Parasyrphus nigritarsis
Parasyrphus nigritarsis is a species of hoverfly, from the family Syrphidae, in the order Diptera. It is known from northern Europe and North America, and has been considered to be a rare species in parts of its range. Adults visit flowers as a source of nutrition, and females lay their eggs on clutches of eggs of leaf beetles (family Chrysomelidae). When the Parasyrphus larvae hatch, they first consume leaf beetle eggs and then consume immature beetles until they reach the pupal stage. This species is related to hoverflies that prey on aphids as larvae, and has been investigated in studies of chemical ecology and food web ecology. Distribution and habitat In Eurasia, P. nigritarsus occurs in the Nordic countries, south to Belgium, Germany, Switzerland and northern Spain, Ireland east through Central Europe into Russia and on to the Russian Far East and Japan. In North America, it occurs from Alaska to Quebec and south to Washington and Idaho. Thus, P. nigritarsus is considered to be present throughout the Northern Hemisphere and it is one of several syrphid species included in the 'Barcode of Life Data System, a project focusing on species occurring in Canada that includes taxonomic information, metadata, and DNA sequences for several individuals at the mitochondrial cytochrome oxidase gene. The flies tend to live in woodland and wetland populated by Alnus, Salix, Populus tremula and Alnus viridis scrub up to in the Alps. Flowers visited by adults include Anemone nemorosa, Potentilla erecta, Prunus cerasus, Prunus spinosus, Ranunculus, Rhododendron aureum, Rubus idaeus, Salix. Description Eggs of P. nigritarsus are white and are smaller than the eggs of their leaf beetle prey (see photo). In the larval stage, mature P. nigritarsus individuals (third instar) are 14–16mm long and approximately 3mm in diameter. Larvae have two pairs of lobes at the anal segment and a complex color pattern with triangular yellow markings on abdominal segments and thin dark brown stripes anterior to them. Adults are medium-sized flies whose legs have pale intermediate segments (femur, tibia) and dark terminal segments (tarsi). They are somewhat unusual among Parasyrphus species in appearance and behavior. Adult wing length ranges from 9-11.5mm. The abdomen is striped and the fly superficially resembles a bee. Abdominal tergites 3 and 4 have a marginal sulcus. The face lacks a black stripe, but has a black edge to the mouth. The frons in females has large dust patches. Consult DipteraMorphology page for definitions of specialized terms describing adult fly morphology. Biological keys to identify adults and larvae are available. Biology and prey use Parasyrphus nigritarsus has been implicated as a major natural enemy of leaf beetles in the subfamily Chrysomelinae within the Chrysomelidae. These leaf beetles lay multiple clutches of 10-30 eggs on host plants in early summer. All beetle species that have been documented as prey to P. nigritarsus or its North American relative Parasyrphus melanderi possess external defensive secretion glands as larvae, from which they evert volatile secretions that are presumed to be repellent to potential predators. Yet