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, the Diglyphus 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 Diglyphus population 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.

Diglyphus isaea is used as a biological leafminer control agent in several greenhouse vegetables (e.g. tomato, sweet pepper, melon, ...) and ornamentals (gerbera, chrysanthemum, ...). As outside temperatures improve (in May in temperate regions), Diglyphus isaea often occurs naturally in greenhouses. Diglyphus isaea parasitises the tomato leafminer, as well as the serpentine leafminer and the pea leafminer. The most important benefit of Diglyphus isaea is the fast population build-up. This enables it to control an increasing leafminer population in a short period of time.

At lower leafminer densities (in early spring in temperate regions) the wasp is however less efficient than Dacnusa sibirica in locating preys. Therefore, at lower leafminer densities, Biobest recommends to start with a mixture of 90% Dacnusa and 10% Diglyphus (Dacnusa-System) in temperate climates. At higher pest densities or later in the season, Diglyphus isaea only can be released at a rate of minimum three weekly introductions of 0.1 Diglyphus/m². The fast population growth of Diglyphus isaea will enable the parasitic wasp to catch up with the leafminer population. To control larger populations, the selective pesticide cyromazine (Trigard) can be applied, which is harmless for the parasitic wasps. An additional advantage of Diglyphus isaea is the fact that it can easily be visually detected, which facilitates the follow-up of the population growth.

Diglyphus isaea is presented in tubes of 250 adult wasps. The tube is provided with a screw cap.

Note: Several pesticides have a negative effect on Diglyphus isaea. Please be careful when controlling diseases and other pests. Consult Biobest's list on side-effects of pesticides on beneficials organisms.

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