudad Real province, central Spain. Mallota dusmeti, M. difformis, and M. obscura were found in water‐filled holes of live Fraxinus angustifolia Vahl. trees and the larva of F. fumipennis was found in a sap run on a live Quercus pyrenaica Wild. tree. Larvae were identified by rearing them to the adult stage. Puparia of these species possessed generic‐level characters found in congenerics. Apparent species‐level characters separating them from early stages of congenerics are proposed. The records reported here are the first for the Iberian Peninsula of M. obscura. Mallota dusmeti, M. difformis, and Myolepta obscura are extremely rare in Europe with M. dusmeti classed as “vulnerable” in the Spanish Invertebrate Red Data Book.

Sampling Methods for Assessing Syrphid Biodiversity (Diptera: Syrphidae) in Tropical Forests

ABSTRACT When assessing the species richness of a taxonomic group in a specific area, the choice of sampling method is critical. In this study, the effectiveness of three methods for sampling syrphids (Diptera: Syrphidae) in tropical forests is compared: Malaise trapping, collecting adults with an entomological net, and collecting and rearing immatures. Surveys were made from 2008 to 2011 in six tropical forest sites in Costa Rica. The results revealed significant differences in the composition and richness of syrphid faunas obtained by each method. Collecting immatures was the most successful method based on numbers of species and individuals, whereas Malaise trapping was the least effective. This pattern of sampling effectiveness was independent of syrphid trophic or functional group and annual season. An advantage of collecting immatures over collecting adults is the quality and quantity of associated biological data obtained by the former method. However, complementarity between results of collecting adults and collecting immatures, showed that a combined sampling regime obtained the most complete inventory. Differences between these results and similar studies in more open Mediterranean habitats, suggest that for effective inventory, it is important to consider the effects of environmental characteristics on the catchability of syrphids as much as the costs and benefits of different sampling techniques.

Final stage larvae and puparia of Platypezidae (Diptera)

Platypezidae occupy an important basal position within the Muscomorpha. However, morphological analyses of larval Platypezidae are incomplete and early stage data is insufficient to inform phylogenetic analysis and recognition of groundplan characters and states within Muscomorpha. For example, knowledge is poor of the characters of respiratory organs, head, head skeleton, thorax and segmental sensilla. In this study we describe and compare these features of 16 species in 11 genera. The head appears as a distinct fleshy organ with atrium and antennae and maxillary organs separated on the dorsal surface. Head skeletons are characterised by an anteriorly projecting labrum and labium with laterally placed mandibles. The prothorax is frequently armoured with sclerotised regions and spicules. A repeated and uniform pattern of up to 11 pairs of sensilla circumvent each thoracic and abdominal segment. Respiratory organs vary little in size and arrangement of spiracular openings. Using a set of 43 larval and puparial characters and based on a Brachyceran outgroup, a sequence of genera is established which places Melanderomyia as the most basal. These results are compared with estimates of phylogeny based on adult characters.

The relationship between feeding mode and morphology in Cheilosia larvae (Diptera, Syrphidae)

Third stage larvae of seven species of Cheilosia are described. The morphology of each species is analysed in relation to feeding mode. A variety of features are identified that appear to be uniquely related to fungal-feeding, leaf-mining, stem/root tunnelling and sap/cambium feeding. An important factor influencing larval morphology appears to be the solidity of the food. A relationship between morphology and feeding mode should be useful in analysing the larval stages of other Cheilosia species, the majority of which are unknown.

Morphology and feeding behaviour of the leaf-mining larva of Cheilosia semifasciata (Diptera: Syrphidae)

In North Wales the larva of Cheilosia semifasciata (Diptera: Syrphidae) makes full-depth blotch mines in leaves of Umbilicus rupestris. Mines occur mostly on shaded plants with one larva per plant. Each larva mines several leaves to complete development and initiates new mines by curling round the leaf margin and puncturing the epidermis under the leaf. Unlike other dipteran leaf-miners which feed on their sides, only the thorax is turned sideways when feeding. The larva uses a grasping organ on the anal segment to grip the substrate when moving externally on the food-plant. Inside leaf mines, position is further secured by the integumental vestiture which grips the epidermis above the larva. The morphology and behaviour of the larva of C. semifasciata differs markedly from larvae of three congeneric species that tunnel in stems and roots.