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Author: François DROUET.
Photographs: François DROUET.
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Look-alike flies
In this chapter, I present the three main look-alike flies of Silba adipata McAlpine that I regularly encouter: Lamprolonchaea smaragdi Walker, Nyctia halterata Panzer, and an unidentified black species.
LAMPROLONCHAEA SMARAGDI (WALKER, 1849)
A little-known fly is usually present in areas where the Black Fig Fly has been detected, and it lays eggs in the ripe figs (but with negligible effect on the crop). Its name is Lamprolonchaea smaragdi (Walker, 1849). And it belongs to the same family like that of Silba adipataMcAlpine (Lonchaeidae).
It has strictly the same flight pattern, strictly identical morphological characters, and the same wings venation (common to all species of the Lonchaeidae family). But this species is generally clearly smaller than Silba adipata McAlpine (with exceptions…), and the metallic emerald green color of its thorax and its abdomen makes possible the identification (not without difficulties…). I have noticed that, in direct sunlight and depending on the light incidence, the abdomen may appear golden in color (in part or in whole).
According to Eugène SÉGUY, who described the species under the synonym Lonchaea aurea Macquart, 1851: " The larva especially develops in fruits already attacked by the medfly (oranges, figs), or by the codling moth (pears, plums, peaches); it is a secondary fruits destructive agent, which hastens their decomposition and favors their invasion by Drosophila ". Reference: Diptera (Brachycères), Faune de France, E. SÉGUY, 1934, vol. 28, page 178, Paul LECHEVALIER et fils, Paris. I noted that Eugène SÉGUY indicated (already in 1934...) that the species was reported in my region (Var French department), as well as in Corsica.
This species is present in my orchard, and I capture every year a few individuals (never more than 10, contrary to certain spots where they are very numerous in the traps). But, I have never been able to observe a living individual, neither on fig trees, nor on other fruit trees. I did not identify any either in the thousands of photographs that I made in the field studying Silba adipata McAlpine, in some of which it could have appeared, after having visually escaped me. And I did not detect any Lamprolonchaea smaragdi Walker
individuals from attacked figs I placed in emergence boxes, in large scale when I was practicing black fig flies breeding.
Lamprolonchaea smaragdi Walker individuals.
Lamprolonchaea smaragdi Walker.
(note that there are no morphological differences with the Black Fig Fly).
Below, two photographs of a Lamprolonchaea smaragdi
Walker individual on the surface of a cup of clear water, where it was transferred from the trap to be observed and photographed under better conditions. Favorable light conditions reveal the metallic green color of the Lamprolonchaea smaragdi Walker's thorax and abdomen.
Lamprolonchaea smaragdi
Walker: specific emerald green colour.
Under a certain light incidence, Lamprolonchaea smaragdi Walker seems to have a golden abdomen (photograph below).
Lamprolonchaea smaragdi
Walker: specific colour.
(note the wing venation common to all Lonchaeidae family species).
I have noticed that a Lamprolonchaea smaragdi Walker individual only reveals its emerald green color when viewed with high light intensity and favorable light incidence. Without these light conditions, it appears of a black color, like Silba adipata McAlpine (to the naked eye, as in the photographs). Suitable light conditions are rather easy to obtain, in direct sunlight and by examining the dead individual, rotating it in all directions with a tweezer to find the correct light incidence (preferably using a magnifier, but sometimes with the naked eye).
Two clues must be kept in mind to trigger a Lamprolonchaea smaragdi Walker identification, if the green color is not immediatly visible. First, the individual looks like an abnormally small black fig fly. Secondly, in direct sunlight, its black color is intensely bright on the surface of the trap liquid, drawing attention compared to all the other flies, including black fig flies.
Below, two photographs showing the difficulty of detecting
the characteristic green color of Lamprolonchaea smaragdi Walker. In the following photograph, the green color of
the Lamprolonchaea smaragdi Walker individual is barely visible, due to light conditions.
A Lamprolonchaea smaragdi Walker individual with barely visible green colour (light conditions).
In the photograph below, a Lamprolonchaea smaragdi Walker individual
is compared to two black fig flies: the size difference is clearly visble, but
the green color and the specific shine of Lamprolonchaea smaragdi Walker are
not visible (due to the light conditions, although the photograph is not
particularly dark).
A Lamprolonchaea smaragdi Walker individual (below) compared to two Silba adipata McAlpine individuals.
NYCTIA HALTERATA (PANZER, 1798)
I have met many times on fig trees, in different places, a small black fly which does not attack figs but which, according to my experience, can lead to a confusion with Silba adipata McAlpine for people who have never seen the latter. It is Nyctia halterata (Panzer,1798) belonging to the Sarcophagidae family. This fly does not lay eggs in the figs, but it can be observed moving on the fig tree leaves and on the figs.
