Acumyia acericola Harris

Harris, Keith M., 2008, The Acer seed midge, Acumyia acericola, an unusual new species and genus of Lasiopteridi (Diptera: Cecidomyiidae) with aciculate ovipositor and larval puparium, Zootaxa 1910, pp. 21-26 : 23-26

Acumyia acericola Harris (new species)

Figures 1–10 .

Adults. Wing length about 2–3 mm, with R5 vein joining costa before wing apex. Anterior edge of wings and distal half of legs with clothing of narrow, elongate black scales, easily lost in slide preparation. Antennae with 16–17 flagellomeres in females, all with very short necks, and 17–18 flagellomeres in males, all except last with distinct long narrow necks. Circumfila simple in both sexes, each flagellomere with distal and proximal thread-like rings connected by two longitudinal strands. Eyes holoptic, with circular ommatidia and median eye-bridge about 5 ommatidia long. Maxillary palps four-segmented. Head with 20–30 frontoclypeal setae and lateral thorax with 15–20 anepimeral setae. Tarsal claws roundly curved and sharp-pointed, empodium extending just beyond claws, pulvilli about half as long as claws and claws on all legs each with a strong basal recurved tooth about a third the size of the claw.

Female abdomen with sclerotized needle-like aciculate bulbous-based ovipositor 0.5–0.7 mm long, retracted into the abdomen (fig. 4). Tergites 1 to 6 rectangular, covered with small scales and each with a single row of fine hair-like setae posteriorly; tergite 7 quadrate and concave laterally, with an anterior pair of trichoid sensilla, a pair of small antero-lateral sclerotized excrescences, similar to setal points of insertion, but without setae, and a posterior row of fine setae; tergite 8 longer than other tergites and divided into two longitudinal separate strap-like sclerites, each with an anterior trichoid sensilla but without setae or scales.

Male genitalia (figs 5, 6) with cerci deeply separated, hypoproct shorter than cerci and shallowly excavate distally, aedeagus narrowly tapered distally and tightly enclosed by strong, light-brown parameres which have distal fine hairing dorsally; haired dorsobasal lobes present at the base of the gonocoxites (fig. 6), which are elongate cylindrical; gonostyle narrow with uniform width, not tapered distally. Tergites 1–6 rectangular, clothed in small scales and each with posterior row of fine setae; tergites 7 and 8 reduced, 7 with a few lateral setae and 8 without setae; all tergites with a pair of anterior trichoid sensilla.

Larvae and puparia. Final instar larva white, about 3 mm long, and developing within a transparent, brown, sclerotized, slightly flattened puparium (fig. 7), formed from the skin of the penultimate instar, as indicated by the presence of the remains of the larval head capsule anteriorly. Sternal spatula of final instar with long shaft and pointed, triangular terminal blade (fig. 8); larval integument entirely shagreened, without obvious mamelons or transverse spinule rows ventrally; terminal papillae with very short setae. Most papillae difficult to distinguish from the shagreened integument but a full complement of dorsal, pleural, lateral, terminal, sternal and ventral papillae present, as illustrated for Dasineura gleditchiae (Osten Sacken) by Gagné (1989), mostly without setae or with very small, inconspicuous micro-setae.

Pupae. Enclosed within the puparium. Lacking antennal and frontal horns but with long cephalic setae (fig. 9) and long, tapering prothoracic spiracles (fig. 10); abdominal tergites with tightly-packed fields of spines and spinules.

Material examined. HOLOTYPE male no. 20554, UK, Essex, Hainault Forest/Lambourne Common, ex fruits Acer campestre collected vii-viii.2006 (B. Ecott), emerged iv-v.2008 (K. M. Harris). Paratypes males nos. 20548, 20549, 20555, and females nos. 20542, 20545, 20547, 20550, 20556, 20557, same data as holotype, plus pupal exuviae on slide no. 20553 and additional specimens of adults, larvae, puparia, and pupae preserved in 70% isopropanol in a 45 x 20 mm screw-topped glass vial. All deposited in the Natural History Museum, London, UK.

