Silba adipata McAlpine

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Author : François DROUET.
Photographs : François DROUET.
(unless indicated).
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Mating

 

 

 

Being able to observe Silba adipata McAlpine mating is incredibly rare. During my many years of observing and studying black fig flies, I never saw a mating. But I was able (once only) to observe two mated black fig flies (June 30, 2016, around noon, as I was walking around an old tuft of the 'Dauphine' variety with ripe breba figs).

 

TWO MATED BLACK FIG FLIES OBSERVATION

 

I could observe the mated black fig flies flies for about a minute on a leaf upper side. To my relative surprise, while being mated they were feeding on a puddle of ripe fig juice that had fallen from a fig above.

The coupling position was of the end-to-end type. The two flies were placed at the same level in opposite directions and were joined by the end of their abdomen. One of the two having the wings open and raised, the other the wings closed. I determined in the photographs that the male was the individual with raised wings, and I confirmed that the other was the female.

Below, a photograh and its enlargement showing the two mated black fig flies.
 

Two mated black fig flies feeding on a fig tree leaf.

Two mated black fig flies feeding on a fig tree leaf.
 

In the photograph enlargement, we can identity the male (open raised wings) by its narrow interocular space, and the identification of the female is confirmed by its tightly segmented abdomen end.
 

Two mated black fig flies feeding on a fig tree leaf.

Two mated black fig flies feeding on a fig tree leaf.
 

The two flies did not move on the puddle of sweet juice at the usual speed of a single fly, but performed slow circular movements almost in place while keeping the wings in the same position.

The two bodies joined by the abdomen were most often found in the continuation of one another (photograph below).
 

Bodies position 1 of two mated black fig flies feeding on a fig tree leaf.

Bodies position 1 of two mated black fig flies feeding on a fig tree leaf.
 

But, sometimes, the movement made them shifted relative to each other, with an angle of an amplitude never larger than 45 ° (photograph below). 
 

Bodies position 2 of two mated black fig flies feeding on a fig tree leaf.

Bodies position 2 of two mated black fig flies feeding on a fig tree leaf.
 

After about a minute, the male fly turned around and went up the leaf, towards the edge of it, seeming to drag the female who kept the wings closed and who was still in the extension of the male abdomen. I could not determine if the female was really being dragged or if it was walking backwards.
 

Two black fig flies in copula going up a fig tree leaf.

Two black fig flies in copula going up a fig tree leaf.
 

Arrived at the edge of the leaf a few centimeters higher than the initial location, the male fly placed its wings flat and in a cross, the female keeping the wings folded.
 

Two black fig flies in copula on the edge of a fig tree leaf.

Two black fig flies in copula on the edge of a fig tree leaf.
 

Then the male took off, the female still attached to it. I am sure the couple did not split up when they took off. And it seemed to me that only the male was flying and that the female had remained with its wings closed, the body in the extension of that of the male. I had the impression that a rigid bar was flying away.

I was not able to observe the black fig flies couple beyond the takeoff, due to the still very fast flight of the male, and despite half an hour of meticulous scrutiny of the fig tree tuft, I could not find the mated flies on the tree or observe them in flight.

Below, two photographs showing the male and female positions on the edge of the fig tree leaf, just before the male took off with the female still attached to it. We note the well developed last abdominal segment of the male, appearing under the closed wings of the female.
 

Two black fig flies in copula on the edge of a fig tree leaf, just before taking off.

Two black fig flies in copula on the edge of a fig tree leaf, just before taking off.

 

Two black fig flies in copula on the edge of a fig tree leaf, just before taking off.

Two black fig flies in copula on the edge of a fig tree leaf, just before taking off.

 

WHERE DOES SILBA ADIPATA McALPINE MATING TAKE PLACE ?

 

In my many years of intensive observations on various fig trees, at all periods of the season and at any times of the day, I was able once only to see two mated black fig flies. I am therefore convinced that Silba adipata McAlpine mating does not occur on fig trees, and that mated flies of this species only very rarely land on these.

I have not found in the specialized literature any information on the mating place of the Black Fig Fly.

For instance, B. I. KATSOYANNOS studied in 1981 and 1982 large populations of black fig flies in the island of Chios (Greece), and he explicitly specifies that he did not observe mating in fields. Reference: KATSOYANNOS B. I., 1983, Field observations on the biology and behavior of the black fig fly Silba adipata McAlpine (Diptera, Lonchaeidae), and trapping experiments, Z. ang. Entomol. 95, pp. 471-476.

A plausible hypothesis is that Silba adipata McAlpine mating could occur in the air, while the flies are flying.

Aerial swarming in insects is generally a mating activity, characterized by pair formation in flight. Numerous references, among which I cite: SULLIVAN Robert T., 1981, Insect Swarming and Mating, The Florida Entomologist, vol. 64 (1), pp. 44–65.

J. F. McALPINE and D. D. MUNROE have described the swarming behavior for 16 species (which do not include Siba adipata McAlpine) of the Lonchaeidae family. Reference: McALPINE J. F., MUNROE D. D., 1968, Swarming on Lonchaeid flies and others insects, with description of four new species of Lonchaeidae (Diptera), The CanadianEntomologist, vol.100, pp. 1154-1178.

With respect to the Lonchaeidae family, the authors believe that, in general, swarming probably facilitates the discovery of mate. But they state that they have little or no evidence to support this belief, and that the possibility that the Lonchaeidae mates meet at places other than the swarm must certainly be considered. And they specify that female lonchaeids occur very rarely if ever in the swarm, and that no matings were ever observed in any lonchaeid swarms.

I only know one reported swarm observation for Silba adipata McAlpine. It was made on August 20, 1982 by B. I. KATSOYANNOS, while he was studying Lamprolonchaea smaragdi Walker swarming in the Chios Island (Greece). Reference: KATSOYANNOS B. I., 1983, Swarming of Lamprolonchaea smaragdi Walker (Diptera, Lonchaeidae) and a few other Diptera observed in Chios, Greece, Bulletin de la Société Entomologique Suisse, vol. 56, pp. 183 -185.

And I have no personal observation of Silba adipata McAlpine swarms. Nevertheless, I regularly observe black fig flies groups flying between two trees in a similar way than that of the swarm described by B. I. KATSOYANNOS. I do not qualify them as aerial swarms because these groups only involve two to three specimens.

The group performs repetitive flights, more or less on the horizontal plane and limited to an elliptic space, with an amplitude of about 2 m, at a height of about 1.5 m. The aerial group is rather stationary, but Inside the group the flies permanently keep their very fast zigzaging characteristic flight pattern.

I can observe this phenomenon for long whiles, sometimes more than one hour, in the late afternoon, at dusk. Over the season, I regularly perform this type of observations at two places: between my ‘Bellone’ variety fig tree and an oriental persimmon (in June), and betweem an olive tree and a silky oak, near a hedge, at 30 m from my fig trees (during certain periods of summer).

I think that these black fig flies grouped in the air are males waiting for females, or males and females just before mating (or mating).

 

 

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