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Insects show diverse flight kinematics and morphologies reflecting their evolutionary histories and ecological adaptations. Many silk moths use low wingbeat frequencies and large wings to fly and display body oscillations. Their bodies pitch and bob periodically, synchronized with their wingbeat cycle. Similar oscillations in butterflies improve weight support and forward thrust while reducing flight power requirements. However, how instantaneous body and wing kinematics interact for these beneficial aerodynamic and power consequences is not well understood. We hypothesized that body oscillations affect aerodynamic power requirements by influencing wing rotation relative to the airflow. Using three-dimensional forward flight video recordings of four silk moth species and a quasi-steady blade-element aerodynamic model, we analysed the aerodynamic effects of body and wing kinematics. We find that the body pitch and wing sweep angles maintain a narrow range of phase differences, which enhances the angle of attack variation between each half-stroke due to increased wing rotation relative to the airflow. This redirects the aerodynamic force to increase the upward and forward components during the downstroke and upstroke, respectively, thus lowering overall drag without compromising weight support and forward thrust. Reducing energy expenditure is beneficial because many adult silk moths do not feed and rely on limited energy budgets.
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Interspecific variation in bristle number on forewings of tiny insects does not influence clap-and-fling aerodynamics
ABSTRACT Miniature insects must overcome significant viscous resistance in order to fly. They typically possess wings with long bristles on the fringes and use a clap-and-fling mechanism to augment lift. These unique solutions to the extreme conditions of flight at tiny sizes (<2 mm body length) suggest that natural selection has optimized wing design for better aerodynamic performance. However, species vary in wingspan, number of bristles (n) and bristle gap (G) to diameter (D) ratio (G/D). How this variation relates to body length (BL) and its effects on aerodynamics remain unknown. We measured forewing images of 38 species of thrips and 21 species of fairyflies. Our phylogenetic comparative analyses showed that n and wingspan scaled positively and similarly with BL across both groups, whereas G/D decreased with BL, with a sharper decline in thrips. We next measured aerodynamic forces and visualized flow on physical models of bristled wings performing clap-and-fling kinematics at a chord-based Reynolds number of 10 using a dynamically scaled robotic platform. We examined the effects of dimensional (G, D, wingspan) and non-dimensional (n, G/D) geometric variables on dimensionless lift and drag. We found that: (1) increasing G reduced drag more than decreasing D; (2) changing n had minimal impact on lift generation; and (3) varying G/D minimally affected aerodynamic forces. These aerodynamic results suggest little pressure to functionally optimize n and G/D. Combined with the scaling relationships between wing variables and BL, much wing variation in tiny flying insects might be best explained by underlying shared growth factors.
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- PAR ID:
- 10295721
- Date Published:
- Journal Name:
- Journal of Experimental Biology
- Volume:
- 224
- Issue:
- 18
- ISSN:
- 0022-0949
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1242/jeb.239798
