Allograpta (Allograpta) obliqua (Say)
Allograpta obliqua belongs to a group, Allograpta obliqua species group, characterized by: face straight, with low indistinct tubercle of variable size; oral opening about 1.5 as long as wide, with oral apex at level of antennal base; antennal pits confluent; plumula well developed; subscutellar fringe distinct; wing partially bare basomedially, without apical dark macula; alula broad, about 1.5 times as broad as cell BM; metasternum pilose; abdomen elongate (mengual et al. 2009).
Allograpta obliqua differs from other species in this group by: scutellum yellow or unicolorous; katepimeron yellow, forming a continuous yellow band from anepisternum to katatergum; 4th tergum medial black vittae and with a pair of parallel yellowish vittae; mesonotum not continuously yellow laterally, black behind transverse suture. The most characteristic feature is the two parallel yellow vittae and two oblique yellow vittae on 4th and 5th terga.
Adults are pollinators and feed on pollen and nectar. Larvae are predators on acari, whiteflies (Aleyrodidae), aphids (Aphididae), mealybugs (Pseudococcidae), butterfly's larvae (Lepidoptera) and on eggs of jumping plant louse (Psyllidae) (Rojo et al., 2003).
From original description (Say 1823):
Thorax greenish bronze, with a yellow dot before the wings; tergum banded and spotted with yellow. Inhabits the United States.
Head yellow, a dusky line above the antennae; orbits yellow to the vertex; antennae blackish on the superior edge; thorax dark green-bronze, a large yellow spot before the wings; scutel bright-yellow; feet whitish, anterior tibia and tarsi a little dilated, the latter with short joints, posterior thighs with one obsolete band and tibia two banded, extremity of all the tarsi dusky; tergum black, first segment with a yellow basal edge; second segment with a band at the base, interrupted into two oblong triangles, a broader one on its middle, yellow; third segment with one band which is sometimes double; fourth and fifth segments each with an oblique oblong oval spot each side, and two longitudinal lines on the middle, yellow.
Length about three-tenths of an inch.
Resembles Scaeva polita [now Toxomerus politus], but there is no line upon the thorax, and the markings of the tergum are different.
Head. Face with facial tubercle, yellow with medial brown vita from antennal base to tubercle, yellow pilose; gena yellow except brownish on genal suture, yellow pilose; lunule dark brown; frontal triangle yellow, yellow pilose; vertical triangle black, black pilose; antenna orangish, basoflagellomere orange, darker dorsally; occiput black, silver pollinose, withish-yellow pilose.
Thorax. Scutum shiny black with bluish iridiscence, yellow pilose; postpronotum yellow; notopleuron yellow; scutellum yellow, black pilose, subscutellar fringe sparce with black pile. Pleuron mostly black, except anterior anepisternum yellow, posterior anepisternum yellow on posterior half, katepimeron and katatergum yellow, and katepisternum with dorsal yellow macula; metasternum pilose; calypter yellow, brownish dorsally with long yellow pile and short black pile on margin; plumula yellow; halter yellow; spiracular fringes yellow. Wing. Wing membrane mostly hyaline, stigma dark; apically microtrichose with basal cells bare. Alula broad, microtrichose. Legs. Entirely yellow except metafemur with a dark subapical ring and metatibia and metatarsus brown; metatibia with a medial yellow ring; yellow pilose except tarsi black pilose.
Abdomen. Parallel-sided. Dorsum mainly black, black pilose dorsally and laterally except 1st tergum yellow pilose laterally and 2nd tergum yellow pilose laterally on anterobasal 3/4; 1st tergum yellow with a black fascia on posterior margin; 2nd tergum black with 2 anterobasally triangular yellow maculae and a medial yellow straight fascia; 3rd tergum black with a broad arcuate yellow fascia; 4th and 5th terga black with 2oblique vittae from posterolateral margin to anteromedial section and 2 other yellow medial vittae, sometimes joined anteriorly ; sterna mainly yellow, yellow pilose.
Their color is probably of a great deal of protective value to them. On cabbage and on dock they very closely resemble the color of the leaves. On cabbage they are frequently in a position among the leaves inaccessible to predaceous enemies; on dock the under side of the leaf is not a conspicuous position; and on persimmon they are most commonly closely rolled about by the curling leaf.
