Silba adipata McAlpine

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

 

 

Life cycle / Generations

 

 

 

According to the following plan : life cycle duration, life span, generations sequence in the year.

 

LIFE CYCLE DURATION

 

OBSERVATIONS OF FILIPPO SILVESTRI

Filippo SILVESTRI is the author of a masterful study of the Black Fig Fly (morphology, biology, fig infestation...), published in 1917. 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.

According to F. SILVESTRI, the duration of one life cycle is 18 to 20 days in summer, 48 days in April. With the following durations for the biological periods.

Egg incubation (time between the egg-laying and the larva birth): 3 days in summer, 8 days in April.

Complete larva development in the fig: 6 to 7 days in summer, 24 days in April.

Complete nymph development (in the pupa): 9 to 10 days in summer, 16 days in April.
 

Note: the F. SILVESTRI' s biological periods observations were performed in the Napoli region (Italy). Depending on warmer or cooler climatic conditions of the region where the orchard is located, the biological periods may be shorter or longer.

 

MY OBSERVATIONS

I have only partial personal observations for durations of the biological periods forming the life cycle of the Black Fig Fly, in my region (Toulon, France).

According to my observations, the larvae exit holes on the fig appear 11 to 26 days after ovipositions performed during the first half of june (uniferous variety 'Bellone'), and 30 to 40 days after ovipositions performed in April (breba figs of the 'Grise de la Saint-Jean' variety). And the life time inside the pupa is 9 to 10 days in summer.

 

PRACTICAL USE OF THE BIOLOGICAL PERIODS

What time separates the larva birth from the egg-laying ? Response: in summer, 3 days; in April, 8 days.

How long do the larvae stay in the fig ? Response: in summer, 6 to 7 days; in April, 24 days.

How long after the egg-laying do the larvae exit holes appear on the fig?  Response: in summer, 9 to 10 days; in April, 32 days.

How long does the larva take to turn into imago in the ground ? Response: in summer, 9 to 10 days; in April, 16 days.

How long after the egg-laying does the young imago emerge from the ground ? Response: in summer, 18 to 20 days; in April, 48 days.

Note : responses for the Napoli region (Italy) - source F. SILVESTRI.
 

The Black Fig Fly larva abandons the fig after a development of 6 to 7 days inside it (in summer).

The Black Fig Fly larva abandons the fig after a development of 6 to 7 days inside it (in summer).

 

Black Fig Fly (Silba adipata McAlpine) : young imago recently emerged from the pupa.

A young imago which has just emerged from the pupa, after a development of 9 to 10 days inside it (in summer).
 (note : it is not yet black-colored, and its wings are not yet deployed ; the ptilinum is not yet retracted in the head).

 

LIFE SPAN

 

When I bred black fig flies, in my first years of studying the species, I had not the idea of trying to assess their life span. I just kept adults for two or three days fed with fig juice, not needing a longer period for my ex situ photography sessions and experiments.

But two authors give an estimate of the Black Fig Fly life span.

Filippo SILVESTRI indicates that the adult lives one month or more. 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.

Jean GHESQUIERE, a Belgian entomologist, kept adult black fig flies alive for six weeks in the laboratory, fed with grape juice. He ensures that in situ the adult life span is much longer. Reference: GHESQUIERE J., 1949, La mouche noire des figues Lonchaea aristella Beck. à la Côte d'Azur, comptes rendus des séances de l'Académie d'agriculture de France, T. 35, pp. 650-653.

I therefore retain the estimate of 1.5 to 2 months for the life span of Silba adipata McAlpine (in order to use it in my analyses of the orchard infestation complex issues).
 

Three black fig flies feeding on a latex oozing (fig tree twig of the year).

Three black fig flies feeding on a latex oozing (fig tree twig of the year).

 

GENERATIONS SEQUENCE IN THE YEAR

 

OBSERVATIONS OF FILIPPO SILVESTRI

F. SILVESTRI describes the annual generations sequence. 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 was able to determine that from the eggs deposited in the ostiole at the beginning of April, adults are obtained at the end of May. The adults of this first generation lay eggs in late May or the first days of June, and these eggs can produce adults of a second generation in late June or the first days of July. In July, August and September the third, fourth and fifth generations are born (full adult development in July and August takes only 19-20 days). A sixth generation is born during the October-November-December period. F. SILVESTRI manages to count six generations because he takes into account the very late varieties of domestic fig trees (for which he mentions Silba adipata McAlpine attacks).

The adults living more than one month, those of the previous generation continue to lay eggs while the adults of the next generation begin to lay, and there is thus an entanglement of the generations.

It should be noted that the first Silba adipata McAlpine flights observed in the year are those of a generation at the end of the previous year autumn, emerging from hibernation and which is at the origin of the first ovipositions of the year, at the beginning of April. The six generations mentioned by F. SILVESTRI are those resulting from the ovipositions of the year (the generation emerging from hibernation not being included in the generations of the year).

 

MY OBSERVATIONS

In 2019, I studied the Silba adipata McAlpine generations sequence in my garden (Toulon region, France) on three fig trees (three different varieties, including a biferous one. I noted that, in spite of the diversity of my fig tree varieties, the generations number of the year was only three.

Beyond the generations sequence, I regularly observe for each of the fig tree varieties that the Silba adipata McAlpine attacks feature a very short period of high intensity, then strongly attenuate, and completely disappear while it still remains on the trees many immature figs. See Silba adipata McAlpine's three-phase attack pattern.

During phase 3 of the pattern, varying from 3 to 6 weeks, Silba adipata McAlpine no longer attacks immature figs still present on fig trees (regardless of their size). It is the existence of this phase 3 that limits the number of generations. I calculated that in the absence of phase 3 (so if Silba adipata McAlpine attacked immature figs until they disappeared) the number of generations would have been 5.
 

Silba adipata McAlpine laying eggs under an unripe fig ostiolar scale.

Silba adipata McAlpine laying eggs under an unripe fig ostiolar scale.

 

I provide in a specific chapter observations concerning the Silba adipata McAlpine activity start and end in the year (emerging from hibernation and first ovipositions, last ovipositions and last presence in my garden).

 

 

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