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Home > Infestation > Immature figs infestation (eggs) : number per fig, implantation by ostiolar scales types.
Author: François DROUET.
Photographs: François DROUET.
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Immature figs infestation (eggs)
Number per fig, implantation by ostiolar scales types
Below, my personal observations (no information reported from the literature). Orchard located in the Toulon region, French souhteastern Mediterranean coast, USDA zone 9b.
Chapter plan: number of eggs contained in a fig, ostiolar scales types, eggs implantation by ostiolar scales types.
Black Fig Fly female laying eggs under an ostiolar scale of an unripe fig ('Bellone' variety).
NUMBER OF EGGS CONTAINED IN A FIG
A fig parasitized by Silba adipata McAlpine usually contains 1 to 5 eggs. This is the number of eggs (or empty eggs envelopes) that I regularly find in a fig by examining the ostiolar scales and the ostiolar canal under a stereomicroscope.
The study of 143 infested figs collected after abscission, which I carried out in July / August 2021 (see chapter), showed that 98% of them contained 1 to 5 eggs, and 80% of them contained 1 to 3 eggs. More precisely : 24% of the figs contained 1 egg, 38% 2 eggs, 18% 3 eggs, 10% 4 eggs, 8% 5 eggs, 2% more than 5 eggs.
The number of large larvae (6 to 7 mm) that I usually find in a parasitized fig without larvae exit holes (1 to 3 most often, 4 or 5 less frequently, but not rare) constitutes an element of confirmation. The number of larva exit holes is not significant because I have observed that several larvae can use the same exit hole, and that it exists a certain mortality rate of the larvae in the fig (see chapter for the correlation between larvae exit holes number and eggs number).
I can also report another element of confirmation by the larvae: in June, July and August 2015, I examined the inside of 200 immature figs infested by Silba adipata McAlpine (varieties 'Grise de la Saint-Jean ' and 'Bellone'). They were largely still provided with their larvae (figs picked up on the tree for the most part). I only found figs containing one to five larvae.
Silba adipata McAlpine: 5 empty eggs envelopes (chorions) under an ostiolar scale.
(reddened unripe fig; the ostiolar scale has been raised).
It happens that I find in a fig (with a low occurrence) a number of eggs much higher than 5, because of the ovipositions plurality in the same fig (fig visited by several females). The highest number of eggs I have observed in a fig is 29, and I counted up to 18 eggs under a same ostiolar scale (as unhatched eggs, and / or empty egg envelopes, named chorions).
Silba adipata McAlpine: ovipositions plurality under a same ostiolar scale (7 eggs and 7 chorions).
(scale raised - the eggs were laid under the chorions when the scale was horizontal).
OSTIOLAR SCALES TYPES
I call "first level" ostiolar scales the scales the base of which is located closest to the surface of the fig (these are the highest ostiolar scales). The first level scales can overlap slightly at the tip. They are thick, tough, and often reddish in color, entirely or on the edges.
And I call "second level" ostiolar scales those that are just below the first level scales. Largely or completely covered by the first level ostiolar scales, they are quite tough or quite soft, depending on the variety. Their color is generally greenish, partially reddish for some varieties.
Below the second level ostiolar scales are thin scales, softer than the previous ones, of a light green color. Generally horizontal, they precede the scales of the ostiolar canal (vertical and whitish). They never shelter eggs. Note: depending on the variety and the level of development of the fig, second-level ostiolar scales may also be tender, thin, and light green in color.
Below is an example of an immature green fig.
Immature fig: first level ostiolar scales, three in number.
(they completely or largely cover the second level ostiolar scales).
Immature fig: second level ostiolar scales, three in number, visible after removal of those of the first level.
(note in three places the traces of cutting with a scalpel of the first level ostiolar scales).
Immature fig: thin horizontal ostiolar scales located under the second level scales (removed with a scalpel).
(Silba adipata McAlpine never lays eggs under this type of scales).
In the case of an immature fig that has reddened several days after Silba adipata McAlpine egg-laying, all the ostiolar scales are totally or partially reddish (see photographs below).
Reddened immature fig (Silba adipata McAlpine oviposition), from left to right: first level scales, second level scales, and scales below those of the second level.
Below, photographs of the ostiolar canal.
