Scaling and functional morphology of wings in thrips

Thrips are the only insect order in which every winged representative has bristled wings. Their size range is greater than in any other group of bristle-winged insects, and they include the largest representatives of bristle-winged insects. Available publications lack comparative morphological data on the scaling of wings in thrips, hindering the study of their flight mechanics. We analyze here the functional wing morphology of thrips across different taxonomic and size groups. Using light microscopy and scanning electron microscopy, we describe the wing morphology of several species. A second row of setae on the trailing edge of the forewing is found only in Thysanoptera. It appears as a short additional row in Tubulifera, where it reduces wing permeability, and as a long row in Terebrantia, where it presumably increases the rigidity and stability of the spread fringe of bristles in combination with the wavy shape of the bristles, found in Thripinae. The microsculpture of the bristles consists of reinforcing ridges in the suborder Terebrantia and small secondary outgrowths in the suborder Tubulifera, possibly increasing the surface area of the bristles. Scaling analysis was performed separately for representatives of each of the two suborders and the results were compared with the available data on other insects with bristled wings. Phlaeothripidae (Tubulifera) demonstrate trends similar to those of feather-wing beetles (Ptiliidae): as body size decreases, the number and diameter of wing setae, relative length and area of the wing blade decrease, whereas the gap between setae increases. The scaling of wing parameters in Thripidae (Terebrantia) is ambiguous for most characteristics. High-speed video recording of flight was conducted and basic kinematic characteristics were obtained. Mechanical analysis based on morphological and kinematic data confirmed that the wings of thrips have minimal inertia while maintaining aerodynamic functionality. The data provided here can be used to construct accurate scaling and numerical models of thrips wings and open the way for studying the aerodynamics of flight in both the smallest thrips and the largest thrips.