Description of the Immature Stages of Paracantha gentilis (Diptera: Tephritidae)

Abstract

Descriptions are provided of the egg, larvae, and puparium of Paracantha gentilis Hering, a native, stenophagous tephritid which infests the capitula of thistles. Detailed examination of larvae led to the discovery of a median oral lobe between the mouth hooks. This is the first structure of this kind described for Tephritidae. Two sensory structures on the anterior lobes of P. gentilis also were discovered, the lateral sensory organ and the pit sensory organ. In comparing the anterior sensory apparatus of P. gentilis larvae with those in Anthomyiidae, Calliphoridae, Drosophilidae, Muscidae, and Syrphidae, striking similarities were apparent. Photographs that illustrate the development of the spiracular system of the puparial stage are the first offered for a nonfrugivorous tephritid.KEY WORDS Insecta, mouth hooks, sensory organs, Cirsium THIS STUDY is an outgrowth of faunistic surveys (Goeden & Ricker 1986) of the thistles Cirsium californicum Gray and C. proteanum J. T. Howell. In this report, we describe the morphology of the heretofore undescribed immature stages of Paracantha gentilis Hering; subsequent papers will treat its biology and ecology. Materials and MethodsAll immature stages were dissected from capitula of C. californicum collected at Mill Creek, San Bernardino National Forest, San Bernardino Co., Calif, from 25 April to 5 June 1987, and C. proteanum capitula collected from Sawmill Mt, Angeles National Forest, Los Angeles Co., Calif., on 29 July 1987. Eggs used to study eclosion were placed on filter paper soaked with Ringer's solution in covered glass Petri dishes and held in darkened growth chambers at 27°C. Other eggs and larvae were preserved in 70% EtOH for later examination. Puparia were dissected from heads, air-dried, then stored in capped, 6-ml glass shell vials.In preparation for scanning electron microscopy, all soft-bodied specimens were sonicated 20 min. Eggs were dehydrated to 95% EtOH overnight, placed in 100% EtOH for 5 min, and fixed in hexamethyldisilizane (Nation 1983). Larvae were placed in 2.5% glycerol and serially saturated to 100% glycerol (Sher & Bell 1975) or rehydrated through graded alcohols to distilled water, and fixed in osmium tetroxide for 24 h (Sabatini et al. 1963). All specimens were mounted on stubs and coated with a gold-platinum alloy. The scanning electron microscope used was a JEOL-JSM-35C3 in the Department of Nematology, University of California, Riverside. Specimens were examined and micrographs were prepared at 15 kV accelerating voltage, except for specimens in glycerol which were studied at 10 kV. Micrographs were prepared with Polaroid 55 P/N film.Third instars were dissected in 70% EtOH with 0.1% acid fuchsin for viewing the median oral lobe.Voucher specimens of P. gentilis are stored in the tephritid collection of the second author. This collection will eventually be offered for incorporation into the insect collection of the Department of Entomology, University of California, Riverside. ResultsEgg. The body of the newly laid egg is smoot...

The Biology of Nonfrugivorous Tephritid Fruit Flies

“…The median oral lobe was first described for Paracantha gentilis (74) and has subsequently been found in every nonfrugivorous species examined by Headrick, Goeden, and coworkers (33-41, 55-60, 74, 77, 78, 80-82, 88, 89) and others (4,5) to date. The median oral lobe is an independently movable, uniquely musculated and innervated structure consisting of a dorsal sclerite and a ventral lobe (cf 78 for detailed anatomical drawings).…”

“…The arrangement of the micropyle and aeropyles is similar among the nonfrugivorous species studied. The pedicel may be only a slight projection (13,88), but it may also occur as an elongated stalk nearly as long (55-57) or longer than the body of the egg (74). The end opposite the pedicel is typically smooth and bluntly rounded without any external openings or structures (see 119 for an exception).…”

“…These include the median oral lobe (74), the presence of functional lateral spiracles accompanied by a variable number of sensilla (77), and several sensilla associated with the sensory organs of the gnathocephalon (60, 74,77,88).…”

“…However, Snodgrass (109) was unable to locate the outer spiracular openings with conventional microscopy, and thus he assumed they were present but did not describe them. With the aid of scanning electron microscopy, the lateral spiracles have been located on the meso-and metathoracic segments and the abdominal segments, excluding the caudal segment, which bears the posterior spiracles (74). The lateral spiracles are always located along the lateral midline near the anterior portion of a segment, and they have a variable number of associated campaniform sensilla posteriorad of the spiracle.…”

“…The pupa forms within the puparium after the prepupal molt. The pupa develops independently of the puparium and has bilobed thoracic spiracles for respiration (74). Headrick & Goeden (74) and Goeden & Headrick (36) showed that the larval tracheae adjacent to the anterior and posterior spiracular openings remain open, thus allowing for gas exchange for the developing pupa within the puparium.…”