The following additional material was also examined: puparia and larvae collected by K. M. Harris from Acer campestre fruits, at Sheepleas, East Horsley, Surrey, viii. 2006 and 28.vii.2008; at Holride Farm, Ripley, Surrey, 05.viii. 2006 and 25.vii.2008; at Westcott Down, Surrey, 16.viii.2006 at Queenswood Country Park, Herefordshire, 09.ix.2006 and at High Wood Country Park, Colchester, Essex, 07.ix.2008; and from A. platanoides fruits at Sheepleas, East Horsley, Surrey, 8.viii and 16.viii.2006.

Biology. On the only occasion that Acumyia acericola adults have been successfully reared, final instars remained alive and active within puparia for up to twenty months before pupating. Seventeen adults reared from larvae collected in summer, 2006, emerged in late April and early May 2008, with peak emergence on 04-06 May. This suggests that normal development of the species, which is almost certainly univoltine, is biennial. This length of development may result from the need for the hard woody covering of the Acer fruits to decay sufficiently to facilitate the emergence of adults from the enclosed fruit, which persist in leaf litter and the soil, and it may also be an adaptation to biennial fruiting of the host plants, but further observations will be needed to confirm these suggestions. Adult emergence in 2008 coincided with the development of soft young fruits on Acer campestre and the females presumably use their aciculate ovipositors to insert eggs into the ovular cavity. One fruit with an oviposition puncture was found at Sheepleas in May 2008 and dissection revealed a cluster of insect eggs within the cavity but follow-up observations failed to confirm the association with Acumyia , possibly because the infestation level was very low at that time (less than 1% fruits infested). Up to seven puparia have been found in single Acer fruits, mostly adjacent to the developing ovule, on which they presumably feed. Damaged ovules have a characteristic lumpy appearance in late summer.

Comments. This species occurs in continental Europe and plant quarantine interceptions in the USA indicate that it is also present in Japan, but I have not seen specimens. Dr R J Gagné (personal communication, August, 2008) has informed me that voucher specimens of larvae and puparia of this or another species intercepted at USA ports of entry are present in the National Museum of Natural History, Washington, DC (USNM). These specimens were collected on five separate occasions between 1966 and 1991 from Acer palmatum , A. japonicum and A. polymorphum imported from Japan, and there are additional specimens from A. platanoides , imported from Russia in 1981 and on A. forestii imported from China in 1994. In this last case the blade of the larval sternal spatula is two-toothed, which suggests that another species may be involved. Two puparia of Acumyia have been found recently in Acer palmatum seeds collected in Aomori Prefecture, Honshu, in northern Japan (Prof. Junichi Yukawa, personal communication, September, 2008).

Figures

FIGURES 1 – 4. Acumyia acerivora gen. nov., sp. nov. 1. Acer campestre fruit with ovular cavity exposed to show two puparia lying near the developing ovule. [Scale line = 5 mm.] 2. male and 3. female [Scale lines = 0.5 mm.]. 4. Micrograph of the aciculate ovipositor partly everted from the abdomen, showing the divided tergite 8 above the bulbous base of the ovipositor. [Scale line = 0.05 mm.]

FIGURES 5 – 10. Acumyia acerivora gen. nov., sp. nov. 5. Micrograph of male genitalia, dorsal view. [Scale line = 0.05 mm.] 6. Micrograph of the male genitalia, lateral view, focused on the brown parameres that enclose the aedeagus and also showing one of the dorsobasal lobes and the hypoproct. [Scale line = 0.05 mm.] 7. Puparium with sternal spatula and head capsule of the enclosed final instar larva visible at left. [Scale line = 1 mm.] 8. Sternal spatula of final instar larva. [Scale line = 0.1 mm.] 9. Pupal exuvium of head showing long cephalic setae. [Scale line = 0.1 mm.] 10. Pupal prothoracic spiracle. [Scale line = 0.05 mm.]