+ Introduction
+ History
+ Morphology
+ Terminology
+ Phylogeny
+ Distribution
+ Ecology
+ Biology
     + Immatures
     + Foraging
     + Prey
     + Courtship
     + Oviposition
     + Mimicry
+ Collecting
+ Determination
+ Photography
+ References

Information on Robber Flies

LONDT (1994): "Once these categories had been established, it became apparent that apart from feeding, oviposition was also well-supported by this classification. Although oviposition has not been observed in the vast majority of genera, ovipostion strategies can be confidently inferred from oviposition morphology as suggested by Melin (1923) in his pioneering work on Swedish asilids. A generic survey of ovipositor structure suggests that there are three main oviposition strategies within the family: i. Random egg-dropping; ii. Oviposition in sand or soil; iii. Oviposition on or in vegetation. Brief elaboration will provide the morphological criteria upon which these oviposition strategies are based.

Random egg-dropping: The female abdomen is circular in cross-section and the genital structures show no special adaptations for oviposition. The abdomen is usually rounded posteriorly, the terminal segments are not usually elongate, the cerci and subgenital plate are simple, and the setae exhibit no unusual adaptions.

Oviposition in sand or soil: The female abdomen is circular in cross-section or dorsoventrally compresed (only occasionally somewhat laterally compressed). The postabdomen is adapted, in one or more ways, for depositing eggs into soil or under loose sand. These adaptations may take the form of elongated terminal segments, pointed and/or upturned cerci and/or subgenital plate, and/or the presence of stout spines or setae.

Dasypogon diadema, oviposition in sand. © Geller-Grimm

Oviposition on or in vegetation: The female abdomen is either circular in cross-section or distinctly laterally compressed (only occasionally somewhat dorsoventrally compressed). The postabdomen is adapted, in a variety of ways, for depositing eggs in crevices, grooves or holes in plant tissue. These adaptations may take the form of elongated terminal segments; when the cross-section is circular the diameter frequently diminishes progressively distally (the abdomen often being telescopic in structure). The cerci may take the form of an elongate extension of the postabdomen or be laterally compressed such that they form part of a knife-like ovipositor. When the ovipositor is not obviously elongate and/or laterally compressed the cerci may be elongate or equipped with long setae which serve to guide eggs into suitable situations.

Eggs of Leptarthrus brevirostris. © Geller-Grimm  Machimus rusticus, oviposition in vegetation. © Geller-Grimm  Choerades marginata, oviposition on vegetation. © Geller-Grimm 

An indication of the ovipostion strategies usually practised within each ecological category proposed has been given in Fig. 2 [see Ecological Classification]. Species which normally hunt from the ground surface always oviposit in sand or soil. Soecies inhabiting grass or bushes either drop their eggs at random to the ground, fly to the ground surface and deposit eggs there, or oviposit on the plants themselves. Tree frequenting species either drop their eggs to the ground or oviposit on or in the tree; as yet no examples of ground visiting species are known.
A further clue to oviposition behaviour may be provided by egg shape. Spherical eggs tyify random egg-droppers while elongate-ovoid eggs are characteristic of species ovipositing in vegetation. Eggs of species which oviposit in soil are intermediate between these two extremes."




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Compiled by: F. Geller-Grimm