Tip Top Bio-Control Technical Bulletin

Dacnusa sibirica
Parasitic wasp

 

Target Pest:
For Leafminer infestations which can occur early in the season. It is important to control the leafminer population early. Therefore, the parasitic wasp Dacnusa sibirica is an indispensable beneficial insect.

Description:
The parasitic wasp Dacnusa sibirica occurs naturally in North America and Europe. The adult is dark brown to black and is 2-3 mm long. It can easily be distinguished from Diglyphus isaea by its long antennae. As an adult, it differs from Opius pallipes, another beneficial insect against leafminers, only in the front wing venation.

The female deposits her egg in a leafminer larva. The egg is laid in the larva, not beside the host (as Diglyphus does). If there are too few hosts, Dacnusa sibirica may deposit more than one egg per larva, but eventually only one parasitic wasp develops in the leafminer larva.

The parasitized leafminer larva does not die, but keeps on feeding. First Dacnusa sibirica evolves in the leafminer larva. Then, when the leafminer larva pupates, the Dacnusa larva mutates. Further development of the pupa also takes place in the leafminer pupa. Finally, not a leafminer, but an adult parasitic wasp leaves the pupa. So the different development stages are not visible without opening the leafminer larva or pupa.

The development of Dacnusa sibirica takes 17.5 to 19.4 days (depending on the host development stage) at 20°C (68°F). For the leafminer L. bryoniae takes 26.5 days at this temperature. At lower temperatures, the parasitic wasp benefits an even greater difference in developmental time with the leafminer. At 25°C (77°F), an adult wasp lives for 7.4 days and deposits an average of 48 eggs. While at 15°C (59°F), this mounts up to respectively 20.2 days and 225 eggs.

Dacnusa sibirica can hibernate in leafminer pupae thereby allowing it to occur simultaneously with its host already early in the season. Adult parasitic wasps do not feed on hosts as Diglyphus isaea does.

Dacnusa sibirica is able to locate mines at very low densities. It looks mainly low in the crop. Once it has found a mined leaf, it searches for larvae with its antennae. The wasp can distinguish parasitized from non parasitized leafminer larvae (host discrimination).

Application:
Dacnusa sibirica is used in a wide range of crops to prevent leafminer damage, both on vegetables (tomato, sweet pepper, lemon, lettuce, ...) and on ornamentals (gerbera, chrysanthemum, ...). Dacnusa effectively controls the tomato leafminer, the serpentine leafminer and the pea leafminer. In this regard it differs from the closely related Opius pallipes, in which the eggs are encapsulated by the serpentine leafminer. Therefore, control of this leafminer species is poor with Opius pallipes.

Dacnusa sibirica can occur in the early season together with its host thanks to its ability to hibernate in leafminer pupae. The importance of this spontaneous parasitation differs from case to case, but is seldom sufficient for good control. For early detection of the first leafminers, yellow sticky cards are a useful tool. Research has shown that by placing the sticky cards horizontally, close to the ground level, will catch more leafminers than if they are hung vertically.

At first signs of mines or feeding spots on the leaves, Tip Top Bio advises a weekly introduction of a Dacnusa-Blend (90% Dacnusa + 10% Diglyphus) at 0.25 wasps/m� until sufficient parasitation. As parasitation is not directly visible, one should take some pupae samples in a glass jar or bottle, and wait and see if a leafminer or a parasitic wasp comes out. By counting the number of emerged wasps and leafminers, one knows the parasitation percentage.

Later in the season or in Mediterranean climates, it is recommended to release Diglyphus isaea only. This parasite controls leafminers better at higher infestation levels and higher temperatures.

Introduction:
When the first leafminers are spotted introduce the parasitic wasps.
Samples of leaves should be tested first to determine the percentage of leafminers parasitised by naturally occurring parasites and predators. Depending on the results, a specific strategy should be determined for each crop separately. The parasitic wasps can be stored for a short period of time. Store the tubes vertically in a cool (6°-10°C, 42.8° - 50°F) and dark place.
Throughout the crop spread the parasitic wasps equally. Open the tube and walk through the crop so that the parasitic wasps can escape. When most of them have flown away, place the tube somewhere horizontally in order to let the last wasps leave the tube.
Every 2 or 3 weeks, samples of leaves should be taken to check parasitism.

Dacnusa-Blend:
The parasitic wasps are supplied in tubes (with screw cap) of 250 adults, of which 90% are Dacnusa sibirica and 10% are Diglyphus isaea.

Benefits:
Applicable on many crops.
Parasitises the three common leafminer species.
Good parasitation at low temperatures.
Excellent ability to search when infestation is low.