Fig 1.
Natural and artificial girdles in euphorb petioles.
(A) Finished girdle in a poinsettia petiole created by a final instar Theroa zethus. (B) Theroa zethus larva scraping the surface of a Euphorbia corollata stem. Scratch marks created by mandibular teeth are readily visible as dark green parallel lines. (C) Binder clip used to compress poinsettia petioles. (D) Effect of VEG acid and petiole compression on latex outflow from the petiole stub (left) and from the leaf blade (right). Arrows indicate locations where the petiole was compressed horizontally and vertically three times by the binder clip. Only outflow from the petiole stub was reduced significantly.
Fig 2.
Effect of abrasion on latex exudation from poinsettia petioles.
Half of the petioles were rubbed on the dorsal surface with sandpaper. The petioles then received 5μL of either VEG secretion or water. After 2.5 hours, the petioles were severed and the wet weight of latex exuding from each petiole stub was weighed. Abrasion facilitated VEG acid penetration resulting in nearly complete elimination of latex outflow from petioles. Bars with different letters differ significantly at P < 0.05 using Games-Howell tests.
Fig 3.
Effect of compression on latex exudation from poinsettia petioles and leaves.
The petioles were treated either with VEG acid for an hour (following surface abrasion), compression with a binder clip, or both acid and compression. Acid treatment followed by compression reduced the wet weight of latex emitted by the petioles more effectively than either acid or compression tested alone (top). In contrast, neither acid nor compressions significantly reduced latex outflow from the leaf blades (bottom). Bars with different letters differ significantly at P < 0.05 using Games-Howell tests.
Fig 4.
Effect of multiple compressions on latex outflow from poinsettia petioles and leaves.
Petioles were compressed 20 times with a binder clip, then they were severed and the wet weight of latex exuding from the petiole stub (top) and leaf blade (bottom) was measured. Compressions made in the petiole from stem to leaf were especially effective at draining latex from the leaf blade. Bars with different letters differ significantly at P < 0.05 using Games-Howell pairwise tests (top) or Tukey tests (bottom).
Fig 5.
Effects of VEG secretion and acid constituents on latex outflow from poinsettia petioles.
Petioles were severed 2.5 hours after being abraded and treated either with T. zethus VEG secretion, a reconstituted acid solution (6.53 M formic acid, 0.05 M butyric acid), or water. The VEG secretion and reconstituted acid solutions caused a similar reduction in wet weights of latex. Bars with different letters differ significantly at P < 0.05 using Games-Howell pairwise tests.
Fig 6.
Effects of formic acid and butyric acid on latex outflow from poinsettia petioles.
Petioles were abraded and treated either with 6.53 M formic acid + 0.05 M butyric acid, 6.53 M formic acid alone, 0.05 M butyric acid alone, or water. After 2.5 hours, the wet weights of latex emitted by severed petioles were measured. Formic acid alone caused a similar reduction in latex outflow as formic and butyric acid combined. Butyric acid by itself at low concentration did not decrease outflow. Bars with different letters differ significantly at P < 0.05 using Games-Howell pairwise tests.
Fig 7.
Effect of T. zethus furrows on cell morphology.
(A) Furrow in a poinsettia midrib created by an intact control T. zethus larva. (B, C) Cross sections through the same poinsettia midrib outside the furrow (left) and in the center of the furrow (right). The black vertical lines represent transects from the phloem to the epidermis, which were used to count the number of cells with concave or convex shapes. Convex cells have round walls with all interior angles ≤180°; concave cells have at least one interior angle >180°. (D, E) Cortical cells outside (left) and within (right) cross sections of the same furrow viewed at higher magnification. An example of a convex cell (blue arrow) and a concave cell (green arrow) are marked in the bottom right image. The black scale bars equal 0.5 mm (B and C) or 0.05 mm (D and E).
Fig 8.
Distortion of poinsettia cell walls within and outside T. zethus furrows.
The fraction of cells with a concave shape in midrib cross sections was measured along a transect from the phloem to the epidermis. Significantly more concave cells were present inside furrows than outside furrows for intact T. zethus larvae (P < 0.01, t-test) and larvae with cauterized spinnerets (P < 0.05), but not for larvae with a blocked VEG that were unable to release acid (P = 0.55).
Fig 9.
Stem and petiole compression by final instar notodontid caterpillars.
(A-C) Theroa zethus larva walking along a Euphorbia corollata stem while compressing the stem from all angles. The dark green compressions are clearly visible. (D) Praeschausia zapata larva creating a girdle in a Chamaesyce hyssopifolia stem by compressing the stem repeatedly from all sides with its mandibles. (E) Datana perspicua larva compressing the rachis of a smooth sumac leaf (Rhus glabra). Hairs on the larva are glued together by exudate. (F) D. perspicua feeding on a smooth sumac leaf. Scars from previous rachis compressions (red arrow) and drops of white exudate (white arrows) are visible. (G) Paraeschra georgica larva compressing the petiole of a water oak leaf (Quercus nigra). (H) Nadata gibbosa larva compressing the petiole of a southern red oak leaf (Q. falcata). A brown scar from earlier compressions is indicated by the white arrow.