Ceroptres cornigera Melika and Buss, new species (Figs. 5-8, Figs. 9-11)

We describe a new species of inquiline, Ceroptres cornigera, reared from galls of the sexual and asexual generations of a cynipid gall wasp, Callirhytis quercuscornigera, on stem and leaf galls of pin oak, Quercus palustris. We also include relevant biological information potentially useful in distinguishing this species from other Ceroptres species.

Diagnosis. Similar to Ceroptres quercusarbos (Fitch, 1859) and C. quercustuber (Fitch, 1859), both reared from stem-swelling like galls of Callirhytis clavula (Osten Sacken). In Ceroptres cornigera submedian pits on the pronotum are distinct and large, separated with a strong carina; the entire body is black, antenna and legs are bright brown. In C. quercusarbos and C. quercustuber submedian pits of the pronotum are indistinct and separated by a weak, narrow carina; the mesosoma only is black, gaster brown, face and mouthparts lighter than the rest of the head; antennae and legs are yellow.

Description. Female. Head, mesosoma, and gaster uniformly black; antenna and legs bright brown. Head broader than thorax, broader than high in front view, gena very slightly broadened behind eye, indistinct striae converging toward clypeus, malar space 0.37 times eye length (Fig. 5); entire head very finely punctate, with dense short white setae on face. Antenna 12-segmented (suture between F10 and F11 invisible), filiform; F1 very slightly longer than F2, F3 equal F2, subsequent flagellomeres progressively shorter, but F10 longer than F8+F9 (Fig. 7). Mesosoma shorter than gaster (Fig. 8); pronotum with two elliptical submedian pits with smooth shiny bottoms, broadly separated medially. Scutum nearly as long as broad in dorsal view, finely transversely rugose, with notauli distinct in posterior 2/3; median line short, anterior parallel lines distinct in anterior 1/3 (Fig. 6). Scutellum rounded, rugose, with much rougher sculpture than scutum (Fig. 6). Mesopleuron smooth and shiny. Fore wing hyaline, pubescent, with cilia on margin; radial cell closed, 2.62.7 times as long as broad; veins pale yellow (Fig. 9). Tarsal claws with strong teeth. Metasoma nearly as long as mesosoma and head together, as high as long; terga 2 and 3 fused into one large segment occupying nearly whole of gaster, smooth, shiny, with white setae at the base; indistinct fine suture present between terga 2 and 3. Subsequent terga are finely punctate (Fig. 8). Ventral spine of hypopygium short, slender. Length 1.62.1 mm.

Male. Differs from female in having 15-segmented antenna, F1 slightly curved and extended proximally (Fig. 10); petiole distinct, longer than in female (Fig. 11); legs and antenna lighter. Length 1.5-1.8 mm.

Types. Holotype female from Lexington, Fayette Co., Kentucky, from asexual galls of Callirhytis quercuscornigera, collected on Quercus palustris (Muenchhausen), 21 April 1998, emerged 18 May 1998.  Also 17 female and 18 male paratypes from the same locality, from sexual and asexual galls of C. quercuscornigera on Q. palustris. Holotype, 5 female and 5 male paratypes in the National Museum of Natural History, Smithsonian Institution, Washington, D.C. (USNM); 5 female and 5 male paratypes in the American Museum of Natural History, New York City (AMNH); 2 female and 3 male paratypes in the Department of Entomology, University of Kentucky, and 5 female and 5 male paratypes in the collection of Systematic Parasitoid Laboratory, Koszeg, Hungary.

Material examined. We examined two similar Ceroptres species from the eastern USA, Ceroptres quercusarbos and C. quercustuber, known as inquilines in stem swelling-like galls of Callirhytis clavula. The type material for the first species, deposited in the USNM, was destroyed with only Fitch’s original label remaining without an insect on the pin. Barnes (1988) mentioned only one type locality for this species: “Salem, NY, 28.iii.1857, irregular knobs from tips of twigs of white oak in brother Harvey’s field, south of Battle Hill, placed in vial, small Cynips found dead, May 27th”. Five females and three males of C. quercusarbos from the USNM, labelled as “Ag. Coll. Mich.”, “Collection Ashmead” were examined. Syntypes of C. quercustuber, deposited in the USNM, were examined. They were mounted on one pin (1 female and 1 male, the third insect totally destroyed) and labeled as “Fitch’s Type”, Fitch’s Coll.,” red “Type No 1809 USNM,” and a handwritten label “Cynips Quercus tuber, Fitch.” Barnes (1988) gave the next type locality “Salem, NY, 19.iv.1859, find several of these galls on Titus’s Hill.” Five females and one male from the USNM were also examined. Two females are labeled as “Accession No 6032d AD Hopkins W. Va., “Ceroptres tuber Fitch;” 1 female as “N. Brunsw. NJ”, ”Coll. Ashmead”, ”Ceroptres tuber Fitch;” 1 female “Portsmouth, 6.28.97;” 1 female “Riley Coll., Marlat”, “Ceroptres tuber Fitch,” and 1 male “Toronto, Ont.”, “Ceroptres tuber Fitch”.

Ceroptres quercuarbos was described by Fitch (1859) on the basis of one male as “a small black gall-fly having all its legs and antennae of a bright pale yellow color.” This is the only description of the wasp given by the author. Such a coloration is typical for nearly all Ceroptres species. Fitch (1859) described Ceroptres quercustuber as “a small black gall-fly with dull pale yellow antennae, mouth and legs, its hind shanks and its antennae towards their tips being dusky, its length 0.08 and to the tips of its wings 0.13”. This species was described on the basis of both the female and male. Fitch (1859) thought that he had described the gall-inducing insects, but they were inquilines.

Other Ceroptres species known from the eastern USA differ strongly from this new species not only in the morphology of the adults, but also in their distribution and trophic associations. Thus, we did not compare the new species to them.

Distribution. Kentucky (Fayette Co., Lexington).

Etymology. Named from the host gall, Callirhytis quercuscornigera, from which it was reared.

Biology. Members of this species are inquilines in galls of the asexual and sexual generations of Callirhytis quercuscornigera, which associates with Q. palustris and other red oaks (Burks 1979).

Ceroptres cornigera is one of several inquilines and opportunistic insects living within stem galls, but it is the only inquiline of the leaf galls. It is the first known species of Ceroptres to inhabit galls from both alternating generations of its host cynipid. Ceroptres cornigera larvae develop in the succulent tissue below a Callirhytis quercuscornigera larval chamber in young stem galls. It is uncertain whether or not this inquiline contributes to gall-maker mortality. Twenty-four female and 17 male Ceroptres cornigera adults emerged from stem galls collected in spring 1998. Most galls from which Ceroptres adults emerged (219 adults from 86 galls reared in 1999) lacked external horns and were of small diameter (2.5 ± 0.1 cm). However, horns typically protrude when galls are 25 months old. Adults may live as many as 6 days without a water or sugar source. Mean female body length is 2.2 ± 0.1 mm, and mean ovipositor length, when dissected and uncoiled, is also 2.2 ± 0.1 mm (Eliason & Potter 2000). When adults emerge in May, female ovaries are not fully mature, and may contain >100 eggs per female.

Individual Ceroptres cornigera develop in each leaf gall, and kill the gall-maker larva while feeding on the succulent gall tissue. In 1998, more than 1000 leaf galls were placed in individual transparent gelatin capsules in the laboratory. Of the 713 galls from which wasps emerged, 37.3% were Ceroptres cornigera (138 female, 128 male). Adults may live as many as 4 days without a water or sugar source. When adults emerge in June and July, female ovaries are not fully mature (Eliason & Potter 2001).