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ARS Home » Plains Area » Lincoln, Nebraska » Agroecosystem Management Research » Research » Publications at this Location » Publication #305721
Title: External morphology of stable fly (Diptera: Muscidae) larvae

Author
item Friesen, Kristina
item CHEN, HAN - University Of Nebraska
item Zhu, Junwei - Jerry
item Taylor, David

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2015
Publication Date: 7/1/2015
Citation: Friesen, K.M., Chen, H., Zhu, J.J., Taylor, D.B. 2015. External morphology of stable fly (Diptera: Muscidae) larvae. Journal of Medical Entomology. 52(4):626-637. DOI: 10.1093/JME/TJV052.

Interpretive Summary: High powered microscopes were used to describe the shapes of sensory structures and other features associated with the skin of stable fly larvae. Stable fly development involves a number of stages including: egg, larva, pupa, and adult. The larva, or maggot, undergoes three sequential moltings called instars, and it was of interest to determine if sensory structures changed between instars. Structures of importance in the head region that did not change among instars included the antennae (used for smelling), labial lobes (used for tasting), and the maxillary palpi (used for tasting and detecting horizontal and vertical pressure). The ventral organ (used to smell and taste) and facial mask (function unknown but may sieve particles from liquid to be ingested) were structures in the head region that were not well developed in first-instars, but became progressively so in subsequent instars. The rest of the larval body was equipped with numerous sensory and regulatory features including the fan-like anterior spiracles (used for breathing and observed only in second and third instars), Keilin’s organs (hair-like sensilla used to determine humidity), pore canals (small pits used to a secrete waxy substance onto the surface of the skin), anal organ (osmoregulatory in function), and posterior spiracular discs (used for breathing). The shape of the posterior spiracular discs changed among instars.

Technical Abstract: Scanning electron microscopy was used to examine the external morphology of first-, second-, and third-instar stable flies (Stomoxys calcitrans (L.)). In the cephalic region, the antennae, labial lobe, and maxillary palpi are morphologically similar among instars. Antennae comprise a prominent anterior dome that is the primary site of olfaction, while the maxillary palpi are innervated with mechano- and chemosensilla and scolopodia. The ventral organ and facial mask, also located in the pseudocephalon, are not well-developed in first instars, but become progressively more so in subsequent instars. When the pseudocephalon is partially retracted, anterior spines cusp around the oral ridges of the facial mask. This indicates the anterior spinose band may be used in conjunction with the facial mask in predigestion. Functional anterior spiracules are absent on first instars, but become evident as a pair of palmate spiracular processes with five to seven lobes in second and third instars. A pair of Keilin's organs, functioning as hygroreceptors, is located on each thoracic segment. Abdominal segments are marked with ventral creeping welts, the anal pad, anus, papillae, and posterior spiracles. Ventral creeping welts are thought to aid in locomotion, while the anal pad acts as an osmoregulatory structure. Posterior spiracles are modified from round spiracular discs with two straight slits in the first instar to triangular discs with two and three sinuous slits in the second and third instars, respectively.