Silba adipata McAlpine

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

 

 

Dead imagos inside ripe figs

 

 

 

According to the following plan: dead imagos presence inside ripe figs, egg-laying date / emergence date, imagos fully emerged from the pupa, imagos partially extracted from the pupa, observations from CIVAMBIO 66.

 

DEAD IMAGOS PRESENCE INSIDE RIPE FIGS

 

I regularly observe the presence of dead imagos (and pupae they emerged from) in early season ripe figs of the 'Bourjassotte Noire' variety. For the presence of pupae, see the specific chapter. I must point out that the variety 'Bourjassotte Noire' (the most important commercial variety in France) is the only variety for which I have observed the presence of dead imagos and pupae in ripe figs. I have never found any in the figs of the other varieties that I practice: 'Grise de la Saint-Jean', 'Bellone', 'Col de Dame Noire' and 'Dauphine' (the last two being widespread commercial varieties in France).

The pupae present in ripe figs are most often empty, and I then find in the infructescence desiccated blackened young imagos. To the naked eye, they are visible as large black dots within the softened infructescence of the ripe fig, most often close to the open pupa in which they have developed. See photograhs below.
 

Silba adipata McAlpine: pupa and desiccated blackened dead imago inside a ripe fig.
('Bourjassote Noire' variety; August 30, 2019).

 

Silba adipata McAlpine: pupa and desiccated blackened dead imago inside a ripe fig.
('Bourjassote Noire' variety; August 30, 2019).

 

Black Fg Fly: pupa and desiccated dead imago inside a ripe fig.

Black Fig Fly: pupa and desiccated blackened dead imago inside a ripe fig.
('Bourjassote Noire' variety; August 30, 2019).

 

EGG-LAYING DATE / EMERGENCE DATE

 

According to my field observations, and my method for dating the ovipositions by the fig examination (exit holes presence, larvae size), Silba adipata McAlpine never attacks ripe figs. The dead imagos found in ripe figs result from ovipositions made in the immature stage, most often several weeks before the maturity stage. On the occasion of an experiment in the field, I was even able to follow the evolution of a 'Grise de la Saint-Jean' breba fig which reached the maturity 2.5 months after egg-laying (that I had directly observed and marked on the branch, on March 31, 2021). I provide the details of this observation in a specific chapter.

It is easy to verify that a dead imago in a ripe fig can only result from an oviposition at the immature stage. According to the biological durations of the life cycle exposed in the chapter "Life cyle / Generations", the emergence of the imago from the pupa in summer occurs at the earliest 18 days after the egg-laying (eggs incubation: 3 days + full larva development in the fig: 6 to 7 days + full nymph development in the pupa: 9 to 10 days). And, for a ripe fig, depending on the state of maturity (before over-ripeness), between 3 and 5 days have passed since the end of the immature stage (start of softening and color change). So, in the most unfavorable case, egg-laying took place 13 days (18 - 5) before the end of the immature stage. This is a minimum value, because the dead imago can be older (that is generally the case).

Concerning the emergence date, if the imago is dried out and blackened, therefore not fresh, the emergence occurred when the fig was in the immature stage. This is what I observed for all the imagos that I found in ripe figs.

However, it would perhaps be possible to find within a ripe fig a dead imago presenting a fresh state, the emergence of which would have taken place in the five days separating the full maturity stage from the end of immature stage (start of softening and color change). The emergence could then have occurred, either on the same day of the imago discovery, or during the four days which preceded it. But I do not know if, during this period, the imago can complete the extraction from the pupa, taking into account the state of the infructescence.

 

OBSERVATION OF IMAGOS HAVING FULLY EMERGED FROM THE PUPA

 

In the infructescence of the ripe fig, the dead Silba adipata McAlpine imagos are close to the pupa from which they managed to extract themselves at the end of the pupation. They have dried out in the unripe fig after emerging from the pupa inside it, and can now be found in the fig that has reached the mature stage See photographs below..
 

