Introduction Currently only 37 species of Cheilosia have information about the morphology of the third instar larva, and we have indications of the foodplant spectrum for only 44 species



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Stuke J-H & Carstensen LB (2000)

[ Biology and morphology of the third instar larva of Cheilosia lasiopa Kowarz, 1885 (Diptera, Syrphidae) ]


Volucella 5: 95-101
Introduction

Currently only 37 species of Cheilosia have information about the morphology of the third instar larva, and we have indications of the foodplant spectrum for only 44 species (Stuke, in press). The present work should supplement this state of knowledge; it describes the unknown third instar larva and the larval biology of Cheilosia lasiopa. In addition to these descriptions the phylogenetic placement of C.lasiopa in the genus Cheilosia is discussed.


Material

The basis for the portrayal of the biology are field observations by LBC on C.lasiopa in Bjerringbro (Jutland). The larvae of lasiopa can be collected from Plantago laceolata. The white eggs are placed at the base of the leaves, from which the larvae can be obtained. Rearing of the larvae is unproblematic: they require a rootstock of Plantago lanceolata. If the rootstock dries out, it is substituted with a new one, in which a small hole has been prepared in advance. For the morphological description, the following material was available: one L3 (viii.98), two exuviae and one puparium (ex larvae, collected 19.ix.98, pupated ix.98, emerged under lab conditions 10.iv.99). Diagnosis of the reared material was done using the key characters of Torp (1994). The morphological terms and techniques are given in Stuke (in press). The material is in the collection of the author.


Description of the L3 of lasiopa

Overview: integument dirty white, not transparent. Thorax: anterior-dorsal and ventral prothorax not obviously expanded; prothoracic plate present. A1-7: lateral sensilla L2 and L3 not separated by clear integumentary folds. L2 mostly above L3. Ventral sensilla V2 and V3 lie closer together than V1 and V2. Dorsal sensilla A7-D1 and A7-D2 not separated by an integumentary fold, A7-D1 not clearly behind A7-D2 and A7-D3. These sensilla (A7:D1-D3) about at the same height as the lateral sensilla A7-L1. Anal segment: posterior spiracles not retractable into the anal segment. Anal segment not elongated. Between A7-D1 and the spiracles there are three (obscure) crossfolds of the integument. Ventrally between A8-7/8 and the spiracles there is one crossfold. Dorsal and ventral parts of the anal segments are approximately of equal length. No anal segment ring created. Lappets level [flat, even], about the same height, rounded. No lappet with sensilla A8-8. Microtrichia on the integument: only one type of microtrichial shape, cone- or hair-like, straight, either rounded or pointed, scarecely broadened at the base. Microtrichia gradually change to being shorter on the thorax towards the anterior. Microtrichia missing on (a) the ventral prothorax; (b) almost completely on the anal segment; (c) partly on the dorsal part of A7. Anal segmental plate not present. Sensilla: antennae and maxillary sensilla not clearly separated. Antennal pegs broader than long. Sensilla on the integument with lower sensillar papillae. 2-4 hairlike sensillar hairs, straight to curved, pointed. Sensillar hairs clearly stand out over the surrounding microtrichia. Prothorax with 11 sensilla pairs, Mesothorax with 3, Metathorax with 9, A1-A7 each with 10, and the analsegment with 7. Anterior spiracles about as high as wide, 8-11 spiracular openings with regular trabeculae lying on a poorly differentiated plate. Posterior spiracles (Figs 1-2) length 0.7-0.8 mm, maximal width of the spiracular tube 0.5-0.7 mm, length of the peritrema 0.2-0.3 mm. Spiracular plate and edge of the peritrema more or less parallel. Spiracular tube clearly converging on the peritrema. Surface structure of the peritrema and tube sclerotized and obviously wrinkled. Spiracular plate turned down towards the tube, (but) approximately level. Half of the plate on a plane, separated by a continuous furrow. Four pairs of spiracular openings clearly separated from one another, elongated, straight to curved. Trabeculae regular. Spiracular scars clearly separate. Glandular hairs shorter than the plate and branched at the base.

Pseudocephalon: dorsal lip and a-m base without microtrichia. Ventral lip with cone- to hair-shaped, straight to curved, pointed to rounded microtrichia. No mandibular ridges on the mandibular lobes. Mouthhooks (Fig 3), with a dominant tooth at the tip ("albipila" type sensu Stuke, in press). Three lateral mandibular teeth, all about the same size, very much smaller than the dominant tooth. Two median mandibular teeth: (from anterior to posterior) (a) one very much smaller than the dominant, (b) one larger, but clearly smaller than the dominant tooth. 10-12 ridges on the [Kaufläche] filter. Each half of the mouthhooks do not separate posteriorly. Dorsal and ventral mandibular bridges present. Posterio-dorsal end of the mouthhooks blunt, not clearly defined. The tying of the mouthhooks is with the mandibular sclerite. The dental sclerite reaches to the ventral mandibular bridge as a more strongly sclerotized area on the mandibular lobe. The central mandibular apodeme drawn out into a point, and about as long as the mouthhooks as a whole. The protrusion at the insertion point of the hypopharyngeal sclerite scarcely broader than the end of the tentorial bars. Hypopharyngeal sclerite (Fig 3): tentorial bars joined posteriorly with the tentoropharyngeal sclerite, posteriorly not narrowed. Tentorial bars anteriorly broadened. Tentorial bridge with obvious rods, fused with the tentorial bars, and projecting forwards. Tentoropharyngeal sclerite (Fig 3): sclerotisation as in the tentorial bars. Posterior part of the tentorium between the dorsal and ventral tentorial arms not protruding. Area between the dorsal sclerite and the parastomal rods completely sclerotised. Dorsal tentorial arm long, longer than the ventral arm. The strongly sclerotised part of the dorsal tentorial arm is relatively short and pointed. Ventral tentorial arm ends in more or less equally long medial and lateral parts. Medial ventral tentorial arm pointed. Lateral ventral tentorial arm more weakly sclerotized, sharply delimited. Dorsal sclerite fused with the tentoropharygeal sclerite, easily recognisable from the partly stronger sclerotisation. Dorsal phragma longer than the pharyngeal filter, ventral phragma shorter. Ventral phragma protruding posteriorly. Dorsal and ventral phragmata clearly overlapping. Accessory sclerites: parastomal rods fused anteriorly with the epipharyngeal plate. Labial sclerite not visible in lateral view.

