Scientific name: Biorhiza pallida
Common name: Oak Apple Gall
Galls of the wasp, Biorhiza pallida can be found on oak trees from April - May. The galls are home to the larvae of the wasp and can contain up to 30 larvae in each gall. They first appear as spongy creamy white-pink apple like balls becoming browner with age and growing up to 4cm across. The female wasp lays her eggs in the bud of an oak stem, the tree then reacts to this by producing the gall in which the larvae are protected from predators. The adult wasps emerge from the gall in June-July and then after mating the female will lay eggs again. The female Biorhiza wasp will also lay eggs in the fine roots of the oak tree by burrowing. The wasps that emerge from these root galls will be only female. The eggs laid on the stem buds will emerge as both male and female adult wasps.
Effects of the pest:
This gall has little effect on the health of the tree despite looking unsightly.
Fig.1 & 2 – Biorhiza pallida wasp gall on oak.
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