Silba adipata McAlpine

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Author: François DROUET.
Photographs: Bernard PEYRE and François DROUET.
All rights reserved.

 

 

Pupae inside ripe figs

 

 

 

According to the following plan: pupae presence inside ripe figs, egg-laying date, species to which the pupae belong, specific observation (pupa on a ripe fig flank).

 

PUPAE PRESENCE INSIDE RIPE FIGS

 

I regularly observe the presence of pupae and dead imagos in early season ripe figs of the 'Bourjassotte Noire' variety. 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 pupae and dead imagos 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).
 

Pupa of Silba adipata McAlpine in a ripe fig.

Pupa of Silba adipata McAlpine in a ripe fig.
('Bourjassotte Noire' variety ; August 30, 2017).

 

Pupa of Silba adipata McAlpine in a ripe fig - 'Bourjassotte Noire' variety.

Pupa of Silba adipata McAlpine in a ripe fig - 'Bourjassotte Noire' variety.
(note the brownish damage caused by the larvae, on the left).
 

When there is an infestation by pupae, the infested ripe fig usually contains only one pupa. I sometimes found two, and more rarely I could count three. In some cases, the pupae are accompanied by dead black-colored larvae, knowing that I also found in the ripe infructescence dead larvae without the pupae being present.
 

Pupa of Silba adipata McAlpine in a ripe fig, surrounded by larvae damage.

Pupa of Silba adipata McAlpine in a ripe fig, surrounded by larvae damage.
('Bourjassotte Noire' variety ; August 30, 2017).

 

I notice that the pupae in ripe figs are open, for the major part of them. And I also find inside the ripe figs the desiccated and blackened imagos that emerged from the pupae, and that did not survive.
 

Empty pupa of Silba adipata McAlpine found in a ripe fig.

Empty pupa of Silba adipata McAlpine found in a ripe fig.
('Bourjassotte Noire' variety ; August 30, 2017).
 

I nevertheless find in ripe figs a minority of pupae which are still full. This does not mean that they necessarily result from ovipositions less old than those corresponding to empty pupae. Indeed, as for the pupae in the ground, it is possible that the pupation did not go to its term, or that the emergence did not take place (the imago dying inside the pupa). 
 

Full pupa of Silba adipata McAlpine found in a ripe fig.

Full pupa of Silba adipata McAlpine found in a ripe fig.
('Bourjassotte Noire' variety ; August 30, 2017).

 

EGG-LAYING 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 pupae 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 stage 2.5 months after egg-laying and fell to the ground, completely dried out, 4 months after it. I provide the details of this observation in a specific chapter.

It is easy to verify that a pupa 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 beginning of the pupation occurs at the earliest 9 days after the egg-laying. 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 (onset of softening, swelling, and color change). So, in the most unfavorable case, egg-laying took place 4 days (9 - 5) before the end of the immature stage for an unopened pupa. If the pupa is open, that means that an imago emerged from it inside the fig after a pupation lasting 9 to 10 days, and egg-laying occurred at the earliest 13 days (18 - 5) before the end of the immature stage. These are minimum values, because the pupa can be older (that is the general case).

 

SPECIES TO WHICH THE PUPAE BELONG

 

IMPOSSIBILITY OF CERATITIS CAPITATA WIEDEMANN'S PUPAE PRESENCE

The presence of pupae in ripe figs leads to the problem of the species to which these pupae belong: Silba adipata McAlpine or Ceratitis capitata Wiedemann (Medfly). I set aside the pupae of Drosophila suzukii Matsumura, which are easily recognizable (by size and shape). Knowing that I have never found pupae of this species by opening a ripe fig before consumption. I have only seen them appear in emergence boxes where I had placed ripe figs. Initially, I wondered if the pupae I found in ripe figs belonged to one or the other of these species (or both...). On examining those that I had extracted from the infructescence, they seemed to me to belong (in size and shape) to the species Silba adipata McAlpine. The pupae of Ceratitis capitata Wiedemann are somewhat larger and significantly wider (more domed).
 

