Fig 1.
Life cycle of cecropia silk moth examined in this study.
Late fifth instar caterpillars (A) spin a cocoon (B) during the summer, in which they pupate and overwinter. The adult moth emerges (C) from its cocoon in the following spring. For (A-C), black bars represent 2.54 cm.
Fig 2.
The dimorphic, multilayered architecture of cocoons constructed by larvae of the cecropia moth.
(A) A cecropia moth cocoon possesses three distinct layers, consisting of an outer envelope (OE), an intermediate space filled with silk (IS), and an inner envelope (IE). Each cocoon is constructed with an escape valve (EV) from which adults can exit the cocoon. (B) A cocoon is constructed to be either a large, fluffy baggy morph (left) or a smaller, more tightly woven compact morph (right). (C) The OEs of baggy (left) and compact (right) cocoons are architecturally dimorphic. (D) The IEs of baggy (left) and compact (right) cocoons (pictured here are the IEs of cocoons contained within the OEs found in [C]), are equivalent architecturally. For (A-B) cocoons are shown attached to branches and still possessing leaves, whereas (C-D) cocoons are shown removed from branches and stripped of leaves. For (B-D), black scale bars denote 1 cm.
Fig 3.
Structural properties of dimorphic cecropia moth cocoons.
(A) Surface area comparisons of the outer envelope and inner envelope of baggy and compact cocoons. (B) Comparisons of the volume of the outer envelope and inner envelope of baggy and compact cocoons. (C) The volume of the intermediate space of baggy and compact cocoons. (D) The spatial relationship between the outer envelope (OE) and inner envelope (IE) of a baggy and a compact cocoon. (E) Comparing the surface area and volume (F) of baggy and compact cocoons that were either field-collected or spun in captivity. For all panels, blue denotes baggy cocoons and red denotes compact cocoons. For (A)–(C), sample sizes are 10 for each group. For (E) and (F), sample sizes are 10 for both cocoon-morphs, in both field-collected and captive-spun groups. Error bars denote standard errors of the mean.
Fig 4.
Ultrastructural properties of dimorphic cecropia moth cocoons.
Flat SEM images (magnification: 175x) of the (A) outer envelope and of the (B) inner envelope of a baggy and compact cocoon. (C) Porosity estimate comparisons between the outer envelope and inner envelope of baggy and compact cocoons. Cross-sectional SEM images (magnification: 706x) of the (D) outer envelope and the (E) inner envelope of a baggy and compact cocoon. (F) Thickness comparisons between the outer envelope and inner envelope of baggy and compact cocoons. For (A) and (B), black bars represent 400 μm and for (D) and (E), black bars represent 100 μm. For both (C) and (F), N = 4 for all groups, and purple bars denote the outer envelope, and green bars denote the inner envelope, of baggy and compact cocoons. Error bars denote standard errors of the mean.
Fig 5.
Emergence of adult cecropia moths from field-collected cocoons.
(A) Emergence dates of adults from baggy and compact cocoons. (B) Daily adult emergence times of adults from baggy and compact cocoons. (C) Sex and condition (weight, g) of adults emerging from both baggy and compact cocoons. (D) Sex and size (thorax volume, mm3) of adults emerging from both baggy and compact cocoons. For all figures, blue bars are baggy cocoons and red bars are compact cocoons.
Fig 6.
Common spinning arena used to assay dimorphic cocoon construction.
(A) Common spinning arena used to assay cocoon construction. Paper grids on walls of arena omitted for clarity (see Methods). Both baggy (B) and compact (C) cocoons were constructed in our common arena apparatus. In both (B) and (C), red arrows indicate silk scaffold assembly for each cocoon.
Fig 7.
Different construction behavioral patterns produce dimorphic cocoons in H. cecropia.
Bar graphs show time budget comparisons between baggy (blue) and compact (red) cocoon spinners for (A) stretch-bend behavior (> 3 pulls), (B) swing-swing behavior, and (C) Figure-8 silk laying, during the first 18 hours of cocoon spinning (see S2 Table for statistical analyses). Error bars denote standard errors of the mean. For (A-C), the cartoon to the left of each bar graph depicts the silk-spinning behavior of the caterpillar for that particular behavior. Solid red lines indicate silk and dashed red lines denote the movement of the caterpillar; structure perpendicular to arena floor (rectangle) is the dowel found in the spinning arena. Cartoons were re-drawn from [16] by Daniel J. Newman.
Fig 8.
The spectral properties of cecropia cocoons.
(A) An example of a baggy cocoon with only its inner envelope and its silk found in the intermediate space (attached to the inner envelope). (B) Baggy cocoons have no difference in infrared (IR; wavelengths > 700 nm) heating with or without the outer envelope. (C) The enhanced IR heating effect of baggy cocoons requires the presence of silk in the intermediate space. For both (B) and (C), intermediate space is designated by IS, and inner envelope is denoted by IE. (D) Heating curves of a baggy cocoon demonstrating the role of the silk in the intermediate space for IR heating (blue: whole cocoon; red: silk in the intermediate space and inner envelope only; green: inner envelope only). (E) Mean irradiance curves (N = 10 for each type) measuring light transmittance through the different envelopes of baggy (outer envelope: blue; inner envelope: light blue) and compact (outer envelope: red; inner envelope: purple) cocoons. Error bars omitted for clarity. (F) Comparison of percent transmittance of IR light wavelengths through the different envelope types of baggy (outer envelope: BOE; inner envelope: BIE) and compact (outer envelope: COE; inner envelope: CIE) cocoons. (G) Comparison of transmittance of IR light into the interior of the cocoon between baggy and compact cocoons. (H) Transmittance of blue light wavelengths into the interior of the cocoon for both baggy and compact cocoons. Sample sizes for each group in (F)–(H) are N = 10. Error bars denote standard errors of the mean.
Fig 9.
Water absorptiveness of baggy and compact H. cecropia cocoons.
Whole baggy: WB, blue bar; Whole compact: WC, red bar; baggy with inner envelope only: IE B, light blue bar; compact with inner envelope only: IE C, pink bar; sponge (control): green bar. N = 6 for each group. Error bars denote standard errors of the mean.