Reddened immature fig (after Silba adipata McAlpine egg-laying): ostiolar canal seen from above.
(all horizontal ostiolar scales have been removed).
Reddened immature fig (after Silba adipata McAlpine egg-laying): ostiolar canal seen from above.
(all horizontal ostiolar scales have been removed).
Immature fig (skin reddened by a Silba adipata McAlpine attack): ostiolar canal seen from below.
EGGS IMPLANTATION BY OSTIOLAR SCALES TYPES
EGGS IMPLANTATION
I regularly observe that most of the Silba adipata McAlpine eggs are located under first level ostiolar scales, a much smaller part, but which remains significant, being placed under second level ostiolar scales. And if the ostiole has slightly widened, I can find eggs in the ostiolar canal, more or less vertically laid (very low occurrence).
The study of 143 infested immature figs collected after abscission, which I carried out in July / August 2021 (see chapter), showed that: for 83% of the examined figs, the eggs are placed under first level ostiolar scales, for 8% under second level ostiolar scales, for 7% under first and second level ostiolar scales, and for 2% in the ostiolar canal.
EXAMPLES OF IMPLANTATION UNDER THE FIRST LEVEL OSTIOLAR SCALES
Example 1: implantation of 1 egg under a first level ostiolar scale.
Silba adipata McAlpine: 1 egg under a first level ostiolar scale.
(of 3 first level scales, one was cut at the base with a scalpel and turned over, revealing 1 egg).
Example 2: implantation of 3 eggs under a first level ostiolar scale.
Silba adipata McAlpine: 3 eggs under a first level ostiolar scale.
(3 first level scales; one was cut at the base with a scalpel and turned over, showing 3 eggs; it partly covered the green bottom scale, on the left).
EXAMPLES OF IMPLANTATION UNDER THE SECOND LEVEL OSTIOLAR SCALES
Example 1: implantation of 1 egg under a second level ostiolar scale.
Silba adipata McAlpine: 1 egg under a second level ostiolar scale.
(the scale under which the egg is located was covered by a first level scale, which was removed with a scalpel).
Example 2: implantation of 2 eggs under a second level ostiolar scale.
Silba adipata McAlpine: 2 eggs under a second level ostiolar scale 1/2.
(the second level scale on the right covers eggs; note the traces of scalpel cutting of the first level scales).
Silba adipata McAlpine: 2 eggs under a second level ostiolar scale 2/2.
(the detached second level ostiolar scale reveals 1 unhatched egg and 1 chorion).
EXAMPLES OF IMPLANTATION IN THE OSTIOLAR CANAL
Example 1: implantation of 1 egg in the ostiolar canal.
Silba adipata McAlpine: white empty egg envelope (chorion) vertically positioned in the ostiolar canal.
(reddened immature fig; horizontal ostiolar scales have been removed).
Silba adipata McAlpine: white empty egg envelope (chorion) vertically positioned in the ostiolar canal.
(reddened immature fig; horizontal ostiolar scales have been removed).
Example 2: exceptional observation of multiple ovipositions in the ostiolar canal (06/26/2024; reddened immature fig from the second crop of the 'Grise de la Saint-Jean' biferous variety; diameter 2.3 cm; collected from the ground, after abscission).
Silba adipata McAlpine: tip of a chorion implanted in the ostiolar canal of a reddened immature fig.
(at this stage of the observation, we cannot know that several eggs have been laid in the ostiolar canal).
Silba adipata McAlpine: cluster of chorions revealed after clearing the ostiolar canal of the reddened immature fig.
(several ostiolar canal scales have been removed).
Silba adipata McAlpine: cluster of chorions extracted from the ostiolar canal of the reddened immature fig.
Silba adipata McAlpine: analysis of the cluster of chorions extracted from the ostiolar canal of the reddened immature fig.
(7 chorions on 3 levels, reflecting three successive ovipositions of respectively 4 eggs, 2 eggs, 1 egg; the eggs laid first
were pushed towards the bottom of the ostiolar canal by the following eggs, at a depth inaccessible to the ovipositor).
Another chapter deals with immature figs infestation by the Silba adipata McAlpine eggs (number of ostiolar scales used in a fig, eggs dissemination according to this number).
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