Trichogramma brassicae

Trichogramma is a small insect (0.3–0.4 mm), which belongs to the family Trichogrammatidae, the order Hymenoptera. The entomophage parasitizes inside eggs of Lepidopteran insects. The imago feeds on nectar. The female lays its eggs separately into eggs of various species. It eliminates pests in the initial stage of development. The female is able to lay 2–4 eggs inside the large eggs of Lepidopteran species (owl-moths, pea moths, garden-white butterflies, leaf-rollers and etc.) After hatching the young larva consumes the contents of a pest egg, then it pupates. Thus the development of the entomophage from a larva to an imago proceeds in the egg of a prey. Before flying out the imago gnaws through its envelope. After mating flown out females initiate a new oviposition (egg-laying). A female of Trichogramma is able to infest 20–40 eggs of the pest. The laying is made during a day (in daytime and in the night) at a temperature higher than 10°C. 80% of the eggs are laid during the first 2–3 hours after flying out. The development of one generation takes 10–13 days. Within vegetation period 3–14 generations can develop. In autumn at a temperature lower than 10°C the imago enters diapause. Trichogramma overwinters in the stage of a larva inside the eggs of a host-insect. Not many individuals of the entomophage survive winter. Their death happens often if the development of the entomophage and the prey development are not synchronous, for example when the laying of host-insect eggs and the flying out of entomophages are displaced for 2–4 weeks. Seasonal colonization is made for the maintenance of necessary entomophage density (there are periodical invasions of the imago).

It is especially interesting the mechanism of entomophage search abilities. Trichogramma uses benzylcyanide to search the eggs of its host-insects. This is a signal substance, which makes a fertilized female less attractive for a pest male than unfertilized one. Having marked the female with benzylcyanid in the process of mating the male by means of it increases the chances of its progeny to survive. Because the possibility of fertilizing by another male becomes less. Having detected a fertilized cabbage butterfly by means of benzylcyanid scent the female of the entomophage sits upon it and flies like rider to the place where the pest lays its eggs. Then Trichogramma lays its eggs in the fresh-laid eggs of moths.

Parasiting inside the eggs Trichogramma brassicae kills the considerable part of a progeny in moth populations. Using for the search of host-insects its own means of chemical communication the parasite may causes essential limitations for the evolution of such means of host-species.

Application

The entomophage is applied on many agricultural (cereal, industrial, vegetable) and ornamental-flower crops in the conditions of glass-covered ground and outdoor planting. The application of the entomophage in the regime of prophylaxis is started under revealing of the first pest flights. The terms of entomophage releases are determined according to the result of pest development monitoring. The rate of invasion varies in dependence on region, defended crops, the density of population and the species of pests (from 40 thousands to 200 thousands individuals per ha). For example the effectiveness of the entomophage against the beet webworm is provided at a ratio of 1:10, against the cabbage butterfly at 1:20 and etc. Invasions are made in 2–3 terms with 5-days intervals. The first term coincides with the beginning of pest egg laying. The colonization of the biological agent should be continued regularly until a risk period passes.

Trichogramma is sensitive to applied synthetic pesticides.

Advantages

• a wide range of pest species;
• the high effectiveness of prophylactic application;
• easy in application.

Storage and transportation

• do not expose to direct sunlight;
• transport and store at a temperature of 5–10°C;
• apply within 18 hours since the moment of reception.