Spiracular Structure Differs Among Adult and Larval Phlaeothripids (Thysanoptera: Phlaeothripidae) Recorded in California Deserts

Abstract

Spiracles on Thysanoptera have a diverse and complex structure suggesting they function as plastrons and enable respiration during submergence from rainfall or flooding. I examined the mesothoracic, metathoracic, and first-abdominal spiracles on adult males and females of 4 species of Phlaeothripidae that inhabit the Mojave and Sonoran Deserts. Spiracles contained open pores surrounded by a network of cuticle. I observed 2 classes of spiracle structure, termed compound and simple. Most pores on compound spiracles contained a central spot of cuticle. Most pores on simple spiracles lacked a cuticular spot. Compound spiracles were observed on Leptothrips larreae Hood. Simple spiracles were observed on Liothrips xanthocerus Hood, Leptothrips fasciculatus (Crawford), and the wing-dimorphic Bagnalliella mojave Hood. First- and second-instar larvae of L. larreae and L. fasciculatus supported the same class of spiracles as adults. Metathoracic spiracles on macropterous B. mojave females were slightly larger than those on brachypterous females. A live L. larreae adult submerged in water, and illuminated obliquely from above, reflected light from its pterothoracic spiracles, indicating that they trap air and likely function as plastrons. Pterothoracic spiracles were also examined on museum slides of adult females of 8 additional, phlaeothripid species recorded in California at desert localities or on desert plants. Four species have compound spiracles, and 4 species have simple spiracles. These 2 classes of spiracles were independent of body size. Spiracle class was weakly, and non-significantly, dependent on brachyptery in either sex. All 4 species with brachypterous males or females produce adult females with simple spiracles. Of the 8 species with only macropters, 5 species support compound spiracles, and 3 species support simple spiracles. Simple spiracles may be more common on desert Phlaeothripidae that produce brachypters and live in enclosed microhabitats, providing more protection from submergence in rainfall.