Octotoma plicatula (Fabricius)

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), Zootaxa 5549 (1), pp. 1-60 : 26-27

Octotoma plicatula (Fabricius)

( Figs. 65–66 , 143 )

Reared specimens. KANSAS: Douglas Co., Baldwin City, Baldwin Woods , 2.vii.2015, em. 5–21.vii.2015, C.S. Eiseman, ex Campsis radicans , # CSE1688 (6 adults, MLBM) ; OKLAHOMA: Payne Co., Mehan , 36.014339° N, - 96.996744° W, 18.vi.2015, em. 10.vii.2015, M.W. Palmer, ex Campsis radicans (1 adult, BG 1086715 ) .

Hosts. Bignoniaceae : Campsis radicans (L.) Bureau.Adults also feed on Oleaceae ( Chionanthus virginicus L., Fraxinus americana L., F. pennsylvanica Marshall , F. quadrangulata Michx. , Ligustrum vulgare L.), and have been reported from several other, unrelated plants, but these occurrences were likely incidental ( Clark 2000; Clark et al. 2004).

Biology. Riley & Enns (1979) state that “larvae, pupae and adults have been taken from trail mines” in leaves of trumpet creeper, and that the beetles seem to prefer partially shaded plants. Staines (1989) gives the following notes on biology: “This species forms tentiform mines. Excrement is accumulated as a black spot near the base of the leaf. Pupation occurs in the mine near the midrib. Adults make oblong holes in leaves.” Octotoma plicatula produces perhaps the most distinctive leaf mines of all North American hispines ( Figs. 65–66 ), and a clearer description is warranted.

The egg is deposited in a pit chewed in the upper surface of a leaflet, centered on the midrib or a lateral vein and toward its distal end (i.e., near the leaflet apex or margin). It is sometimes adorned with excrement, and there is often a small cluster of adult feeding holes nearby. The larva mines basally, forming a track about 2 mm wide that is centered on the midrib or vein. Some mines are merely irregularly lobed along their length, but more often there are several branches of varying length, likewise about 2 mm wide, radiating out from this central track. These branches cross the lateral veins freely, but we observed just one instance of the midrib being crossed. This was in the apical half of a leaflet that was crowded with mines of three larvae, all originating from eggs laid on lateral veins to one side of the leaflet. Occasionally the branches are themselves forked. Frass tends to be concentrated toward the basal end of the main corridor, forming a diffuse dark patch, but brown streaks and strips are also dispersed throughout the branches, except sometimes for the last several millimeters, which then appear clean and whitish. Pupae from our Oklahoma collection were found outside the mines, but normally pupation takes place in the dark central/basal area of the mine. Adults apparently eat holes in leaves that are still young and tender, but by July their feeding sign consists of oblong to elongate patches on the upper leaf surface.

Parasitoids. A male and female of Pnigalio Schrank ( Eulophidae ) emerged from mines of the Kansas collection on 7 and 13 July 2015 (CSE1684, BMNH). The only parasitoid previously reported from Octotoma plicatula is P. maculipes (Crawford) ( Burks 1979) , but our specimens evidently represent a different species as their legs are immaculate ( Yoshimoto 1983). In his “material studied” section for Closterocerus trifasciatus Westwood ( Eulophidae ), Hansson (1994) listed two females “ex Exephanes sp. , (as Octatoma plicatula on the label) on Tecoma radicans .” Species of Exephanes Wesmael ( Ichneumonidae ) are parasitoids of Noctuidae ( Lepidoptera ) larvae in grass stems (G. Broad, in litt.), so it is unclear how Hansson concluded that this was the host if the specimens were labeled as having been reared from O. plicatula on [ Campsis ] radicans , but we are inclined to believe the label.

Notes. In Central America, several other hispines are known to form mines with similar radiating channels, including Octhispa haematopyga (Baly) , Uroplata sculptilis Chapuis , and a species of Probaenia Weise. In each of these species, the larva constructs a chamber beneath the egg, covers the dorsal surface with frass, and makes channels radiating out from it, ultimately pupating in the chamber ( Hespenheide & Dang 1999).

Figures

FIGURES 65–66. Leaf mines of Octotoma plicatula on Campsis radicans.

FIGURES 142–161. Chrysomelidae adults; 142: Octotoma marginicollis; 143: O. plicatula; 144: Odontota dorsalis; 145: O. floridana; 146: O. horni; 147: O. scapularis; 148: Stenopodius cf. lateralis; 149: Sumitrosis ancoroides (reared from Stylosanthes biflora); 150: S. ancoroides (reared from Strophostyles helvola); 151: S. inaequalis; 152: S. pallescens; 153: S. rosea (reared from Hylodesmum glutinosum); 154: S. rosea (reared from Laportea canadensis); 155: S. rosea (another individual reared from same collection of L. canadensis leaves); 156: S. rosea (reared from Celastrus orbiculatus); 157: Oulema palustris; 158: Altica cf. lazulina; 159: Dibolia borealis; 160: D. chelones; 161: D. melampyri.