Silba adipata McAlpine

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Author : François DROUET.
Photographs / videos : F. DROUET.
(unless indicated).
All rights reserved.

 

 

Black Fig Fly flight

 

 

 

I present below my observations relating to the Silba adipata McAlpine flight, according to the following plan: flight pattern, group flight, aerial swarms.

 

FLIGHT PATTERN

 

The Black Fig Fly walks slowly, but its flight is very fast. And it has a characteristic which enables to easily identify the species (with some practice…) : it is a sharp zigzag flight, composed of permanent back and forth 30-50 cm in length, in all directions.

Inside the fig tree, the Black Fig Fly moves from one place to another by shorts direct flights, but keeping its specific lively zigzag flight pattern, even for a very small distance.

This flight pattern is a major detection mean, because (especially if several flies are involved) it induces a lot of movements at the fig tree periphery that we cannot miss.

 

Silba adipata McAlpine : flight at the periphery of a fig tree.

 

When very close to the targeted leaf, twig, or ripe fig, the Black Fig Fly moves back and forth much shorter (about 5 cm ), and progressively slower, before ending up landing. See example below.

 

Silba adipata McAlpine : approach flight before landing on the underside of a fig tree leaf.

 

Below, another flight example  : a black fig fly flies very briskly around a broken branch before slowing down to land but, probably startled, it very quickly flees far to the right.

 

Silba adipata McAlpine : flight close to a broken fig tree branch, before fleeing away.

 

Note : I would point out that we do not hear the Black Fig Fly when it flies (this is a question frequently asked by those who do not know it).

 

GROUP FLIGHT

 

I have never observed more than three Black Fig Fly adults flying together. Flight in threes is rare, flight in twos is less so, and flying alone is the most common. Group flight is a confused mix of the back and forth vortices of each of the individuals, which densifies the movements zone through which black fig flies are spotted.

I can report two observations about the Silba adipata McAlpine aerial groups, limited to 2 to 3 specimens.

The first is the common feeding activity at the periphery of the fig tree. Black fig flies have a gregarious behavior. So, when a flying individual brushes against another which is on a twig or on a leaf underside, most often the latter joins it in a swirling flying duo (this can be observed on the first video above).

The second is a one-off observation. In June 2019, I was on my observation post near my ‘Bellone’ fig tree, to check the effectiveness of glue micro-traps baited with fresh latex, and I was surprised by the arrival of a pair of black fig flies that I distinctly saw coming from the outside of the fig tree. With their characteristic flight pattern, they dived at highspeed towards a glue micro-trap. They seemed to touch the trap, but they sharply moved away at the last moment, without landing on it. Then, starting from a distance of about 1 m, they strictly repeated the same operation, and left the fig tree without separating. I deduced that the glue was repellent for them, and I was impressed by the perfect flights synchronisation of these two black fig flies.
 

Black Fig Fly (Silba adipata McAlpine) flight during feeding activity.

Black Fig Fly flight during feeding activity.

 

Black Fig Fly (Silba adipata McAlpine) flight during feeding activity.

Black Fig Fly flight during feeding activity.

 

AERIAL SWARMS

 

Formation of aerial swarms is a rather common phenomenon among the Lonchaeidae family, to which Silba adipata McAlpine belongs. Reference : McAlpine, J. F. & Munroe, D.D. 1968. Swarming of lonchaeid flies and other insects, with descriptions of four new species of Lonchaeidae (Diptera). Can. Entomol. 700: 1154-1178.

 

B. I. KATSOYANNOS OBSERVATIONS

B. I. KATSOYANNOS, while studying Lamprolonchaea smaragdi Walker swarming in the Chios Island (Greece), in 1982, had the opportunity to observe a Silba adipata McAlpine swarm, but only once (on August 20, 1982). 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.

The author describes this aerial swarm as follows : " The swarm occurred in a free space of 2 m between two large branches of a fig tree and consisted of ca. 20 individuals flying very rapidly in a pattern similar to that observed for Lamprolonchea smaragdi. The swarm danced mostly in the shade and was difficult to notice, because of the very rapid flight pattern. Of 8 specimens netted, only one was a female " .

And he gives some information about Lamprolonchea smaragdi Walker swarms pattern : "The flies in the swarm moved extremely rapidly in a whirling pattern. The axis of the movement approximated the horizontal plane. The overall shape of the swarms was rather elliptic, occupying a space of 1-2 m in diameter. Usually the swarms were more or less stationary. However, from time to time, they changed their location slightly, moving horizontally or vertically.".

B. I. KATSOYANNOS does not provide an explanation for the formation of swarms, simply evoking male behavior in relation to mating.

Some additional information on the Lamprolonchaea smaragdi Walker swarms observed by B. I. KATSOYANNO : they were between 1 and 3 m from the ground, almost always in full sun. Most of them were observed in calm weather, with temperatures of 22 to 28°C. But the swarms were also visible on days with light to moderate winds. They did not appear on a day of strong wind and on two days of cloudy weather. The individuals captured by nets in the swarms during two years of observation were males, with the exception of a single female.

It seems to me interesting to point out that the author observed the Lamprolonchaea smaragdi Walker swarms in the same places, from one day to the next. And to note that his main observations related to two swarms neighbors of 5 to 10 m, and located in an open space between, and under, the branches of a large fig tree and two large mulberry trees ; the foliage of the fig tree touching that of one of the mulberry trees.

 

MY OBSERVATIONS

I regularly perform observations of black fig flies groups flying in a similar way between two trees, but I do not qualify these as aerial swarms because the 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).

 

LAMPROLONCHAEA SMARAGDI Walker OBSERVATIONS

I have never observed a living individual of Lamprolonchaea smaragdi Walker in my fig trees, or on other fruit trees (directly or through photographs). It would however be easy to identify, especially on the photographs, the upper and lateral parts of its thorax and its abdomen being of metallic green color. But I catch a few individuals of this species every year in McPhail-type traps placed on my fig trees (loaded with a 40 g/l aqueous solution of diammonium phosphate or ammonium sulphate).
 

Lamprolonchaea smaragdi Walker.

Lamprolonchaea smaragdi Walker.
 

I noted that Eugène SÉGUY already indicated in 1934 that the species Lonchaea aurea Macquart, 1851 (synonymous with Lamprolonchaea smaragdi Walker, 1849) was reported  in the Var French department (where I live). Reference : SÉGUY E., 1934, Diptères (Brachycères), Faune de France, vol. 28, page 178, Paris.The author indicates that the species lays its eggs in various fruits already infested by other insects, for example figs attacked by the Mediterranean fruit fly (Ceratitis capitata Wiedemann).

In addition Fabian COUSINIÉ, who has carried out an internship at CIVAMBIO 66  in 2017, with the subject of  Silba adipata McAlpine mass trapping, told me that he had identified about ten Lamprolonchaea smaragdi Walker individuals in the traps he had placed on the fig trees.

 

 

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