Alimentary canal and anal organ (Fig 3). Pharyngeal filter with 9 filter ridges. Filter filaments not demonstrable with the light microscope. Lateral pharyngeal wing reinforcement obvious. Pharyngeal filter dorsally without sclerotisation. No sclerotised plate at the exit of the pharynx. Anal opening elongated-oval. Anal organ could not be studied in the available material.


Diagnosis

The following combination of characters differentiates lasiopa from all other currently known syrphid larvae: 4 pairs of narrow, straight to curved spiracular slits; posterior spiracles without lappets [?]; dorsal lip without microtrichia; mandibular lobes without mandibular ridges; mouthhooks with ridges on the filter [Kaufläche]; dorsal and ventral bridges to the mouthhooks present; posterior part of the tentorium between dorsal and ventral tentorial arms not protruding; ventral and dorsal phragmata overlap.

With the key in Stuke (in press), the larva of lasiopa would be identified as a member of the subgenus Dasychilosia. The subsequent key to the larvae of Dasychilosia should be modified as follows:

[...]
Biology of lasiopa

Foodplants: Apart from the evidence here of Plantago lanceolata as a hostplant, Torp (1994) reported oviposition behaviour of a female on Plantago major.

Oviposition: The female approaches the plant slowly and lands on the upperside of a leaf. It runs down the leaf with ovipositor extended, and lays an egg on the inner side of the leaf, about 1 cm above the base of the leaf. Finally the female flies away or cleans itself with its legs. Eggs are laid mostly singly, but occasionally two larvae are found in the same plant. She uses Plantago plants that grow in very high thick grass or in more sparse vegetation. Oviposition was also seen immediately next to a pavement.

Use of the foodplant and feeding strategy: After eclosion the larva crawls right down the leaf to the base of the plant. There a cavity in the rootstock develops, which is filled up with the larva. The larva probably lives on the plant saps translocated for growth.

Diapause: The presence of a prothoracic plate is an indication of a prepupal stage. This remains in the rootstock of the hostplant.

Pupation: As far is known, pupation ensues in autumn after leaving the hostplant.

Overwintering: as a pupa

Phenology: From the flight period of the adults and observations of the development of the larvae, lasiopa has a univoltine lifecycle.

Associations: none established so far

Parasites: no evidence of any yet.
Remarks on the phylogenetic position of lasiopa

Lasiopa has all the characters that were interpreted as synapomorphies of the subgenus Dasychilosia by Stuke (in press). Within Dasychilosia, lasiopa and variabilis create a monophyletic clade, characterised by the following synapomorphies: (a) posterior part of the tentorium between dorsal and ventral tentorial arms not protruding; (b) strongly sclerotised part of the dorsal tentorial arm relatively short and pointed. In a parsimony analysis, membership of Dasychilosia and the monophyly of lasiopa and variabilis were established (methods and character matrix in Stuke, in press).

The oviposition behaviour of lasiopa corresponds to the observations of other authors on other Cheilosia species (Doczkal 1996, Hövemeyer 1995, Stuke 1996). In the genus Cheilosia it must be derived from a fixed pattern of oviposition behaviour. Variation (in this behaviour) that supplies phylogenetic evidence within Cheilosia has not yet been found. That the egg is stuck direct onto the plant corresponds to the behaviour of almost all members of Dasychilosia and other Cheilosia species. Unusual for species of Dasychilosia is that lack of feeding tunnels in the hostplant. It is true that within Dasychilosia, variabilis and canicularis have only very short feeding tunnels (Dusek 1962, Stuke & Claussen 2000, unpublished observations of the first author). The presence of a Cheilosia larva in Plantago species is surprising. Until now no Cheilosia larva is known from the Plantaginaceae. It is remarkable that of the known Cheilosia larvae, variabilis occurs in the most closely related plant family, the Scrophulariaceae. Lasiopa and variabilis are the only two Dasychilosia species that do not live in Asteraceae.



The phylogenetic position of lasiopa has not yet been discussed by other authors. On the basis of the morphological similarity between adults of variabilis and lasiopa, these two species have been placed together again and again in the typological suggestions for dividing up the genus Cheilosia of Loew (1857) (Becker 1894, Gaunitz 1960, Hellen 1912).
Translated by Francis Gilbert. 22.6.2001

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