Silba adipata McAlpine

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Home > Infestation > Immature figs infestation (pupae, dead imagos).

 

Author: François DROUET.
Photographs: Bernard PEYRE, Alain COSTA.
All rights reserved.

 

 

Immature figs infestation

 

(pupae and dead imagos)

 

 

 

After staying in the fig central cavity, the Silba adipata McAlpine larva leaves it to dig a gallery in the thickness of the parenchyma. When the larva reaches it complete development, it  pierces a hole in the skin to get out of the fig. It lets itself fall to the ground and buries itself to turn into a pupa. But it sometimes happens that the pupation takes place inside the immature fig, and even that the pupation can reach its term there, thus causing the emergence of an imago within the infructescence (which does not survive because it fails to extract itself from the fig...).

I deliver below various observations on these atypical phenomena, according to the following plan: pupation inside immature figs, causes of pupation, emergence of imagos inside immature figs.

 

PUPATION INSIDE IMMATURE FIGS

 

MY OBSERVATIONS

I could observe pupae inside immature figs, but very rarely. While I opened over 1000 attacked immature figs of various varieties, I found a pupa inside only half a dozen figs.

But I regularly observe at the beginning of the season of the 'Bourjassotte Noire' variety the presence of pupae in ripe figs, which all result from ovipositions carried out at the immature stage (and which, for the majority of them, have fully formed during this stage). The fig generally contains only one pupa. I sometimes find two, and more rarely I have been able to count three. See chapter dedicated to the presence of pupae in ripe figs.

 

OBSERVATIONS OF F. SILVESTRI

Filippo SILVESTRI indicates that the pupation of Silba adipata McAlpine can take place inside the immature fig, but that it is very rare. He specifies that the pupa is then in the gallery dug by the larva in the parenchyma, and that he found a pupa in the fig central cavity only once, whereas he opened more than 5000 attacked figs of the 'Troiano' variety. 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.

 

OBSERVATIONS OF B. PEYRE

Bernard PEYRE, former fig grower and consultant-trainer for commercial fig cultivation, shared with me three personal observations of Silba adipata McAlpine pupation in immature figs.

During 2013, in his orchard, he photographed several immature figs attacked by the Black Fig Fly. In one of them, which however had larvae exit holes, he found a brown pupa of Silba adipata McAlpine (see photographs below). This observation shows that larvae left the fig to pupate in the ground (larvae exit holes), but that one of them remained in the fig to pupate there (pupa found inside the fig). I is difficult to explain why one of the larvae did not abandon the fig. I can simply relate this observation to two observations of a well-developed larva that I found dead in an unripe fig gallery, very close to an exit hole that the larva had not used. Would some well-developed larvae no longer have enough strength to come out the fig, and either die or begin their pupation ? 

The second observation of Bernard PEYRE concerns a fig containing two pupae. On July 29, 2016, in the garden of the Toulouse city Museum, which houses three fig trees, he noted a large number of attacked immature figs that had fallen to the ground. By opening one of these figs (diameter of 3.5 cm, purple colouring, no larvae exit holes) he found in the central cavity two brown pupae about 4 mm in length.

His third observation is rare, because it relates to three pupae inside a same fig. On August 11, 2023, during a visit to fig trees commercial orchards of the biferous variety 'Colar', in Albatera (Spain), he opened some immature figs of the second crop attacked by Silba adipata McAlpine, and found three pupae in the central cavity of one of them which was still on the tree.
 

Immature fig attacked by the Black Fig Fly.

Immature fig attacked by the Black Fig Fly.
Credit: Bernard PEYRE.

 

Pupa found inside an immature fig attacked by the Black Fig Fly.

Pupa found inside an immature fig attacked by the Black Fig Fly.
(the pupa was initially in the central cavity).
Credit: Bernard PEYRE..

 

CAUSES OF PUPATION INSIDE THE FIG

 

I do not know the causes of Black Fig Fly pupation in the infructescence. The excessive density of flowers (or fruits) in an almost non-existent central cavity could be a hypothesis. F. SILVESTRI mentions this cause to explain the death of the larvae inside the caprifigs. 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.