GenBank accession number for this species are: protein-coding gene COI (EF127310), rRNA 28S (EF127389) and 18S (EU241833).
Ecology and Distribution
Washington to Quebec, south to Argentina; Hawaii (introduced). See GBIF: http://data.gbif.org/species/16217378/
Larvae are predators on acari, whiteflies (Aleyrodidae), aphids (Aphididae), mealybugs (Pseudococcidae), butterfly's larvae (Lepidoptera) and on eggs of jumping plant louse (Psyllidae), and can be found on several plants. For a complete list of prey species and associated plants, see Rojo et al. (2003).
Oviposition for the first spring generation began about the middle of May. A female taken on May 17 laid 35 eggs on May 22, 13 the following day, and by May 26, when she died, had deposited nearly 100 eggs. The first of these hatched the morning of the 25th, a few others the 26th, making the duration in the egg-stage (indoors) from 2.5 to 3.5 days (Metcalf, 1912). Data collected in United States.
The duration in the pupal stage varied in captivity from 3.5 to 5.5 days in the case of those taken from persimmon in the spring, while in Autumn in specimens from cabbage the duration in the pupal stage was in some cases as much as 10 days.
Egg: elongate oval in outline, narrowing slightly to the roundly-pointed anterior end and the truncate, posterior, micropylar end. The egg is slightly inflated dorsally, flattened against the surface to which it is attached ventrally. Length about 0.8 mm., diameter 0.3 mm. (Figs. 61 and 62). Color chalk-white with the usual microscopic sculpturing (Fig. 63). When highly magnified, sometimes tinted with yellowish in the depressions between the sculptures. In this case the main bodies of the projections are broader than in Syrphus americanus (3 to 4 times as long as broad); somewhat oval in shape, the arms thicker and not so long as in S. americanus; usually about fifteen around each body. The space between the bodies is about two thirds as wide as the body. There are about 28 of these projections the length of the egg, about 55 around it transversely at the middle.
Larva: When just hatched (Fig. 65) the larvae have a length of 1.2 mm., width 0.25 mm. They are irregular in outline, nearly cylindrical, broadest near the middle; feeble and inactive. Color whitish, with a yellowish or greenish tinge. The usual small, fleshy, conical elevations are present, twelve to each segment, but the segmental bristles were not discernible, apparently absent. The posterior breathing appendages are rather prominent, longer than in a young larva of S. americanus, and light in color like the rest of the body. Their tips are, at first, rather remote from each other though with subsequent growth and their greater elevation above the general body surface they become contiguous. The two longitudinal fat bodies are discernible as a white line on each side of the dorsal blood-vessel which is more prominent in the posterior half of the body. The skin is faintly wrinkled transversely. From this condition there seems to be a gradual growth until the larva, when full-grown, has reached a length of about 8 mm., width 2 mm., height 1.25 mm. It may then be described as follows: Shape elongate oval, but much more pointed at the anterior end when extended. The outline is somewhat irregular due to folding and wrinkling of the skin. The posterior end is rounding, truncate except for the projections of the posterior breathing organ(Fig. 66).
Color green, very similar to that of the cabbage leaf (on which they occur commonly) with two longitudinal white stripes. This color is due to colored visceral bodies which show through the transparent skin. Along the mid-dorsal line for two-thirds the length can be seen the narrow, dark, pulsating blood-vessel, its prominence varying with different specimens. It is irregularly limited at the sides by a narrow mass of greenish, fatty globules changing gradually to whitish. This whitish adipose matter forms the two prominent longitudinal white stripes, 0.2 or 0.3 mm. wide and extending to within a few millimeters of either end where they become much attenuated. The rest of the body, except the appendages is green, darker on the sides. The breathing tubes are light brown, black at the tips where the spiracles are located.