The first difference with Silba adipata McAlpine is that it exclusively stays on the upper side of the leaves. It is never found on the underside of the fig tree leaves, which is the Silba adipata McAlpine privileged place of residence. In fact, it is slightly larger than Silba adipata McAlpine, it walks clearly faster, and unlike it, it keeps its wings apart while walking. Its abdomen appears longer and has long hairs at its end. Its wings with pronounced black veins are partially smoky, while those of the Black Fig Fly are more finely ribbed and are uniformly translucent.
I occasionally catch a Nyctia halterata Panzer individual in my traps, but this species is more frequently visible on the fig tree than in them. Below, three photographs showing Nyctia halterata Panzer.
Nyctia halterata Panzer on a fig tree leaf.
Nyctia halterata Panzer on a fig tree leaf.
Nyctia halterata Panzer on a fig tree leaf.
UNIDENTIFIED BLACK LOOK-ALIKE SPECIES
A SOURCE OF ERROR FOR THE UNTRAINED EYE
The third main look-alike of Silba adipata McAlpine that I have detected is entirely black, and shows a particularly deceptive appearance for the untrained eye. Below, a photograph which compares the look-alike species with the Black Fig Fly. Only an experienced eye can notice that the venation of the wing anterior edge and the pillosity of the black look-alike species (on the right in the photograph) are different from those of the Black Fig Fly.
Silba adipata McAlpine (on the left) versus unidentified black look-alike species (on the right).
Credit: Fabian COUSINIÉ, CIVAMBIO 66.
I have never observed this black look-alike fly on a fig tree, both with the naked eye and among the thousands of photographs taken over many years. But, I regularly catch individuals of this species in my traps placed on fig trees, more or less numerous depending on the year. I deduce that this species is in no way attracted to the Fig tree (leaves, current-year wood, latex, ripe figs), and is found in the traps only because it is attracted to the liquid bait. As it is the case with the olive fly, of which I regularly catch many specimens in my traps, having never observed an individual of this species on a fig tree.
BLACK LOOK-ALIKE SPECIES SIZE
The usual size of the look-alike species is a body length of 5 mm. But on a few occasions I have found in the traps smaller individuals (body length: 4 mm). According to my observations, they are males, but I do not have a sufficient number of observations to say that this is always the case. We note that there is an overlap with the Silba adipata McAlpine size (common body length 4 mm, and a females minority part with a body length of 5 mm). Below, a photograph showing two individuals of the black look-alike species, respectively of a 5 mm and 4 mm length.
Black look-alike species individuals with a different size.
Below, a photograph showing a male specimen of the black look-alike species 4 mm long, smaller than the common size (5 mm).
Small black look-alike species individual (male, 4 mm).
COMPARING THE WING ANTERIOR EDGE VENATIONS
The main criterion allowing to distinguish the black look-alike species from Silba adipata McAlpine is the venation of the wing anterior edge. To observe the wing venation, it is necessary to use a strong magnifier and examine the deployed wing flat on the surface of the liquid contained in the trap, or of clear water in a cup.
In the photograph below (black look-alike species), we observe that the venation of the wing anterior edge is not that of the Lonchaeidae family. If we compare this photograph with the Silba adipata McAlpine photograph that follows it, we note that the subcosta clearly diverges from the radius to join the costa much forward than it is the case for the Black Fig Fly. We also note that the subcosta is thiner than the radius, and that the subcosta curve is not regular.
Black look-alike species: venation of the wing anterior edge.
Silba adipata McAlpine: venation of the wing anterior edge.
There is, like for Silba adipata McAlpine, a costal break just before the junction of the subscosta and the costa, with the presence of a spine more long than the spinules which border the costa (photograph below).
Black look-alike species: costal break just before the junction of the subscosta and the costa.
OTHER DIFFERENCES WITH SILBA ADIPATA McALPINE
I also observed that the look-alike fly shows differences with Silba adipata McAlpine in terms of pillosity: more bristles on the top of the head; presence of numerous bristles on the top of the prescutum and the scutum; significantly longer hairiness on the abdomen; bristles on the lower face (below the antennae), forward and on the underside. Below, a photograh showing the unidentified black look-alike species. We note the details of the wing anterior edge and the clear difference of pillosity with the Black Fig Fly.
Unidentified black look-alike species (note the pillosity).
I also have noticed that the legs of the unidentified look-alike species are longer than those of Silba adipata McAlpine (see photograh below).
Black look-alike species legs length.
(note also that the millimeter graduations indicate a body length of 5 mm).
The venation of the wing anterior edge of the look-alike species is that of the Muscidae family, but also that of several other Diptera families. And in these families, I have found several dozens of completely black flies. So I was not able to determine the taxonomic designation of the black look-alike species.
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