He indicates that for certain varieties the small immature caprifig is depressed, and the central cavity is entirely occupied by the flowers. Thus the larvae almost all die there, compressed between the flowers. And he specifies that it is the same for the larvae which are born in immature caprifigs in which the blastophage has already penetrated, as a result of the disappearance of the central cavity due to the development of the flowers containing the galls.

Alain COSTA, agricultural engineer-consultant and fig grower in Albatera (Spain), informed me of the following observation: in July and August, second crop figs of the 'Colar' variety have a thick parenchyma, a favorable factor for the Silba adipata McAlpine larva to feed there and complete its usual cycle, with exit from the fruit and pupation in the soil. In September, the figs can present a finer parenchyma, and Alain COSTA noted that it therefore happens that the larvae do not continue their usual growth, and transform into pupae inside the fig (the latter falling to the ground).

But would the pupation in the infructescence always be linked to a physical factor preventing the larva from leaving the fig? Might it not result in certain cases from a biological disorder leading the larva to remain at the level of the infructescence without feeling the need to join the parenchyma? or abnormally weakening the larva?

 

EMERGENCE OF IMAGOS INSIDE IMMATURE FIGS

 

Alain COSTA (introdiuced above) reported to me that he sometimes observes the emergence of Silba adipata McAlpine imagos from pupae, inside immature figs of the 'Colar de Albatera' variety. Young imagos often succumb during emergence because they are unable to completely extract themselves from the pupa (this also happens during pupations in the ground). So we notice a part of their black dried up body outside the pupa, the rest of the body having remained stuck inside it.

See the photograph below, that Alain COSTA kindly sent me, and that appears on page 143 of his book relating to fig tree cultivation in the Albatera region (Spain), published in April 2019. Reference: COSTA A., 2019, El cultivo de la Higuera en el campo de Albatera, Newton publicaciones, 183 pages (ISBN 978-84-943430-3-2). For the dead individual for which the focus is sharp, the head and most of the thorax are outside the pupa, and we note between the eyes a yellowish ptilinum remainder, not retracted in the head.
 

Silba adipata McAlpine: imago (dead) having partially emerged from a pupa inside an immature fig.

Silba adipata McAlpine: imago (dead) having partially emerged from a pupa inside an immature fig.
Credit: Alain COSTA.
 

Alain COSTA also sent me in mid-December 2019 observations of imagos which managed to emerge completely from the pupa inside the central cavity of immature figs. These observations were made on latest immature second crop figs from an orchard of the 'Colar de Albatera' variety. See an example in the two photographs below. According to the position of the young imago with respect to the pupa it emerged from, it seems that it has traveled a short distance in the fig central cavity. But it did not survive because it could not leave the fig.
 

Silba adipata McAlpine: young imago having emerged from a pupa inside an immature fig, and which did not survive.

Silba adipata McAlpine: young imago having emerged from a pupa inside an immature fig, and which did not survive.
(note that it is at a certain distance from the pupa).
Credit: Alain COSTA.

 

Silba adipata McAlpine: young imago having emerged from a pupa inside an immature fig, and which did not survive.

Silba adipata McAlpine: young imago having emerged from a pupa inside an immature fig, and which did not survive.
Credit: Alain COSTA.
 

I notice that the young imago failed to unfold its wings in the fig central cavity before dying, and that these are in the state in which they are at the exit of the pupa, or after a few minutes of life (see photograph below).
 

Silba adipata McAlpine: non unfolded wing of a young imago (dead) having emerged from a pupa inside an immature fig.

Silba adipata McAlpine: non unfolded wing of a young imago (dead) having emerged from a pupa inside an immature fig.
Credit: Alain COSTA.
 

According to my timings of ex situ emergences, it takes 14 to 16 minutes after Silba adipata McAlpine exit from the pupa  for the wings to fully unfold, and be flat and taut. The state of the wings of the dead imago inside the fig central cavity indicates that it succumbed within the first five minutes of life.

In my opinion, the non-unfolding of the wings does not come from mechanical reasons (compression in the infructescence). With the space available in the central cavity of most attacked figs (for example, the one pictured above), the unfolding of the wings could take place much more extensively - if the lifespan allowed it.

 

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