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Parasitic Wasp of Leafminer

Diglyphus isaea is a black parasitic wasp of 2-3 mm long, that occurs naturally in Europe, North-America and Asia. The short segmented antennae differentiate it from Dacnusa sibirica, another parasitic wasp against leafminer. Females are slightly bigger than males, and can be recognized by the yellow stripe on the hind legs.

The female Diglyphus isaea punctures a leafminer larva of the late 2nd or 3rd stage to paralyze the larva. Then she deposits an oval egg next to the leafminer larva. Therefore, Diglyphus isaea is called an ectoparasite. After hatching, theDiglyphus larva starts feeding on the leafminer larva. The Diglyphus isaea larva has 3 stages. The first instar larva is transparent, the second one is yellowish, and the third one is bluish green. In the last stage the larva crawls a little bit back in the mine to pupate. With excrements it builds six columns around it, which separate the lower and upper leaf epidermis. These columns can easily be seen by the naked eye through the leaf as six black spots. First the pupa is green, but it turns to black later on. Finally, a new adult parasitic wasp leaves the mine through a round hole on the upper side of the leaf.

The total development time takes 13 days (at 25°C or 77°F) to 33 days (at 16°C or 60.8°F). The adult wasp lives for 10 days (at 25°C or 77°F) to 32 days (at 20°C or 68°F) and deposits in total about 200-300 eggs. This is why a Diglyphuspopulation already increases faster than a leafminer population from 15°C (59°F) on.

To feed a female Diglyphus punctures leafminer larvae of the late 1st and 2nd stage and sucks them empty (host feeding). At 20°C (68°F) she kills about 70 larvae for feeding only. A predated leafminer larva can be recognized by a short mine that stopped early.

While searching for leafminers, the Diglyphus female alights on mined leaves. She then drums on the leaf surface with her antennae to locate the pest larva. At lower leafminer densities she has more problems with locating a larva.