Metamorphosis of the pretarsus in Frankliniella fusca (Hinds) (Thripidae) and Haplothrips verbasci (Osborn) (Phlaeothripidae) (Thysanoptera)

Abstract

During the propupal and pupal stages of Frankliniella fusca and Haplothrips verbasci, each leg consists of coxa, femur, and tibiotarsus.The adult pretarsus, tarsomeres, and tibial gland of F. fusca arise during the pupal stage through morphogenesis of the distal tibiotarsal epidermis. These structures become functional at the time of adult emergence on the completion of cuticle deposition. Most leg epidermal cells degenerate soon thereafter.The imaginal tarsal depressor muscle develops during the pupal and pharate adult stages through fusion and differentiation of myoblasts originating elsewhere in the body. Myofibrils of the larval pretarsal depressor muscle disappear during the propupal stage but reappear during the pupal and pharate adult stages with a different, adult configuration.At the larval–propupal apolysis, the larval restraining tendons detach at both ends from the larval cuticle, contract, and, throughout metamorphosis, nestle between the epidermis of unguitractor apodeme and tibiotarsus. During the pupal stage the tendons rotate transversely 90° and grow laterally through addition of new material to their sides.In H. verbasci, completion of these events requires an additional pupal stage.Leg metamorphosis in thrips is compared with that occurring in other insects and additional remarks are made on the origin of holometabolism in Thysanoptera.Chez la pronymphe et la nymphe de Frankliniella fusca et d'Haplothrips verbasci, chaque patte est constituée d'une coxa, d'un fémur et d'un tibio-tarse.