Gall wasp parasite - Megastigmus brevivalvus

Citrus gall wasp parasites

Megastigmus trisulcus

Megastigmus brevivalvus

Adult gall wasp parasites Megastigmus brevivalvus and M. trisulcus are about 2.5 mm long. Females are honey-coloured with red eyes, while males are black on top and brown underneath. A female M. brevivalvus has a plump abdomen with a short, black ovipositor. A female M. trisulcus has a longer, more slender abdomen with an ovipositor approximately the same length as its body. M. brevivalvus generally emerges in October and *M. trisulcus a week or two later. After emerging, the parasites lay their eggs into those of the gall wasps. The parasite egg hatches after the gall wasp larva has hatched and the parasite larva develops slowly in the host larva for several months, finally destroying the host. When parasites are active, the gall wasp population is much reduced and galls tend to be smaller and fewer in number.

Citrus gall wasp galls in grapefruit

Target pest

Citrus gall wasp Bruchophagus fellis

Adult citrus gall wasps are small shiny-black wasps about 2.5 mm in length. The adult wasps emerge around late September (later in southern districts). After mating, the females immediately lay eggs into the new season flush. Eggs hatch after 2 - 4 weeks and the young larvae burrow into the bark. Distinctive woody galls form around the larvae during summer. The new generation emerges the following spring, completing the year-long life cycle. Adult wasps live for only one week after emergence.

Historically, citrus gall wasp appeared in many districts unaccompanied by its parasites. This has allowed the pest to achieve very high levels and cause a considerable amount of damage. Where gall wasp parasites have been introduced, gall wasp pressure has been reduced to a low, tolerable level in most varieties within a few years.

Suitable crops/environments

Citrus gall wasp is specific to citrus. It has a preference for grapefruit, orange and lemon varieties. Rough lemon and Troyer citrange rootstocks are also vulnerable, while mandarins are least susceptible. Heavily infested trees can become covered with galls, resulting in very little leaf or fruit production and severe dieback.

Individual gall housing many citrus gall wasp

Before release

Gall wasp parasites should be released near infested citrus flush soon after gall wasps have emerged. Because gall wasp emerges later in southern areas it is important to monitor their progress so that parasite releases are timed accordingly.

At release

Gall wasp parasites are supplied in plastic tubs. Strips of waxed paper coated with honey are supplied as nourishment for the parasites. It is normal for some mortality to occur during transit and extra parasites are supplied to allow for this.

Releases should be made on the shaded side of trees or in the late afternoon or early morning. Remove the lid of the container and tap the parasites out onto foliage in the vicinity of freshly damaged citrus flush. Place the honey paper near the galls as well.

Chemical use

Avoid using pesticides for four weeks before and for two weeks after release.

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