Silba adipata McAlpine

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

 

 

Immature figs infestation (eggs)

 

 

 

Below, my personal observations (no information reported from the literature). Orchard located in the Toulon region, French souhteastern Mediterranean coast, USDA zone 9b.
 

Black Fig Fly female laying eggs under an ostiolar scale of an unripe fig.

Black Fig Fly female laying eggs under an ostiolar scale of an unripe fig.

 

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.

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.

Silba adipata McAlpine: 5 empty eggs envelopes (chorions) under an ostiolar scale.
(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).

 

EGGS IMPLANTATION BY OSTIOLAR SCALES TYPES

 

I regularly observe that most of the eggs are located under first level ostiolar scales (i. e. the ones that are on the surface of the fig), a much smaller part, but which remains significant, being placed under second level ostiolar scales (located just below the previous ones). 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 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.

 

NUMBER OF OSTIOLAR SCALES USED IN A FIG

 

When the fig contains 1 egg, I observe that this one can be implanted under an ostiolar scale or in the ostiolar canal. When it contains 2 to 5 eggs, I observe that these are implanted under a single ostiolar scale, under several ostiolar scales (maximum 3), and/or in the ostiolar canal.

The study of 143 infested figs collected after abscission, which I carried out in July / August 2021 (see chapter), showed that: 64% of the examined figs contain eggs under a single ostiolar scale; 28% contain eggs under 2 ostiolar scales; 6% contain eggs under three ostiolar scales; 2% contain eggs in the ostiolar canal alone. Note: in the examined batch, none of the figs simultaneously contain eggs in the ostiolar canal and under one or more ostiolar scales, but I have observed these cases before.

When the fig contains a number of eggs greater than 5 (multiple ovipositions in the same fig), I have observed that their dissemination often concerns 1 to 3 ostiolar scales, and sometimes more than 3 ostiolar scales. The maximum number of ostiolar scales containing eggs that I could observe in a fig is 7 (these were first and second level scales, for a total of 29 eggs).

Whatever the number of eggs contained in the fig, the maximum number of eggs grouped in the ostiolar canal that I have observed is 3.

 

EGGS DISSEMINATION ACCORDING TO THE NUMBER OF USED SCALES

 

The study of 143 infested figs collected after abscission, which I carried out in July / August 2021 (see chapter), provides the number of eggs implanted under each of the ostiolar scales of the examined figs. It follows that we can know the eggs dissemination in the different cases of ostiolar scales use in a fig (one, two or three).

When a single ostiolar scale gathers all the eggs (64 % of the 143 examined figs), I count: 1 egg in 37% of the cases; 2 eggs in 40% of cases; 3 eggs in 14% of cases; 4 eggs in 3% of cases; 5 eggs in 6% of cases.

When all the eggs are scattered under two ostiolar scales (28% of the 143 examined figs), I count: 2 eggs in 38% of the cases - 15 figs (1,1) - i.e. 1 egg under each of the two scales; 3 eggs in 30% of cases - 12 figs (1,2 ) - i.e. 1 egg under a scale, and 2 eggs under the other scale; 4 eggs in 23% of cases - 9 figs, including 7 figs (2,2) and 2 figs (1,3); 5 eggs in 7% of cases - 3 figs, including 2 figs (1,4) and 1 fig (2,3); 7 eggs in 2% of cases - 1 fig (2,5).

When all the eggs are scattered under three ostiolar scales (6% of the 143 examined figs), I count: 3 eggs in 11% of cases - 1 fig (1,1,1); 4 eggs in 33% of cases - 3 figs (1,1,2); 5 eggs in 33% of cases - 3 figs, including 2 figs (1,2,2) and 1 fig (1,1,3); 6 eggs in 22% of cases - 2 figs (1,2,3).

When the eggs are located in the ostiolar canal (2% of the examined 143 figs; 3 figs), I count: 1 egg in the case of one fig, and 2 eggs in the case of 2 figs.

 

 

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