Cystiphora sonchi (Vallot, 1827)

Hesler, Louis S., Gates, Michael W. & Beckendorf, Eric A., 2020, New records document Cystiphora sonchi (Vallot) (Diptera: Cecidomyiidae) and associated parasitoids (Hymenoptera) in the continental United States, Insecta Mundi 2020 (815), pp. 1-8 : 3-5

Cystiphora sonchi (Vallot, 1827) (Diptera: Cecidomyiidae)

Gall midges that emerged from pustule galls on sowthistle leaves from Brookings, South Dakota, and Nisswa, Minnesota, were identified as C. sonchi , and these specimens were vouchered at the SEL. Additional specimens of C. sonchi obtained from the other sampling sites in 2018 and 2019 were vouchered in the NCARL insect collection. Based on these various samples, new state records of C. sonchi are presented here from Minnesota, North Dakota, and South Dakota ( Fig. 1 ).

South Dakota (new state record), 1 km N of Brookings, Brookings County, N 44°20.406 ′, W 96°47.335 ′, 10-VII-2018, Ex. Sonchus arvensis , coll. Eric Beckendorf. USA, South Dakota, Brookings County, Opland Loop Road, 1 km S of Brookings, 9-VII-2018, Ex. Sonchus arvensis , coll. Eric Beckendorf. USA, South Dakota, Brookings County, 1.5 mi N Brookings, Eastern South Dakota Soil and Water Research Farm, N 44°19 ′, W 96°46 ′, 16-VII-2018, Ex. Sonchus arvensis , coll. Louis Hesler.

Minnesota (new state record), Crow Wing County, Nisswa, N 46.5416633°, W 94.3492720°, 13-VII-2018, Ex. Sonchus sp., coll. Sophia Conzemius. USA, Minnesota, Dakota County, Eagan, N 44.824245, W 93.170886, 15-VII-2018, Ex. Sonchus arvensis , coll. Sophia Conzemius.

North Dakota (new state record), Tomahawk National Wildlife Refuge, 2 km NW of Rogers, Barnes County, N 47°04 ′ 54.6 ″, W 98°11 ′ 31.9 ″, 24-VI-2019, x. Sonchus sp., colls. Eric Beckendorf and Janna Julius.

Sowthistles with pustule galls of C. sonchi were common in the areas sampled. Additional observations of leaves of Sonchus spp. with pustule galls consistent with infestation by C. sonchi were observed (but no specimens collected) at the following locations: USA, North Dakota, Steele County, North Golden Lake, 7 km SW of Hatton, N 47°35 ′ 08.7 ″, W 97°37 ′ 40.6 ″, 24-VI-2019. USA, Minnesota, Koochiching County, International Falls, 16-VIII-2019.

Galled sowthistles varied widely in the degree to which leaves were galled, with moderate to heavily galled leaves common ( Fig. 2 ), including an instance of one leaf with at least 201 pustule galls ( Fig. 2C ). Dissections of individual pustule galls from the Brookings area show that they typically contained a single C. sonchi larva or parasitoid larva, but occasional dissections revealed multiple C. sonchi larvae per gall ( Fig. 3 ). Galls with multiple parasitoid larvae were not found.

Online records of C. sonchi . No USA records of C. sonchi were found in the SCAN database. However, digital images of blister galls on S. arvensis were found online for two locations in the USA. One was from Grand Forks, Grand Forks County, North Dakota, on 5 August 2015 submitted by Carl D. Barrentine, with images showing galls on sowthistle leaves consistent with those made by C. sonchi (https://bugguide.net/node/view/1116608/bgimage). A second image consistent with C. sonchi- galled sowthistle leaves was from Le Sueur, Le Sueur County, Minnesota, N 44.4883346558, W 93.8752746582, 2019-08-10 (https://www.discoverlife.org/mp/20l?id=INAT31078790). These reports corroborate our discoveries in other locations in North Dakota and Minnesota.

Recovery of parasitoids from pustule galls of sowthistle leaves. Parasitoid wasps emerged from galled leaves of S. arvensis from: USA, South Dakota, 1 mi N Brookings, Brookings County, N 44°20.406 ′, W 96°47.335 ′, 10-VII- 2018, 11-VII-2018, ex. Sonchus arvensis , coll. Louis Hesler. The parasitoids belonged to three genera, Aprostocetus sp. ( Hymenoptera : Eulophidae ), Lyrcus sp. ( Hymenoptera : Pteromalidae ), and Ceraphron sp. ( Hymenoptera : Ceraphronidae ). These specimens are vouchered at the Smithsonian Institution, National Museum of Natural History.

Aprostocetus cf. atticus ( Fig. 4A ): both males and females key easily to A. atticus in Graham’s key (1987) to European species of Aprostocetus and matches the description and illustrations. It does not key in Burks (1967). To our knowledge, this species is only known from the type series (7 males and 2 females) in the NHMUK. Hence, that species is not represented in the USNM, so we are unable to compare against authoritatively identified material. It would not be surprising if A. atticus was co-introduced with C. sonchi .

Lyrcus , possible new species ( Fig. 4B ): males and females were run through the incomplete, unpublished key to North American species of Lyrcus . Although these specimens are superficially similar to L. justicia , they keyed beyond that couplet to an unidentified new species. It is possible that this particular species was introduced along with C. sonchi .

Ceraphron sp. ( Fig. 4C ): a single specimen was recovered from the rearing and species in this genus are parasitoids of insects in semi-concealed situations ( Diptera, Hemiptera, Neuroptera and Thysanoptera ) or hyperparasitoids of Hymenoptera prepupa.

Figures

Figure 1. Distribution map of Cystiphora sonchi in North America. Pink indicates Canadian provinces with previous records of C. sonchi and orange indicates states with new records in the USA.

Figure 2. Sowthistle leaves with pustule galls of Cystiphora sonchi. A) International Falls, Minnesota, USA, in 2019.B–C) Heavily galled leaves near Brookings, South Dakota, USA, in 2018.

Figure 3. Individual pustule galls on Sonchus arvensis with variable numbers of larval Cystiphora sonchi per gall.

Figure 4. Hymenoptera associated with pustule galls of Cystiphora sonchi. A) Aprostocetus cf. atticus. B) Lyrcus,