Microrhopala laetula LeConte
Creators: name: Eiseman, Charles S.
name: Feldman, Tracy S.
name: Palmer, Michael W.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Chrysomelidae
Microrhopala
Microrhopala laetula

description: Microrhopala laetula LeConte
(Figs. 12, 58–60, 137–138)
Reared specimens. IOWA: Howard Co., Hayden Prairie State Preserve, 15.vii.2015, em. 1.viii.2015, C.S. Eiseman, ex Silphium laciniatum, # CSE 1904 (1 adult, ZFMK); Winneshiek Co., MJ Hatfield’s farm (43.442361, -92.002867), 25.vi.2019, em. 27.vi.2019, C.S. Eiseman & J.A. Blyth, ex Silphium integrifolium× perfoliatum, # CSE 5374 (1 adult, MLBM); same collection, em. 8–22.vii.2019, # CSE 5480 (52 adults, MLBM); OKLAHOMA: Payne Co., Marena, 20.vi.2018, em. 23.vi.2018. M.W. Palmer, ex Silphium laciniatum, #4256.1 (1 adult, USNM); same collection, em. 13.vii.2018, #4256.2 (1 adult, USNM).
Photographed mine. IOWA: Winneshiek Co., Decorah Community Prairie, 18.vi.2018, MJ Hatfield, Silphium perfoliatum (BG 1626105).
Hosts. * Asteraceae: Silphium integrifolium Michx. × perfoliatum L., S. laciniatum L., S. perfoliatum L. This species also feeds on S. terebinthinaceum Jacq. according to Clark et al. (2004), but it is unclear whether this record refers to adults or larvae. Popenoe (1877) reported it being found on Solidago rigida L. in Kansas, but Clark et al. (2004) suggest this record may be based on misidentified Microrhopala vittata (Fabricius). It is possible that a specimen of “ M. vittata ” reared from Helianthus in Illinois is actually M. laetula; see the M. vittata species account below for details.
Biology. As with Microrhopala vittata, eggs are deposited in clusters on the lower leaf surface and coated in dark, liquid excrement (Fig. 12). (Hendrickson (1930), apparently referring to this species, reported M. “ vittata ” eggs being laid on the upper surface of a Silphium laciniatum basal leaf. In our experience it is sometimes difficult to determine which leaf surface is which on this host, due to the vertical orientation of the leaves. Johnson & Boe (2022) stated that on S. perfoliatum “the eggs are placed at the distal adaxial area of the leaf (Figure 5),” but the caption for their Figure 5 correctly indicates that the eggs are on the abaxial surface.) Larvae mine gregariously to form a brown, full-depth blotch mine, typically at the leaf apex, with frass evenly distributed in short strips (Figs. 58–60). In our experience they readily establish new mines in fresh leaves when necessary, whereas Johnson & Boe (2022) cited “persistent group mining within a protective single leaf of S. perfoliatum ” as characteristic of M. laetula, in contrast with the host leaf changing that is commonly observed in M. vittata, which they hypothesized makes larvae of M. vittata more likely to be parasitized.
Notes. As summarized by Johnson & Boe (2022), 19 th century authors alternately treated Microrhopala laetula as a full species or as a variety of M. vittata. Weise (1911) listed M. laetula as a synonym of M. vittata, and this was followed by McCauley (1938) and Clark (1983) in their revisions of the genus, as well as by Staines (2006, 2015). However, Downie & Arnett (1996) treated the two as distinct species, with M. vittata being found on Solidago spp. and M. laetula on Silphium perfoliatum; adults of M. vittata have the “pronotal and elytral punctures coarse; reddish elytral stripe usually complete” (Fig. 140), as opposed to “pronotum and elytra punctures not as coarse; reddish elytral stripe often abbreviated to short humeral stripe” in M. laetula (Figs. 137–138). Clark (2000) agreed with this assessment, stating that M. laetula is a distinct species occurring in natural prairie areas of several Midwestern states, and citing the same distinguishing characters (along with the differing host plants): “the orange vittae usually do not extend beyond the middle of the elytra, and the strial punctures of the elytra are much smaller than in M. vittata.” Johnson & Boe (2022) noted possible differences between larvae of the two species. Riley et al. (2003) listed IA, IL, IN, KS, MN, and WI as the confirmed distribution of M. laetula, with South Dakota added by Johnson & Boe (2022), so our Oklahoma specimens (not examined by S.M. Clark) would represent a new state record. Although the differences in puncture size are unclear in our photographed specimens of the two species and the reddish stripes of our reared M. laetula vary in length from about ⅓ to the full length of the elytra, we accept M. laetula as a valid species based on the barcode of our specimen reared from Silphium laciniatum (BIN BOLD:ADF6349) showing a difference of 6.42% or more from all other M. vittata barcodes (BIN BOLD:AAH0112). We look forward to a future revision of Microrhopala that will clarify the “subtle but consistent” morphological differences between the two species (S.M. Clark, in litt.).
description: Published as part of Eiseman, Charles S., Feldman, Tracy S. & Palmer, Michael W., 2024, New larval host records, parasitoid records, and DNA barcoding data for North American leaf-mining leaf beetles (Coleoptera: Chrysomeloidea), pp. 1-60 in Zootaxa 5549 (1) on pages 21-22, DOI: 10.11646/zootaxa.5549.1.1, http://zenodo.org/record/14387856