Black-Fig-Fly pupae (on the right) and Medfly pupae (on the left).

Pupae of Ceratitis capitata Wiedemann (on the left), and of Silba adipata McAlpine.
 

In fact, considering the egg-laying limits and the life cycle of Ceratitis capitata Wiedemann, I concluded that it is impossible that pupation of this species could occur in a ripe to very ripe fig.

Indeed, for a pupa found in a fig, taking into account the duration of the eggs incubation (3 days), that of the complete larva development (6 to 7 days), egg-laying at the origin of the pupa occurrs at least 9 to 10 days before the start of pupation. And, according to my observations, the edible ripe fig stage is reached 3 to 6 days after the end of the immature stage (start of softening, swelling, and color change), depending on the variety and the considered stage of maturity. More precisely, just ripe figs: end of the immature stage (EIS) + 3 days for the 'Grise de la Saint-Jean' variety and + 4 days for the 'Bourjassotte Noire' variety; ripe figs: EIS + 4-5 days; very ripe fig: EIS + 5-6 days; beyond: overripe fig.

Thus, considering the longest time (very ripe fig of the 'Bourjassotte Noire' variety: EIS + 6 days), and being reminded that the time separating the start of pupation and egg-laying is 9 to 10 days, egg-laying takes place 3 to 4 days before the end of the immature stage (therefore in a green and hard immature fig). This is possible for Silba adipata McAlpine, which positions its eggs under the ostiolar scales. But that is impossible for Ceratitis capitata Wiedemann, which only lays eggs in ripe figs (or figs having just begun to soften and to change color), either through the epidermis (too hard in the case of an immature fig), or in the ostiole when it is well open (almost closed for an immature fig). So, the pupae found in ripe or very ripe figs cannot be of the species Ceratitis capitata Wiedemann, and are mandatorily of the species Silba adipata McAlpine.

 

PARTICULAR CASE

It is worth mentioning a special case of rare occurrence: the egg-laying of Ceratitis capitata Wiedemann in an immature fig trough a Silba adipata McAlpine larva exit hole. Alain COSTA, an agricultural engineer who advises fig growers in the Albatera region, in Spain,reported to me that he had made this observation several times on immature breba figs of the 'Colar de Albatera' variety, that had fallen to the ground as a result of an attack by Silba adipata McAlpine.

I was able to observe this phenomenon two times, but on figs still on the tree. And I noticed that in the two observed cases the concerned immature fig had softened and partially changed color, due to the time separating the egg-laying and the exit holes appearance (9 to 10 days). See on the photographs below one of my observations I made on July 17, 2019, on an immature fig of the 'Bellone' variety.
 

Ceratitis capitata Wiedemann laying eggs in a Silba adipata McAlpine larva exit hole.

Ceratitis capitata Wiedemann laying eggs in a Silba adipata McAlpine larva exit hole.
(immature fig of the 'Bellone' uniferous variety which has softened and partially changed color).

 

Ceratitis capitata Wiedemann laying eggs in a Silba adipata McAlpine larva exit hole.

Ceratitis capitata Wiedemann laying eggs in a Silba adipata McAlpine larva exit hole.
(immature fig of the 'Bellone' uniferous variety which has softened and partially changed color).
 

I placed the fig in an emergence box, and no larvae were released. It was perhaps a "sterile sting" (without egg emission, or with unfertilized eggs), encountered quite frequently in Ceratitis capitata Wiedemann. Or maybe the larva was born, but it died in the central cavity. I do not know the ability of the Ceratitis capitata Wiedemann's larva to subsist in the inflorescence of an immature fig. The presence of a Silba adipata McAlpine larva exit hole makes it possible to date the corresponding egg-laying to at least 9 to 10 days before (egg incubation: 3 days; complete development of the larva: 6 to 7 days). During this time, the attacked immature fig has softened and partially changed color. The larva of Ceratitis capitata Wiedemann could possibly survive and develop in the softened inflorescence.