The skin is finely papillose when magnified. The character of the visceral matter often gives the larva a very granular appearance. The segments are marked by the usual twelve bristles in a transverse row. These are light in color, not elongate and not at all conspicuous; and are the only vestiture present. The character of the mouth-parts is more or less perfectly represented by Figure 67. The outer pair of mouth-hooks is present.The caudal branchial appendage is prominent, elongate, about 0.5 mm. in length by 0.125 mm. in breadth; of two cylinders fused mesad except at the extreme tip where they diverge slightly (Figs. 66c, 68). The usual three elongate spiracles and circular plate are present on each half. The spiracular elevation is about three times as long as broad. There is a short, spur-like spiracular spine between each two spiracles, one between the most dorsal spiracle and the plate, and one mesad from the most ventral spiracle. These spines are continued down the sides of the tube as more or less evident ridges.
Puparium: Dimensions, average of eight: Length about 5.25 mm., maximum breadth 2.5 mm., maximum height 2.3 mm. This neglects the breathing tubes at the posterior end of the body which may project 0.5 mm. farther posteriorly or be directed more dorsally.
The puparium is broadest and deepest in front of the middle, the anterior end bulbous; strongly and evenly depressed and com¬pressed to the posterior end, the posterior elevation very gradual (See Figs. 69 and 70). The color in this stage changes very decidedly during the development of the nymph within the translucent puparium. The color is not resident in the pupal envelope but due almost entirely to the inclosed matter. Consequently at first the colors are those of the larva (light pea-green with a brownish remnant of the dorsal blood vessel and, at the sides of this, the two whitish lines). The flattened posterior end of the puparium, including the breathing tubes, however, is light testaceous brown, the tips about the spiracles black. Midway on the length of the breathing appendages is a dark brown ring.
As the pupa developes within, the color changes, gradually losing all trace of the green and assuming more and more the colors of the adult. The first thing to be noticed is the reddish brown color of the eyes replacing the green in the anterior third of the pupa. Later the black and yellow abdominal markings become apparent.
The puparium is smooth, bare; the segmental spines inconspicuous. The breathing tubes as in the larva, prominent subcylindrical, the tips around the spiracles becoming black. The wrinkles of the skin often remain rather prominent.
In general, the female fly lays eggs singly on the surface of leaves and shoots of aphid-infested-plants; the eggs hatch to larvae that move actively in search of aphids or other prey. When the aphid or other arthropod is found, it is entangled with sticky salivary secretion, lifted away from the plant, and sucked dry.
Enemies and parasitoids
Numerous larvae of the autumn generation on cabbage are parasitized by the small ichneumonid, Bassus laetatorius Fabr. (Metcalf, 1912).
Evolution and Systematics
Nomenclature and Synonymy
Originally described as Scaeva obliqua by Say (1823), Osten Sacken (1875) placed this species under the genus Allograpta.
Scaeva obliqua Say 1823: 89
Syrphus securiferus Macquart 1842: 100
Syrphus baccides Walker 1849: 594
Syrphus dimemsus Walker 1852: 235
Syrphus signatus Wulp 1867: 144
Allograpta dejongi Doesburg 1958: 44
The results of Mengual et al. (2008a) placed Allograpta obliqua as sister group of Allograpta fuscotibialis, a South African species; both forming a separate clade from the rest of Allograpta (Allograpta) species.
Adult syrphids are crucial pollinators of flowers and the immatures recycle nutrients. Aphidophagous species have an important role as biological control agents. Several studies have shown that hey are the most abundant aphid predators in outdoor crops, but their effectiveness is little understood.
Metcalf, CL. 1912. Life histories of Syrphidae IV. Ohio Naturalist. 12(8):533-541. Ohio Naturalist 12: 533
Mengual, X, Ruiz C, Rojo S, Ståhls G, Thompson CF. 2009. A conspectus of the flower fly genus Allograpta (Diptera: Syrphidae) with description of a new subgenus and species. Zootaxa. 2214: 1-28.
Mengual, X, Ståhls G, Rojo S. 2008. Molecular phylogeny of Allograpta (Diptera, Syrphidae) reveals diversity of lineages and non-monophyly of phytophagous taxa. Molecular Phylogenetics and Evolution. 49(3): 715-727
Osten Sacken, CR. 1875. A list of the North American Syrphidae. Bulletin of the Buffalo Society of Natural Sciences. 3:38-71.
Rojo, S, Gilbert F, Marcos-Garcia MA, Nieto JM, Mier PM. 2003. A world review of predatory hoverflies (Diptera, Syrphidae: Syrphinae) and their prey. CIBIO Ediciones, 319 pp.