Ecomorphology of Cyclorrhaphan Larvae (Diptera) by Graham E. Rotheray

Author:Graham E. Rotheray
Language: eng
Format: epub, pdf
ISBN: 9783319925462
Publisher: Springer International Publishing

6.3 Accessing Decay

If decay is exposed, such as frequently the case with dung, leaf litter, wrack beds, etc., female saprophagous flies are able to oviposit directly on or into it with the result that larvae are close to food which minimises access problems. Sometimes, however, even if decay is exposed females are more selective. For instance, female dung flies of the Sepsidae and Scathophagidae oviposit in crevices at the dung surface (Parker 1972; Blanckenhorn et al. 2010), but the common European dung fly, Rhingia campestris (Syrphidae ), oviposits on overhanging vegetation and emerging larvae drop on to the dung (Coe 1938). The difference could be due to a number of factors. For instance, sepsid and scathophagid eggs may possess mechanisms to prevent drowning that are absent in the syrphid. Surrounding vegetation may provide environmental conditions better suited to R. campestris eggs and avoids interference from other dung inhabitants. It may also be a mechanism to evade natural enemies who are more active on the dung than the surrounding vegetation.

Aquatic eristalines (Syrphidae) are similar to R. campestris in ovipositing on emergent or marginal vegetation and larvae move out of the water to pupate on these plants (Hartley 1963) (Fig. 6.1). This not only avoids drowning but prevents eggs and puparia floating or washing away. Avoiding being washed away is also a factor at sap runs. As the name suggests exuding sap flows or ‘runs’ down the plant and tends to dry with distance from the source. Female sap-run flies, such as those within the Aulacigastridae , Drosophilidae and Syrphidae, usually oviposit adjacent to the flowing sap or on pieces of bark above it and usually close to the source (unpublished observations). The development site of the extraordinary petroleum fly, Halaeomyia petrolei (Ephydridae ), is probably an example of a medium used by larvae that is almost certainly toxic to eggs. Eggs have not been found in the tar pools inhabited by larvae and the oviposition site is unknown, but marginal vegetation is likely (Thorpe 1930). Larvae develop on dead and dying insects caught in the tar and also, remarkably, imbibe the tar itself (Thorpe 1930; Kadavy et al. 1999).

Fig. 6.1 Helophilus pendulus (Syrphidae ), adult, oviposition of an egg batch on vegetation above an artificial oviposition bait, a tray of decaying vegetation, image from Ellen Rotheray

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