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Author: François DROUET.
Photographs: François DROUET.
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Evolution of an infested breba fig reaching maturity
To understand the attacks of Silba adipata McAlpine in an orchard, it is useful to know the durations of the different stages through which an attacked fig passes, up to abscission. During the study of these durations, I was able to observe over a period of 4 months the evolution of a breba fig infested by Silba adipata McAlpine which reached the stages of maturity, overmaturity, and complete desiccation on the tree. I report below the observation of this fig.
March 31, 2021: I observed a sequence of successive ovipositions by a Silba adipata McAlpine female, which focused on 7 breba figs from my fig tree of the 'Grise de la Saint-Jean' variety. During the ovipositions sequence, I was able to mark six of the seven attacked figs (green plasticized link cut in advance to a length of 10 cm). My objective was to know the durations of the different stages of evolution of the attacked figs, up to abscission. So, I proceeded to a daily examination of the six marked attacked figs, from the day after the ovipositions sequence until their abscission.
April 30 (30 days after egg-laying): the infested breba fig of which I report the observation still has the green color of a fig not attacked by Silba adipata McAlpine. According to my observations (Toulon region, France), for the breba figs of the 'Grise de la Saint-Jean' variety, the time between Silba adipata McAlpine egg-laying and the fig reddening allowing an untrained eye to detect the attack varies from 30 to 40 days. It being specified that, for a small percentage of attacked breba figs of this variety, significant reddening does not occur because they are still almost entirely green at the time of abscission.
May 3 (33 days after egg-laying): the infested breba fig, 3.2 cm in diameter, presents for the first time a larva exit hole. Reddish streaks starting from the ostiole are individualized on the epidermis stilll almost entirely green, but which has darkened. The fig has reached a blushing stage which makes Silba adipata McAlpine attack visible to the untrained eye. See photographs below. On these, the breba fig temporarily bears a second marking (red), to indicate that it must be the subject of particular attention in the days that follow to detect the appearance of other larvae exit holes.
According to my observations, the time it takes for the larvae exit holes to appear varies from 30 to 40 days for egg-laying in breba figs of the 'Grise de la Saint-Jean' variety (mainly carried out during the first fortnight of April). And the average time for the appearance of larvae exit holes after egg-laying is 34 days. Note: the time it takes for the larvae exit holes to appear after egg-laying is actually the sum of the eggs incubation time and that of the full development of the larvae.
Infested breba fig: appearance of the first larva exit hole.
(33 days after Silba adipata McAlpine egg-laying).
Infested breba fig: appearance of the first Black Fig Fly larva exit hole.
(33 days after egg-laying ; note the larva exit hole below the ostiole, in the center).
Infested breba fig: Black Fig Fly larva exit hole.
May 4 (34 days after egg-laying): a second larva exit hole appears on the fig, located on the side and halfway up the fig.
Infested breba fig: appearance of the second Black Fig Fly larva exit hole.
(34 days after egg-laying ; note the larva exit hole on the flank of the fig, on the left).
Infested breba fig: second Black Fig Fly larva exit hole.
May 14 (44 days after egg-laying): the reddening has spread, but is still of the same type (more or less wide reddish streaks, starting from the ostiole and individualized on the epidermis which remains largely dark green) . No additional larva exit hole.
June 14 (75 days after egg-laying): the breba fig is still on the tree. The epidermis has yellowed. The fig is still erect, but it is beginning to soften. This is the start of the final phase of evolution towards maturity.
Infested breba fig: yellowed epidermis; start of evolution to maturity.
(75 days after Black Fig Fly egg-laying).
Infested breba fig: yellowed epidermis; the two Black Fig Fly larvae exit holes are visible.
(75 days after egg-laying).
Infested breba fig: yellowed epidermis (start of evolution to maturity); the two larvae exit holes are visible.
(75 days after Black Fig Fly egg-laying).
Infested breba fig: second Black Fig Fly larva exit hole.
June 16 (77 days, i.e. 2.5 months, after egg-laying): the breba fig, with a diameter of 4.2 cm and bearing 2 larvae exit holes since May 4, reaches the beginning of maturity. It suddenly grew (+ 0.8 cm), took on the color of maturity, and slightly softened. The neck has started to bend, the fig is now horizontal, whereas it was erect at 45° to the twig when immature.
Start of maturity for the infested breba fig, which bears 2 Black Fig Fly larvae exit holes.
(77 days after egg-laying).
Start of maturity for the infested breba fig, which bears 2 Black Fig Fly larvae exit holes.
(77 days after egg-laying).
Ripe infested breba fig: the two Black Fig Fly larvae exit holes.
June 21 (82 days after egg-laying): the breba fig has reached the overripe stage. It hangs vertically along the branch. One of the two larvae exit holes is clearly visible on the side of the fig.
Infested breba fig: overripe stage.
(82 days after Back Fig Fly egg-laying; note the larva exit hole).
June 24 (85 days after egg-laying): the breba fig has started its desiccation phase on the tree. The ants are interested in it, but moderately.
Infested breba fig at the beginning of the desiccation phase on the tree.
(85 days after Black Fig Fly egg-laying).
July 10 (101 days after egg-laying): the breba fig is very desiccated.
Attacked breba fig in the process of desiccation on the tree.
(101 days after Black Fig Fly egg-laying).
July 15 (106 days after egg-laying): the breba fig is very desiccated. But despite the intermittent visits of ants, it is still well attached to the twig. The larva exit hole located on the side of the fig is no longer visible due to the folds of the epidermis, but the one located below the ostiole is still clearly visible.
The attacked breba fig.is very dried out.
(106 days after Black Fig Fly egg-laying).
The attacked breba fig.is very dried out.
(106 days after Black Fig Fly egg-laying; note the larva exit hole, below, on the right).
Very dried out breba fig: still visible Black Fig Fly larva exit hole (below, on the right).
July 27 (118 days, i.e. nearly 4 months, after egg-laying): the desiccated breba fig is still on the tree.
July 28: the breba fig is no longer on the tree, but it is also not on the ground. A magpie probably took it, completely dried out (the magpies make incursions on this fig tree, and those nearby). Another hypothesis: it fell to the ground (abscission), and was carried away by a magpie or another animal. According to my observations, for the breba figs of the 'Grise de la Saint-Jean' variety, the time separating Silba adipata McAlpine egg-laying from fig abscission is of the order of 40 days. And we see that this period can be three times longer for the low percentage of breba figs which do not fall following infestation by Silba adipata McAlpine. In my experience, mature figs infested with Silba adipata McAlpine in the immature stage represent between 2 and 5% of the harvest, depending on the variety and the year.
Synthesis: for the breba fig of the 'Grise de la Saint-Jean' variety which continued to evolve after Silba adipata McAlpine egg-laying until maturity and beyond, the two larvae exit holes respectively appeared 33 and 34 days after egg-laying, maturity was reached 2.5 months after egg-laying, and abscission of the completely desiccated fig occurred 4 months after egg-laying.
Note: in summer (for the second crop of the biferous varieties, or for the crop of the uniferous varieties), the durations of these phases are much shorter.
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