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Author: François DROUET.
Photographs: François DROUET.
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Distinguishing the male and the female
Beyond the anatomical knowledge of the species, knowing how to recognize the male and the female presents many practical interests. This was useful for me when studying the size variability, and for observing the precocity of the male individuals for the emergence out of the pupae. This also made it possible to search for any specific attitudes depending on the sex when individuals of the species mutually push back, when one of them shows an aggressive behavior, or during mating. And this allowed me flies population observations: male / female ratio for individuals concomitantly frequenting a fig tree; countof feeding females on the fig tree during the intense egg-laying period in the season, to compare their number with that of egg-laying ones.
The size is not a sex distinguishing criterion for Silba adipataMcAlpine, due to the sizes overlap between males and females. According to my measurements, the male has a size of 3.5 to 4 mm (or a little more, exceptionally 5 mm), while the common size of the female is 4 mm, with, quite often, a maximum size of 5 mm and a minimum size of 3.5 mm. Two anatomical characteristics allow to recognize male and female for Silba adipata McAlpine: the abdomen end and the interocular space.
ABDOMEN END
For the female: narrow segmentation; wide orifice with the ovipositor tip slightly protuding. For the male: last visible segment very developped; below it, presence of the terminalia, which is a rather complex structure containing the copulatory organ. Determination of males and females by the abdomen end is impossible to achieve with the naked eye, or even with an ordinary magnifier, due to the tiny size of Silba adipata McAlpine. But this is possible for me with the highly magnifying part of my manual bifocal magnifier, and this is easy with photographic and video enlargements or close-ups. And, of course, when using a stereomicroscope. Below, four photographs illustrating the abdomen end difference between a female and a male
Silba adipata McAlpine: abdomen end of a female.
Silba adipata McAlpine: abdomen end of a male.
And two other photographs (ventral views) illustrating the difference between a female and a male).
Silba adipata McAlpine: abdomen end of a female.
Silba adipata McAlpine: abdomen end of a male.
INTEROCULAR SPACE
I observed that the interocular space of the male is significantly narrower than that of the female. In this, I confirm the observations which have been published in 1934 by Eugène SÉGUY. Reference: SÉGUY E. - Diptères (Brachycères), Faune de France, vol. 28,
page 176, Paul LECHEVALIER et fils, Paris, 1934. Determination of males and females by the interocular space width is impossible to achieve with the naked eye, or even with an ordinary magnifier, due to the tiny size of Silba adipata McAlpine. But this is possible for me with the highly magnifying part of my manual bifocal magnifier, and this is easy with photographic and video enlargements or close-ups. And, of course, when using a stereomicroscope. Below, two photographs illustrating the interocular space difference between a female and a male
Silba adipata McAlpine: interocular space of a female.
Silba adipata McAlpine: interocular space of a male.
EXAMPLES OF MALES AND FEMALES DETERMINATION
Below, four examples of the use of both sex determination criteria for simultaneously identified black fig flies.
Two Black Fig Fly males, recognizable one by its interocular space and the other by its abdomen end.
Two Black Fig Fly females, recognizable one by its interocular space and the other by its abdomen end.
Two black fig flies, a male (recognizable by its interocular space) and a female (recognizable by its abdomen end).
Three black fig flies, a male (recognizable by its abdomen end) and two females (recognizable by their interocular space).
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