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First published online September 19, 2006
Journal of Experimental Biology 209, 3913-3924 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02438
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Proprioceptive encoding of head position in the black soldier fly, Hermetia illucens (L.) (Stratiomyidae)

Angelique Paulk* and Cole Gilbert{dagger}

Department of Entomology, Cornell University, Ithaca, NY 14853, USA


Figure 1
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  		Fig. 1. Hermetia illucens, head angle directions, and the experimental setup. (A) Dorsal view of a standing fly. Scale bar, 1 cm and applies to all panels. (B) Lateral and (C) ventral views of a mounted fly with both flags fixed to the head. Air puffs to the two flags move the head around the pitch (black arrows to distal flag 2), yaw (hatched arrows to proximal flag 2), and roll (white arrows to flag 1) axes. White circles flanking the mouth in C indicate the digitized points.

 

Figure 2
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  		Fig. 2. Activity in the prosternal organ nerve (PN) during head movements. (A) Raw recording shows sustained PN excitation associated with sustained pitch down and resting yaw and roll head positions (lower three traces). (B) Sustained PN inhibition associated with pitch up and resting yaw and roll. (C) Integrated spiking activity levels for the raw traces in A (diamonds) and B (triangles). Scale bars apply to A and B.

 

Figure 3
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  		Fig. 3. The prosternal organ in Hermetia illucens. (A) Scanning electron micrograph of the ventral cervical region of an H. illucens female. The white box indicates the region that is magnified in B. Scale bar, 5 mm. (B) The cervical sclerites (CvS) are lateral to contact sclerites (CS) that are little more than folds of cervical membrane anterior to the prosternal organ (PO), which is an anterior extension of the presternum (Pr). Scale bar, 50 µm. (C) Higher magnification light micrograph reveals that the surface of the CS is covered with oriented microtrichia. Scale bar, 1 µm. (D) The PO is composed of two hair plates with differently oriented sockets separated by a strip of glabrous cuticle. Scale bar, 50 µm. (E,F) Scanning electron micrographs reveal variation in asymmetry of the socket orientation with region on the PO, as indicated by the square in the insets. Scale bars, 3 µm.

 

Figure 4
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  		Fig. 4. Relationships of prosternal organ nerve (PN) activity with pure pitch, roll and yaw head movements. (A,C,E) Data from all eight individual flies identified by different symbols (inset in A) and regression lines determined by ANCOVA. (B,D,F) Pooled data for each axis of rotation and grand regressions. Note different axis scales.

 

Figure 5
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  		Fig. 5. Relationship of prosternal organ nerve (PN) activity with roll head position divided into positive angles (roll down, filled symbols; broken regression line) and negative angles (roll up, open symbols, dotted regression line). The solid line indicates the regression line for the whole data set.

 

Figure 6
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  		Fig. 6. Effect of different values of head pitch on the encoding of roll. (A-C) Plots of prosternal organ nerve (PN) activity versus roll with different constant pitch increments in each panel. The average pitch values within ±2.5° for each plot are as follows: (A) 0.99°, (B) 18.2° (rest) and (C) 23.2°. (D) The slopes of the linear regressions (solid lines) from A-C, plus others (data not shown), are plotted against their associated constant pitch angle. The fitted line is significantly different from zero, indicating that varying the pitch posture of the head affects the relationship of PN activity versus roll.

 

Figure 7
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  		Fig. 7. Four-dimensional plots of prosternal organ nerve (PN) activity versus head angle. (A) Complete raw data set (B) angular data binned into 5° cubes for clarity. In both panels the level of PN activity is expressed by the false color scale.

 

Figure 8
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  		Fig. 8. Prosternal organ nerve (PN) activity is tonic while the head is held at arbitrary constant positions around all three axes. (A) A constant head position, or plateau, signified by the filled (open) circle at the beginning (end), is illustrated. The slope of each angular plateau is between ±0.1° frame-1. (B) PN activity regressed on time during the plateau. The slope of this line is not significantly different from zero indicating that the PN afferents responded tonically during this period.

 




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