Silba adipata McAlpine: pupa and desiccated blackened dead imago inside a ripe fig.

Silba adipata McAlpine: pupa and desiccated blackened dead imago inside a ripe fig.
('Bourjassote Noire' variety; August 30, 2019).

 

Silba adipata McAlpine: pupa and desiccated blackened dead imago inside a ripe fig.

Silba adipata McAlpine: pupa and desiccated blackened dead imago inside a ripe fig.
('Bourjassote Noire' variety; August 30, 2019).

 

Black Fig Fly: open pupae and desiccated dead imagos inside a ripe fig.

Black Fig Fly: open pupae and desiccated dead imagos inside a ripe fig.
('Bourjassote Noire' variety; August 30, 2019).
 

Some detailed observations.

Pupae and desiccated dead imagos are found near brownish damage from larvae.
 

Black Fig Fly: desiccated dead imago near larvae damage, inside a ripe fig.

Black Fig Fly: desiccated dead imago near brownish larvae damage, inside a ripe fig.
('Bourjassote Noire' variety; August 30, 2019).
 

The imagos that succumbed after emergence failed to unfold their wings inside the fig. On some of them, we can distinguish these ones in the unfolded state in which they are at the time of emergence or after a few minutes of life.
 

Black Fig Fly (Silba adipata McAlpine) : desiccated imago inside a ripe fig.

Silba adipata McAlpine: desiccated dead imago inside a ripe fig.
(note the unfolded wing, on the left; 'Bourjassote Noire' variety; August 30, 2019).

 

OBSERVATION OF IMAGOS PARTIALLY EXTRACTED FROM THE PUPA

 

The two photographs below show a dead Black Fig Fly imago partially extracted from the pupa, in a ripe fig ('Bourjassotte Noire’ variety). Only the head and a part of one leg are outside the pupa. The fact that the visible part of the imago is desiccated and blackened (not fresh) indicates that the failed emergence occurred at the immature stage of the fig.
 

Dead imago of Silba adipata McAlpine in a ripe fig, partially extracted from the pupa.

Dead imago of Silba adipata McAlpine in a ripe fig, partially extracted from the pupa.
('Bourjassotte Noire' variety; August 30, 2017).

 

Dead imago of Silba adipata McAlpine in a ripe fig, partially extracted from the pupa.

Dead imago of Silba adipata McAlpine in a ripe fig, partially extracted from the pupa.
('Bourjassotte Noire' variety; August 30, 2017).

 

OBSERVATIONS FROM CIVAMBIO 66

 

Margaux ALLIX, in charge of technical support in organic arboriculture at CIVAMBIO 66, informed me in September 2019 that she observed pupae and dead young imagos in ripe figs of the 'Bourjassotte Noire' variety (commercial fig trees orchards, in the Roussillon region, southwest of France).

She specified that the pupae were empty (complete imago emergence), or with the desiccated body of a dead young imago partly protruding out of them (imago emergence not having reached its end).
 

Black Fig Fly: open pupa and desiccated dead imago inside a ripe fig ('Bourjasotte Noire' variety).

Black Fig Fly: open pupa and desiccated dead imago inside a ripe fig.
(note the brownish larva damage on the central cavity surface; 'Bourjasotte Noire' variety).
Credit: Margaux ALLIX.

 

Black Fig Fly: open pupa and desiccated dead imago inside a ripe fig.

Black Fig Fly: open pupa and desiccated dead imago inside a ripe fig.
(note the brownish larva damage on the central cavity surface; 'Bourjasotte Noire' variety).
Credit: Margaux ALLIX.

 

Black Fig Fly: open pupa and desiccated dead imago inside a ripe fig.

Black Fig Fly: open pupa and desiccated dead imago inside a ripe fig.
(note the brownish larva damage on the central cavity surface; 'Bourjasotte Noire' variety).
Credit: Margaux ALLIX.

 

 

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