If so, it also takes 9 to 10 days for the Ceratitis capitata Wiedemann's pupa to begin to form. To find a pupa of this species in the ripe fig, the fig with the Silba adipata McAlpine larva exit hole must not fall to the ground and continue to evolve towards maturity (reminder: 2 to 5% of harvested ripe figs, for certain varieties only), and it must reach maturity at least 9 to 10 days after the oviposition in the larva exit hole. The rarity of Ceratitis capitata Wiedemann oviposition in a Silba adipata McAlpine larva exit hole, and the requirement to fulfill the two aforementioned conditions, make negligible the probability of finding a Ceratitis capitata Wiedemann's pupa in a ripe fig. But, in all rigor, it cannot be ruled out.

 

SPECIFIC OBSERVATION: PUPA ON A RIPE FIG FLANK

 

Bernard PEYRE, former fig grower and consultant-trainer for commercial fig cultivation, reported to me on September 17, 2019 a curious observation made on a ripe fig of the 'Bourjassotte Noire' uniferous variety. A pupa was located on the flank of the fig, in a crack of the epidermis (photograph below). I have never encountered such a case, but since it is not possible for a pupa of Ceratitis capitata Wiedemann to form in a fig at the mature stage as it appears in the photograph, it is a pupa of Silba adipata McAlpine.
 

Pupa on the flank of a ripe fig ('Bourjassotte Noire' variety).

Pupa on the flank of a ripe fig ('Bourjassotte Noire' variety).
Credit: Bernard PEYRE.
 

Bernard PEYRE specified that the pupa was empty. The arrangement of the pupa in such a deep crack could suggest that the larva was not in the fig that ripened, but came from outside (falling from above, for example). It would have lodged in the crack and would have transformed there into a pupa, as easily do, according to my observations, the Silba adipata McAlpine larvae above ground (in the most unlikely places).

But the pupa being empty, this means that the larva would have arrived in the crack at least 9 to 10 days before. And the evolution of the concerned ripe fig seems to be at the end of the immature stage (start of softening and changing color) + 5 days. The larva would therefore have arrived in the crack 4 to 5 days before the end of the immature stage, at a time when the crack in the epidermis did not exist. Being emphasized that pupation on the surface of an immature fig is unlikely, although not impossible. One hypothesis would be that the pupa formed inside the fig near the epidermis, in a gallery (maybe close to the exit hole of another larva), and that it appeared outside the fig during the tearing of the epidermis when the fig swelled, in the final phase of ripening.

By enlarging the photograph sent by Bernard PEYRE to the maximum limit, we can see several small holes on the pupa (detail below).
 

Presence of several holes on a pupa located on a ripe fig flank ('Bourjassotte Noire' variety).

Presence of several holes on a pupa located on a ripe fig flank ('Bourjassotte Noire' variety).
Credit: Bernard PEYRE.
 

We could deduce that the pupa was attacked by a parasite. I only know one parasite for Silba adipata McAlpine: Pachyneuron vindemmiae Rondani (see details in the chapter "Biological control"). F. SILVESTRI indicates that the female of this parasite searches for pupae on the surface of the ground, between fallen fruits, or at a shallow depth, in the aim of egg-laying. Reference: SILVESTRI F., 1917, Sulla Lonchaea aristella Beck. (Diptera : Lonchaeidae) dannosa alle infiorescenze e fruttescenze del caprifico e del fico, Bollettino del Laboratorio di Zoologia Agraria in Portici, vol.12, pp. 123 -146. The observed pupa clearly flush with the surface of the fig and is therefore in a position conducive to the attack of this parasite.

But if I examine the photograph above with a magnifier, I quite clearly distinguish 3 holes in an oblique line, and I perceive 4 to 5 others grouped at the top of the pupa. I do not know how to explain these holes. We might suspect that they result from ovipositions of Drosophila suzukii Matsumura in the empty pupa, but this species usually lays its eggs directly into the fig through the epidermis. Unless we imagine that the larvae from the eggs laid in the empty pupe join the infructescence to feed there...

 

 

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