La colonisation des cônes et galbules des genévriers méditerranéens par les insectes et acariens et son influence sur les possibilités de régénération naturelle de ces essences.

Abstract

Les ravageurs des structures reproductrices femelles des genévriers méditerranéens semblent étroitement inféodés aux Cupressacées et dans leur majorité exclusivement au genre Juniperus. La composition de leurs faunes propres ne respecte pas les divisions botaniques du genre et parait liée à des facteurs climatiques. J. oxycedrus L. et J. phoenicea L., caractéristiques de l'étage de végétation méditerranéen, présentent sur toute leur aire de distribution française une faune identique, très différente de celle de J. thurifera L., espèce répartie dans l'étage supraméditerranéen. Des taux élevés d'attaque des galbules sont fréquemment observés pour les trois essences avec des différences entre les peuplements continentaux et corses. Mais le faible nombre de ravageurs s'attaquant aux graines -comme la quantité importante de graines pleines par galbule -limitent, sauf chez J. thurifera L., la réduction des possibilités de régénération des peuplements naturels de ces genévriers par les insectes et acariens.

Efficiency of pollination and satiation of predators determine reproductive output in Iberian Juniperus thurifera woodlands

“…Damage by arthropods differed by a factor of 2.5 across the 14 populations, with even larger variations when damage by individual arthropod species was assessed. Variability was higher among trees within populations (see also Roques et al 1984), and there was a strong relationship between individual tree characteristics and levels of fruit and seed damage by arthropods. Mites are important agents of seed damage in Spanish juniper (Roques et al 1984).…”

“…After fertilisation, fruits grow until reaching their full size in late summer and then mature for over a year, ripening during the autumn of the year after pollination. During this period, fruits are vulnerable to damage at different stages of their development, largely through the actions of three arthropod species (Roques et al 1984;Mezquida & Olano 2013). Mites (Trisetacus quadrisetus, Acarina, Eriophyidae) enter the fruit early after pollination and use the seeds as growth chambers.…”

“…Mites (Trisetacus quadrisetus, Acarina, Eriophyidae) enter the fruit early after pollination and use the seeds as growth chambers. Seeds used by mites show a characteristic fluted seed wall and a deformed, elongated tip (Roques et al 1984;Montesinos et al 2010). Chalcid wasps (Megastigmus thuriferana, Hymenoptera, Torymidae) (Auger-Rozenberg et al 2006) are seed predators that oviposit their eggs into seeds during mid-to late summer when fruits are almost fully grown, but before the seed coat hardens (Roualt et al 2004).…”

“…Chalcid wasps (Megastigmus thuriferana, Hymenoptera, Torymidae) (Auger-Rozenberg et al 2006) are seed predators that oviposit their eggs into seeds during mid-to late summer when fruits are almost fully grown, but before the seed coat hardens (Roualt et al 2004). Larvae develop inside seeds for a year, with a diapause period during winter, and adults emerge from fruits leaving a characteristic exit hole (Roques et al 1984). Moths (Pammene juniperana, Lepidoptera, Tortricidae) oviposit on the fruit surface during the first summer, and their oviposition period overlaps with that for chalcid wasps.…”

“…Moths (Pammene juniperana, Lepidoptera, Tortricidae) oviposit on the fruit surface during the first summer, and their oviposition period overlaps with that for chalcid wasps. Larvae hatch, enter the fruit and develop for about a year while feeding on the pulp and seeds, before leaving the fruit during the ripening phase to pupate in the soil (Roques et al 1984). Damaged fruits present galleries with faecal pellets from the larva and an exit hole on the fruit surface, which is easily distinguishable from chalcid wasps' emergence holes.…”